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The present study aims to quantify the flow field, flow velocity, and heat transfer features over a horizontal flat plate under the influence of an applied magnetic field, with a particular emphasis on low Prandtl number fluids. Nonlinear partial differential expressions can be incorporated into the ordinary differential framework with the use of appropriate transformations. This research utilizes the variational iteration method (VIM) to approximate solutions for the system of nonlinear differential equations that define the problem. The objective is to demonstrate superior flexibility and broader application of the VIM in addressing heat transfer issues, compared to alternative approaches. The results obtained from the VIM are compared with numerical solutions, revealing a significant level of accuracy in the approximation. The numerical findings strongly suggest that the VIM is effective in providing precise numerical solutions for nonlinear differential equations. The analysis includes an examination of the flow field, velocity, and temperature distribution across various parameters. The study found that improving temperature patterns, velocity distribution, and flow dynamics were all positively impacted by increasing the Prandtl numbers. As a result, this leads to the thickness of the boundary layer to decrease and improves heat transfer at the moving surface. Thus, the convection process becomes more efficient. When the strength of the magnetic field is increased, the velocity of the fluid decreases. This observation aligns with expectations since the magnetic field hampers the natural flow of convection. Notably, the convection process can be precisely controlled by carefully applying magnetic force. [ABSTRACT FROM AUTHOR]

The topologies of 3D lattice structures were reviewed and their overall heat transfer and heat dissipation performances compared, under the fixed mass flow rate, pressure drop and pumping power conditions, respectively. In total 12 lattice structures, with 6 different materials and in 2 orientations, were compared. The conjugate heat transfer in the lattice structures was solved with validated numerical models. Numerical results indicate that, the lattice topology, the lattice material and the operating conditions significantly affect the heat transfer and cooling performances. The optimal lattice differs under different comparison conditions. Under the fixed mass flow rate condition, the shifted X-lattice in orientation A and the octet lattice in orientation A exhibit the best heat transfer performance; the shifted X-lattice in orientation A also has the best cooling performance. Under the fixed pressure drop condition, the shifted X-lattices in both orientations A and B exhibit the best heat transfer performance; while the cubic lattice in orientation B and the shifted X-lattice in orientation B show the best cooling performance. Under the fixed pumping power condition, the shifted X-lattice in orientation A and the rectangular pyramid lattice in orientation B exhibit the best heat transfer performance; the shifted X-lattice in orientation B and the rectangular pyramid lattice in orientation B show the best cooling performance. The heat transfer and cooling performance database under a given lattice porosity and A characteristic length was presented as the benchmark for performance comparison of newly developed lattice structures. In addition, the data- base can benefit various engineering designs in selecting the appropriate lattice structures. [ABSTRACT FROM AUTHOR]

In this paper, numerical investigations are carried out to examine the laminar fluid flow and heat transfer characteristics of three various base fluids, six different water-based mono nanofluids, and six types of hybrid nanofluids (five binary and one ternary types) in a rotating U-shaped microchannel. In addition, the entropy generation is determined in microchannel for Cu/water nanofluid and pure water using both constant wall temperature (CWT) and constant heat flux (CHF) boundary conditions. This is accomplished using an Eulerian–Eulerian two-phase model for nanofluid simulation. In fact, this study aims to determine the impacts of various base fluids and nanofluids, Reynolds number (Re = 200–900), rotational speed (0–600 rad/s), and thermal boundary conditions on the entropy generation, pressure drop, heat transfer enhancement, thermal performance coefficient, and so on. It is observed that water-based fluids have better performance in rotating and stationary microchannels in comparison with those of EG and EO fluids. A survey on the thermal performance coefficient and efficiency in stationary and rotating microchannels shows that all examined nanofluids perform better than pure water and the Cu/water and SiO2/water nanofluids have the best and worst thermal performances, respectively. Moreover, the combination of Al2O3 and Cu nanoparticles with an equal volume fraction provides the highest Nusselt number compared to other types of nanofluids in rotating microchannel. The results show that the total entropy generation has a rising trend with increasing Reynolds number and rotational speed for CWT, while the contrary happens for CHF one. The total entropy generation of nanofluids is also lower than that of pure water in both CHF and CWT conditions. Finally, two correlations for total Nusselt number and friction factor are proposed that cover comprehensively all types of fluid examined. [ABSTRACT FROM AUTHOR]

Graphene foam composite is a promising candidate for advanced thermal management applications due to its excellent mechanical strength, high thermal conductivity, ultra-high porosity and huge specific surface area. In this study, a three-dimensional physical model was developed in accordance with the dodecahedral structure of graphene foam composite. A comprehensive numerical simulation was carried out to investigate the fluid flow and convective heat transfer in open-cell graphene foam composite by using ANSYS Fluent 2021 R1 commercial software. Research results show that, as porosity increases, the pressure gradient for graphene foam composite with circular and triangular cross-section struts is reduced by 65% and by 77%, respectively. At a given porosity of 0.904, when the inlet velocity increases from 1 m/s to 5 m/s, the pressure gradient is increased by 11.3 times and 13.8 times, and the convective heat transfer coefficient is increased by 54.5% and 43% for graphene foam composite with circular and triangular cross-section struts, respectively. Due to the irregularity of the skeleton distribution, the pressure drop in Y direction is the highest among the three directions, which is 8.7% and 17.4% higher than that in the Z and X directions at the inlet velocity of 5 m/s, respectively. The convective heat transfer coefficient in the Y direction is significantly lower than that along the X and Z directions. Furthermore, triangular cross-section struts induce a greater pressure drop but offer less effective heat transfer compared to circular struts. The research findings may provide critical insights into the design and optimization of graphene foam composites, and promote their potential for efficient thermal management and gas/liquid purification in engineering applications. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

AbstractThe aim of the current study is to examine the effect of an ellipse-protruded twisted strip on thermo-hydraulic performancein a circular tube. When elliptically protruded twisted tape tube is compared to plain twisted tape tube, the deviation is between 30% and 33%. The modeling results of Nusselt number vs Reynolds number of the plain twisted tape tube with actual data show a variance of 9.5%. A plain tube has a friction factor of one, whereas a plain twisted tape tube has seven times the friction factor. An elliptical protruding twisted tape tube has 1.5 times the thermal performance factor of a regular twisted tape tube. A correlation between the Nusselt number and the friction factor for the elliptical protruded twisted tape domain has been given; the expected and numerical results are 7.5–8.5 and 6–8% of each other. [ABSTRACT FROM AUTHOR]

Experimental and numerical investigations are conducted on a rotating disk from the perspective of convective heat transfer to understand the effect of heating on the stability of flow. A non-invasive approach with a thermal camera is employed to determine local Nusselt numbers for different rotational rates and perturbation parameters, i.e., the strength of the heat transfer. A novel transient temperature data extraction over the disk radius and an evaluation method are developed and applied for the first time for the air on a rotating disk. The evaluation method utilizes the lumped capacitance approach with a constant heat flux input. Nusselt number distributions from this experimental study show that there is a good agreement with the previous experimental correlations and linear stability analysis on the subject. A significant result of this approach is that by using the experimental setup and developed approach, it is possible to qualitatively show that instability in the flow starts earlier, i.e., an earlier departure from laminar behavior is observed at lower rotational Reynolds numbers with an increasing perturbation parameter, which is due to the strength of heating. Two experimental setups are modeled and simulated using a validated in-house Python code, featuring a three-dimensional thermal model of the disk. The thermal code was developed for the rotating disks and brake disks with a simplified geometry. Experimentally evaluated heat transfer coefficients are implemented and used as convective boundary conditions in the thermal code. Radial temperature distributions are compared with the experimental data, and there is good agreement between the experiment and the model. The model was used to evaluate the effect of radial conduction, which is neglected when using the lumped capacitance approach to determine heat transfer coefficients. It was observed that the radial conduction has a slight effect. The methodology and approach used in this experimental study, combined with the numerical model, can be used for further investigations on the subject. [ABSTRACT FROM AUTHOR]

The present study reports experimental investigations on jet impingement parameters such as nozzle shape, nozzle-plate spacing, Reynolds number, and effect of angle of cut for inclined nozzles on heat transfer. It is observed that the stagnation Nusselt number decreases with an increase in the angle of cut for inclined nozzles. Inclined nozzles produced a higher Nusselt number in the transition and wall jet region than reference nozzles. The radial velocity at the exit of the nozzle is higher for inclined nozzles toward the long lip. The turbulence intensity increases with an increase in nozzle exit angle. [ABSTRACT FROM AUTHOR]

The development of microchannel manufacturing technology has led to a growing interest in using them as heat exchangers. Microchannels are used to control the temperature of equipment and components that generate a high amount of heat flux. Heat transfer can be further increased by dispersing particles (nano-sized particles) with a low volume fraction into the base fluid (nanofluid). A nanofluid can change the thermophysical properties of a base fluid and improve its thermal performance. The purpose of this study was to examine the heat transfer characteristics of oil-based nanofluid within wavy microchannels in series and parallel arrangements of microchannels. In order to examine the performance of each microchannel separately and to make it easier to draw their diagrams, they are named 1 and 2. Experiments were performed on TiO2 and SiO2 oil-based nanofluids in volume fractions of 0.05 and 0.1, flow rates of 0.5, 1.0, and 1.5 lit/min, and inlet temperatures of 40°C, 45°C, 50°C, 55°C. The results show an increase in the Nusselt number of the base fluid up to 41.8% in the series arrangement and also a decrease in the surface temperature in the series arrangement compared to the parallel arrangement. Also, TiO2 and SiO2 nanofluids with a volume fraction of 0.1 caused the highest increase in heat transfer, up to 56% and 52.7% in parallel arrangement and up to 45.8% and 42% in series arrangement compared to the base fluid, respectively. The pressure drop of the test section in series arrangement was up to 82.1% higher than parallel.

In order to study the thermal conductivity of large volume vehicle liquid hydrogen bottle and its influencing factors, a numerical model of large volume vehicle liquid hydrogen bottle was established. The changes of thermal conductivity of liquid hydrogen bottle with fluid velocity, ambient temperature and inside position during storage and transportation were studied under different filling rates. The results show that with the increase of filling rate, the temperature stratification area in the bottle increases, the gas phase velocity increases and the temperature changes obviously. With the increase of filling rate and ambient temperature, the temperature inside liquid hydrogen bottle also increases, the heat flux increases and the temperature increases. With the increase of the filling rate, the amplitude and frequency of temperature fluctuation at different positions from the free liquid surface increase, and the temperature change at the free liquid surface becomes more drastic. • A liquid hydrogen bottle collision model considering heat transfer is proposed. • In the early stage of collision, the temperature in the gas phase changed greatly. • The temperature change at the free surface is the highest. [ABSTRACT FROM AUTHOR]

Abstract\nHIGHLIGHTSThis study presents a numerical evaluation of the performance of low Global Warning Potential (GWP) refrigerants R600a, R290, R1270, and R134a in heat dissipation by forced convection in a microchannel heat sink. The heat sink comprises 50 parallel microchannels with a cross-sectional area equal to 123 × 494 [µm2]. The differential equations describing the physical behavior interaction between the refrigerant and the copper matrix are solved using the finite volume method and the SIMPLEC coupling algorithm. The numerical model is used to predict fluid mechanics and heat transfer for single-phase laminar conditions including the friction factor, the Nusselt number and the average wall temperatures, as well as the whole performance of the microchannel heat sink. The accuracy of the numerical model is validated by comparing the performance of R600a with experimental data, resulting in deviations within the range of the uncertainty of each parameter. The evaluation of the performance of different refrigerants reveals that the friction factor and Nusselt number are significantly influenced by the microchannel geometry and thermal conditions, exhibiting unique yet similar trends for different refrigerants. Furthermore, the analysis of the average wall temperature in the microchannels demonstrates that the hydrocarbon-based refrigerants effectively reduce the temperature of the copper matrix compared to R134a, suggesting a superior performance in the dissipation of heat flux under single-phase laminar conditions.Thermal performance of refrigerants in heat dissipation by microchannel heat sink.FVM numerical prediction of fluid mechanics and heat transfer in microchannels.Computational model for R600a flow with experimental and predictive correlations.Hydrocarbon-based refrigerants demonstrate superior performance compared to R134a.Thermal performance of refrigerants in heat dissipation by microchannel heat sink.FVM numerical prediction of fluid mechanics and heat transfer in microchannels.Computational model for R600a flow with experimental and predictive correlations.Hydrocarbon-based refrigerants demonstrate superior performance compared to R134a. [ABSTRACT FROM AUTHOR]

Ordinary differential equations have recently been extended to fractional equations that are transformed using fractional differential equations. These fractional equations are believed to have high accuracy and low computational cost compared to ordinary differential equations. For the first time, this paper focuses on extending the nonlinear heat equations to a fractional order in a Caputo order. A new perturbation iteration algorithm (PIA) of the fractional order is applied to solve the nonlinear heat equations. Solving numerical problems that involve fractional differential equations can be challenging due to their inherent complexity and high computational cost. To overcome these challenges, there is a need to develop numerical schemes such as the PIA method. This method can provide approximate solutions to problems that involve classical fractional derivatives. The results obtained from this algorithm are compared with those obtained from the perturbation iteration method (PIM), the variational iteration method (VIM), and the Bezier curve method (BCM). All solutions are tested with numerical simulations. The study found that the new PIA algorithm performs better than the PIM, VIM, and BCM, achieving high accuracy and low computational cost. One significant advantage of this algorithm is that the solutions obtained have established that the fractional values of alpha, specifically α , significantly influencing the accuracy of the outcome and the associated computational cost. [ABSTRACT FROM AUTHOR]

The heat exchange between bridges and external environments is the primary cause of the temperature effect on bridges. The complexity of the two-phase (gas–solid) heat transfer mechanism, the diversity of the surface characteristics of bridge materials, and the uncertainties of the environment in which bridges are located make the numerical calculation of the heat exchange between bridges and external environments difficult. Several studies have been conducted by scholars around the world. In this work, the research on convective and radiative heat exchange between bridges and external environments is surveyed, analyzed, and summarized. The influencing factors and calculation methods of bridge temperature are examined, and the convective heat transfer and radiation mechanisms, theoretical calculations, and experimental measurement methods used to investigate the relation between bridges and external environments are summarized and analyzed. The value determination methods for convective heat transfer and radiation absorption coefficients in the calculation of the bridge temperature field are summarized. In addition, the problems and shortcomings of current research are evaluated, and future research directions are identified and discussed. [ABSTRACT FROM AUTHOR]

This paper reports experimental investigations on cold plates made from Low-Temperature Co-fired Ceramic (LTCC) technology for liquid cooling of supercomputer microprocessors. LTCC, a ceramic substrate-based technology with lightweight and ease of fabrication for miniaturization of cooling devices, can be a potential alternative to the existing copper cold plates for future three-dimensional stacked chip architectures. LTCC cold plates were fabricated using ceramic substrates whose thermal conductivity was enhanced using thermal vias. They were embedded with microchannels for liquid with different flow configurations. Their thermal performance is compared against copper cold plates. Deionized (DI) water is used as a coolant. Pressure drop and thermal resistance across different cold plates are measured as per water-cooled data center standards (W3 and W4 class). Obtained experimental results show that the tested LTCC cold plates can be used to cool supercomputer processors. It is concluded that LTCC cold plates can be a potential alternative for existing copper cold plates. [ABSTRACT FROM AUTHOR]

The study of compressible flow plays a fundamental role in the design of heat exchangers at high temperature and pressure. Compressible flow is used to design the aerodynamic structure, engines, and high-speed vehicles. In view of these utilities, this paper is deliberated to acquire the analysis of the unsteady compressible flow of a viscous fluid through an inclined asymmetric channel with thermal effects. Special attention is paid to convective heat transfer with impact of viscous dissipation, source/sink, and joule heating effects. In addition, thermal flow is analyzed through slip boundary conditions. The current problem is modeled through the laws of energy, momentum, and mass with the help of a fluid’s response towards compression. As a result, the coupled nonlinear partial differential equations are obtained, which are investigated through a well-known numerical approach, the explicit finite difference method. The study examines impact of several parameters on the flow rate, velocity, and temperature with the help of graphical representations. The behavior of flow rate is intended to change with time. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xi'an Jiaotong University is the property of Editorial Office of Journal of Xi'an Jiaotong University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

AbstractDeveloping structure optimization methods is critical for the design of more effective convective heat transfer channels. This paper proposes a new structure optimization method that can directly design the optimal rib structure under optimization targets and constraints. This method sets up the gradients between the objective functions and optimization variables by numerical differentiation, uses the Brinkman penalty method to generate the solid in the fluid domain, and obtains the optimal solution by the gradient descent method. When optimizing the rib structure, this method only considers the growth of the rib structure on the fluid-solid boundary and simplifies the 3D rib structure optimization into 2D rib height distribution, significantly reducing the computational load. The advantage of this method lies in its high flexibility and applicability to different objective functions and constraint conditions. It is first applied to the rib structure optimization of unilateral-heated channels under a periodic flow with the minimum average temperature of the heated surface as the optimization target. Optimization examples on the optimal average temperature of three solid materials, TC4, SS, and Al demonstrate decreases of 26.9%, 26.9%, and 27.3%, respectively, compared with the initial average temperature. Then, in the optimization with the target of minimum maximum temperature on the heated surface under a periodic flow, the obtained optimal rib structure reduces the maximum temperature from 400.4 K to 329.6 K, a 17.7% decrease. Given the comprehensive heat transfer coefficient (PEC) as the optimization target and constraining the mass flow, the optimized PEC can reach 2.4 at Re = 700. This method can be extended to optimal rib heat transfer structure design with different constraints, such as total rib volume, flow rate, pump power, etc., and with different optimization targets, such as Nusselt number, flow resistance, minimum maximum temperature, minimum temperature difference, etc. [ABSTRACT FROM AUTHOR]

The use of nanofluids for convectional heat transfer has become a spry area of research in recent years with the aim of improving heat transfer efficiency. Hybrid nanofluids have attracted significant attention and are advancing research and industrial applications since they involve employing more than one type of nanoparticle(s) in a base fluid. They enhance heat transfer by combining the chemical and physical properties of several nanoparticles concurrently and providing the properties in a homogeneous state. However, few experimental studies have focused on natural convective heat transfer using hybrid nanofluids. In this study, the natural convection of alumina – multiwalled carbon nanotube/water hybrid nanofluids formulated using a two-step method at a percentage weight ratio of 10:90 Al2O3: MWCNT at various nanoparticles volume concentrations of 0.00, 0.05, 0.10, 0.15, and 0.20 vol% was studied inside a square cavity (AR = 1) with two vertical walls which are isothermal, aimed at the Rayleigh number (Ra) range of 2.81 × 108 to 8.58 × 108. The average Nusselt number (Nuav), heat transfer coefficient (hav), heat transfer (Qav), and Rayleigh number (Ra) were considered at varying temperature gradients of 20°C – 50°C. Al2O3-MWCNT/water hybrid nanofluid with 0.10 vol% volume concentration was discovered to have the maximum value for hav,Qav, and Nuav. However, it was also observed that a further increase in the hybrid nanoparticles' volume concentration led to their deterioration at various temperature gradients. The maximum enhancements of 44%, 49%, and 42% were noted for hav,Qav, and Nuav, respectively, at ∆T = 50 °C, in comparison with the base fluid. Al2O3-MWCNT/water hybrid nanofluids application in a square cavity demonstrated enhanced natural convection. This present study concluded that hybrid nanofluids as heat transfer fluid significantly improved heat transfer performance compared to the base fluid. [ABSTRACT FROM AUTHOR]

In the present work a numerical analysis is presented to identify the separate effect of cooling by radiation and convection, in evaporative meat weight loss during beef carcass cooling process. A transient heat and mass transfer model is proposed using a 3D beef side geometry. Water activity variations are incorporated in the model. Convective coefficients are obtained from correlations by considering buoyancy effect due to temperature and vapor concentration gradients, and forced air flow. For the purpose of model water mass diffusion into the carcass, a first approximation of the meat layer thickness affected by drying is obtained from an analytical analysis as a semi-infinite solid. The model is solved numerically and it is validated with experimental data from the literature. Results of heat load and weight loss are compared to models proposed by other authors. Temperature and surface water activity evolution, and temperature and water content profiles are analyzed also. Finally, a sensitivity study is carried out on the main result of the model, total evaporated mass, varying heat convection coefficient and radiative cooling. It is found that there is a convective heat transfer coefficient that maximize the evaporative losses, so it is important to operate far from this point in order to reduce the evaporated mass. Furthermore, radiation during the meat cooling process turns out to be an interesting method to rapidly cool meat without increasing the evaporated mass (radiation cooling). Results shows that combining properly the convection and radiation heat transfer, evaporation losses can be reduced. • A simplified model to predict beef side weight loss is validated. • Both natural and forced convection are relevant during meet chilling process. • An upper limit of meat thickness affected by drying is analytically estimated. • There is a convective coefficient value that maximizes weight loss. • Theoretically a reduction in evaporated mass might be achieved by radiative cooling. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of transient temperature and thermal stress around a thermal insulated crack in a finite thermoelastic strip subjected to thermal shock based on the dual-phase-lag (DPL) heat conduction. A detailed investigation of the effect of convective heat exchange between the lateral surfaces of the strip and the ambient environment is conducted. By employing integral transform technique, the thermoelastic crack problem is reduced to a set of singular integral equations, and solutions for the transient temperature distribution and dynamic stress intensity factors (SIFs) at the crack tips are then obtained. Numerical results reveal a considerable temperature gradient near the heating surface when both the high convective heat transfer coefficient and thin strip are involved. Consequently, the SIFs in such scenarios where cracks are located close to the heating surface are significantly larger compared to those calculated by neglecting the convective heat loss. Furthermore, during the initial period following a thermal shock, the SIFs may exhibit higher magnitudes than the steady-state values. These findings emphasize the importance of accounting for the influence of convective heat exchange with the ambient environment in material design and optimization to enhance fracture resistance under transient thermal loading. [ABSTRACT FROM AUTHOR]

Copyright of China Mining Magazine is the property of China Mining Magazine Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study investigated the convective heat transfer coefficient and friction coefficient in a copper helical double pipe heat exchanger utilizing biosynthetic aqua-based silver (Ag) nanofluids prepared with Histiopteris incisa leaf extract. The nanofluids were characterized using UV–Vis spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy. The experimental approach involved the constant heat flux method under laminar flow conditions with flow rates ranging from 100 to 160 litres per hour (LPH). Biosynthesized aqua-based silver nanofluids were synthesized using a one-step biosynthesis method, resulting in volume concentrations ranging from 0.3 to 0.9%. Our findings demonstrated that the biosynthesized aqua-based silver nanofluids exhibited enhanced convective heat transfer compared to pure water. Additionally, the heat transfer coefficient showed an increasing trend with higher volume concentrations of biosynthesized aqua-based silver nanofluids. Notably, the most significant improvement in convective heat transfer, reaching 40%, was achieved with a 0.9% volume concentration of biosynthesized aqua-based silver nanofluids, a flow rate of 140 LPH, and a Dean number of 1400. Moreover, the friction coefficients observed for biosynthesized aqua-based silver nanofluids were 35% higher than those of water in the Dean number range of 1400–2400. [ABSTRACT FROM AUTHOR]

In industrial plants, metal strips are quenched using convective heat transfer. This involves accelerating gas through a nozzle system onto the material to be quenched, resulting in a fast and uniform cooling process. The efficiency of the heat transfer is determined by the specific nozzle system. The presented work is focussed on the analysis of the heat transfer by forced convection through impingement jets both theoretically and experimentally. A unique method for determining the forced convective heat transfer coefficient is described and its application to industrial size nozzle arrays of annealing-line cooling sections is presented. [ABSTRACT FROM AUTHOR]

In this work, the effects of jet impact angle and water flow on the heat-transfer coefficient in boron steel probes were analyzed. Angles of 90°, 75° and 60° were used with stirring flows of 33 l·min−1, 25 l·min−1, 13 l·min−1 and 6 l·min−1. The aim consisted of determining the heat-extraction rates by analyzing the correlation programmed in the Ansys Fluent 2020R2 software when different cooling conditions are used, avoiding many experiments, and establishing quenching conditions free of surface defects on the workpiece. This process is currently used in heavy machinery, requiring high hardness and wear resistance. The fluid-dynamic field was validated using a scale physical model using the particle image velocimetry technique, PIV. In contrast, the thermal field was validated with transient state experiments solving the inverse heat conduction problem, IHCP. The results show that for high flows (33 l·min−1), the jets with an angle of 90° impact the entire surface of the piece, but their cooling rate is slower compared to the other angles, being 243.61 K·s−1, and 271.70 K·s−1, 329.56 K·s−1 for 75° and 60°, respectively. However, for low flows (6 l·min−1), the impact velocities are very similar for the three cases, promoting more homogeneous cooling rates of 58.47 K·s−1, 73.58 K·s−1 and 63.98 K s−1 for angles of 90°, 75° and 60°, respectively. Likewise, through the use of CCT diagrams, it was determined that regardless of the cooling rate, the final structure will always be a mixture of martensite–bainite due to the effect of boron as determined experimentally, which implies a more significant proportion of martensite at higher cooling rates. [ABSTRACT FROM AUTHOR]

Ternary hybrid nanofluids offer significant advantages in heat transfer due to their enhanced thermal conductivity compared to traditional fluids. Investigating their flow behavior over expanding surfaces can contribute to the development of more efficient heat exchangers and cooling systems in the electronics, energy production, and transportation industries. This paper presents a detailed analysis of the flow and thermal transfer characteristics of a ternary hybrid nanofluid (SiO2–Cu–Al2O3/H2O) over a radially stretching surface, utilizing both numerical techniques (Keller Box method) and statistical techniques. Furthermore, the model includes factors like convective heat transport, radiation, internal fluid friction, and suction. Similarity transformations transform the governing equations for fluid flow and heat transfer into a system of nonlinear ordinary differential equations. Then the equations are solved numerically using the Keller Box method with the aid of MATLAB software. Additionally, we have employed statistical techniques such as correlation analysis, probable error estimation, and multivariate regression to validate and ensure the accuracy of the numerical outcomes. Parameter ranges for Biot number, radiation, unsteadiness, Eckert number, and energy generation parameter are 0.1 ≤ Mp ≤ 0.7, 0.1 ≤ Ks ≤ 1.5, 0.2 ≤ Ps ≤ 0.8, 0.1 ≤ EN ≤ 0.4, 0.5 ≤ RN ≤ 2, 1≤ BT ≤ 2.5, 0.1 ≤ Hsc ≤ 0.7 and found to significantly impact heat transfer behavior within these bounds. This study utilizes 3D surface plots to visualize the influence of key parameters on engineering quantities. R squared values show that the data strongly match the regression model. The findings demonstrate excellent concordance between the predicted values and the actual Nusselt number and skin friction measurements. Biot number has a very strong correlation with heat transfer, with minimal chance of error. And the same is evidenced by the correlation matrix and multiple regression analysis. Eckert number also exhibits a negative correlation with the Nusselt number. This translates to a situation where increasing Eckert number directly leads to a decrease in the rate of heat transfer, with no margin for error. Energy generation parameter demonstrates a negative correlation with heat transfer. However, there's a slight possibility of error, with an estimated error percentage of around 0.0017.

In this analysis, the creep responses of a non-constant thickness annular plate was presented. The material of disc is assumed functionally graded magneto-electro-elastic (FGMEE) in which the material properties change through the radius. Also, the heat transfer coefficients for convection and conduction are functions of radius and temperature. At first, the equation of heat transfer accounting for thermal gradient, convection boundary conditions, internal heat generation, and solar radiation effects was derived. The differential transformation method (DTM) was used to solve the resulting nonlinear differential equation. The equilibrium equation for the annular plate including creep strain effects was then obtained. Ignoring creep strains, an analytical solution was obtained for the zero-time of this equation. Then, creep strains were introduced using Norton's law and the Prandtl-Reuss relations to find the stress and strain rates under fixed temperature boundary conditions. Next, the equation of strain rates including creep strains was solved analytically. Finally, an iterative approach was used to evaluate the time-dependent redistribution of creep stresses at any time point. Numerical examples highlighted the influences of key parameters like internal heat generation, convective heat transfer, grading index, solar radiation, thickness profile, and angular speed on the stresses, deformations and electric and magnetic potentials.

The pin-fin design of the heat sink optimizes thermal dissipation by enhancing surface area and enabling efficient heat transfer in high-performance devices. The primary objective of the highly functionalized and convenient heat sink is to provide a competitive advantage in the field of efficient thermal management systems. The primary objective of this study is to investigate various designs of pin-fin heat sinks with unique shapes. These heat sinks are intended to operate in varying dynamic situations and necessitate an efficient convective heat transfer. The current technique has been thoroughly confirmed using earlier research, and computational investigations were conducted to improve the hydrothermal performance of staggered organized pin-fin heat sinks compared to the baseline case adopted from previous studies. Research is underway to examine the collective impact of the fin's unique structure, ideal aerodynamic form, and quality of perforations. A simulation of three-dimensional incompressible flow was conducted using the realizable k- ԑ model to generate turbulence flow that satisfies the relevant boundary conditions for solving the governing equations. When comparing fins shaped like a bishop to the standard hemispherical instance mentioned in recent work, the Nusselt number is 33 % higher. In addition, when the Reynolds number reaches 21,367, the presence of almond-shaped fins with circular perforations leads to a significant reduction in pressure drop, namely by 53.24 %. The almond-shaped hexagonal perforated fins, formed of a copper-diamond composite material, achieved the maximum hydrothermal performance factor (HTPF) of around 1.52 at a Reynolds number of 21,367. These layouts can be considered in various industrial applications.

The distribution of heat absorption and the mechanisms of conductive, convective, and radiative heat transfers between cold particle clusters (Tp = 300 K) and high-temperature surfaces (Tw = 1173 K) in fluidized beds were investigated through numerical simulations using the MFiX-DEM approach. The influence of cluster characteristics (εc and Dc), restitution coefficients (ep and ew), and particle properties (dp, ρp, kp, and cp) on heat absorption and various heat transfers was examined. The simulations indicate that convection predominantly governed the heat transfer behavior during the process of mesoscale clusters impacting the surfaces. A significant increase in heat transfer can be attained by reducing the cluster volume fraction, cluster size, particle diameter, and particle density. Besides, decreasing the restitution coefficients allowed for a relatively small enhancement of heat absorption. The maximum difference in ep was 2.11 kW/kg, while the maximum difference in ew was 0.99 kW/kg. The specific heat capacity and thermal conductivity of the particle had little influence on the distribution of heat absorption and heat transfer with a maximum relative error of up to 5.8 %. Finally, the mathematical correlation during surface-to-cluster heat transfer was established. This work introduces a novel application of the MFiX-DEM approach to analyze surface-to-cluster heat transfer at the particle scale, providing valuable insights for optimizing fluidized bed systems.

An experimental study evaluated heat transfer with perpendicular and wall-impinging air jets on stainless steel foil, for Reynolds numbers Re = 3000, 5000, 8000, and 10000, where the perpendicular jet targets the bottom and the wall jet the top, creating a unique, non-interacting effect. Distances to nozzle diameter ratios for wall jets (S/d = 4, 6, 8, 10) and perpendicular jets (Z/d = 2, 4, 6, 8) were varied. Significant heat transfer increases were noted, with the Nusselt number rising by up to 49.20 % for a Z/d = 6 and S/d = 8 combination at Re = 5000. Improvements ranged from 10.03 % to 49.20 %, peaking when the jets' high heat transfer regions overlapped. Optimal performance for Re = 3000 was at S/d = 10, aligning the wall jet's maximum with the perpendicular jet's stagnation area. For Re = 5000 to 10000, optimal S/d values were 8 and 4 for Z/d = 6, 8 and Z/d = 2, 4, respectively. The Nusselt number increase ranged from 29.21 % to 46.57 % at S/d = 10 for Re = 3000, the highest among all tested values. Wall jet heat transfer downstream increased by 90–105 % over perpendicular jets in corresponding regions. Increasing the wall to perpendicular jet distance improved heat transfer near the stagnation point, suggesting this cooling method for high-density electronics like CPUs and GPUs.

Addressing the critical issue of heat generation in electronic devices due to miniaturization and higher power density is essential. As electronic components become more compact, they generate more heat flux, necessitating efficient thermal management solutions. Traditional methods and fluids, such as water, struggle to meet the demand for efficient heat dissipation. To address this challenge, the utilization of nanofluids presents a promising solution. The objective of this study is to use CFD methods to examine how a nanofluid can improve heat transmission and lower the maximum temperature in a microchannel heatsink. This article presents the study of microchannel heatsinks with two distinct channel counts (five and eight). A constant flow, incompressible, laminar model was used to verify the findings. The working fluids used in the study were water in various concentrations, water-based nanofluids of Fe3O4-water and MWCNTs. CFD simulations revealed that a MWCNT-water nanofluid at 0.2 % concentration significantly improved cooling performance compared to water, demonstrating the potential of nanofluids for efficient thermal management in electronic devices.

To meet the energy requirement of the world, this work addresses the MHD flow of ternary hybrid nanofluid between two rotating and stretchable disks having porous medium. Thermal radiation effects along with velocity slips at the interface of fluid and disk are considered in this study. Three types of nanoparticles, namely, Al2O3 (alumina), CuO (copper oxide) and Cu (copper), have been taken with water as the host fluid. The flow and thermal characteristics of hybrid (Al2O 3 + CuO) and ternary (Al2O 3 + CuO + Cu) nanofluids formed by the combination of nanoparticles have been observed. This combination aids in the breakdown of dangerous compounds, environmental purification and the cooling of other equipment. The corresponding equations are modeled in terms of PDEs, and these PDEs are transformed into ODEs using Von Karman similarity transformations. The resulting equations are solved by using finite difference method based ND solver. The rate of heat transfer increases with the rise in thermal Biot numbers. Moreover, the solution predicts that for variations in radiation parameter from 0.5 to 1.5, heat transfer upsurges 88% for traditional nanoparticles, 92.4% for hybrid nanoparticles while for trihybrid nanoparticles, it grows up from 0% to 95%. [ABSTRACT FROM AUTHOR]

Rocket nozzles are often cooled by passing liquid propellants through channels in the nozzle walls. Estimating heat transfer to the wall from the hot gases in the nozzle is essential in deciding on the coolant flow requirements. The present work examines the computational estimation of convection heat transfer to the nozzle walls for compressible turbulent flows. Computations were performed using the rhoPimpleFoam solver in OpenFOAM® with two different turbulence models. We simulate the supersonic flow over a flat plate and validate the heat flux calculation method and turbulence model characteristics. We compare two methods of calculating convection heat transfer in the context of the nozzle flow case presented by Back & Massier. We find that the realizablek-e turbulence model works well in estimating the heat transfer coefficient. [ABSTRACT FROM AUTHOR]

Impellers are utilized to increase pressure to ensure that a radial pre-swirl system can provide sufficient cooling airflow to the turbine blades. In the open literature, the pressurization mechanism of the impellers was investigated. However, the effect of impellers on the cooling performance of the radial pre-swirl system was not clear. To solve the aforementioned problem, tests were carried out to assess the temperature drop in a radial pre-swirl system with various impeller configurations (impeller lengths l/b ranging from 0 to 0.333). Furthermore, numerical simulations were used to investigate the flow and heat transfer characteristics of the radial pre-swirl system at high rotating Reynolds numbers. Theoretical and experimental investigations revealed that the pre-swirl jet and output power generate a significant temperature drop, but the impellers have no obvious effect on the system temperature drop. By increasing the swirl ratio, the impellers reduce the field synergy angle and thus improve convective heat transfer on the turbine disk. In addition, increasing the impeller length can reduce the volume-averaged field synergy angle and improve heat transfer, but the improvement effectiveness decreases as the impeller length increases. Thus, the study concluded that impellers could improve the cooling performance of the radial pre-swirl system by enhancing disk cooling. [ABSTRACT FROM AUTHOR]

Using the power of numerical computation through Levenberg Marquardt backpropagation ($LMB$LMB), the fluidic issue in the present study has features of heat transfer by convection in the hybrid nanofluid suspension of magnesium oxide and gold nanoparticles. The influence of slip effects on boundary layer flow with viscous dissipation at the nodal/saddle stagnation point is examined using a mathematical model. The current study considers water to be the base fluid, $MgO$MgO and $Au$Au as nanoparticles, and the circular cylinder to be the medium’s surface. Non-linear partial differential equations are converted into ordinary differential equations via similarity transformations. The dataset for Levenberg Marquardt backpropagation is generated in Mathematica software using an explicit RK-4 approach by varying different parameters such as the slip parameter ($\lambda $λ), convective parameter ($Bi$Bi), Eckert number ($E{c^*}$Ec∗) and volume fraction (${\phi _2}$ϕ2), Bi with Ec. Validation, training, and testing are utilized for network modeling through the Levenberg-Marquardt backpropagation approach for various scenarios of the fluidic model. The result shows that the base fluid’s thermal behavior is quickly increased by the $MgO - Au$MgO−Au/water hybrid nanofluid. The reliability of the findings is evaluated using autocorrelation, regression, mean square error, absolute error, and error histogram analyses. [ABSTRACT FROM AUTHOR]

Context: In the past decade, rapid advancements in microtechnology and nanotechnology have propelled modern science and technology into the nanoscale domain, where miniaturization and high integration have found extensive applications across various fields, including industry, biotechnology, and information technology. Mechanisms of nanofluid flow and heat transfer properties have received increasing attention. In the flow and convective heat transfer of fluids at the nanoscale, the shape and dimensions of the surfaces play a crucial role. So, the main purpose of our paper is to investigate the influence of surface roughness with different shapes and quantities on fluid flow and convective heat transfer. In this study, we have chosen argon atoms as the fluid and used copper atoms to simulate the nanochannel walls. In order to investigate the influence of the shape and quantity of roughness on the convective heat transfer of fluids within nanochannels, we computed and analyzed the velocity, temperature, and density distributions of fluids inside channels with triangular, hemispherical, and rectangular roughness. Through simulation results, we found that triangular, hemispherical, and rectangular surface roughness at the same height can result in differences in temperature and velocity of the fluid within nanochannels. With a nanochannel roughness number of 5, the temperature and velocity of the fluid at the middle position of the nano-channel for the triangular roughness increased by 6% and 25% compared to the rectangular roughness, and by 4% and 10% compared to the hemispherical roughness. The fluid temperature and velocity are highest in channels with triangular surface roughness and lowest in those with rectangular roughness. Furthermore, increasing the quantity of surface roughness decreases the temperature and velocity of the fluid within nanochannels. When the quantity of rectangular surface roughness is 5, the fluid temperature within the nanochannel decreases by 12%, and the velocity decreases by 38% compared to a roughness quantity of 1. We also found, through velocity contours, that the presence of roughness increases the local fluid velocity in the rough regions of nanochannels. Roughness also reduces the density fluctuations of the fluid near the walls within the nanochannel. Roughness significantly affects the heat transfer performance of the fluid during its flow, and this influence should not be overlooked. Methods: In this study, molecular dynamics theory was employed, and simulations were conducted using the open-source software LAMMPS to investigate the influence of different shapes and quantities of surface roughness on fluid flow within nanochannels. The model in this paper was constructed using the LAMMPS software, and the surface roughness shapes on the walls were implemented as rectangular, hemispherical, and triangular. The wall surfaces were composed of copper atoms, while the fluid consisted of argon atoms. The copper atoms were arranged in a face-centered cubic (FCC) lattice with a lattice constant of 3.615 Å. Similarly, the argon atoms were arranged in a face-centered cubic (FCC) lattice with a lattice constant of 5.62 Å. The interactions between copper atoms were modeled using the EAM (Embedded Atom Method) potential, while the interactions between argon atoms were described using the LJ (Lennard-Jones) potential. The LJ potential was also employed to represent interactions between argon and copper atoms. [ABSTRACT FROM AUTHOR]

AbstractThe double-wall cooling system containing jet impingement and full-length pin-in cooling structures shows good performance in heat transfer enhancement and uniformity, which has-been used in the blade cooling design. However, the pressure loss induced by the full-length pin-fin is relatively high. It is very meaningful to get a cooling type which can balance the heat transfer performance of double-wall cooling and flow resistance, especially for the blade leading edge. In this study, numerical simulations have been carried out to study the influences of truncated pin-fins height and arrangement on heat transfer increment and flow behavior of jets impinging onto a concave double wall channel with varying truncated pin-fins arranged, considering the heat transfer enhancement potential and relatively weaken pressure loss penalty of truncated/broken pin-fin. Jets impingement on a smooth-concave surface is regarded as Baseline. Streamlines in two-dimensional sections in the channel and limiting streamlines near the target wall conjugated with flow characteristics figures are applied to better understand the flow structures in the channel. The local and averaged heat transfer performance is analyzed based on the flow discussions. The overall parameters, i.e., thermal performance, friction factor and pumping power, are also obtained. The results show that the introduction of relatively high truncated pin-fins located on the upper wall presents higher heat transfer enhancement and lower pressure loss comparing with the full-length case and truncated pin-fins located on pressure loss comparing with the full-length case and truncated pin-fins located on target wall cases. The truncated pin-fins placed on the upper surface with relative height of 0.75 reaches the highest overall thermal performance and uniformity in this work. [ABSTRACT FROM AUTHOR]

This work focuses on investigating the characteristics of restricted horizontal jet fire caused by fuel leakage as a pipeline or tank fracture. The study aims to quantify the effect of the exit velocity and nozzle-facing wall distance on the flame height and width, as well as developing a new non-dimensional heat release rate, *Qn, to better characterize the flame geometry. The study conducted three nozzle-facing wall distances (0.05 m, 0.10 m, and 0.15 m) with varying fuel ejection speeds from 1.04 m/s to 6.25 m/s. Results show that the flame height and width increase with both the nozzle-facing wall distance and fuel ejection speed. The sidewall constrains the air entering into the fire plume, which pushes the flame closer to the sidewall. A new non-dimensional heat release rate, *Qn, was proposed on the basis of plate-nozzle distance, that the flame height and width fit well with the 1/4 and 2/5 power of *Qn, respectively. The global model was developed for flame size under multiple restrictions. The findings of this study are crucial in improving our understanding of the restricted horizontal jet fire accidents caused by fuel leakage and can aid in developing measures to minimize potential casualties and economic losses. [ABSTRACT FROM AUTHOR]