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Some errors exist in the above paper. [ABSTRACT FROM AUTHOR]

Highlights • GFRP composite with artificial inclusion was tested by LIT. • Wavelet transform was used to compute the phase angle images from the thermal data. • An investigation was performed for the selection of wavelet parameters; scale and shift. • The effects of inclusion size and depth on phase contrast were analysed. • Experimental verification of simulated LIT was done to assess inclusions. Abstract In this work, we focused on lock-in infrared thermography as a non-destructive testing method for detection of inclusions in glass fiber reinforced plastic composite structures. The sample consisted of artificial inserts made of copper sheets to simulate inclusions of different shapes and sizes at varying depth levels. In an experimental study, the sample was excited at several modulation frequencies by a sinusoidal heat flux, and a thermal infrared camera was utilised for monitoring of surface temperature of a thermal wave that propagated into the sample. In simulation, ThermoCalc™-3D software based on finite difference method was used for the replication of the physical phenomena that were present in the experiment. The effect of the applied heat flux and time for different sizes and depths of inclusions was analysed to investigate the thermal response. Wavelet transform was applied to compute phase angle data from the temperature-time history of each pixel for the assessment of the inclusions. The investigation into the effects of wavelet parameters; scale and shift, modulation frequencies, inclusion sizes, and depths on the phase contrast was conducted and discussed. The simulation results were found to have a good correlation with the experimental results, thus demonstrating potential in detecting inclusions. [ABSTRACT FROM AUTHOR]

Carbon/carbon (C/C) composites impress with their excellent high-temperature mechanical properties. In this paper, in order to simulate the complex service conditions of aerocraft thermal protection systems, an experimental platform for simultaneous ablation and tension was designed. The mechanical and ablation properties of the C/C composites were tested under an oxyacetylene flame at heat flux of 2185 kW/m2. Meanwhile, the mechanism of mutual influence of ablation and tensile loading was revealed by microstructural characterisation. By comparing the tension-only and ablation-only conditions, the results show that the strength of the C/C composites under ablation conditions decreased by 52.0%, which was associated with the crack propagation and porosity increase caused by flame. The tensile loading increased the linear and mass ablation rates by 21.8% and 82.9%, respectively, which was due to the interfacial damage caused by tensile stresses provides more channels for flame to enter the material interior, thus accelerating oxidative ablation. [ABSTRACT FROM AUTHOR]

Polymer-derived ceramics (PDCs) are increasingly recognized as promising materials for high-temperature thin/thick film sensors (HTTFSs). However, a large linewidth and poor dimensional accuracy have severely restricted the practical application of PDCs HTTFSs. Our study employed a picosecond laser to precisely pattern the polymer-derived ceramic (PDC) thick film while applying no obvious damage to the interface between ceramic and substrate. Through parameters optimization, the laser-affected area was minimized to 6 μm wide, and a minimum feature size of about 30 μm was achieved. Furthermore, 7 rounds of high-temperature tests of the patterned film revealed good temperature-resistance repeatability within a temperature range of up to 800 °C. To demonstrate practical application potential, we successfully fabricated a heat flux sensor, and it exhibited a sensitivity of 1.32 mV/(kW/m2), a response time of 600 ms, and excellent repeatability over a range of 0–75.4 kW/m2. In summary, this paper proposes a novel approach toward miniaturizing the linewidth of the polymer-derived ceramics thick film sensor, showing significant potential for precise measurements in extreme environments. [Display omitted] [ABSTRACT FROM AUTHOR]

Pin fin-interconnected reentrant microchannels (PFIRM) of microchannel heat sink cooling systems provide a promising solution for efficient heat dissipation of high heat flux devices. They feature interconnected Ω-shaped reentrant configurations in cross-section, with large circular cavities at the bottom and diamond pin fins at the top. In this paper, a micro ball-end milling process was proposed to fabricate PFIRM. The burr formation process and deformation mechanisms during the micromilling process of PFIRM were investigated with experiments and finite element (FE) simulations. Results revealed that the burrs were mainly formed under the vertex of diamond pin fins on both up-milling and down-milling sides. The burrs on the up-milling side were pushed by the tool neck to the left side of feed direction, whereas the burrs on the down-milling side were thrusted by the flank face to the right side of feed direction. Besides, two unique types of chips, i.e., swallowtail-shaped chips and half swallowtail-shaped chips, were found to be formed during the micro ball-end milling process. Moreover, the effects of spindle speed and feed rate on the machining accuracy and surface roughness of PFIRM were also explored. The machining accuracy and surface roughness firstly increased and then decreased with increasing spindle speed. As the feed rate increased, the machining accuracy decreased in general, and the surface roughness firstly decreased and then increased. The present study suggested that the spindle speed of 15000 r/min and feed rate of 20 mm/min was optimal to improve the surface quality and machining accuracy. • Manuscript's Highlights. • Micro ball-end milling process was developed to fabricate pin fin-interconnected reentrant microchannels (PFIRM). • Burr formation process and deformation mechanisms of PFIRM were explored. • Swallowtail-shaped chips and half swallowtail-shaped chips were formed. • Effects of spindle speed and feed rate on machining accuracy and surface roughness of PFIRM were studied. [ABSTRACT FROM AUTHOR]

In the high-temperature environment, a larger thermal expansion mismatch of a bimaterial leads to pronounced thermal stresses and interface crack growth. In this paper, a generalized fractional heat conduction model is used to determine the instantaneous thermal fracture behaviors of a bimaterial interface crack. An axisymmetric thermoelastic problem is solved with the aid of Goodier's thermoelastic displacement potential and Love's potential functions. A mixed initial-boundary value problem is then converted to a singular integral equation of second kind by using the Hankel and Laplace integral transforms. Numerical results of the intensity factors of heat flux and thermal stresses are evaluated using Stehfest's Laplace inversion scheme. The influence of fractional kernel functions with power and exponential law are analyzed, respectively, for aluminum-steel and steel-epoxy, respectively. The thermal stress intensity factors exhibit more wave-like behaviors based on Riemann-Liouville and Atangana-Baleanu models which is different from Caputo-Fabrizio and the complete diffusion model. • An interface crack between dissimilar materials is analyzed. • Goodier's and Love's potential functions are utilized for solving the problem. • Transient heat flux and thermal stress intensity factors are investigated. • Characteristics for various fractional heat flux kernel are considered. [ABSTRACT FROM AUTHOR]

This paper is aimed at clear ice making. To this end, a purpose-built apparatus that controls the solidification rate was specially designed and constructed to assess the trade-offs between ice clearness (quality) and production rate (quantity). An image-based ice clearness evaluation technique was devised and adopted to compute a figure-of-merit for the ice quality. 30 ml ice cube samples were produced in a closed ice tray for either prescribed heat flux (650, 1300 and 1700 W m−2) or surface temperature (−4, −8 and −12 °C) at the bottom wall, while a 25 mm EPS insulation was adopted for top and lateral walls. The experiments were carried out using both tap and boiled water, whose initial amount of dissolved gas was monitored. The results pointed out the heat transfer and initial air concentration conditions that rule the quality and quantity trade-offs in clear ice making. [ABSTRACT FROM AUTHOR]

• This paper presents R290 (propane) and R1270 (propylene) local boiling heat transfer coefficients inside a BPHE. • R1270 exhibits boiling heat transfer coefficients very similar in trend, and 5–10% higher in magnitude, than those of R290. • Nucleate boiling seems to be the governing heat transfer regime both in R290 and R1270 tests. • Longo et al. (2015) model exhibits the best predicting performance with a MAPE of 7.7% and 6.9% for R290 and R1270, respectively. • R290 and R1270 exhibit boiling heat transfer performance between those of R404A and those of R410A. This paper presents the local heat transfer coefficients of R290 (propane) and R1270 (propylene) boiling inside a Brazed Plate Heat Exchanger (BPHE). A new test section was designed for measuring the local heat transfer coefficient in refrigerant two-phase heat transfer in a BPHE. The test section includes two thick AISI316L stainless steel corrugated plates instrumented with 36 T-type thermocouples for measuring the local plate surface temperature, the local heat flux and the local heat transfer coefficient in 9 positions along the refrigerant channel. The experimental tests were carried out at a boiling temperature of 10 °C, in the refrigerant mass flux range 5 − 17.5 kg m −2 s−1 with an inlet vapour quality ranging from 0.24 to 0.37 and an outlet vapour quality around 1.00. The global uncertainty of the local heat transfer coefficient measurement is within ±12.7%, and ±15.6%, for R290, and R1270, respectively. Nucleate boiling seems to be the governing heat transfer regime both in R290 and R1270 tests. Consolidated correlations for nucleate boiling inside BPHE show a fair agreement with all the experimental data. R290 and R1270 exhibit boiling heat transfer performance between those of R404A and those of R410A. [ABSTRACT FROM AUTHOR]

Abstract: A heat sink consisting of microchannels of rectangular or trapezoidal cross-section through which a polar fluid is circulated by means of an electro-osmotic pump was studied numerically. The equivalent pressure head—volume flow rate curve was determined for both geometries and the influence of the aspect ratio was investigated. The dimensionless temperature profile was calculated taking also the effect of Joule heating into account. The cross-sectional Nusselt number was determined for the above conditions and was found to be strongly influenced by the ratio of Joule heating to convective heat flux, . The dependence of the Nusselt number on the dimensionless electro-osmotic diameter () was also investigated for the two geometries and for increasing values of , and a comparison with the values obtained analytically for slug flow under the same conditions was made. The value of the Nusselt number, as a function of the aspect ratio, was also calculated for increasing values of . The numerical data presented in this paper can be useful to optimize silicon micro heat-sinks in terms of thermal performance. [Copyright &y& Elsevier]

The high energy content of hydrogen and zero carbon emission from hydrogen combustion is very important for compression ignition engine development. Hydrogen requires a very high auto-ignition temperature, which encourages replacing nitrogen with noble gases with higher specific heat ratio during compression process. In noble gases-hydrogen combustion, higher combustion temperature potentially leading to a higher heat loss. This paper aims to investigate the effect of hydrogen combustion in various noble gases on heat distribution and heat transfer on the cylinder wall. Converge CFD software was used to simulate a Yanmar NF19SK direct injection compression ignition engine. The local heat flux was measured at different locations of cylinder wall and piston head. The heat transfer of hydrogen combustion in various noble gases at different intake temperatures was studied using the numerical approach. As a result, hydrogen combustion in light noble gases such as helium produces faster combustion progress and higher heat temperature. The hydrogen combustion that experienced detonation, which happened in neon at 340 K and argon at 380 K, recorded a very high local heat flux at the cylinder head and piston due to the rapid combustion, which should be avoided in the engine operation. At a higher intake temperature, the rate of heat transfer on the cylinder wall is increased. In conclusion, helium was found as the best working gas for controlling combustion and heat transfer. Overall, the heat transfer data gained in this paper can be used to construct the future engine hydrogen in noble gases. • Combustion. • Heat flux; detonation. • Heat distribution. • Heat transfer. • Intake temperature. [ABSTRACT FROM AUTHOR]

• Characteristics of plate evaporator under low heat flux conditions are investigated. • Orifice diameter is the most sensitive to performance compared to orientation and pitch. • Distribution is categorized two profiles and improved at d o = 0.6 mm and φ = -45°. • Superheat oscillation shows high relevant to distribution and performance. • Flow coefficient for distribution pipe design is considered as a constant value of 1.15. Refrigerant distribution among channels plays an important role on performance of plate evaporator, especially under low heat flux conditions. Behaviors of plate evaporator under low heat flux condition are comprehensively and experimentally investigated based on distribution pipe solution in this paper. Influences of orifice diameter d o , orifice pitch d p and injection orientation φ are figured out on overall heat transfer coefficient (HTC), refrigerant distribution, and superheat oscillation. Results show that d o significantly affects evaporator performance compared to d p and φ. The HTC can be improved by 30 % with d o deceasing from 1.0 mm to 0.6 mm. φ obviously influences distribution when d o ≥ 0.7 mm and such effect is diluted at small orifice diameter. Two categories of distribution profiles are observed: rear flooded – front starved shape for the orientation of -45° and rear starved -front flooded shape for -90°. Refrigerant distribution is dramatically improved when d o = 0.6 mm and φ = -45°. Superheat oscillation shows strongly relevant to refrigerant distribution and affects plate evaporator performance distinguishedly. Pressure drop over the orifice is absolutely dominant in total pressure drop of plate evaporator. Flow coefficient of distribution pipe, α is defined and α can be considered as a constant value of 1.15×10−3 for predicting pressure drop and guiding distribution pipe design. The upper and lower deviations between calculated values and test data are within ±8.7 %. [ABSTRACT FROM AUTHOR]

• Spray evaporation of L-GWP refrigerant on enhanced tube bundles. • Influence of miscible oil on heat transfer performance. • Foaming characteristics of refrigerant/oil mixtures. • Impact of lubricant oil on spray evaporation of enhanced surfaces. • Comparison between square and triangular configurations of tube bundles. Lubricating oil is used in compressors of vapor compression-based refrigeration systems. The oil that escapes from the compressors inevitably circulates in the heat exchangers, affecting their thermal performances. This paper presents a comprehensive study on the impact of lubricating oil on the heat transfer performance of spray evaporator tube bundles used in air conditioning and refrigeration systems. The research includes valuable data on the heat transfer coefficient of tube bundles when subjected to refrigerant and lubricant mixtures of R134a (HFC) and R1234ze(E) (HFO) with synthetic polyolester (POE) lubricant. The investigation delves into the influence of three crucial factors: heat flux, oil circulation ratio (OCR), and saturation temperature. The saturation temperature was examined across a range of −6.7 to 10 °C (20–50 °F), while the heat flux was varied from 6 kW/m2 to 17 kW/m2. OCR was controlled at 1.2 %. The effects of oil on spray evaporation of R1234ze(E)/POE mixture on enhanced tube bundle was studied by varying tube surface structure and bundle layout, that is, square and triangular configurations. The bundle heat transfer coefficient decreased by at least 10 % when lubricant was present in the mixture but, in some cases, varied by 50 % or more compared to the performances with refrigerant only (i.e., no lubricant). The data suggested that the oil penalized the heat transfer coefficient of the bottom tube rows of the bundle, which in many conditions, starved and experienced a partial-dry out state. Externally enhanced boiling-type tubes were more sensitive to the presence of oil than externally enhanced condenser-type tubes. [ABSTRACT FROM AUTHOR]

All structural materials contain certain microdefects. Various elements of aircraft and spacecraft made from these materials are subjected to high mechanical loads and thermal effects during operation, which, in turn, can lead to the evolution of defects and total fracture of individual parts of the mechanism. Therefore, a quantitative and qualitative estimation of the stress and temperature fields in different bodies with complex configuration of external loading and temperature disturbances is needed. This paper presents a technique for numerical modeling of the temperature field in a medium weakened by a large system of partially heat penetrable cracks, including the possibility of considering it as an infinite periodic system. The method is based on a numerical algorithm, which uses the expansion of the solution into a finite series. Every term of this series is a certain analytical solution of the heat conduction theory obtained by the authors. To verify the method, the numerical results were compared with the well-known analytical solutions both for a configuration with finite number of cracks and for the periodic system. Also the heat flux intensity factors for a doubly periodic system were determined. • The numerical modeling of the temperature field in a medium weakened by partially heat penetrable cracks is presented. • The possibility of considering an infinite periodic system of cracks is included. • The numerical results were compared with the well-known analytical solutions and showed good agreement. • The heat flux intensity factors for a doubly periodic system were determined. [ABSTRACT FROM AUTHOR]

The present comment concerns some doubtful results included in the above paper. • The comment concerns a paper published in JML. • The slip parameter and the local Reynolds number are dimensional and wrong. • The local skin friction coefficient and the local Nusselt number are dimensional and wrong. [ABSTRACT FROM AUTHOR]

[Display omitted] • Diapers with moisture-adaptive embossment reduce skin wet and cold discomfort. • Designed embossments increase height by 92% after absorbing urine. • Peak heat flux of designed diapers decreases up to 44% than control group. • New diapers improve the urine absorption speeds by 12.5% to 42.8%. • Moisture-adaptive embossment can be extended to other absorbent hygiene products. Diapers are essential living consumables to infants and elderly. Thermal and tactile comfort of diapers are critical to the well-being of those who use them daily. Prolonged contact with moisture and fecal matter has been identified as a primary factor contributing to diaper dermatitis. The embossing patterns on the diaper's next-to-skin surface can reduce the contact area and decrease the risk of dermatitis. Current surface embossing designs of baby diapers have limitations in addressing issues related to prolonged usage, lack of support under body pressure, and insufficient reduction of skin contact with the surface layer. This paper reports on the development of a novel moisture-adaptive embossed surface layer through the embedment of a moisture absorbing hydrogel [viz. acrylic acid-co-sodium acrylate (AA-co-SA)] in the embossing structure. The incorporation of tailored AA-co-SA hydrogel dots within the diapers' inner surface layer resulted in superior thermal and moisture comfort in comparison with existing commercial products. The designed embossments proved effective in reducing the contact area and maintaining an air gap between the skin and the diaper under heavy compression. [ABSTRACT FROM AUTHOR]

In the above paper the first Rivlin-Ericken parameter is dimensional, not dimensionless as the authors claim. In addition, although the problem is non-similar, the authors used the similarity method of solution which is not accurate. • The comment concerns a paper published in Journal of Molecular Liquids. • The first Rivlin-Ericken parameter is dimensional, not dimensionless as the authors claim. • The similarity method used for the non-similar problem is not accurate. [ABSTRACT FROM AUTHOR]

• Flow boiling heat transfer and pressure drop data for R513A. • HTC shows both nucleative and convective behavior with operating conditions. • Pressure drop increases with mass flux and decreases with saturation temperature. • New composite prediction method (MAPE = 25.3%) for heat transfer coefficient. • Frictional pressure gradients well predicted by Friedel correlation (MAPE = 13.8%). This paper presents two-phase heat transfer coefficient and pressure drop data of refrigerant R513A, a new azeotropic mixture conceived as possible alternative to R134a for medium temperature small-size refrigeration systems. All the experiments were performed in a commercial horizontal stainless-steel tube having an internal diameter of 6.0 mm and an outer diameter of 8.0 mm. The channel heating was obtained through DC current and Joule effect. The effect of the main operating parameters in terms of mass flux (from 150 to 500 kg/m2s), heat flux (from 5.0 to 40 kW/m2), saturation temperature (from 30 to 50 °C) and vapor quality (from the onset of boiling up to the dry-out occurrence) was analyzed and discussed for the heat transfer coefficient values, finding that both convective and nucleate boiling were significant contributions. The same ranges of mass flux and saturation temperature were also applied to frictional pressure gradient trends with vapor quality, taken in adiabatic conditions. The thermo-hydraulic performances were then compared with those of R134a, obtaining lower heat transfer coefficients and very similar pressure gradients. Finally, the collected experiments were assessed with values predicted from the most quoted correlations available in literature. A new composite method for nucleate-dominant or convective-dominant mechanisms was proposed for the evaluation of the heat transfer coefficient, with a mean absolute error of 25.3%, whereas the frictional pressure gradient values were well predicted with the Friedel correlation, that provides a mean absolute error of 13.8%. [ABSTRACT FROM AUTHOR]

This figure shows the results from the CoolPINNs framework for forward and inverse problems. Heat is supplied to the bottom of the plate, and the top surface is free to convect and radiation. A flowing fluid through an embedded vasculature—in the shape of a sine wave—regulates the plate's temperature. The forward problem calculates the temperature field, whereas the inverse problem predicts thermal conductivity using noisy temperature data. [Display omitted] Emerging technologies like hypersonic aircraft, space exploration vehicles, and batteries avail fluid circulation in embedded microvasculatures for efficient thermal regulation. Modeling is vital during the design and operational phases of these engineered systems. However, many challenges exist in developing a modeling framework. What is lacking is an accurate framework that (i) captures sharp jumps in the thermal flux across complex vasculature layouts, (ii) deals with oblique derivatives (involving tangential and normal components), (iii) handles nonlinearity because of radiative heat transfer, (iv) provides a high-speed forecast for real-time monitoring, and (v) facilitates robust inverse modeling. This paper addresses these challenges by availing the power of physics-informed neural networks (PINNs). We develop a fast, reliable, and accurate Scientific Machine Learning (SciML) framework for vascular-based thermal regulation—called CoolPINNs: a PINNs-based modeling framework for active cooling. The proposed mesh-less framework elegantly overcomes all the mentioned challenges. The significance of the reported research is multi-fold. First , the framework is valuable for real-time monitoring of thermal regulatory systems because of rapid forecasting. Second , researchers can address complex thermoregulation designs since the approach is meshless. Finally , the framework facilitates systematic parameter identification and inverse modeling studies, perhaps the most significant utility of the current framework. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the confined distance near the floor(0∼28 mm) and wire size (the ratios of copper core diameter to entire wire diameter are: 6mm/8 mm,6mm/10 mm,8mm/12 mm and 6mm/12 mm for type Ⅰ, type Ⅱ, type Ⅲ and type Ⅳ, respectively) on the flame spread over polyethylene (PE) wires. It is indicated that, when the confined distance is relatively small, the extinction occurs for all types.The typical parameters of flame shape including of flame width, flame height and flame area, flame spread rate and mass loss rate with the increase of confined distance s can be separated into continuous growth stage and stable fluctuation stage. At the continuous growth stage, the flame area shows an exponential relationship with s as: A ∼ s 5 2 . And at the stable fluctuation stage, the flame width is larger than that at the unconfined condition accounting for a large portion.While, the flame height is always smaller than that in the unconfined case.In order to explicitly describe the heat transfer, the upward large main flame and downward small flame are firstly introduced in this paper. Correspondingly, the heat flux feedback of components to the preheating zone is established with the upward main flame flux q ˙ f (u p) ″ [includes of q ˙ v f (u p) ″ + q ˙ r f (u p) ″ ], the downward small flame heat flux q ˙ f (d o w n) ″ [ includes of q ˙ v f (d o w n) ″ + q ˙ r f (d o w n) ″ ], the conductive heat flux q ˙ c ″ and the gypsum board heat flux q ˙ g ″. With the increase of s, q ˙ f (d o w n) ″ shows an increasing and then decreasing trend, making it take a second role during heat flux feedback. Meanwhile, the analysis demonstrates that for the larger copper core (type Ⅲ) and the smaller of PE thickness (type Ⅰ), the ratio of heat flux of q ˙ f (d o w n) ″ q ˙ f (u p) ″ + q ˙ f (d o w n) ″ will be increased, which will enhance the heat transfer effect of downward small flame. [ABSTRACT FROM AUTHOR]

In the two-dimensional heat transfer experiments of aero-engine rotating disk cavities, the inverse heat transfer problem method can be used to obtain the wall heat flux numerically, which uses the two-dimensional measured wall temperature to solve the rotating disk heat conduction equation. A back propagation (BP) neural network data approximation method is proposed to reduce the ill-posedness of the two-dimensional inverse heat transfer problems in rotating disk cavities in this paper. The priori knowledge of wall temperature characteristics expressed by two-dimensional wall temperature first-order radial partial derivative distribution is used for BP neural networks' regularization. The distribution characteristics of the wall temperature first-order radial partial derivative in a typical preswirl rotating disk cavity were investigated by the flow-thermal coupling numerical simulation. Based on these characteristics, the BP neural network construction and training method with uncertain regularization coefficient is adopted. The numerical experiment results show that compared with the traditional polynomial fitting methods, the BP neural network approximation methods in this paper show significant advantages in data processing performance and stability; The fluctuation amplitude of the wall heat flux relative error on the disk surface can be reduced by 1–3 orders of magnitude, reducing the relative error of wall heat flux in most areas of the disk to within 20 % of the original value; The maximum wall heat flux relative error suppression area where | δq r ,cal / δq r ,mea × 100 %| < 100 % of BP neural network approximation method can reach 1.93 times that of the traditional fitting method, and 3.18 times for the area where | δq r ,cal / δq r ,mea × 100 %| < 30 % in the current study. • Wall temperature first-order radial partial derivative priori knowledge is used for BP neural network regularization. • The construction and training method of BP neural network with uncertain regularization coefficient is proposed. • The two-dimensional heat flux relative error fluctuation amplitude can be reduced by 1–3 orders of magnitude. • BP neural network shows significant advantages in data processing effect and stability compared with polynomial fitting. [ABSTRACT FROM AUTHOR]

• The applications of machine learning in predicting boiling heat transfer were reviewed. • Some important parameters for boiling by machine learning were presented. • The limitations of machine learning in boiling heat transfer researches were discussed. Boiling heat transfer, one of the most common and effective heat dissipation methods, is prevalent in industries and crucial for cooling electronic components such as chips. The key to boiling heat transfer research lies in enhancing improve its heat transfer performance, which is typically characterized by complex physical phenomena. Moreover, how to accurately predict the heat transfer process is still an important problem to be solved. Boiling heat transfer is generally associated with multiple parameters that are not accurately predicted by the usual mathematical form of empirical correlations. Therefore, this paper mainly reviews the applications of machine learning in predicting boiling heat transfer in recent years and provides a brief introduction to the main machine learning algorithms currently in use. The paper discusses the application of machine learning for predicting important parameters such as heat flux, heat transfer coefficient and critical heat flux, and examines the limitations of machine learning in boiling heat transfer researches. [ABSTRACT FROM AUTHOR]

• The safety and interlock protection system constitute integral components of HHFTF's overall control system, providing the capability to manage various subsystems, many of these systems are operated reliably close to their performance limits in order to achieve the desired goals. • Demonstration of an enhanced interlock protection system, encompassing both software and critical hardwired interlocks, within the high heat flux test facility. • Three different types of architecture have been developed: (1) Slow Architecture based on PLCs, for functions where response time of longer than 20 ms is adequate; (2) Fast Architecture based on FPGAs, for functions requiring fast response time beyond the capabilities of the PLC; and (3) Hardwired Architecture for critical functions. • Activation times of interlocks are demonstrated within a range from 100 microseconds to 116 milliseconds. This paper introduces the safety and protection measures implemented in the High Heat Flux Test Facility (HHFTF). The interlock system has been enhanced and integrated into HHFTF to ensure the protection of the facility and the safety of personnel, thereby mitigating risks during operations. The primary purpose of these interlocks is to secure the entire facility under well-defined conditions to prevent accidents. The safety and interlock protection system constitute integral components of HHFTF's overall control system, providing the capability to manage various subsystems, many of these systems are operated reliably close to their performance limits in order to achieve the desired goals. The overall safety, interlock protection and the control system encompasses both hardware components and software, employing Programmable Logic Controllers (PLCs) and Field Programmable Gate Arrays (FPGAs), along with wired logic based on relays and special logic cards. Three different types of architecture have been developed: (1) Slow Architecture based on PLCs, for functions where response time of longer than 20 ms is adequate; (2) Fast Architecture based on FPGAs, for functions requiring fast response time beyond the capabilities of the PLC; and (3) Hardwired Architecture for critical functions. The paper showcases the successful testing and outcomes of an enhanced interlock protection system, encompassing both software and critical hardwired interlocks, within the HHFTF. Key parameters monitored include the maximum allowable job threshold temperature, flow rates (for coolant loss detection), and chamber pressure. Activation times of interlocks were observed within a range from 100 microseconds to 116 milliseconds. [ABSTRACT FROM AUTHOR]

This paper presents pioneer experimental data on critical heat flux (CHF) during flow boiling of low-pressure fluid R514a in a microchannel. The authors conducted experiments in a single smooth and horizontal microchannel, with an internal diameter of 1.1 mm and heating sections of 46 and 100 mm, a saturation temperature range of 56 to 122.7 °C, and a mass velocity range of 1500 to 7500 kg/m2s. This research achieved high critical heat flux values, up to 1.85 MW/m2. The results were compared with the CHF of R123 under similar conditions and a higher CHF for R514a was observed. The performance of CHF predictive methods against the experimental data was performed. Since predictive methods for the CHF in microchannels need surface tension data, but there is a lack of experimental information about this property for R514a in the literature, this paper also presents experimental results for the surface tension of R514a and an expression for calculation of this property as a function of the temperature. • Pioneer critical heat flux experimental results for R514a are presented. • High values of mass velocities and saturation temperatures were tested. • Critical heat flux up to 1.85 MW/m2 were obtained. • Pioneer surface tension experimental data for R514a were measured. • Results are compared against predictive methods. [ABSTRACT FROM AUTHOR]

The investigation of jump cooling performance on turbine endwall independently causes its actual cooling effectiveness to deviate from the design values. In this paper, the endwall jump cooling structure with combustor-turbine interface cavity and combustor liners is modeled. Taking the realistic combustor-turbine interface features into account, the effect of jump coolant on turbine endwall film cooling and heat transfer characteristics is numerically studied. Under different endwall misalignment modes, the aerodynamic interaction mechanisms of realistic combustor outflow profile, jump coolant jet and cascade secondary flows at turbine endwall region are revealed. The modification effects of combustor-turbine interface features on jump cooling of the endwall are investigated. The results show that the combustor outflow severely ingests into the combustor-turbine interface cavity after flowing across several steps. Two branches of cavity vortex are subsequently generated in the middle-pitch region of cascade to affect the jump coolant jet. At low coolant blowing ratio, the attachment and separation sides of cavity vortex individually result in high and low cooling regions, while the horseshoe vortex leads to a large wedge-shaped cooling region. At z / C ax < 0, the backward step leads to a higher cooling effectiveness than forward step by 0.2. The jump coolant only leads to phantom cooling effect on downstream part of the vane suction side surface. The net heat flux reduction (NHFR) between two cavity vortexes and at pressure side junction are individually 0< NHFR <0.2 and −0.2< NHFR < −0.1. At high blowing ratio, the jump coolant can cover the pressure side junction with the highest cooling effectiveness of 0.5. The jump coolant can flow across the horseshoe vortex and directly upwash the vane surface. The weak protection regions between two cavity vortexes and near the attachment line of the pressure side horseshoe vortex enlarges. Compared with the forward step, the backward step achieves a lower NHFR by up to 0.1 and a higher Nusselt number. This paper provides an in-depth analysis of the aero-thermal physics of endwall jump cooling concerning realistic combustor-turbine interface conditions. [ABSTRACT FROM AUTHOR]

• The values of the recovery heat flux at superfluid helium boiling is differ from immersion depth and liquid temperature. • There is no influence permeability on the recovery heat flux at backfill particles diameters greater than 240 µm. • The calculated results are in satisfactory agreement with the experiment. • Porous insert has a significant effect on the interface dynamics\ (amplitude, frequency, stationary vapor film). The paper presents experimental data on the recovery heat flux during the boiling of superfluid helium (He II) on a flat heater located inside a U-shaped channel. The lower part of the channel is filled with monodisperse porous backfill. The paper includes information on the experimental cell, the data processing and synchronization technique, and the results of experiments conducted at different heater immersion depths and liquid temperatures. The paper presents also a mathematical description of heat transfer processes in superfluid helium for confined conditions. The calculated values are compared with experimental data. The effect of the porous backfill permeability on the recovery heat flux, including the case of a free channel is discussed. It is demonstrated that the increase in the heat flux in the channel initiates oscillations of the phase interface. [ABSTRACT FROM AUTHOR]

IVR-ERVC (In-Vessel Retention – External Reactor Vessel Cooling) is a critical accident management method for ensuring the integrity of the reactor pressure vessel (RPV) lower head. One of the most crucial aspects within this method is to enhance the CHF (Critical Heat Flux) on the outer surface of the reactor pressure vessel (RPV) lower head. This paper explores the application of graphene nanofluids in IVR-ERVC. This paper uses computational fluid dynamics to numerically simulate the CHF characteristics of graphene nanofluids under different undercooling, mass flow rate, concentration, tilt angle, and gap size conditions and analyzes the impact of different factors on CHF and the coupling effects between different factors. The undercooling range is 5 K–100 K, the mass flow rate range is 150 k g / (m 2 ∙ s) to 3000 k g / (m 2 ∙ s) , the concentration range is 0–1%, the inclination angle range is 0°–90°, and the gap sizes are 10 mm and 20 mm. The results show that the CHF can be effectively improved by adding nano-graphene into the base solution, and the CHF increases with the increase of subcooling degree, mass flow rate, concentration, dip Angle and gap size. Within the simulation range, the strengthening effect on CHF weakens when raising the undercooling and mass flow rate. And the larger the concentration and inclination angle within the simulation range, the better the enhancement effect on CHF. The maximum increase was 290%, while the average increase was 75.6%. This article studies the coupling effects between different parameters through numerical simulation. It can be concluded that increasing the mass flow rate weakens the enhancement of subcooling and concentration on CHF, increasing the subcooling weakens the enhancement effect of mass flow rate and concentration on CHF, and increasing the concentration enhances the enhancement effect of subcooling and mass flow rate on CHF. Enhance the mass flow rate will weaken tilt angle effect, while increasing the concentration will enhance the strengthening effect of tilt angle on CHF. [ABSTRACT FROM AUTHOR]

Modeling and optimization of liquid hydrogen (LH 2) pumps require accurate in-cylinder heat transfer correlations. However, the applicability of existing correlations based on gas mediums to LH 2 remains to be verified. In this paper, the unsteady heat transfer and fluid flow in a closed LH 2 pump cylinder are numerically studied by adopting the gas spring model. The phase shifts and temperature distribution in the closed pump cylinder are investigated. LH 2 is less affected by in-cylinder heat transfer and has a more uniform temperature distribution compared to nitrogen gas, while a low-temperature zone appears near the piston face at 120 rpm. Finally, the validity of Lekic's correlation in predicting the heat flux of the LH 2 compression process in the closed pump cylinder is verified, and the efficiency decrement versus rotational speed is analyzed based on the correlation. This work would be useful for selecting a proper in-cylinder heat transfer model for predicting the thermodynamic process in reciprocating LH 2 pumps. [Display omitted] • Gas spring model is applied for unsteady heat transfer process of LH2 compression. • Low-temperature zone appears near piston surface at 120 rpm due to LH2 properties. • Heat flux on piston surface with rotational speed differs from that of other walls. • Lekic's correlation predict heat flux on cylinder wall well excluding piston face. • Rotational speed has a notable effect on efficiency decrement from 0 to 200 rpm. [ABSTRACT FROM AUTHOR]

Arc plasma is the heat source in electrical discharge machining (EDM), it affects the material removal and discharge crater formation directly, so it is necessary to clarify its characteristics. However, it is challenging to understand the physical mechanisms behind each pulse discharge through experimental methods, as it is a transient, multi-physical process that occurs in a very short time and small gap. In this paper, a two-temperature model was proposed to investigate the characteristics of the arc plasma and the energy distribution considering the multi-physics fields in the steady state. In this model, the electrons and the heavy species of the arc plasma were considered separately in the energy conservation equations, so that the temperature of the electrons and heavy species can be calculated separately. Besides, the velocity distribution, pressure distribution, electrical potential distribution, and diameter of the arc plasma, as well as the heat flux distribution and the energy distribution into the anode and cathode were analyzed. Then the variations in arc plasma properties and energy distribution with different discharge conditions were studied. The results showed that, at a lower discharge current, the electron temperature was higher than the heavy species temperature, which means that the arc plasma did not reach a local thermodynamic equilibrium (LTE) state under these discharge conditions. To validate the simulation results, the arc plasma was observed with a high-speed camera, and the diameter of craters on the surface of both the cathode and anode was measured with single-pulse discharge experiments. The experiment results were consistent with the simulation results. • A two-temperature model was established to study the arc plasma in EDM. • The temperature of electrons and heavy species of arc plasma was obtained. • The arc plasma did not reach the local thermodynamic equilibrium state under the given simulation conditions. • The energy distribution ratio into the anode, cathode, and dielectric were calculated, respectively. • The arc plasma characteristics and the energy distribution under different discharge conditions were studied. [ABSTRACT FROM AUTHOR]

• Boiling of ammonia in a vertical dimpled tube bundle: bare tubes, full length round PVC inserts and 33% cut inserts. • Study of wide range of experimental parameters. • Heat transfer comparison. This paper is the last leg of the previous three papers of the same series with experimental study carried on a vertical shell and tube heat exchanger comprising of seven dimpled enhanced tubes. Three different tube configurations were tested. (1) bare tube (2) with full length solid PVC nonconductive round rod insert (12.7 mm diameter) and (3) 33% cut insert. For the same flow, tubes with rods developed annular flow within the annular portion between the tube and the rod. Source of heat was hot ethylene glycol/water solution flowing on the shell side. Saturation temperature of ammonia was -20 °C ≤ T sat ≤ -2 °C, heat flux range 5 kW m−2 ≤ q ˙ ≤ 45 kW m−2 and mass flow rate of 0.008 and 0.015 kg s−1. Tests were conducted for each mass flow rate at four saturation temperature. Two-phase heat transfer coefficient increased with saturation temperature and heat flux for all cases with initial increase and then a drop at the onset of partial dry out. The tube with 33% cut rod exhibited better overall performance. Results were also compared with plate type evaporator data. [ABSTRACT FROM AUTHOR]

• Experiments were conducted for flow boiling of zeotropic mixture refrigerants in horizontal tube. • Experimental data are obtained under high pressure and high heat flux conditions. • Local temperature and composition shift in vapor and liquid are analysed from the data. • Thermal resistance and mass transfer resistance are discussed. The paper reports an experimental investigation of local saturated flow boiling heat transfer of two environmentally-friendly zeotropic mixture refrigerants – R454B and R449A – in a horizontal 8.7 mm ID smooth tube, under high pressure and high heat-flux conditions. The test section is divided into five subsections to obtain quasi-local heat transfer and the refrigerants are heated by hot water in counter-current flow. For R454B, mass flux varied from 201 kg m−2 s−1 to 269 kg m−2 s−1 and the inlet pressure varied from 1.691 MPa to 3.282 MPa. For R449A, mass flux varied from 178 kg m−2 s−1 to 328 kg m−2 s−1 and the inlet pressure varied from 1.449 MPa to 3.244 MPa. The temperature glide and composition shift during flow boiling due to volatility difference between components were investigated. R454B and R449A displayed a temperature glide respectively from 1.12 K to 1.33 K and from 3.04 K to 4.61 K at the inlet of the test section in the present tests. During the process of saturated boiling, for R454B, mass fraction of the less volatile component, R1234yf, in liquid phase was over 7% more than that in vapor phase; For R449A, mass fractions of the less volatile components, R134a and R1234yf, in liquid phase were around 6% and 4% more than those in vapor phase. Thermal resistance and mass transfer resistance were discussed. Before the occurrence of partial dry-out, heat-transfer coefficients of R454B were mainly located between 6.5 kW m−2 K −1 and 10 kW m−2 K −1 while most of data of R449A lay in the range of 3.5 – 8 kW m−2 K −1. The results of heat-transfer coefficient indicate that R454B exhibited greater heat transfer than R449A under close operating conditions. For both refrigerants, the heat transfer performance was locally enhanced in the region of near-zero vapor quality and gradually declines before intermediate vapor quality. After intermediate vapor quality, it tended to rise with vapor quality until a dramatic fall due to partial dry-out. [ABSTRACT FROM AUTHOR]

Deploying shallow geothermal solutions is critical for meeting energy demands while supporting decarbonisation targets. In densely populated areas, drilling large numbers of boreholes may lead to thermal interactions between closely located borehole heat exchangers. This paper presents a novel method termed the infinite borehole field model to estimate the technical shallow geothermal potential, especially in urban regions. The thermal interactions between boreholes are considered using finite element models simulating the operation of a single borehole in a larger field. Mathematical optimisation is used to find the amount of thermal energy that can be annually extracted while keeping the borehole wall temperature above freezing point of water. The method considers thermogeological details of geological formations including downward-increasing ground temperature, geothermal heat flux, thermal conductivity, heat capacity, porosity, density, and advective heat transfer. Results of our case study indicate that 100 m deep thermally independent boreholes can produce 14.20 MWh/a for 50 years on average. However, boreholes in an infinite borehole field spaced 20 m apart produce 7.80 MWh/a. A further investigation including advective heat transfer indicated that high velocity groundwater flow can significantly enhance borehole yield. Our method provides a generalised approach which can be beneficial prior to detailed site investigations. [ABSTRACT FROM AUTHOR]

In this paper, a near-field thermophotovoltaic (TPV) system with a dual TPV cell design is considered and studied numerically. The fluctuational electrodynamics accompanied by the dyadic Green's function are utilized for calculating the radiation heat flux. The generated photocurrent and the conversion efficiency are obtained by solving the photon-coupled charge transport equations. It was discovered that the addition of the second TPV cell to the system, increases the generated photocurrent of the system due to the absorption of the low-energy photons and generation of the electron-hole pairs. By increasing the gap size between the emitter and Si TPV cell from 50 nm to 1 μm, the generated photocurrent decreases because of the reduction of the near-field thermal radiation effects. Finally, the tandem nano-gap TPV system shows higher conversion efficiency compared with the single Si TPV cell for different values of the vacuum gaps, and the gap size of d 1 = 200 nm is the optimum gap size due to the improvement of the conversion efficiency of the system. [ABSTRACT FROM AUTHOR]

• Typical CRUD depositions are obtained via accerlated deposition method in rod array channels. • Effective CRUD thermal conductivity decreases as heat flux increases with 1.3866 W/(m × K) on average. • CRUD growth process is a combination of soluble precipitation and particulate aggregation. • Fouling resistance of corrosion product deposition behavior has been experimentally measured. CRUD depositions on fuel cladding are the main cause of power shift and localized corrosion in nuclear power plants. This paper is the first of a three-part study concerning the formation mechanism of CRUD depositions and its related heat transfer issues. In this paper, CRUD depositions are obtained under subcooled boiling conditions in 2 × 2 rod array channels via accelerated deposition method to explore corrosion product deposition and its feedback on heat transfer. Imbalance of deposition and erosion at initial stage causes fouling resistance to increase first and then decrease. CRUD growth is proposed as a relatively pure fouling process combining soluble precipitation and particulate aggregation. Through high-resolution characterizations, boiling chimney diameters span from 3 μm to a dozen microns. Principal components are nickel ferrite and nickel elemental with Fe/Ni ratio of 1.9:1. Static contact angle decreases to less than 30°. Effective CRUD thermal conductivity decreases with the increase of heat flux with 1.3866 W/(m × K) on average. The results of this study provide a precise method for understanding corrosion product deposition and its impact on heat transfer to further establish accurate CRUD-related models and predict CRUD-related safety issues. [ABSTRACT FROM AUTHOR]

• Predicted the occurrence position and power of the rod bundles' CHF. • Compared the influence of cladding materials' properties on the rod bundles' CHF. • Provided a detailed analysis of the impact of grid spacers on the rod bundle' CHF. The critical heat flux (CHF) is one of the safety standards for core thermal design and is crucial for the normal operation of the reactor. The CHF problem of rod bundles with grid spacers is a hot topic in related research. The successful design of grid spacers can improve channel CHF by affecting the flow of downstream coolant, and this detection analysis can be achieved through numerical simulation methods. In addition, most simulation studies have not considered the solid region of the cladding, so there is little research on the effect of cladding materials on CHF. The role of grid spacers in rod bundle CHF is the focus of this paper, and the influence of cladding materials is another discussion direction. In this paper, following meticulous mesh generation and computational model validation, a study on the CHF of the 5 × 5 rod bundle with multiple grid spacers and different cladding materials is carried out by using CFD software. The verification results indicated that the physical model established in this study can reasonably predict the generation location and critical power value in the 5 × 5 rod bundle with grid spacers. Furthermore, the study identified that the grid spacer exerts a significant influence on coolant flow within the channel, while the weakening of the mixing effect of the grid spacer on the coolant flow is the main factor to lead the boiling crisis upstream of the grid spacer. By comparing the effects of thermal properties of different materials on CHF, it was found that when the thermal conductivity ratio of the two materials is 1.08, CHF is almost identical under the condition of a reference heat flux of 0.1 MW/m2 as a step size. In addition to thermal properties, further attention may be paid to the influence of surface characteristics of materials on CHF in future work. [ABSTRACT FROM AUTHOR]

Efficiently and actively dissipating accumulated heat within asphalt pavement is crucial for reducing pavement distress and improving subgrade stability. This paper proposed a novel inverted "T" shaped heat induced structure (IT-HIS) that facilitates the rapid transfer of heat from the pavement to the subgrade and shoulders. The IT-HIS consists of two components: a vertical gradient thermal conductivity structure utilizing steel slag, and a horizontal oriented carbon fiber heat induced structure. The heat transfer behavior of the IT-HIS was analyzed using a finite element heat transfer model created in ABAQUS, and the results were validated through indoor irradiation experiments. The findings demonstrated that the IT-HIS enhanced heat flow and promoted secondary aggregation in the vertical direction, while facilitated lateral heat dissipation. Compared to the ordinary group (OG), the heat flux of IT-HIS at depths of 5 cm and 6.5 cm increased by 19.8 % and 64.6 %, respectively. The indoor irradiation experiment results indicated that during the heat absorption period, the IT-HIS reduced temperatures at depths of 0 cm, 2 cm, and 5 cm by 1.5 ℃, 1.7 ℃, and 1.1 ℃, respectively. During the heat dissipation period, the IT-HIS reduced temperatures at depths of 0 cm, 5 cm, and 10 cm by 0.9 ℃, 0.7 ℃, and 1.8 ℃, respectively. The IT-HIS enhanced the cooling effect during daytime and inhibited heat upward during nighttime based on the gradient thermal conductivity structure. The proposal and validation of this structure provide a fundamental approach to forming large-scale high-speed microchannel heat dissipation within asphalt pavements, and is expected to provide experimental and theoretical foundations for the development of directional active cooling technologies. • In order to reduce heat accumulation within asphalt pavement, this paper proposed a novel inverted "T" shaped heat induced structure (IT-HIS). • IT-HIS enhanced heat flow and promoted secondary aggregation in the vertical direction, while facilitated lateral heat dissipation. • IT-HIS enhanced the cooling effect during daytime and inhibited heat upward during nighttime. [ABSTRACT FROM AUTHOR]

Porous surfaces are a common modified surface used to enhance boiling heat transfer. In this paper, a method for preparing gradient porous surfaces is presented, that is, magnetic stirring is added to the electrolyte and the cathode surface to be deposited is placed vertically downward. Within the Cl ion concentration range of 30–140 mg/L, increasing the Cl ion concentration results in lager pore sizes. When the Cl concentration was greater than 120 mg/L, the average pore size of the surface gradually increased from the center to the edge, and the number of pores gradually decreased from the center to the edge. All surfaces showed superhydrophilicity. The critical heat flux of Sample#3 is 158.72 W/cm2, which is 67% higher than the smooth surface. The wall superheat of Sample#3 was only 15 °C in the critical state. This porous surface has plenty of nucleation sites. These nucleation sites are gradually activated when the heat flux increases. At low heat fluxes, heat transfer on these porous surfaces presents a disadvantage because the nucleation sites are not fully activated. At high heat fluxes, these porous surfaces show a decrease in wall temperature. Consequently, the porous surface prepared in this paper has good boiling heat transfer at high heat flux. [Display omitted] • An inverted deposition method was designed to prepare gradient porous surfaces. • The gradient porous surface is superhydrophilic and provides a large number of nucleation sites. • An appropriate increase in Cl-ion concentration increases the pore size and pore wall thickness. [ABSTRACT FROM AUTHOR]

Liquid-vapor behavior characteristics near CHF conditions are investigated through flow visualization experiments and theoretical analysis. The detailed liquid-vapor behavior near CHF is captured by high-speed camera in this paper. With the increase of heat flux, the periodic vapor layer occurs due to numerous large bubble coalescence. A three-layer structure is observed close to CHF conditions, i.e., liquid film, vapor layer, and liquid core. The physical triggering mechanism of CHF is the complete evaporation at the liquid film wave trough position close to the end of the heating rod. Furthermore, based on the separated flow model and instability analysis, respective prediction models for essential liquid-vapor characteristics, including thickness of vapor layer, interfacial wavelength, and the maximum thickness of liquid film, are developed. The predicted results are in good prediction performance with MAE of 16.9 %, 12.8 %, and 26.1 % compared to experimental results, respectively. The relevant research in this paper provides an important foundation for further development of the mechanistic CHF model. • A novel CHF mechanism is observed through flow visualization experiment. • A new interfacial friction factor prediction model is developed. • Models for essential liquid-vapor characteristics near CHF are established. [ABSTRACT FROM AUTHOR]

• A superimposed model applicable for predicting the growth rates of both stationary and sliding bubbles is proposed. • The force balance model for predicting bubble departure diameter and lift-off diameter is modified. • Present modified model predicts both departure and lift-off diameters with mean absolute percentage errors of 25.0 % and 24.0 %, respectively. The calculation of heat flux for each component in the wall heat flux distribution model involves a crucial parameter, namely the characteristic bubble diameter. The bubble departure diameter and lift-off diameter are two of the most significant characteristic bubble diameters. In this paper, the bubble growth rate and bubble force analysis in subcooled flow boiling under various inclination angles of the heating surface are investigated, and the bubble departure and lift-off diameters are calculated based on force balance. According to the energy balance method, a superimposed bubble growth model is proposed that incorporates the effects of superheated layer evaporation around the bubble, microlayer evaporation, and condensation at the top of the bubble on the bubble growth rate. This paper proposes a force balance model for heating surfaces with varying inclination angles, based on accurate calculations of wall superheat. The model has been validated by a large amount of experimental data and exhibits superior accuracy and stability compared to existing models. [ABSTRACT FROM AUTHOR]

The preheating process of the solar receiver in the Concentrated Solar Power (CSP) plant is necessary but dangerous before filling the molten salt, because the empty pipe is easy to overheat, but it is required to heat up quickly to match the preheating requirement. In this paper, a lab-scale receiver was used to study the preheating process, and a transient numerical model was also developed for a better understanding of the preheating process. A detailed description of the receiver's performance on the 20% xenon lamp power was conducted, and the numerical modeling was verified through the comparison with the experimental results. The preheating process of the receiver under different xenon lamp power was performed, and a non-linear relationship existed between the period of the preheating process and the different xenon lamp power. Moreover, this paper also reported that the negative feedback control was used to realize the dynamical preheating process, and the method worked according to the surface temperature of the receiver until the preheating requirement was reached. Finally, the effect of environmental temperature on the preheating process was conducted, and the preheating duration of the receiver with the same heat flux was prolonged by about 30 s with the environment temperature of −2 °C. [ABSTRACT FROM AUTHOR]

A compound parabolic concentrator (CPC) with a flat absorber is widely used in low-concentrating photovoltaic thermal (CPVT) systems. CPC certainly develops non-uniform heat flux distribution over the absorber surface which is significantly reduced by the integration of homogenizer referred as Elongated CPC (ECPC). The objective of the present work is to analyse the effect of homogenizer ratios, truncation ratios and concentration ratios on the heat flux distribution characteristics of a CPC collector. In this paper, a ray tracing simulation is carried out to obtain the heat flux distribution profiles and the same is incorporated within CFD software to obtain the temperature distribution profiles. As a result, it is observed that the optimum truncation ratio would be 0.7 at which uniformity in flux distribution is improved by 3%, with just 2% reduction of average heat flux value. Furthermore, with optimized homogenizer ratio of −0.35 at concentration ratio of 3, 64% improvement in uniformity of flux distribution has been noticed. From the study, it has been concluded that for different concentration ratios of 1.5, 2, 3, 4, 5, 6, 7 and 8, the optimum homogenizer ratio is observed to be −0.9, −0.55, −0.35, −0.25, −0.2, −0.15, −0.15 and −0.05 respectively. [ABSTRACT FROM AUTHOR]

When exposed to high non-uniform heat fluxes on the receiving surface, significant temperature gradients develop in the tubes, producing thermal stress and deformations in the receivers. This paper reports a detailed investigation of the thermal and structural performance of a solar tower system that operates with direct steam generation tubes when the fins are added to the internal surface and thickness varies. Six tubes were evaluated, two without fins varying the wall thickness (5 mm and 3 mm) and four with fins under different configurations. The thermal system corresponds to a representative tube of an external tubular receiver of a central tower system. The thermal receiver operates with direct steam generation under a non-uniform concentrated solar flux with a maximum value of 0.93 MW/m2. The best configuration of the tube was with fins on the frontal surface of the tube, maintaining a receiving wall thickness of 3 mm and an adiabatic wall thickness of 5 mm. It could reduce maximum thermal gradients and temperature by 31% and 14%, respectively, maximum thermal stresses by 38%, and maintain vapor mass flow at the output (276 kg/h). [ABSTRACT FROM AUTHOR]

Since their development at the end of the 50s, panel methods were widely used for the fast simulation of aerospace objects reentry. Although improvements were proposed for the continuum regime formulations, the bridging functions usually employed in the transitional regime did not go through major changes since then. With the current interest in designing Very Low Earth Orbit satellites and more efficient reentry vehicles, a greater level of preciseness is now required for the fast computation of the aerodynamic and aerothermodynamic wall quantities in rarefied regime. In this context, this paper presents a new approach to build Machine Learning based surrogates going from the choice of the design variables and the Design of Experiments, to the models training and evaluation. Hence, kriging and Artificial Neural Networks are respectively trained to predict the pressure and heat flux stagnation coefficients, and the pressure, friction and heat flux coefficient distributions in the rarefied portion of any aerodynamic shape's reentry. • New reduced models for the wall quantities in hypersonic rarefied conditions. • Kriging models for the stagnation heat flux and pressure coefficients. • Neural networks for the friction, heat flux and pressure coefficient distributions. • A thorough and challenging validation of the models has been carried out. • A more precise and generic alternative to classic panel methods. [ABSTRACT FROM AUTHOR]

Five components of heat flux, viz: conduction, q c o n d ″ , sensible mass diffusion, q d i f f ″ (s) , formation mass diffusion, q d i f f ″ (o) , sensible convection, q c o n v ″ (s) , and formation convection, q c o n v ″ (o) have been analyzed extensively in this paper for the unwrapped model of the rotating detonation engine (RDE), using an explicit large-eddy simulation (LES) approach with a kinetic mechanism consisting of eight reaction steps and seven chemical species. The results shown are from averaged fields obtained after the attainment of the quasi-steady state condition. The maximum static pressure occurs at the transverse detonation wave, with a value that is one order of magnitude higher than the relatively uniform values that are found in most part of the domain. By y ≈ 0.0044 m , which is roughly one-tenth of the axial distance in the domain with (x , y) ε [ 0,0.1 ] × [ 0,0.04 ] m, most of the reacting species (H 2 , O 2) have been depleted at all transverse locations. From the mass averaged magnitudes of the heat flux components, it has been found that q c o n v ″ (o) , has the largest contribution, followed very closely by its sensible counterpart, q c o n v ″ (s) , whose magnitude is roughly half of that for the formation enthalpy heat flux. This is followed (in magnitude) by q d i f f ″ (o) and q d i f f ″ (s) , which are of comparable values and are over three orders of magnitude smaller than the convective heat flux components. The conductive heat flux q c o n d ″ is roughly an order of magnitude smaller than the mass diffusion values. The Nusselt number and heat transfer coefficient for the present problem are significantly higher than those encountered in low-speed, non-reacting flow fields. • Five components of heat flux in a model of the rotating detonation engine (RDE) were extensively investigated in this study using the large-eddy simulation (LES) approach within the context of combustion and detonation. • The critical structures in the RDE combustor (shock waves, slip lines, contact discontinuities, etc.) significantly determine the magnitudes and distributions of the three heat flux components that are based on molecular diffusion. • The formation convective heat flux has the largest contribution, followed very closely by its sensible counterpart, whose magnitude is roughly half of that for the formation enthalpy heat flux. The conductive heat flux has the smallest magnitude, which is roughly one order smaller than the mass diffusion values. • The maximum static pressure occurs at the transverse detonation wave, with a value that is one order of magnitude higher than the relatively uniform values that are found in most part of the domain. • The axial distance at which a significant amount of the reactions occur was determined. [ABSTRACT FROM AUTHOR]

In this paper, microchannel flow boiling heat transfer and critical heat flux (CHF) are numerically characterized under both static and rolling conditions. The volume of fluid (VOF) based numerical model of a rectangular microchannel with the dimension of 4 × 400 mm is established. The additional force induced by rolling motion is loaded via a user defined function (UDF). Rolling amplitude and rolling period vary in the range of 10∼20° and 1∼2 s, respectively. The results demonstrate that bubble flow, slug flow, stretch bubble flow and annular flow are observed under static conditions. However, under rolling conditions, bubbles are more difficult to agglomerate and coalesce under the influence of additional forces. Rolling motion maximumly deteriorates CHF by 81.1% and wall temperature by 18.8%, respectively. Moreover, CHF decreases with the increase of rolling period while increases with the increase of rolling amplitude. The purpose of this research is to understand the microchannel CHF triggering mechanism under rolling conditions to aid in marine heat exchanger design. [ABSTRACT FROM AUTHOR]

Crack measurement after thermal shock is usually considered as a replacement because real-time observation of thermal shock experiments is difficult to achieve. This paper presents an experimental approach for real-time displaying thermal shock cracking using oxygen-acetylene flame and high-speed imaging of translucent ceramic. We capture the crack propagation process, calculate the crack propagation speed, discuss the effect of sample size and flame heat flux on the crack propagation, and analyze the difference between the crack propagation under cold shock and hot shock. This paper further improves the mechanism of thermal shock damage of ceramic materials. [ABSTRACT FROM AUTHOR]

• Heat transfer of supercritical R1234yf was experimentally investigated in a horizontal micro-fin tube. • Operating parameter effects on heat transfer were analyzed. • Heat transfer comparisons were conducted between R1234yf and R134a. • Prediction accuracy of existing correlations for R1234yf was analyzed. R1234yf is regarded as an ideal substitute for R134a in supercritical organic Rankine cycles. This study experimentally analyzed the convective heat transfer coefficients of supercritical R1234yf in a micro-fin tube. The experiments show the influence of the system operating parameters including pressure, heat flux and mass flux on the heat transfer. Then, this paper compares the heat transfer rates for R1234yf and R134a at supercritical pressures and the ability of existing correlations to predict the heat transfer coefficients with R1234yf. The results show that as q / G increases, the buoyancy increases Nu bottom , while the variations in Nu top are divided into two regions based on the bulk fluid enthalpy. The influence of pressure on the heat transfer is also related to the bulk fluid enthalpy. When the bulk fluid enthalpy is less than a critical value, Nu bottom and Nu top both increase with decreasing pressure and then decrease above this critical enthalpy. The heat transfer coefficient is no longer enhanced at the top with large buoyancy forces. For low mass fluxes, the heat transfer coefficients of R134a and R1234yf are similar. For high mass fluxes, the heat transfer coefficients of R134a are higher than those of R1234yf. The Wang correlation, that was based on R134a data, more accurately predicts the heat transfer coefficients than other correlations for supercritical R1234yf in the horizontal micro-fin tube. Among all the 4050 experimental points, 90.17% of Nu top and 84.49% of Nu bottom were predicted with errors of less than 30% by the Wang correlation. [ABSTRACT FROM AUTHOR]

• In-situ measurements of eddy covariance are used to examine the Bowen ratio over the Tibetan Plateau. • The Bowen ratio is found to be sensitive to soil moisture in arid and semiarid regions. • Vapor pressure deficit is the dominant factor influencing the Bowen ratio in arid and subhumid regions. Turbulent heat fluxes across the surface are an important mechanism of land-atmosphere coupling. But there is still a lack of sufficient observational measurements, particularly over the climate sensitive Tibetan Plateau (TP). This paper examines the partitioning between sensible and latent heat fluxes during growing season using the Bowen ratio as a diagnostic based on eddy covariance measurements from 12 observational sites located on the TP with the altitudes ranging between 3327 m and 4509 m above sea level. The results show an average Bowen ratio of 1.13, indicating that sensible heat flux is only slightly dominant in surface energy balance. For different climate zones, Bowen ratio varies from 0.56 to 1.05 in the semi-arid zone, 0.53 and 0.57 in the subhumid region, and 2.73 to 3.11 in the arid zone. The Bowen ratio shows sensitivity to soil dry and wet condition, with higher values during drier soil conditions. In the arid to semi-arid regions, the Bowen ratio shows a clear positive correlation with the Drought Soil Index (DSI) and a negative correlation with the Normalized Difference Vegetation Index (NDVI), suggesting sensitivity to soil moisture conditions. In the sub-humid climate zone, vapor pressure deficit (VPD) is the dominant factor influencing the Bowen ratio. In the wet and dry transition zone, soil moisture, VPD, NDVI and land-air temperature difference all have a role to play. [ABSTRACT FROM AUTHOR]

This paper summarizes the phenomena and challenges in regenerative cooling, including transcritical thermophysical properties, fuel pyrolysis, and surface coking. The corresponding numerical methods are classified according to their characteristics, including the fuel surrogate, pyrolysis, surface coking, and turbulence models. The scope of application and the advantages and disadvantages of the models are discussed. Currently, only the differential global reaction method achieves model generality over a wide range of continuous pressures (3–7 MPa) and conversion rates (up to 75%), and it is recommended to adopt non-invasive methods and direct cooling unit to improve the accuracy of pyrolysis models. Future surface coking studies should focus on two-way coupling and consider coking and species concentration interaction. The actual coking distribution and porous effects need to be investigated simultaneously, and more kinetic models are urgently required to meet a wide range of pressures. Besides, an overview of parameterized studies in recent years is presented, including operating pressure, heat flux, mass flux, flow direction, flight acceleration and channel configuration. The weaknesses of existing parametrical studies are analyzed from a practical point of view. Heat transfer correlations of endothermic hydrocarbon fuels are also summarized and classified. Establishing heat transfer correlations for the hot spot of the heated side is essential for designing the regenerative cooling system, and the surface coking effect should be introduced. • Kinetic models of fuel pyrolysis and pyrolysis effects on cooling performance are discussed. • Surface coking studies are summarized and divided into one-way and two-way coupling. • Recommended turbulence models for regenerative cooling studies with EHFs are summarized. • Numerical progress on parametric studies of regenerative cooling technology with EHF is reviewed. • Shortcomings of parametrical studies are discussed from a practical point of view. [ABSTRACT FROM AUTHOR]