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The fabrication of most current thermal insulation materials from polymeric foams has created an unfavorable impact on the environment. With the aim of reducing the use of foam plastic, this paper focuses on honeycomb paperboard, an alternative thermal insulation material which is recyclable and cost-effective, and evaluates its heat transfer performance under different conditions. The experimental results show the effective thermal conductivity of honeycomb paperboard increases as the honeycomb height or the side length increases. This paper also establishes a novel theoretical model based on a newly developed convective heat transfer correlation to predict the effective thermal conductivity under different conditions. The model's results conform well to the experimental results, and the effect of convective heat transfer is investigated quantitatively using this model. As the vertical adiabatic boundary surfaces are replaced by honeycomb walls, the convection heat transfer strictly depends on the thermal boundary condition of the honeycomb walls and highly depends on honeycomb height and side length. • The novel theoretical models involving convective heat transfer are established under different conditions. • The different heat transfer paths are quantitatively investigated based on the proposed models. • Under the condition of hot-above and cold-below, convective heat transfer in honeycomb paperboard increases as the honeycomb height increases, but decreases as the side lengths increases. • Under the condition of cold-above and hot-below, convection heat transfer in honeycomb paperboard increases as the honeycomb height or the side length increases. [ABSTRACT FROM AUTHOR]

The environment inside a spacecraft, or a space habitat, can greatly differ from those on earth, affecting the burning behavior of solid fuels. Because in a gravity field there is a flame-induced buoyancy, it is very difficult to reproduce on Earth the environmental conditions of a spacecraft, or a habitat in the Moon or Mars, thus making fire testing and burning predictions harder. A potential alternative approach to overcome this problem is to reduce buoyancy effects by using reduced ambient pressure in normal gravity. The objective of this work is to explore the possibility of simulating the effect of gravity, and in turn buoyancy, through changes in ambient pressure, on upward/concurrent flame spread over a thin combustible solid. Comparisons with available data at different gravity levels are used to determine the extent to which low-pressure can be used to replicate flame spread characteristics at different gravities. Experiments of the upward/concurrent flame spread over thin Kimwipe paper sheets were conducted in normal gravity inside a pressure chamber with ambient pressures ranging between 100 and 30 kPa and a forced flow velocity of 10 cm/s. Results show that reductions of pressure slow down the flame spread over the paper surface, and also reduces flame intensity. Comparison with published partial gravity data shows that as the pressure is reduced, the normal gravity flame spread rate approaches that observed at different gravity levels. The data presented is correlated in terms of a mixed convection non-dimensional number that describes the convective heat transferred from the flame to the solid, and that also describes the primary mechanism controlling the spread of the flame. The correlation provides information about the similitudes of the flame spread process in variable pressure, flow velocity and gravity environments, providing guidance for potential ground-based testing for fire safety design in spacecraft. [ABSTRACT FROM AUTHOR]

This paper describes an accurate model of the Electrical Power Subsystem (EPS) of the Thermal Analysis Support and Environment Characterization Laboratory (TASEC-Lab), a university experiment developed for using in high-altitude balloon missions to measure and analyze the convection heat transfer. A Li-ion battery and two high efficient DC–DC converters have been characterized through laboratory tests and fitting to the experimental results. The developed mathematical models described in this paper are used to carry out accurate EPS simulations and are validated by comparison with the experimental data. • Design and modeling of the electrical power subsystem of a stratospheric balloon experiment. • New Li-lion battery discharging model that describes the three main parts: initial decay, linear, and exponential decay. • Formulation of a new DC/DC converter efficiency model. • Simulation and model validation of the electrical power subsystem. [ABSTRACT FROM AUTHOR]

Stratospheric ballooning flights are becoming more relevant due to these platforms can place payloads to an altitude above almost 99% of the atmosphere, where the environmental conditions are very similar to the space ones. From a thermal point of view, during the ascent phase convection is very relevant and, despite what a priori may be thought, depending on the element considered, convection may not be negligible at the float phase. With this in mind, the Thermal Analysis Support and Environment Characterization Laboratory (TASEC-Lab) was born. It is an experiment based on COTS, which consists in a 3U CubeSat-like experiment, which was launched onboard a stratospheric balloon in León (Spain) on 16th, July 2021. The upper unit of the 3U box contains a heated plate, with the aim of quantifying the relevance of convection during the flight. In this paper, the relevance of convection during the ascent phase is described, the correlation of in-flight temperature measurements with those provided by the thermal mathematical model developed in ESATAN-TMS is performed, using the air mass flow inside the cavity as a fitting parameter with a fitting error lower than 5 °C during the ascent phase. [ABSTRACT FROM AUTHOR]

Chemical ablation and mechanical erosion of hybrid rocket nozzles can cause loss of nozzle thermal protection material, resulting thrust reduction. In this paper, the chemical ablation and mechanical erosion mechanisms of nozzle thermal protection materials are studied through numerical simulation. For chemical ablation, a coupled thermal-mechanical-chemical model is established, considering three mechanisms: wall regression caused by non-homogeneous chemical reactions at the wall, convective heat transfer and fluid-structure interaction. For mechanical erosion, a Fluent DPM model and an Abaqus DEM model are established, which are investigated from the perspectives of empirical formula and solid mechanics mechanisms respectively, and validated against each other. The comprehensive effect of chemical ablation and mechanical erosion on the morphology of the nozzle is considered. The results show that both chemical ablation and mechanical erosion dominate the wall regression rate at the downstream of the converging section and upstream of the throat while the other location is only dominate by chemical ablation. After 5s of operation, thrust of rocket engine decreases by 5.8%. The Abaqus DEM model presented by this paper breaks the limitations of the empirical formulae due to the introduction of the material constitutive model and the failure criterion. • A coupled thermal-mechanical-chemical model is established. • Mechanical erosion is studied from perspective of empirical formula and the solid mechanics mechanism. • Comprehensive effect of chemical ablation and mechanical erosion on nozzle inner wall morphology is studied. [ABSTRACT FROM AUTHOR]

A novel air-carrying energy radiant diffuse terminal is proposed, and the response of the terminal is investigated by field experiment and numerical simulation. This paper explores the dynamic operation characteristics of the new system to guide the optimal operation of the system. A transient simulation method of three factors (conduction, convection, and radiation) with dual-circulation (air-carrying energy zone and occupied zone) is put forward for the radiant diffuse terminal with a fresh air system. This transient simulation sets up the porous baffle model coupling radiation model concurrently, revealing the dynamic thermal performance for the system's response accurately, quickly, and comprehensively. This method avoids the limits for the complexity of mini porous (Pore size of 1 mm–3mm) geometric models and the transient uncertainty in multiple combination models. The results show that the average error between the convective-conductive model and the convective-conductive-radiative model is about 8% at five different heights. This system has high response performance, which can quickly heat the room while maintaining the comfort requirements of vertical temperature. The radiated heat transfer between the radiant diffuse terminal and the occupied zone is greater than the convective heat transfer (Radiation accounts for 74%). This system has a short response time, high energy efficiency, uniform airflow, and eliminates draught rating. Moreover, the indoor non-uniform transient thermal and humid environments, the thermal comfort, and air quality for the response of the terminal with fresh air system under four different diffuser placements are compared using computational fluid dynamic simulation. The results indicate that introducing heating strategies featuring higher-positioned fresh air inlet and lower-positioned recirculation return air outlet for this system leads to a temperature efficiency increase by 5%, velocity uniformity by 8%, and age of air reduction by 16–50% in human-breathed zone and the response time by 25%, which shows substantial potential for energy savings. The transient simulation and experiments in the paper are beneficial to optimize design parameters and carry out energy-saving applications of operation energy consumption for the response of this terminal with a fresh air system in the future. [Display omitted] • Dynamic feature of the new terminal system is explored by experiments and simulation. • The validated porous baffle model simplifies geometry modeling for mini perforations. • A new transient simulation method of dual-cycle three factors is proposed. • High performance of thermal and humid environment for the response of the system. [ABSTRACT FROM AUTHOR]

Nanochannels consisting of hot and cold walls with periodic rectangular and triangular nanostructures were simulated by molecular dynamics in this paper, the periodic size dimensionless parameters φ was defined to describe the dimension of nanostructures on the wall. The results show that the addition of nanostructures leads to the variation of mass density distribution of fluid near the wall. A hot wall with nanostructures can promote the appearance of a fluid high-potential area near it. The discrepant attraction for fluid from the wall caused by the different wall conditions leads to different flow characteristics in nanochannels. Fluid velocity growth rate near the hot wall is 10.5% higher than that near the cold wall. Average velocity of the fluid near the hot wall is 5.1% higher than that of fluid near the cold wall. A wall with rectangular nanostructures at φ = 0.28 shows minimum flow resistance among rough hot walls, while a wall with triangular nanostructures at φ = 0.14 has minimum flow resistance among rough cold walls. Heat is transferred from the hot wall to the cold wall through fluid flow. Wall conditions impact the heat transfer situation of fluid in flow boundary by changing the fluid mass density contribution. The addition of nanostructures and decrease of nanostructures size is beneficial for heat transfer while unfavorable for fluid flow, convective heat transfer was influenced by their combination. For a wall with 300 K, the addition of rectangular nanostructures at φ = 0.07 has the best convective heat transfer performance. For a wall with 200 K temperature, increasing triangular nanostructures at φ = 0.14 on the wall can reach the best convective heat transfer capacity. This paper can provide a theoretical foundation for the optimization of nanochannels to achieve best convective heat transfer ability. [ABSTRACT FROM AUTHOR]

The presence of magnetic field results in a reduction in natural convective heat transfer and entropy generation in cavities. The use of nanofluids improves the performance of thermal systems. The present paper discusses the impact of uniform and non-uniform magnetic fields on the second-law performance of nanofluid-filled and porous cavities, introduces artificial intelligence (AI) approaches, and examines the applications of AI in optimizing heat transfer and entropy generated in these systems. The mathematical formulation is presented in terms of the entropy generation for natural convection in cavities. This paper demonstrates the influences of various important non-dimensional parameters on entropy generation in cavities. Besides, advances in the second-law performance of cavities and the role of AI techniques in the field are discussed and future directions are provided. [ABSTRACT FROM AUTHOR]

Unsteady oblique stagnation-point flow and heat transfer of fractional Maxwell fluid with convective derivative towards an oscillating tensile plate are discussed in this paper. The fractional operator is introduced to material derivative for the first time to obtain a newly defined constitutive equation of Maxwell fluid. The Fourier's law is modified accordingly. The pressure gradient is innovatively obtained by solving the differential equation, which bases on the momentum equation away from the plate. Furthermore, the numerical solutions are acquired by virtue of the finite difference method combined with L1-algorithm. It turns out to be convergent through constructing numerical example. The influence of related parameters on the velocity and temperature are performed graphically in detail. Results show that the fluid velocity and temperature distributions tend to periodic oscillation near the plate. Both the velocity and the temperature reduce with the augment of fractional derivative parameters, which indicates the velocity and the temperature boundary layer become thinner. The smaller velocity relaxation time parameter leads to enhanced velocity, meaning that the pressure promotes the fluid velocity. It is evident that all the temperature curves have a tendency to increase first and then decrease with the diverse parameters due to the thermal relaxation characteristic. [ABSTRACT FROM AUTHOR]

Combustion of iron powder is a promising option for clean and sustainable generation of heat and power. However, a fundamental understanding of the flame propagation mode is missing, especially under strong convection effects. In part I of this work, we analyzed the modes of flame propagation under weak convection effects and estimated the discreteness parameter as a ratio of the particle burn time to the conduction timescale. We found that both, the selection of temperature at which thermal properties are evaluated, and the selected length scale, are critical for a reliable prediction of the transitional particle spacing indicating the transition from the continuous to the discrete mode. In this paper, we extend our previous work by studying the effect of convection on inter-particle heat and mass transfer using boundary layer resolved numerical simulations. It is shown that for increasing convection, iron flames transition from the continuous to the discrete mode at higher particle distances. Taking into account both diffusion and convection-dominated heat transfer, an extension for the scaling of transitional particle spacing of part I is proposed. Furthermore, since iron flames could experience varying ranges of particle distances at different velocities in a practical flame, a regime diagram is constructed which is based on the Péclet number and the particle spacing with a boundary separating the two modes of flame propagation. The regime diagram offers orientation for simulations of large-scale flames using Euler–Lagrange methods where boundary layers around the particles are not resolved. [ABSTRACT FROM AUTHOR]

To deal with inverse nonlinear heat transfer problems in a two-dimensional heat conduction problem, this paper presents a hybrid approach combining fuzzy logic and the extended Kalman filter (EKF). The proposed algorithm has been applied to the real-time reconstruction of the temperature field, time-varying convective heat transfer coefficient, and time-varying boundary heat flux using temperature data from a set of sensors. The effects of the covariance of the initial estimation error, the time step of data acquisition by the sensors, and the number of installed sensors on the precision and stability of the estimation results has been investigated by numerical experiments. To compare and validate the results, all these parameters were investigated using the EKF method. The results show that the adaptive fuzzy extended Kalman filter (FEKF) method for estimating temperature, convection coefficient, and heat flux at the boundaries is precise and stable. The comparison shows that the performance of the FEKF method in parameter estimation is better than the EKF method, and the highest increase in precision and stability of the results is related to the convective heat transfer coefficient. [ABSTRACT FROM AUTHOR]

• A reservoir-assisted loop thermosyphon with a micro-grooved evaporator (MGTPLT) was fabricated. • Micro-grooved structures allowed faster startup and more stable operation of the MGTPLT. • The convection heat transfer ratio was proposed to evaluate the heat transfer enhancement. • The MGTPLT reduced evaporator temperatures and achieved thermal performance enhancement. The two-phase loop thermosyphon (TPLT) offers significant advantages in high-efficiency and long-distance heat transport for various thermal and energy-related applications without external power consumption. In this paper, the startup and heat transfer characteristics of a reservoir-assisted loop thermosyphon with a micro-grooved evaporator (MGTPLT) were experimentally investigated and compared with a loop thermosyphon having a smooth-tube evaporator (STPLT). R245fa was used as a working fluid at volumetric filling ratios of 50–80 %. The results demonstrated that the additional microgrooves allowed a shorter startup time characterized by a lower maximum temperature with respect to the temperature overshoot. Compared to the STPLT, the MGTPLT exhibited lower evaporator temperatures and better temperature uniformities; the micro-grooved structures could alleviate local intermittent dry-out at moderate and high levels of power input for filling ratios of 50 and 60 %. The addition of micro-grooved structures enhanced the heat transfer performance of the TPLT characterized by lower thermal resistances. The convection heat transfer ratio (CHTR) was proposed to evaluate the enhancement of the convection heat transfer within the evaporator region after using microgrooves. The CHTR showed a decreasing tend with increasing the power input. At moderate filling ratios, the value of the CHRT was greater than 1.1, and an approximately 18 % increase in the convection heat transfer was achieved under the combined condition of 60 % filling ratio and 250 W power input. The fundamental mechanism of heat transfer performance enhancement with the aid of micro-grooved structures was analyzed and elucidated. [ABSTRACT FROM AUTHOR]

• Presents an analytical solution for thermal spreading in a cylindrical body with spatially varying side wall cooling. • A series solution is derived, with coefficients shown to be the solution of a set of linear algebraic equations. • Impact of key non-dimensional parameters on temperature field and thermal resistance is investigated. • Results are shown to be in excellent agreement with past work for special cases. • Results are of relevance for edge cooling of microprocessor chips as well as batteries. Thermal spreading and constriction resistance play an important role in thermal management of a variety of engineering systems, including semiconductor devices. Moreover, thermal contact resistance at interfaces between materials is also governed by spreading and constriction processes. Most of the past literature on theoretical modeling of thermal spreading from a source into a larger body assumes an adiabatic side wall, whereas several recent thermal management problems involve active cooling at the side wall. This work addresses such scenarios by solving the thermal spreading problem in a finite thickness cylinder with spatially varying convective heat transfer on the side wall. An eigenfunction-based series solution for the temperature field is written, the coefficients of which are shown to be governed by a set of coupled algebraic equations. Results are shown to agree well with past work for special cases of the general analysis presented here. Thermal spreading resistance is computed for a number of practical scenarios, including step function, periodic and sinusoidal convective cooling on the side wall. In each case, it is shown that the temperature distribution is consistent with the nature of the spatially varying boundary condition. A key theoretical insight from this work is that under certain conditions, the classical definition of thermal spreading resistance may become negative due to the presence of two heat sinks in the problem. Therefore, analysis based on total resistance may be more appropriate. This work offers a significant generalization of past papers, making it possible to analyze realistic thermal management problems, in which, side wall cooling plays an important role. [ABSTRACT FROM AUTHOR]

As a phase change material, ice slurry has been successfully applied in HVAC&R systems due to its high energy storage density. The heat exchangers are the key equipment realizing energy conversion of ice slurry. In HVAC&R systems, U-tubes are frequently used in shell and tube heat exchanger. However, there are few studies on thermo-fluidic characteristics of ice slurry in U-tubes. Therefore, the thermo-fluidic characteristics of ice slurry in U-tubes are numerically studied in this paper using Euler-Euler approach. The results indicated that as enlarging the inlet ice content and velocity, the ice concentration distribution becomes more uniform along in vertical profile. Due to the secondary flow in bend section, the ice concentration decreases in the inner wall and increases in the outer wall as the inlet velocity increases; At the high Reynolds number, the inlet ice content and ice particle diameter have a more significant fluence on pressure drop (Δ p). The local heat transfer coefficient (h lo) in bend section exhibits a tendency of first increasing and then decreasing, with the maximum value of h lo occurs at θ = 90° of the bend section. Finally, a correlation is suggested between the average resistance coefficient (f ave) and local Nusselt number (Nu lo). • The melting process of ice slurry in U-tubes is investigated. • The factors affecting thermo-fluidic behavior of ice slurry in U-tubes are discussed. • This peak value of h lo is located within the bending section at an angle of θ = 90°. • The correlation of f ave and Nu lo in U-tubes is obtained for ice slurry. [ABSTRACT FROM AUTHOR]

• An analytical model for thermoelastic crack problems in a strip is developed. • Convective heat transfer on lateral surfaces of the strip is considered. • Analytical solutions for thermoelastic field at crack tips are obtained. • Convective heat transfer impacts the SIFs and energy release rate significantly. • It is helpful in improving the understanding of thermoelastic fracture mechanics. Most existing thermoelastic crack models commonly overlook the convective heat exchange occurring on the lateral surfaces of the structures being studied. Consequently, there is often a concern regarding the accurate estimation of temperature fields and the resulting thermal stresses. To address this concern, this paper presents a two-dimensional (2D) thermoelastic model for a cracked strip that incorporates convective heat transfer between the lateral surfaces and the ambient environment. The crack problem is reduced to a set of singular integral equations with Cauchy kernels which are solved numerically. Analytical solutions for temperature distribution, stress intensity factors (SIFs) and energy release rate at crack tips are obtained. The influence of the ratios of convective heat transfer coefficient to thermal conductivity and thickness to height of the strip on the key fracture parameters is investigated through the numerical results. It has been discovered that classical thermoelastic crack models often exhibit a significant underestimation of the SIFs and energy release rates for cracks located near the hot boundary of the strip. The analytical model proposed in this paper has significant potential to advance our understanding of thermoelastic fracture mechanics. [ABSTRACT FROM AUTHOR]

Long Duration Balloons are suitable platforms for scientific research to study the Earth and the Solar System. From the thermal point of view, these platforms are analysed at the floating altitude using data of the thermal environmental conditions considering the local characteristics and the seasonal variability. Nevertheless, depending on the launch site conditions and the launch day time, the minimum temperatures could appear during the ascent phase. This is because the balloon-payload system is exposed to free air and the convective heat transfer could drive the thermal behaviour of the onboard equipment. This analysis requires a dynamic study of the balloon trajectory for determining the relative speed with respect to the air as well as an appropriate thermal modelling considering the radiative and convective heat transfer. The aim of this paper is to explain the main characteristics of the ascent phase from a thermal point of view and to show how an ascent phase analysis for a Long Duration Balloon system can be performed using ESATAN-TMS. In order to give examples for the explanation the full process has been particularized to the SUNRISE III mission. • Thermal modelling of a generic payload onboard a Long Duration Balloon for ascent phase analysis. • Determination of the balloon film influence on the payload thermal behaviour. • Determination of the worst-case relative wind speed on the balloon-borne system for forced convection estimations. • Thermal analysis of SUNRISE III mission during the ascent phase using ESATAN-TMS. [ABSTRACT FROM AUTHOR]

• A 3D printer is designed for on-orbit servicing/manufacturing missions. • A thermal control strategy that uses P and fuzzy PI controllers is designed. • The PEEK material is selected to study the thermal control performances. • The simulation results show that the 3D printer is feasible to work on-orbit. On-orbit manufacturing can reduce the cost and time needed by space exploration missions because in-situ maintenance activities can be achieved without the need for additional launches. Furthermore, recent developments in materials science in terms of better mechanical and thermal performance have allowed this application to become a potential reality. However, the deployment of on-orbit manufacturing presents several challenges, including the lack of convective heat transfer and human intervention. This paper proposes an on-orbit 3D printing device capable of operating at a temperature up to 400 °C in the vacuum environment. To validate its feasibility for on-orbit manufacturing, we designed four extruders with different characteristics. We investigated the temperature profiles across the extruders under the vacuum condition through a heat transfer model. Based on the thermal analysis, a thermal control method, which combines the Proportion (P) and Fuzzy Proportion and Integration (Fuzzy PI) strategies, is designed to regulate the 3D printing device operation. With the extrusion rate of 8654.6 mm3 /h and the printing temperature at 400 °C, the melting and solidification status of the PEEK (Polyether ether ketone) material is verified. [ABSTRACT FROM AUTHOR]

This review paper presents an overview of transpired solar collectors (TSCs) - a clean energy technology that has gained considerable attention due to its potential to minimise building energy demand and contribute to achieving net zero emissions. The review is mainly focused on scrutinising the disparities in heat and mass transfer mechanisms, specifically the impact of homogeneous and inhomogeneous suction flow distributions on the TSC, encompassing performance improvement methods, performance assessment, and optimisation strategies for TSCs. The inconsistency between the theoretical and real-world performance of TSCs was observed, attributed to the high turbulence wind with non-uniform speed distribution and suction flow interactions with the main flow in the plenum. Corrugations on the absorber improved thermal performance but increased wind heat loss on the exterior surface, which could be mitigated by adding glazing to corrugated TSCs. The review highlighted the flexibility of integrating TSCs with other technologies, including coupling with separate phase change material (PCM) thermal energy storage units, which outperformed those placing the PCM plate into the plenum. Moreover, integrating TSCs with desiccant wheel cooling systems showed some interesting results in terms of cost and payback period, while integration with heat pump systems could reduce electricity consumption, but it was not recommended in cold climates. Exergetic analysis has been frequently used to determine thermodynamic losses of TSCs and it could provide a more accurate performance assessment when integrating TSCs with power generation systems. The review identified several research gaps in related study fields and provided recommendations, encompassing dimensionless analysis of the relationships between wind effect and heat transfer of TSC absorbers, the development of convective heat transfer correlations for TSC's absorber, and the exploration of cost-effective design and optimisation strategies for hybrid TSCs. • Heat and mass transfer mechanisms of transpired solar collectors (TSCs) were analysed. • TSCs can be integrated with different energy technologies to improve flexibility. • Various designs of TSC systems and their main design parameters were discussed. • It provides some insights into developing convective heat transfer correlations. [ABSTRACT FROM AUTHOR]

• Performance evaluation of three different cooling methods for data centers is conducted. • Single-phase immersion cooling has advantages in heat transfer and energy consumption. • Correlation between oil properties and immersion cooling performance is established. • Dynamic viscosity has the greatest impact on the flow and thermal performance of oil coolants. This paper conducts a comprehensive performance evaluation and optimization of single-phase immersion cooling (SPIC) systems to address challenges in data center server cooling. A three-dimensional model of blade servers with different cooling methods is constructed and numerically solved to compare thermal transport performance, flow characteristics, and energy consumption performance. Furthermore, the influence mechanisms of different oil coolants and operating conditions on SPIC system performance are studied. The results indicate that the SPIC scheme exhibits significant advantages in terms of heat transfer capability, heat transfer uniformity, and flow resistance loss. Moreover, the power usage effectiveness (PUE) of SPIC systems decreases by 20.8 % and 17.6 % compared to forced air cooling and water cooling plate solutions, respectively. The dynamic viscosity of oil coolants has the greatest impact on the SPIC performance. Moreover, high-viscosity silicone oil increases the flow resistance of SPIC systems and weakens the convective heat transfer capability between the coolant and components. By ensuring safe operation, increasing the inlet temperature of oil coolants reduces flow resistance losses and enhances heat transfer capacity. Additionally, initially increasing the mass flow rate improves convective heat transfer capacity. However, the heat transfer improvement gradually diminished beyond a certain threshold while flow resistance losses increased significantly. [ABSTRACT FROM AUTHOR]

The electronics in logging tools are susceptible to thermal failure due to the extreme thermal environment. Passive thermal management system (PTMS) has been proven to protect the electronics for several hours. In this paper, a numerical model based on the equivalent thermal conductivity method was developed to determine the transient temperature of downhole electronics. Compared with the traditional analytical model or numerical model considering only one single heat transfer process, the complex heat transfer in the logging tool were comprehensively considered through the proposed model. Briefly, the heat transfer processes in the vacuum bottle were theoretically calculated rather than empirically acquired, and the convective and radiative heat transfer inside the vacuum bottle was equated to the temperature-dependent thermal conductivity of air. In addition, the proposed numerical model was compared with experiments and previous numerical models to verify the accuracy of the model, and the temperature deviation of the electronics was within 5 °C. Moreover, the computational time was greatly reduced compared with the traditional three-dimensional numerical simulation process while ensuring the accuracy of calculation. Therefore, the proposed numerical model achieved both computational accuracy and efficiency, which was expected to be widely used in the development of PTMS for logging tools. • A numerical model based on equivalent thermal conductivity method was proposed. • The complex heat transfer processes in PTMS were comprehensively considered. • The proposed model possessed high computational accuracy and efficiency. [ABSTRACT FROM AUTHOR]

At present the ion-wind has been applied to portable electronic equipment heat dissipation because of its excellent heat dissipation performance. In this paper, sawtooth-mesh and sawtooth-plate ion-wind generators are studied. In addition, the best structure of single-stage ion-wind is found through the local maximum velocity, average velocity, and average mechanical efficiency.For single-stage sawtooth-mesh ion wind generator,when the number of sawteeth is 6 and the electrode gap is 20 mm,the average velocity that can achieve the best ion wind 1.7 m/s, and the average mechanical efficiency is 0.84%.For single-stage sawtooth-plate ion wind generation devices.When the number of sawteeth is 4 and the electrode gap is 15 mm.The average wind velocity of ion wind can reach 1.42 m/s, and the average mechanical efficiency is 1.14%.On this basis, the multi-stage sawtooth-plate ion-wind generator is studied. The more number of stages, the higher the average velocity of ion-wind is, but when the number of the stage is more than 2, the average mechanical efficiency decrease then the practicality is limited.When the number of multistage electrode stages is 2, the average heat transfer coefficient can reach 86.1 W/m-2·K-1, which is 34% higher than the single-stage structure. [ABSTRACT FROM AUTHOR]

This paper presents a model of heat and moisture transfer through multilayer firefighter protective clothing, which for the first time has taken into account all the major heat and moisture transport mechanisms including conductive and convective heat transfer, two-flux radiative heat transfer, moisture bulk flow, moisture absorption/desorption by fibers, moisture diffusion and phase change. The model was solved by Crank–Nicolson scheme of the finite difference method. Numerical analysis showed that our model can accurately predict the second-degree burn time with an error ranging from 0.37% to 3.55% for different types of clothing assemblies. With this model, the distributions of heat and moisture within the protective clothing system are elucidated and the relative importance of key clothing parameters on thermal protection better understood. It revealed that the thickness of the moisture barrier layer has the greatest influence on the skin burn time. This study is significant in providing a theoretical framework for optimizing the design of thermal protective clothing. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of heat transfer enhancement and pressure drop in a Coiled Flow Reverser (CFR) with a twisted tape insert. Both laminar (10 < Re < 2000) and turbulent (12,000 < Re < 18,000) regimes have been studied using both experimental and numerical methods. The effects of twist ratio of twisted tape, inlet Reynolds number, and perforating the twisted tapes have been investigated. The study found that the best performance in the laminar regime is achieved with a twisted tape with a twist ratio of 15.73 and no holes on it at a Reynolds number of 2000. In the turbulent regime, the same twisted tape performs the best at a Reynolds number of 17,000. The highest Thermal Performance Ratio (TPR) in laminar regime is 1.55 and in turbulent regime is 0.99. In comparison to the straight pipe, all types of CFRs show better performance in heat transfer enhancement. Also, as the Reynolds number increases, the friction coefficient decreases in all configurations. The study reveals that the twisted tape insert enhances heat transfer performance while increasing pressure drop. This study provides valuable insights into the design and optimization of heat exchangers with CFR. The findings can be used to improve the efficiency and performance of various industrial processes, such as refrigeration systems, air conditioning, and power plants. • Fluid flow and heat transfer in a coiled flow reverser (CFR) were studied. • Effects of tube insert on the heat transfer enhancement of CFR were investigated. • Effects of perforation of tube insert on heat transfer enhancement of CFR were examined. • The effects of tube insert at laminar flow are more than turbulent flow. • Perforation has no significant effects on the thermal performance ratio. [ABSTRACT FROM AUTHOR]

Flip-chip packaging technology is widely used in the field of electronic packaging. The thermal contact resistances (TCRs) of its double-layer thermal interface materials (TIMs) impact its thermal characteristics. In this paper, a flip-chip package thermal contact model is first constructed considering the internal rough contact interface of double-layer TIMs. Secondly, the effects of friction coefficient, pressure, elastic modulus of double-layer TIMs, thermal conductivity of double-layer TIMs, interstitial medium, and convective heat transfer coefficient on the flip chip package's contact mechanics and thermal properties are analyzed. Finally, the influence of secondary thermal effects on contact mechanics and thermal properties is investigated. The results show that the friction coefficient, pressure, and elastic modulus of double-layer TIMs have a significant influence on the TCRs by changing the actual contact area, but the impact on the heat dissipation of the chip is limited, and the maximum temperature reduction does not exceed 10 K. However, the interstitial medium, convective heat transfer coefficient, and thermal conductivity of double-layer TIMs greatly influence the heat dissipation of the chip and maximum temperature by directly affecting heat transfer performance. Furthermore, secondary thermal effects have varying degrees of influence on contact stiffness, TCRs, and temperature distribution. [Display omitted] • A thermal contact model of flip-chip package considering the TCRs was established. • The effects on contact mechanics and thermal properties of the model were analyzed. • Secondary thermal effects on contact mechanics and thermal properties was analyzed. [ABSTRACT FROM AUTHOR]

Integrating nanotechnology into phase change materials (PCMs) has emerged as a novel approach to improving PCM thermal properties and performance in various thermal energy storage applications. Nanofluids, nanoparticle suspensions in a base fluid, have been identified as a promising method of increasing the thermal conductivity of PCMs and thus reducing thermal energy charging and discharging duration. This review paper investigates recent advances in incorporating nanotechnology into PCMs, focusing on their applications in the solar energy sector. Thermal conductivity, specific heat, viscosity, density, and convective heat transfer coefficient of nanofluids are discussed, as are the thermal properties of nano-enhanced PCMs (NEPCMs), including thermal conductivity, latent heat, specific heat, viscosity, supercooling, and phase-change temperature. The paper also gives an in-depth look at the uses of nanofluids and NEPCMs in solar collectors, photovoltaic/thermal (PV/T) systems, coolants, and desalination, emphasizing their potential to improve system efficiency. The review also considers the potential environmental and human health concerns connected with using nanofluids and NEPCMs, emphasizing the importance of rigorous evaluation and risk assessment in developing and applying these materials. Overall, the review provides valuable insights into the potential benefits and challenges of incorporating nanotechnology into PCMs and emphasizes the importance of ongoing research and development in this field to further advance the use of thermal energy storage technologies in various applications, including solar energy systems. [Display omitted] • Nanofluids and nanomaterials are considered as innovative heat transfer medium. • Phase change materials (PCMs) for harvesting thermal energy are scrutinized. • Recent developments and properties of nanofluids and nano-enhanced PCM. • Potential applications of nanofluids and nano-enhanced PCM are fully presented. • Environmental impacts and human health risks are comprehensively discussed. [ABSTRACT FROM AUTHOR]

Highlights • Particle image velocimetry (PIV) was used to capture flow characteristics near heat transfer fins. • A large eddy simulation (LES) provided deeper insight into the flow structures occurring around the fins. • Near wall turbulence and flow patterns responsible for heat transfer enhancement were discussed. • Two unsolved problems on micro-fins were addressed. Abstract Internally enhanced surfaces such as micro-fins are an important class of heat transfer enhancement in commercial applications. Many research papers discuss the design and optima of these surfaces. However, most previous studies have demonstrated only the macro relationship between the geometries of the micro-fins and heat transfer. The need for a deeper understanding of these fins arose from some currently unsolved problems that limit future development of enhanced surfaces. First, why are increases of heat transfer larger than area increases in micro-finned tubes in most cases? Second, why do internally micro-finned tubes typically have lower heat-transfer-enhanced ratios in laminar and transition flows? This work presents a novel method to analyze the detailed relationship between flow characteristics and heat transfer for one type of micro-fin. The goal of the paper was not to find a new Reynolds number-based correlation, but to find flow patterns responsible for heat transfer enhancement and understand the mechanisms that cause this. First, this paper introduces comprehensive experimental measurements including particle image velocimetry (PIV), measurement of the heat transfer coefficient and accuracy of pressure-drop measurements, all used to validate numerical approaches. Validated large eddy simulations (LES) are then used to predict flow characteristics and coherent structures (Q criterion). The numerical simulation includes both heat conduction in the metal structure and heat convection on the solid–fluid interface. Finally, the paper documents how the flow structures link with the enhancement of heat transfer in the micro-finned duct. [ABSTRACT FROM AUTHOR]

Abstract This paper presents analyses of complex flows and heat transfer induced by twin oblique turbulent slot-jets of different directions (divergent, convergent or parallel) impinging a heated wall. A comparison of the heat transfer characteristics between perpendicular and three cases of twin oblique jets (parallel, convergent and divergent). The twin slot jets are located on a confining adiabatic wall at a distance of 8 slot jet width. Convective heat is investigated numerically examining the effect of Reynolds number (Re) and jet inclination angle (α). This problem is relevant to a wide range of practical applications including nuclear engineering devices, manufacturing, material processing, electronic cooling, drying paper or textile, tempering of glass, etc. All computations are performed using two dimensional large eddy simulations (LES) approach with Smagorinsky sub-grid scale (SGS) models. For all directions and inclinations of the jets, the location of the stagnation points is changed and hence, the location and magnitude of the maximum Nusselt number on the heated wall vary. When Reynolds number increases, Nusselt number is improved for all types of inclination. The averaged Nusselt number shows that the perpendicular impingement gives better heat transfer than that of the oblique jets. The poor heat transfer is obtained for the parallel oblique jets. For the same angle, divergent jets give smallest heat transfer than the convergent jets. Graphical abstract Twin-jets flow configuration. (a) Perpendicular (b) Divergent (c) Parallel (d) Convergent. Image 1 Highlights • Four types of flow patterns of impinging twin jet are studied by Large Dissipation Simulation. • Nusselt number is enhanced for all types of inclination for increasing Reynolds number. • Averaged Nusselt number of the perpendicular impingement gives better heat transfer than that of the oblique jets. • The poor heat transfer is obtained for the parallel oblique jets. • For the same angle, divergent jets give smallest heat transfer than the convergent jets. [ABSTRACT FROM AUTHOR]

Highlights • Transport characteristics in porous media are reviewed, including flow and heat transfer. • Transport phenomena of nanofluids are comprehensively summarized, involving heat conduction, convection and radiation. • Transport literatures for the combination of nanofluid and porous medium are classified and concerned. • Phase change heat transfer of nanofluids and porous media are summarized for liquid-gas type and solid-liquid type. • This review involves conduction, convection, radiation and phase change for specified media. Abstract Increasing the heat transfer rate of heat transfer equipment is an ever-lasting topic in thermal engineering. Due to the advantages of light weight, high specific surface, high thermal conductivity, metal foam is a good extending surface for heat transfer enhancement. Nanofluid has a higher thermal conductivity than the traditional base fluid, so it can be used as an efficient heat transfer medium. This paper focuses on various flow and heat transfer modes of nanofluid, metal foam and the combination of the two, with the physical properties of nanofluid and metal foam summarized. The characteristics of flow and heat transfer are introduced. The motivation of this review paper is to arouse the researchers to pay attention to the basic transport understandings for the heat transfer enhancement of nanofluids in porous media. The knowledge reviewed in this paper is useful for improving the performance of compact heat exchangers, and heat sinks for cooling electronics with porous media and nanofluids. [ABSTRACT FROM AUTHOR]

Highlights • Vertical fins contribute to melting by enhancing natural convection mechanism. • Extending fin length is more beneficial than increasing number of fins. • The cases with longer fins could have a higher overall heat transfer coefficient. • The compromise in energy density could be minor due to sensible energy gain. Abstract This paper investigates the effect of vertical fins, as an enhancement technique, on the heat transfer rate and energy density of a latent heat thermal energy storage system. This contributes with knowledge on the interaction of heat transfer surface with the storage material for optimizing storage capacity (energy) and power (heat transfer rate). For the assessment, numerical modeling is employed to study the melting process in a two-dimensional rectangular cavity. The cavity is considered heated isothermally from the bottom with surface temperatures of 55 ˚C, 60 ˚C or 70 ˚C, while the other surfaces are insulated from the surrounding. Aluminum and lauric acid are considered as fin/enclosure material and phase change material, respectively. Vertical fins attached to the bottom surface are employed to enhance the charging rate, and a parametric study is carried out by varying the fin length and number of fins. Thus, a broad range of data is provided to analyze the influence of fin configurations on contributing natural convection patterns, as well as the effects on melting time, enhanced heat transfer rate and accumulated energy. The results show that in addition to increasing the heat transfer surface area, the installation of vertically oriented fins does not suppress the natural convection mechanism. This is as opposed to horizontal fins which in previous studies have shown tendencies to reduce the impact of natural convection. This paper also highlights how using longer fins offers a higher rate of heat transfer and a better overall heat transfer coefficient rather than increasing the number of fins. Also, fins do not only enhance the heat transfer performance in the corresponding melting time, but also maintain similar total amount of stored energy as compared to the no-fin case. This paper discusses how this is the result of the enhanced heat transfer allowing a larger portion of sensible heat to be recovered. For example, in the case with long fins, the relative mean power enhancement is about 200% with merely 6% capacity reduction, even though the amount of PCM in the cavity has been reduced by 12% as compared to the no-fin case. Although the basis for these results stems from the principles of thermodynamics, this paper is bringing it forward with design consideration. This is because despite its importance for making appropriate comparisons among heat transfer enhancement techniques in latent heat thermal energy storage, it has not been previously discussed in the literature. In the end, the aim is to accomplish robust storage systems in terms of power and energy density. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a simple one-dimensional heat transfer model for the nanofluid-based direct absorption parabolic trough collector (NDAPTC) was developed, which was quick to solve, easy to understand, and unnecessary to solve the complicated differential equations. In an actual system, the vacuum condition between the inner tube and glass cover may be changed gradually over time. Therefore, a continuous function for calculating the convective heat transfer in the annulus from near vacuum to atmospheric pressure was established. Combined with it, the derived heat transfer model was suited to evaluating the long-running thermal performance of a NDAPTC quickly. The heat transfer model for a conventional indirect absorption parabolic trough collector (CIAPTC) was also constructed, aiming at comparing the heat transfer processes of this two kinds of collectors. Both the heat transfer models were validated by the test data from the reference. Additionally, the effects of physical parameters, operational and weather conditions on the collector thermal performance were analyzed. It was shown that improvement of the glass transmittance and emittance was crucial to raise the collector efficiency, especially at a higher inlet temperature. The pressure change in the annulus affected the collector thermal performance greatly, thus it tried to avoid the vacuum damage. The collector efficiency was raised with the solar irradiance and ambient temperature increasing and wind velocity reducing, which was more sensible to these weather conditions at a higher inlet temperature and pressure in the annulus. The results in this paper were useful for guiding the collector improvements and engineering designs theoretically, and were beneficial for cleaner production in civil and industrial heat utilization further. Highlights • A one-dimensional heat transfer model for the novel NDAPTC was developed. • A continuous convective heat transfer function in the annulus was derived. • The model was simple and feasible compared to the results from other research. • Effects of glass properties, operation and weather conditions on η c were studied. • The results were useful for evaluating collector long-running thermal performance. [ABSTRACT FROM AUTHOR]

The combination of the high conductivity of nanofluids with the huge accessible surface area of open-cell metal foam would indeed be a superb heat exchange technology. While individual ingredients of this technology have been separately investigated, the combination of the two has received only scant attention. Actually, there are only few studies that are focused on nanofluids flow and heat transfer in metal foam. This paper is intended to serve as an orientation for researchers who are interested in both nanofluids heat transfer and metal foam. The paper thus includes discussion of various aspects of nanofluids and their heat-transfer applications, as well as fundamentals of flow and heat transfer of ordinary fluids in metal foam. A section on recent heat transfer studies in metal foam is included, and another section on pore-scale modeling of transport in metal foam is provided. Nanofluids are presented in terms of their definition, brief history, preparation methods, theoretical models, properties, and engineering applications related to heat transfer. The paper then moves to describe metal foam and its morphology, as well as current understanding and theoretical treatment of flow and heat transfer in this class of highly-porous media. Key heat transfer and flow properties of the foam are outlined. The paper also presents the case for nanofluids forced convection heat transfer in open channels to serve as a background for the more complex case that involves heat transfer in porous media in general. The case of forced convection of nanofluids in metal foam in particular is presented next. Studies including complex effects, e.g. magnetism, are briefly described. Based on the above information, some key findings, conclusions and recommendations are made for interested researches. [ABSTRACT FROM AUTHOR]

In this paper Double Multi Relaxation Time Lattice Boltzmann method (DMRT-LBM) is utilized to investigate the particle motion in a modeled room for the first time. The effect of indoor heating system location has been considered on both particle deposition and convective heat transfer so six different positions have been selected for the heating system. Results are shown for two Rayleigh numbers (104 and 105) and different particle sizes (1 μ m and 10 μ m). To study the particle motion, after the flow reaches steady state, 50 000 particles are randomly injected to the room and the number of deposited particles on the walls has been reported for 100 s. Considering the present results, when the heating system is in the middle of the wall, the maximum heat transfer rate is seen for both Rayleigh numbers. Also, the number of deposited 1 μ m particles on the walls for all locations of the heating system is zero for R a = 104, so the number of suspended particles is the maximum. For both Rayleigh numbers and 10 μ m particles, the number of deposited particles is maximum when the heating system is fixed on the top of the wall. It is also concluded that when the heating system is located on the top of the wall, the number of suspended 1 μ m particles for R a = 105 reaches its maximum value. [ABSTRACT FROM AUTHOR]

Devices utilizing high voltage direct current (HVDC) necessitate effective heat dissipation using heat sinks to ensure stable and dependable operation. This paper introduces a novel spiral grooved cooling path heat sink concept, which uses a combination of propylene glycol and water as a coolant. A numerical analysis thoroughly explores how modifications to the cooling path structure can affect fluid dynamics and heat transfer characteristics. A series of simulations are conducted to scrutinize the performance of these innovative geometric modifications according to Friction factor, Nusselt number and Thermal performance factor. The heat sink's performance is also examined in the context of the working fluid's flow rate. Results show that the novel spiral grooved cooling path heat sink design exhibits the best thermal performance compared to a plain cooling path heat sink. Among the spiral grooved cooling path designs, SGCP 2 shows the highest thermal performance factor, indicating higher convective heat transfer rates. The thermal performance factor of SGCP 2 is 2.6–5.0% higher than SGCP 1 and 1.3–1.4% higher than SGCP 3. The proposed numerical approach provides a comprehensive understanding of cooling path configurations for heat sinks used for the purpose of cooling HVDC devices. [Display omitted] • A novel heat sink is presented for the cooling purpose of HVDC devices. • Experimental results are well matched with simulation results. • SGCP heat sinks exhibit higher heat transfer rate as compared to PCP heat sink. • Among SGCP heat sinks, SGCP 2 shows enhanced thermal performance factor. [ABSTRACT FROM AUTHOR]

Deep reinforcement learning (DRL) has gradually emerged as a novel and effective method for intelligent control of conjugate heat transfer. Through proper training, DRL agent usually can find a better control strategy than the one optimized manually. For numerous numerical simulation-based investigations, the promising results have only been obtained on 2-dimensional models due to the heavy burden of data acquisition. This paper proposes a novel strategy of transferring the control policy learned in 2-dimensional environment into a new 3-dimensional environment. PDD-DQN (Prioritized Dueling Double Deep Q-Networks) algorithm is used to recognize the underlying relationship between the forced fluid flow and heat transfer performance to produce a control strategy. The DRL controller is first trained on a simple 2-dimensional cavity with one heat source, and the DRL controller is able to reduce the maximum temperature to 315 K which is 2 K lower than the manually optimized control strategy; then the control strategy is transferred to 3-dimensional models where the maximum temperature is further reduced to 308 K; and compared to training the DRL agent directly on 3-dimensional model, the policy-transfer strategy requires only 10% computational expenditure. The proposed strategy is then applied to a more complex testbed with multiple heat sources for further investigating its ability; in both 2D and 3D environment, the DRL controller can cool the maximum temperature to be 307 K which is 8 K lower than the manually optimized control policy; and the computational cost drop to be 3%. The generalization ability of the trained DRL agent in inter-dimensional geometries is confirmed. For the cases with huge grid size, the policy-transfer strategy can economize exponential computational cost, which is of great significance for applying DRL methods to practical thermal control problems. [ABSTRACT FROM AUTHOR]

An efficient battery thermal management system is crucial for ensuring the working temperature environment of batteries and extending their lifespan. In this paper, a novel battery thermal management system combining vapor chambers and thermoelectric coolers is proposed to improve the battery's thermal behavior. Also, a complete fluid-thermal-electric multiphysics numerical model for the proposed system is built to predict its thermal performance under different cooling parameters. Results show that the use of thermoelectric coolers and vapor chambers can greatly lower the maximum temperature and temperature difference of batteries. Although the maximum temperature decreases with the increase of air convection heat transfer coefficient and coolant flow rate, the temperature difference increases at the same time. Under the given optimal air and water cooling parameters, it is noticed that as the input current of thermoelectric coolers increases, the maximum temperature and temperature difference show a pattern of decreasing first and then increasing. The optimal air convective heat transfer coefficient, coolant flow rate, and input current of 50 W/(m2·K), 0.04 m/s, and 1.5 A, respectively, are suggested, which corresponds to the maximum temperature of 39.83°C and temperature difference of 5.97°C. The present research introduces a fresh perspective on efficient battery thermal management, offering detailed insights into the utilization of thermoelectric cooling for this purpose. • A novel BTMS integrating with thermoelectric coolers and vapor chambers is proposed. • The use of TECs can greatly reduce the maximum temperature and temperature difference. • The battery temperature first increases and then decreases as the increase of input current. • Optimal input current, air and water parameters of 1.5 A, 50 W/(m2·K) and 0.04 m/s are suggested. [ABSTRACT FROM AUTHOR]

• Optimizing Permanent Magnets for Ferrofluid Cooling Breakthroughs. • Ferrofluid Cooling with Permanent Magnet Configurations for Efficient Thermal Management. • Unravelling the Impact of Permanent Magnet Configurations on Ferrofluid Cooling Efficiency. • Optimizing Magnet Configurations for Ultra-Efficient Heat Transfer in Ferrofluids. Many industries, such as microelectronics and power electronics, face challenges in removing large amounts of heat from small areas to prevent overheating. Recent research has shown that microchannel flow of ferrofluids driven by an external magnetic field (MF) has the potential to deliver efficient cooling systems for modern electronics. Despite this potential, robust optimisation of the MF has not been undertaken. This paper addresses this shortcoming by reporting the effect of the MF produced by three permanent magnets in various configurations on the heat transfer of ferrofluids undergoing laminar flow through a microchannel under constant heat flux boundary conditions at Peclét number Pe=73. Observations from numerical simulation show that the rate of convective heat transfer varies strongly with position and orientation of the magnets. We show that for the optimum magnet configuration, the maximum and average Nusselt numbers increase by more than 146% and 51% over the unperturbed flow, some of the highest values reported in the literature. These results show that significantly accelerated heat transfer is possible in magnetically driven ferrofluids, with potential for further enhancement with more rigorous optimisation. [ABSTRACT FROM AUTHOR]

• The retention angle models are modified considering the flow vicious effect. • Convection mechanism is adopted at high heat flux. • The new model has satisfactory predictions for liquid film profile and heat transfer coefficient. • Flow and heat transfer characteristics at high heat flux and low temperature are analyzed. In this paper, a new analytical model is developed for the condensation of refrigerants outside low-finned tubes. It is based on the flow and heat transfer characteristics at low saturation temperatures and high heat flux, such as those in the LNG intermediate fluid vaporizer (IFV). Due to the increase of viscous effect at lower saturation temperature and higher heat flux, the previous condensate retention angle models are modified by adding the viscous term. At high heat flux and condensate rate, the condensate profile at the fin root is simplified to be arc-shaped and obtained directly by force analysis. Furthermore, considering the heat transfer enhancement caused by the circumferential flow at high heat flux, the convective mechanism is included for the heat transfer through the thick liquid film between the fins. The distributions of liquid film and fin surface temperature are also predicted. The present analytical model is in good agreement with different experimental and numerical results, while most deviations are within 10% for predicting the heat transfer coefficients at high heat flux. Because of the increased flow viscosity and surface tension, the optimal fin spacing and fin height increase as the heat flux increases and the saturation temperature decreases. [ABSTRACT FROM AUTHOR]

• Inversion of physical properties of strong extinction materials. • Error filtering using wavelet analysis. • Analysis of the influence of wavelet parameters. • Experimental verification and comparison of traditional methods. The accurate acquisition of the physical properties of strongly extinction materials limits their application development. In order to solve the problem of large errors in the high temperature measurement of these materials, this paper constructs an inversion model for the radiative and conductive coupled heat transfer through wavelet decomposition coefficients, and compares it with traditional methods. The radiative and conductive coupled heat transfer model is solved by finite volume method and Monte Carlo method. Daubechies nine wavelet is used for signal wavelet analysis. It has been discovered that the wavelet decomposition parameters of the temperature field are mainly concentrated in the 4–8 wavelet frequency band of wavelet, it can separate from the random error that is mainly concentrated in the 1–3 frequency band of wavelet. Most of physical properties like the heating power, convective heat transfer coefficient, material thermal conductivity, extinction coefficient has a great impact on the waveform and amplitude of wavelet detail coefficient and approximation coefficient, and the change trend of approximation coefficient and detail coefficient amplitude is consistent with the trend of temperature field. However, the effect of scattering albedo on wavelet parameters is tiny. Through inversion, it is found that the inversion model based on wavelet decomposition parameters of 5–7 frequency band has higher accuracy when random error exists. [ABSTRACT FROM AUTHOR]

Fluid transport through microvascular networks—a hallmark for homeostasis in living systems—has transcended to engineered materials, primarily made possible because of modern manufacturing advancements. Vascular-enabled multifunctionality, including thermal regulation and self-healing, holds great potential for extending the lifetime of structural materials and expanding the operational envelope. Prior studies on vascular-based active cooling use a "combined" heat transfer coefficient (HTC): a single parameter lumps convection and radiation effects. Although the resulting mathematical models are linear—an attractive feature for computational modeling, the combined coefficient approach may not be accurate or even applicable if the operating temperature is unknown, which is the case with many thermal regulation applications (e.g., space probes). In this paper, we illustrate the remarked limitations of the lumped approach and advocate the need to use a decoupled HTC by splitting convective and radiative heat transfer modes. We show the broad applicability of the proposed method by applying it to three material systems: glass and carbon fiber-reinforced polymer composites and an additive manufactured metal. We show, using numerical simulations, the differences in the predictions from the decoupled approach with that of the combined HTC; these differences are prominent at higher heat fluxes. Also, the decoupling has enabled us to establish a scaling law that allows transferring of solutions fields across material systems, strengthening further the validity and utility of our approach. This work's significance is two-fold. First , the research is fundamental, providing accurate measurement protocols for critical model parameters. Second , this work facilitates the development of mathematical models for vascular-based thermal regulation that are predictive even for hostile environments (which are often difficult to realize in laboratories), such as outer space. • Theoretically consistent heat transfer coefficient (HTC) measurements and analyses. • A heat transfer framework for improved prediction of microvascular active-cooling. • Multi-material experimental validation of a reduced-order model. • Self-similar scaling strategy to transfer solution fields across material systems. [ABSTRACT FROM AUTHOR]

Aerogel is widely used in the field of thermal insulation. However, aerogel exhibits brittleness and infrared radiation transparency at high temperatures. Fiber composite aerogel achieved great progress, but the homogeneous structure hardly allowed heat convection, heat conduction, and heat radiation to be controlled simultaneously. In this paper, inspired by bamboo's multilayer and gradient structure, SiC fiber loaded with TaSi 2 and WSi 2 antioxidant particles was prepared by electrostatic spinning. The fiber was incorporated into the silicoboron carbonitride (SiBCN) aerogel to prepare gradient multilayer SiC/SiBCN ceramic fiber aerogel. The fiber network enhanced the mechanical properties. Antioxidant particles improved antioxidant performance. Heat radiation was reduced through the fiber, while heat conduction and heat convection were decreased by the aerogel. The results showed that the ceramic fiber aerogel exhibited ultra-low thermal conductivity, excellent infrared radiation shielding, and antioxidation performance. This study is expected to provide new ideas for constructing high-temperature thermal insulation ceramic fiber aerogel. • Novel gradient multilayer composites were constructed for thermal insulation. • The "gradient multilayer" structure of ceramic fiber aerogel had an excellent ability to shield thermal radiation. • The composites exhibited fire resistance and ultralow thermal conductivity at 1400 K. • The composite with TaSi 2 and WSi 2 particles provides it the antioxidant property. [ABSTRACT FROM AUTHOR]

This paper investigated the surface radiation-natural convection heat transfer with entropy generation in a 2D rectangular cavity. Also, the effects of Ra and ε were analyzed on radiation entropy generation (REG), conduction entropy generation (CEG), and fluid flow friction entropy generation (FEG). For problem simulation, energy and momentum equations were solved by the lattice Boltzmann method (LBM), and thermal radiation was investigated using the surface radiation method with gray surfaces. The top and the bottom walls are adiabatic, and the sidewalls are at a constant temperature. Simulations were conducted for Ra = 10 4 , 10 5 , and 10 6 , and ε = 0, 0.5, 0.8, and 1. Results show that REG has a symmetrical distribution on the constant temperature walls and the cold wall has the most REG. Higher REG and lower CEG are the consequence of increasing ε, furthermore, both of them increase by increasing Ra and vice versa. FEG has the lowest value of entropy generation for all Ra and can be neglected, therefore Be is very close to 1 in all cases. In addition, conduction (for ε = 0 , and 0.5) and radiation (for ε = 0.8 , and 1) have the most entropy generation. Generally, The total entropy generation (TEG) increases with increasing Ra and ε. [ABSTRACT FROM AUTHOR]

Nowadays, a bio-inspired heat exchanger incorporating a triply periodic minimal surface (TPMS) structure has demonstrated great potential in the fields of new energy research and aerospace, which necessitates achieving a balance between low volume and high heat transfer efficiency while maintaining low pressure drop. In this paper, the adjustable heat efficiency of the heat exchanger with TPMS in gradient thicknesses is specially designed. A steady-state conjugate heat transfer (CHT) model is coupled with computational fluid dynamics (CFD) analysis. In addition, the temperature profile and velocity streamline are also checked to analyze the fluid flow behavior of the radiator. The results show that the convective heat transfer coefficient of the Gyroid with gradient level set values is 26.02–60.10% higher than that of the uniform Gyroid model, and the pressure drop is decreased by 9.66–18.05%. Both high heat transfer efficiency and low pressure drop can be achieved when the thickness is 0.2–0.3 mm and Re is 100–125. The heat exchangers with a TPMS thickness gradient in the ratio of 2:4:6 demonstrate a remarkable enhancement in overall heat transfer efficiency, achieving a 30.22% improvement compared to those with a TPMS thickness gradient in 6:4:2. [ABSTRACT FROM AUTHOR]

In this paper we carry out a numerical investigation of forced convection heat transfer from a heated elliptical cylinder in a uniform free stream with angle of inclination θ °. Numerical simulations were carried out for 10 ≤ R e ≤ 120 , 0 ° ≤ θ ≤ 18 0 ° , and P r = 0. 71. Results are reported for both steady and unsteady state regime in terms of streamlines, vorticity contours, isotherms, drag and lift coefficients, Strouhal number, and Nusselt number. In the process, we also propose a novel method of computing the Nusselt number by merely gathering flow information along the normal to the ellipse boundary. The critical R e at which flow becomes unsteady, R e c is reported for all the values of θ considered and found to be the same for θ and 18 0 ° − θ for 0 ° ≤ θ ≤ 9 0 ° . In the steady regime, the R e at which flow separation occurs progressively decreases as θ increases. The surface averaged Nusselt number (N u av ) increases with R e , whereas the drag force experienced by the cylinder decreases with R e. The transient regime is characterized by periodic vortex shedding, which is quantified by the Strouhal number (S t). Vortex shedding frequency increases with R e and decreases with θ for a given R e. N u av also exhibits a time-varying oscillatory behavior with a time period which is half the time period of vortex shedding. The amplitude of oscillation of N u av increases with θ. • For steady state, flow for θ is a mirror image of 18 0 ° − θ. • The surface averaged Nusselt number increases with Re for a given θ. • At steady state, drag on cylinder decreases with Re and increases with θ. • Vortex shedding frequency increases with Re, and decreases with θ for a given Re. • N u av varies periodically with time, its time period = 1 / 2 × the time period of vortex shedding. [ABSTRACT FROM AUTHOR]

• The two-way coupled transient multiphase flow and heat transfer modeling framework. • Validation of the heat transfer models based on full-scale distributed temperature sensing (DTS) data. • Benchmarking of convective heat transfer correlations for transient multiphase flow against DTS data. • Analysis of coupling methods for the energy conservation equation with the Drift-flux model. Effective management of gas influxes during drilling for either oil-gas or geothermal wells is crucial for ensuring operational safety and minimizing non-productive times, especially for high-pressure, high-temperature (HPHT) situations. In recent years, there has been a growing demand for comprehensive modeling techniques that can accurately predict gas influx behaviors during Managed Pressure Drilling (MPD). However, many existing approaches have neglected the heat transfer processes between wellbore fluids and the surrounding formation during gas influx management, which can significantly impact the estimation accuracy. To address this issue, this paper presents an advanced transient multiphase flow and heat transfer modeling framework that integrates the solution of the energy conservation equation with the multiphase mass and momentum equations using a two-way coupled approach. A set of full-scale experimental data, including fiber-optic-based Distributed Temperature Sensing (DTS) measurements, were used to perform thorough validation and verifications of the developed modeling framework. Multiple existing heat convection correlations were benchmarked against the DTS measurements to determine the best match. The data from multi-depth downhole temperature sensors and Distributed Acoustic Sensing (DAS) were also compared to the results from numerical simulations. The estimation results of the wellbore fluids temperature profiles showed good agreement with the DTS data for both transient single-phase flow cases and gas influx management scenarios. A comparative analysis revealed that the selection of convective heat transfer correlations could significantly affect the simulation accuracy of fluid temperature distributions and gas influx behaviors. The benchmarking and optimized selection of convection correlations help to improve the performance of transient heat-transfer modeling. In addition, the two-way coupled approach shows improved accuracy compared to the decoupled methods, particularly for HPHT situations and more transient processes. [ABSTRACT FROM AUTHOR]

• An analytical model describing sublimation process with volumetric heating source under most sensitive temperature input in a half-porous space is investigated. • Convection driven by fluid flow in dried and in frozen porous region is considered. Rate of evaporation of water vapour in dried region is also considered. • Exact solution of the problem is obtained by using similarity transformation. • Convective heat/mass transfer and volumetric heating source provides faster sublimation rate than usual. • Newton type temperature source offers faster sublimation rate in compare to the constant and flux type temperature source. Sublimation heat-mass transfer has great applications in the pharmaceutical and food industries, such as the preservation of biological products, accelerated freeze-drying (AFD), energy storage systems, microwave freeze-drying, and enabling long-time active covid like vaccines. The current technological demand encourages investigators to provide new knowledge for freeze-drying so that it reduces the high economic cost, prevents materials from being denatured, and remains stable for a long time. In connection with this, it is of key interest to analyze the impact of convective heat and mass transfer, the rate of water vaporization, and the volumetric heating source under the most realistic temperature inputs. Despite the available works on sublimation, there is still a lack of mathematical modeling that accounts for these informations together and is presently being considered. This paper presents a heat and mass transfer problem describing sublimation in a half-porous space. The mathematical model accounts for convective heat/mass transfer and a volumetric heat source within dried and frozen regions. In addition, convection driven by the mass transfer of ice crystals within the dried region is also considered. Three different types of temperature input are placed at the surface x = 0 to obtain the rapid sublimation process without harming the material properties. The exact solution to the problem is obtained successfully by using similarity transformation. The impact of various problem parameters on sublimation is comprehensively studied. In this study, it is found that with a volumetric heating source term G 0 , material sublimates faster than without one. Furthermore, convective heat transfer in terms of P e 1 and P e 2 , enhances the temperature within the porous medium, and as a result, material sublimates faster than usual. As the value of the convective term β goes up, a reduction in the temperature field is observed. The temperature of the medium rises as the value of the Kirpichev-like number K i increases. Similar observation is found in the case of Biot like number B i. The concentration profile decreases as the value of the Luikov number L u increases. It is also found that Newton-type temperature input offers a faster sublimation rate in comparison to constant and flux-type temperature input. The analytical results obtained in this study show excellent agreement with previous available results. These results provide a comprehensive theoretical and mathematical understanding of sublimation heat/mass transfer and are expected to be useful in energy storage systems, food technology, and accelerated freeze drying. [ABSTRACT FROM AUTHOR]

This paper studied the buoyance-aided mixed convective heat transfer of air-cooling flow in a 5 m long and 1.2mX0.3 m cross-section vertical channel. One of the channel walls was uniformly heated and the rest three walls were unheated and insulated. Heat was transferred from the heated wall by convection and radiation, and heat was also transferred from unheated walls to the air flow by convection originated from their net radiation gain from the heated wall. The air flow rate, the inlet and outlet air flow temperatures, and local surface heat fluxes and temperatures on the heated wall were measured. The Reynolds number of air flow was from 2900 to 221,000 and Richardson number was changed from 0.006 to 90.6. The results showed that for walls with larger emissivity the total convection heat transfer was not deteriorated in mixed convection zone. Therefor a modified heat transfer correlation was developed for the aiding mixed convection in the asymmetrically heated channel considering both mixed convection and radiation. It predicted the experiment results with a deviation less than 18%. [ABSTRACT FROM AUTHOR]

The following paper presents a simple method of determining the presence, distribution and values of heat losses from external building walls as thermodynamic partitions using a Thermal Imaging Camera (TIC). According to Fourier's equation, the value of heat loss is proportional to the temperature gradient ∂ t /∂ y | y=0 in air in the y direction perpendicular to the heated surface. Unfortunately, air temperature cannot be measured with a TIC, as gases do not emit thermal radiation. It is therefore suggested that a grid placed vertically in the air and perpendicularly to the heated surface should be used as a detector of temperature field. Warmed by convective air flows, such a grid becomes a source of infrared radiation. The temperature distribution reproduced on the grid constructed from thin strands of a low thermal conductivity material is sufficiently distinct and sharp to be recorded with a TIC. The correctness of the TIC method has been tested in laboratory conditions on the example of a vertical heating plate, as well as in real-life conditions − on a single pane of glass serving as a building partition. When compared to the works of other authors, the result obtained as Nu  = 0.571· Ra 0.25 relation reveals a satisfactory correlation for the heating plate, while estimated temperature distributions and heat fluxes from the room to the surface of thermodynamic partition wall Q loss,conv,in and on the outside of the building Q loss,conv,ext successfully and quite precisely correlate (5–7% for both internal and external sides) with theoretical calculations. Therefore, the TIC method proposed in this paper can significantly extend the range of application of TICs in energy audits, especially for buildings [ABSTRACT FROM AUTHOR]

Finite amplitude convection in a inclined porous layer heated from below is studied by using local thermal non-equilibrium (LTNE) as mathematical model which takes into account the heat transferred between the solid phase and the fluid phase. Consequently, in addition to Darcy-Rayleigh number Ra and the inclination angle ϕ , two further non dimensional numbers are introduced: the inter-phase heat transfer parameter H and the porosity modified conductivity ratio γ . In a recent paper (Barletta and Rees, 2015), the linear stability analysis of the basic monocellular flow indicated that the inclination angle promotes the appearance of longitudinal rolls as the preferred mode of convection. The current paper focuses on the nonlinear evolution of longitudinal rolls in a supercritical regime of convection. A weakly nonlinear analysis, using a derived amplitude equation, is adopted to determine the nonlinear effects of the parameters Ra , ϕ , H and γ . The results indicate that in inclined layers (i) the nonlinearity decelerates the mean flow; (ii) the heat transfer, determined by the evaluation of the Nusselt number ( Nu ) at the layer boundary, corresponds to the one obtained for horizontal layers by scaling Ra with cos ϕ , i.e. Nu = Nu ( Ra cos ϕ , H , γ ) ; (iii) in accordance with existing laboratory experiments, the slope of Nu is less than 2, where 2 is the value predicted by the local thermal equilibrium model, and the slope represents the derivative of Nu with respect to the distance of the critical parameter from the threshold value for the onset of instability; (iv) increasing values of both H and γ produce an enhancement of the heat transfer across the layer. Finally, the comparison between the LTNE theoretical predictions and existing experiments conducted with various combinations of solid matrix and fluids suggests a possible alternative way to determine the heat transfer coefficient H . [ABSTRACT FROM AUTHOR]

The aim of the present paper is to establish the detailed numerical results for bioconvection boundary-layer flow of a two-phase dusty nanofluid. The dusty fluid contains gyrotactic microorganisms along an isothermally heated vertical wall. The physical mechanisms responsible for the slip velocity between the dusty fluid and nanoparticles, such as thermophoresis and Brownian motion, are included in this study. The influence of the dusty nanofluid on heat transfer and flow characteristics are investigated in this paper. The governing equations for two-phase model are non-dimensionalized and then solved numerically via two-point finite difference method together with the tri-diagonal solver. Results are presented graphically for wall skin friction coefficient, rate of heat transfer, velocity and temperature profiles and streamlines and isotherms. To ensure the accuracy, the computational results are compared with available data and are found in good agreement. The key observation from the present analysis is that the mass concentration parameter, D ρ , extensively promotes the rate of heat transfer, Q w , whereas, the wall skin friction coefficient, τ w , is reduced by loading the dust parameters in water based dusty nanofluid. [ABSTRACT FROM AUTHOR]