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

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

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

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

Abstract In this paper the relative performance of two different differential stress and flux models for computing natural convection in an enclosure is examined. One model is the low-Reynolds number differential stress and flux model and the other model is a recently developed elliptic blending based differential stress and flux model. The primary emphasis of the study is placed on investigating the accuracy of the both models for the turbulent natural convection in an enclosure. Both models are used to predict turbulent natural convections in a square cavity with hot and cold side walls and conducting top and bottom walls (Ra = 1.58 × 109). The relative performance between both models is examined through comparing their solutions with the experimental data. It is shown that both models predict the vertical mean velocity component and mean temperature well. It is also shown that the low-Reynolds number differential stress and flux model slightly under-predicts the turbulent kinetic energy and vertical turbulent heat flux. It is also noted that the implementation of the elliptic blending second moment model is easier since this model does not contain any wall-related parameters and damping functions. [ABSTRACT FROM AUTHOR]

Nanorefrigerants are a special type of nanofluids which are mixtures of nanoparticles and refrigerants and have a broad range of applications in diverse fields for instance refrigeration, air conditioning systems, and heat pumps. In this paper thermal–physical properties of nanoparticles suspended in refrigerant and lubricating oils of refrigerating systems were reviewed. The effects of nanolubricants on boiling and two phase flow phenomena are presented as well. Based on results available in the literatures, it has been found that nanorefrigerants have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional refrigerant. This can be considered as one of the key parameters for enhanced performance for refrigeration and air conditioning systems. Because of its superior thermal performances, latest up to date literatures on this property have been summarized and presented in this paper as well. The results indicate that HFC134a and mineral oil with TiO 2 nanoparticles work normally and safely in the refrigerator with better performance. The energy consumption of the HFC134a refrigerant using mineral oil and nanoparticles mixture as lubricant saved 26.1% energy with 0.1% mass fraction TiO 2 nanoparticles compared to the HFC134a and POE oil system. [ABSTRACT FROM AUTHOR]

This paper presents a numerical analysis of a horizontally oriented constant surface area isothermal helical coil under natural convection heat transfer and surface radiation. Numerical computations are carried out in the laminar regime of Rayleigh number (104 ≤ Ra ≤ 108), surface emissivity (0 ≤ ε ≤ 1), and geometrical parameters of the helical-coil, like diameter of the coil (8 ≤ D / d ≤ 24), pitch (3 ≤ p / d ≤ 7.5), and coil height (40 ≤ H / d ≤ 60) to study the heat transfer characteristics. This study is used for effectively designing the helical coils, which are typically manufactured at an extremely high temperature. The numerical computation has been validated by comparing the average Nusselt number (Nu) with the previous experimental results. Temperature-dependent fluid properties are incorporated to achieve precise results over a wide range of temperatures. The effect of the geometrical parameters on the heat transfer characteristics has been depicted graphically in terms of average Nu , relative convection and radiation heat transfer rate, and the temperature profile. It is found that the relative contribution of radiative heat transfer is 87.8% at an emissivity of 0.9 and Ra of 10(Ali, 1994 4), whereas, for an emissivity of 0.1 and Ra of 10(Moawed, 2005 8), the relative contribution of radiation heat transfer is only 6.4%. Lastly, a correlation has been developed for the average Nu based on all the pertinent parameters which can be beneficial to the engineers in the industry and also academic researchers. The developed correlation has been used to predict the cooling curve of the helical coil in certain situations. [ABSTRACT FROM AUTHOR]

We present Large Eddy Simulation (LES) results of heat transfer and flow evolution of a turbulent two-dimensional rectangular jet of air, of height H, impinging upon a flat wall. Rectangular jet is quasi-two dimensional, i.e. planar jet with infinite slot-width. Exit of jet is set at four distances, D , from wall, D = 4H, 3H, 2H, H. Distance of slot exit to wall modifies flow evolution, reported as mean and instantaneous, compared to experimental data. In mean flow Undisturbed Region of Flow, URF, and, in instantaneous flow, Negligible Disturbances Flow, NDF, and Small Disturbances Flow, SDF, are reported for the various distances D/H. In order to evaluate influence of flow parameters on heat transfer and flow evolution, two levels of turbulence are imposed on slot jet exit, i.e. 1% and 6%. The level of turbulence modifies heat transfer results, as far as convective heat transfer and Nusselt number are concerned. The shape of Nusselt number distribution along impinged wall is different according to level of turbulence. The paper presents a very good comparison with experimental Nusselt numbers, for the first time in literature. • A quasi-two dimensional jet, i.e. with infinite slot-width, of air impinges a flat wall. • Large Eddy Simulation approach is compared successfully to experiments. • Distance from the wall influences flow evolution and heat transfer. • Lengths of URF, NDF and SDF are influenced by the distance from wall. • Heat transfer is compared successfully to experimental results, for the first time in literature. [ABSTRACT FROM AUTHOR]

The phase change material (PCM) receives more and more attention on account of the large amount of heat absorption and release during the process of phase change. In order to further investigate the heat transfer behavior of phase change, a discrete unified gas kinetic scheme (DUGKS) derived from Boltzmann equation for solid-liquid phase change has been developed in this paper. The phase change problems, including the phase change by conduction and by convection, are solved to verify the present DUGKS. The results of DUGKS agree well with that of analytical solution or benchmark solution. In the simulations of natural convection with phase change, the non-uniform mesh has been considered to evaluate the performance of DUGKS. Besides, no phase interface effect, with which the temperature is lower than the initial one in lattice Boltzmann (LB) method, is obtained in present DUGKS. [ABSTRACT FROM AUTHOR]

Natural heat convection, mixed heat convection and heat transfer by conduction and convection with solidification of a ternary alloy are described by the finite volume method using a geometric multigrid approach. The objective of this paper is to analyze the effects of the multigrid technique on the accuracy and efficiency in describing convective heat transfer in closed and open cavities with and without liquid-solid phase changes of Newtonian and shear-thinning non-Newtonian fluids. It is found that the multigrid scheme reduces the computation time in natural convection in a square cavity from two times for Rayleigh number Ra = 10 5 up to seven times for Ra = 10 3 , between 50% and 2.7 times for mixed convection with an inner solid when the Richardson number decreases from Ri = 10 to 0.1 and the Reynolds number Re = 100, and 20% for natural convection/heat conduction in solidification of a ternary aluminum alloy (Ra = 10 4 ) with a shear-thinning rheology and a power index equal to 0.5. [ABSTRACT FROM AUTHOR]

A novel method of inserting a radiation enhancement plate in a turbine blade internal cooling channel is established in this paper. It can extend cold surfaces for radiation and thus enhance total heat transfer. Numerical investigations are carried out to explore the flow and coupled convection and surface radiation in the rotating channel for different channel models. The results indicate that the model inserting the radiation enhancement plate roughed with W-shaped ribs (model D) exhibits the highest cooling performance. Compared with the existing channel model (model A), the total Nusselt number ratio and the performance evaluation criterion increase by 90.53% and 21.67%, respectively, and the maximum and average temperature decrease by 339.80 K and 73.07 K, respectively. In addition, the heat transfer difference between the leading and trailing walls caused by the Coriolis force is remarkably reduced. Influences of pertinent parameters including the Reynolds number, the rotation number, the wall heat flux, and the wall emissivity are also investigated. It is demonstrated that the method has an excellent self-enhancement effect. • Heat transfer is enhanced in internal cooling channel of gas turbine blade. • A novel method by inserting radiation enhancement plate is established. • Coupled convective and radiative heat transfer in the channel is studied. • The maximum and averaged temperature decrease by 339.80 K and 73.07 K. • The method has an excellent self-enhancement effect. [ABSTRACT FROM AUTHOR]

In this paper, turbulent flow of aviation kerosene at supercritical pressure through cooling channels respectively with streamwise sinusoidal corrugation, spanwise sinusoidal corrugation and streamwise and spanwise coupled sinusoidal corrugations are numerically studied. The Reynolds-averaged Navier-Stokes method with RNG k − ε turbulence model is used to perform numerical simulation. The independence of grids is first examined, and the numerical results are compared with experimental data for validation. The present results show that the streamwise corrugation significantly improves convective heat transfer performance of cooling channels, the increase ratio of Nusselt number and Thermal Performance Factor reaches 20.44% and 6.7%. With the streamwise and spanwise corrugations coupling, the increase ratio of Nusselt number and Thermal Performance Factor are both larger than those in cooling channels with only streamwise corrugation. Furthermore, the results of flow and heat transfer of aviation kerosene at supercritical conditions with corrugations effect show that corrugations can eliminate heat transfer deterioration occurring at supercritical conditions. The present study is aimed to provide useful references for cooling optimization with wall microstructures for engineering applications. [ABSTRACT FROM AUTHOR]

With the increasing development of industrial technology, the thermal load of advanced equipment and devices is constantly improving in the engineering fields, such as energy, power, bio-chemical, aerospace, microelectronics, laser technology and so on. Dynamic flow control technique is applied in heat engines field to enhance convection heat transfer, and meet dynamic heat transfer demand. Based on the existing research on the influence of stationary and vibration turbulent generators on convection heat transfer, this paper developed a new enhancement convection heat transfer method of adopting periodic contraction and expansion vibration cylinder in rectangular channel. The heat wall temperature as the research object can be maintained in a reasonable and safe range. The investigation indicates that comparing with traditional stationary structure, new flow control technique can obviously decrease maximum heat wall temperature, and increase convection heat transfer performance. Comprehensive convection heat transfer performance can be enhanced by 20.12%. That indicates such enhancement heat transfer method is meaningful, and new contraction and expansion vibration disturbance method is credible for enhancing heat transfer. [ABSTRACT FROM AUTHOR]

• One-phase cylindrical Stefan problem with size-dependent thermal conductivity and convection is considered. • Time dependent temperature and Newton type temperature boundary conditions are subjected at the outer surface of the body. • Heat Balance Integral Method is applied to obtain the numerical result of the problem. • Convection produced pronounced impact on propagation rate of the melting interface. • It is observed that size-dependent thermal conductivity produced pronounced effect on melting process. The melting of a phase change material is the most applicable process in thermal energy storage system to capture heat transfer phenomena arising in a class of moving boundary problem. Demand of present technology motivates researchers to develop new theories and techniques for thermal management of a material. Experimental work on melting of a material may be difficult and development of robust theoretical formulation in cylindrical geometry with convection is critical. While there is already available study on cylindrical moving boundary problem, but still insufficient modeling of a size-dependent thermal conductivity and convection effect is not addressed properly, which is being considered in this paper and is expected to improve the previous understanding. In this work, a one-dimensional moving boundary problem with size-dependent heat conductivity and convection effect is analyzed in cylindrical geometry. In the mathematical model, we have considered a time-dependent temperature boundary condition which later assumed in periodic form, and a convective boundary condition at the outer surface of the body. The numerical result of the problem is obtained successfully via heat-balance integral method. Our numerical result is compared with a previous work and found in good acceptance. From mathematical framework, it is found that convection delayed melting process. With a size-no independent thermal conductivity, the rate of moving front decreases more in comparison to the fixed thermal conductivity. [ABSTRACT FROM AUTHOR]

Heat transfer during ice accretion is a complex process that couples heat convection, drop impingement, evaporation, fusion, and heat conduction. However, in most numerical simulations of ice accretion in the literature, heat conduction in both the ice layer and the wall is neglected for simplification. This paper examines whether this approximation is acceptable by proposing a scheme for the calculation of the coupled heat transfer during ice accretion, including heat conduction inside both the ice layer and the solid wall. A glaze-ice scenario is used for the coupled heat transfer analysis, and the results show that latent heat generated during the freezing process is transferred to the ice and wall through conduction, raising their temperature above the incoming temperature. The heat conduction in surface tangent direction dominants in the solid wall while heat conduction in the normal direction dominants in the ice layer. The results also show that the heat transferred from the ice layer to the water film is negligible, meaning heat conduction in the ice layer and solid wall can be neglected, which, however, can cause relatively large errors at the upper and lower ice coverage limitations. • Proposed a method for calculation of the coupled heat transfer in ice accretion. • The temperature of the ice and wall is above the incoming temperature. • Tangent heat transfer in the ice layer along the surface is negligible. • The heat transferred from the ice layer to the water film is negligible. [ABSTRACT FROM AUTHOR]

This paper is related to a theoretical study to analyze the nanoclusters and their structural effects on the laminar forced convection heat transfer coefficients of Al 2 O 3 -water nanofluids in a circular tube. In this study, Eulerian/Eulerian two-phase model is used with regard to nanoclusters Brownian motion and their fractal structure. The hydrodynamic effects, nanofluid concentration, size, and fractal structure of nanoclusters were investigated. Modeling results were compared to the experimental data and it was shown that the numerical predictions agree well with the experimental data. Based on the results, convective heat transfer coefficient increases by increasing the nanoparticles concentration and reducing of the nanoclusters fractal dimension. The results clearly showed that Brownian motion has a significant effect on the convective heat transfer coefficient enhancement of Al 2 O 3 /water nanofluids . [ABSTRACT FROM AUTHOR]

This paper experimentally investigates the heat transfer performance and characteristics of a heat sink with bio-mimetic oscillating foil. The oscillating foil is driven by a novel mechanism of grooved cam with linkage. The air flow is drawn into a rectangular duct through the motion of the bio-mimetic oscillating foil. Various heat sinks were set at the outlet of the duct to study the thermal performance. Two types of grooved cams were designed to obtain different angular velocity profiles for the oscillating foils. The angular velocity was specified as fast forward/slow backward and sinusoidal patterns. Foils with three flexural stiffness values were utilized in the study. The averaged velocity at the inlet was measured to estimate the Reynolds number and Strouhal number. The effects of configuration of heat sink design with oscillating foil were also under investigation. The junction temperature of the heat sink was measured to obtain the effective thermal resistance. Results show that the angular velocity profile and flexural stiffness of the oscillating foil have a significant effect on the thermal performance of the heat sink. [ABSTRACT FROM AUTHOR]

This paper focuses on designing an artificial neural network which can predict thermal conductivity and dynamic viscosity of ferromagnetic nanofluids from input experimental data including temperature, diameter of particles, and solid volume fraction. The experimental data were extracted and they were used as learning dataset to train the neural network. To find a proper architecture for network, an iteration method was used. Based on the results, there was no over-fitting in designed neural network and the neural network was able to track the data. ANN outputs showed that the maximum errors in predicting thermal conductivity and dynamic viscosity are 2% and 2.5%, respectively. Based on the ANN outputs, two sets of correlations for estimating the thermal conductivity and dynamic viscosity were presented. The comparisons between experimental data and the proposed correlations showed that the presented correlations were in an excellent agreement with experimental data. [ABSTRACT FROM AUTHOR]

This paper describes in detail the measurement of the overall heat transfer coefficient and phase transformation latent heat by modified pattern search method (PSM). By introducing the pattern search algorithm into finite element analysis, the measurement of heat transfer coefficients and phase transformation latent heat can be simplified as recording the temperature with time. Comparison of the measurements by PSM and temperature gradient method (TGM) shows that PSM can evaluate the overall heat transfer coefficient accurately. Experiments and simulations show that bainite transformation latent heat in 26NiCrMoV10-10 steel is about − 90.5 J/g, and the latent heat increases the surface temperature of a cylindrical specimen by a maximum of 76 °C. Error analysis shows that the highest difference between calculated temperature and measured temperature is 11.7 °C, which verifies that the heat transfer coefficient and phase transformation latent heat estimated by PSM are accurate, and that the pattern search method is reliable. [ABSTRACT FROM AUTHOR]

In this paper, the melting and solidification processes and the thermal conductivity enhancement of the phase change material (PCM) inside a sphere have been experimentally investigated to facilitate a greater understanding and improvement of the phase change heat transfer of PCM inside a sphere. The experiments are conducted by inserting a sphere filled with organic PCM into a constant temperature bath of hot/cold water. Through measuring and analyzing the temperature field inside the sphere under conditions of various initial and final temperatures, the thermal characteristics of melting and solidification processes of PCM are obtained. To determine the thermal conductivity enhancement effect of aluminum powder, the PCM-aluminum composite material in which the mass fractions of aluminum are 1% and 2%, respectively, is tested. And the experimental data of PCM-aluminum composite material are compared with those of pure PCM. Results indicate that the PCM in the upper part of the sphere melts faster than that in the lower part, and the PCM near the inner wall solidifies faster than that in the center of the sphere. The initial PCM temperature has little effect on the solidification process of the PCM inside the sphere when Stefan number ( Ste ) is small and Rayleigh number ( Ra ) is large. The thermal conductivity of the PCM inside the sphere is enhanced by adding aluminum powder. And the sedimentation of aluminum powder is more beneficial to accelerate the heat transfer of the whole sphere in the melting process, compared with the uniform diffusion of aluminum powder in the PCM. [ABSTRACT FROM AUTHOR]

In this paper, laminar forced convective heat transfer of water/alumina nanofluids in a straight microchannel is studied numerically using CFD modeling. In the first part, single-phase and two-phase mixture models have been used for prediction of hydrodynamics and heat transfer parameters of nanofluids in a simple microchannel heat sink. The CFD predictions were compared to the experimental data and it was concluded that the two-phase approach gives better predictions compared to the single-phase model. The effects of ribs turbulators on the fluid flow and heat transfer performance of microchannel were investigated in the second part. The effects of geometrical characteristics of the ribs were studied, and the results showed that the Nusselt number and friction coefficient of nanofluids in the ribbed microchannel are higher than those of simple microchannel, and this enhancement increased with increasing the width of the ribs. [ABSTRACT FROM AUTHOR]

Based on constructal theory, the construct of a three-dimensional cylindrical heat sources with convection heat transfer is investigated in this paper. The heat source model is composed of several cylindrical heat sources surrounded with a cylindrical fin or a conical fin. The heat source model not only exists in the heat generating electronic component surrounded with a fin to enhance heat transfer, but also in the heat generating fuel rod with zircaloy cladding. For the specified volumes of the fin and the heat sources, this construct is optimized by taking the minimization of the dimensionless hot spot temperature as optimization objective. The results show that the hot spot temperature of the model is effectively reduced after constructal optimization, which will provider some theoretical guidelines for the optimal design of heat source system. [ABSTRACT FROM AUTHOR]

In this paper, the characteristic variational multiscale (C-VMS) method is proposed to solve the nonstationary conduction–convection problems. The stability analysis is carried out using the energy estimate method. Compared with the standard variational multiscale (VMS) method, the C-VMS method does not need nonlinear iteration. Finally, some numerical examples are given, which show that the C-VMS method is efficient, reliable and can save a lot of CPU time for this problem, besides, it can deal with the high Rayleigh number. [ABSTRACT FROM AUTHOR]

This paper reviewed the application of nanofluids in vehicle engine cooling system. So far, nanoparticles have been used in engine oil, transmission oil, and radiator coolant to enhance heat transfer removal from vehicle engine. The heat transfer performance of nanofluids has been reported to perform better compared to pure fluid. This review focused on the experimental and numerical studies by previous researchers and their suggested amount of nanoparticles for optimum performance in vehicle engine cooling system. Finally, the conclusions and important summaries were presented according to the data collected. [ABSTRACT FROM AUTHOR]

In this paper, we examined the significance of nonlinear thermal radiation on 2-D magnetohydrodynamic flow of hybrid nanoliquid across two distinct geometries. The hybridized nanoliquid is encompassed with CuO and Al 2 O 3 nanomaterials suspended in the base liquid (water). The suitable similarity transmutations are utilized to convert the PDE's to the non-dimensional ODE's and solved them by employing Runge-Kutta method with shooting procedure. Further, simultaneous solutions are witnessed for flow over cone case and plate case respectively. The stimulus of dimensionless parameters on velocity and thermal fields are discussed thru plots, further, the wall friction and local Nusselt number are presented thru the tables. The results reveal that, the nonlinear thermal radiation has a propensity to boosts the thermal distributions and to decays the rate of heat transfer. The flow and thermal distributions are significant in flow over a plate as compared with flow over a cone case. Moreover, the thermal transport rate of the flow above a cone is considerably advanced than that of flow over a plate. [ABSTRACT FROM AUTHOR]

This paper provides an hitherto new approach of a heat transfer correlation based on heat flux to mass flux ratio for predicting wall temperature of supercritical water flowing in a bare vertical tube. Totally 10,174 numbers of experimental data were collected, Out of which 4236 data are heat flux/mass flux ≤0.4 and 5938 data are heat flux/mass flux>0.4. These data were obtained from various experimental resources and Lookup table and it covers q/G ranges from 0.085 to 1.295, mass flux ranges from 201 to 3500 kgm−2 s−1, heat flux ranges from 129 to 1600 kWm−2, pressure ranges from 225 to 320 bar, diameter of the tube 4.4 to 38 mm and bulk fluid enthalpy ranges of 250 to 3200 kJkg−1 of vertical tube working at various supercritical working conditions based on normal, enhancement and deteriorated heat transfer regions. By using these data, a new heat transfer correlation is derived for finding the wall temperature by Levenberg-Marquardt (LM) algorithm of multi dimensionless analysis method with Nonlinear curve fitting method. A general form of forced convection heat transfer correlation was obtained by Buckingham Π theorem. The Wall temperatures predicted by various 7 existing correlations along with this new correlation are found by Visual basic program and compared with experimental data for evaluating the deviations. The rank was provided based on error band from ±0.5% to ±50% etc., and error analysis were conducted for proving the best fitting correlation. [ABSTRACT FROM AUTHOR]

The main objective of the present paper is to investigate the effect of using connecting holes on the hydrothermal performance and irreversibility behavior of laminar forced convection flow of a nanofluid (NF) inside a microchannel heat sink (MCHS). The biologically synthesized silver/water NF is employed as coolant. The influences of the volume concentration of NF (φ), the Reynolds number (Re) and the number of connecting holes on the performance features of MCHS and NF are considered numerically. It was observed that the CPU temperature is reduced and became more uniform due to boosting of Re and φ , and the consequence augmentation of the convective heat transfer. However, the pumping power and frictional irreversibility get raised as Re and φ are increased. The figure of merit is above unity for all Re and φ which indicate that the utilization of connecting holes is a suitable option to improve the MCHS performance from the first-law point of view. The heat transfer irreversibility, however, increased by using the connecting holes. Also, the merit of NF over the pure water is observed for Re of 500 and 2000 and φ of 0.1% and 1%. [ABSTRACT FROM AUTHOR]

This paper explores machine learning approach as a heat transfer correlation. Machine learning significantly reduces the effort to develop multi-variable heat transfer correlations, and is capable of readily expanding the parameter domain. Random forests algorithm is used to predict the convection heat transfer coefficients for a high-order nonlinear heat transfer problem, i.e., convection in a cooling channel integrated with variable rib roughness. For 243 different rib array geometries, numerical simulations are performed to train and test ML model based on six input features. Machine learning model predicts closely to numerical simulation data with high determination of coefficient (R2), e.g., R2 > 0.966 for the testing dataset. The capability and limitation of random forests algorithm are discussed with validation dataset. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the hydrothermal and irreversibility behaviour of a biological water-Ag nano-fluid in a new heatsink with helical microchannels. Two-phase mixture model is applied to precisely simulate the behavior of nanofluid in the nanoadditive concentration (φ) range of 0–1% and Reynolds number (Re) range of 500–1500. The influences of φ and Re on the convective heat transfer coefficient, CPU surface temperature, pumping power, as well as the irreversibilities due to heat transfer and fluid friction are examined. The findings depict that boosting the Re and φ augments the performance of heatsink by intensifying the convective heat transfer coefficient of the working fluid which favourably declines the CPU surface temperature and the heat transfer irreversibility and importantly results in the temperature uniformity of the CPU surface. However, intensification in Re adversely affects the pumping power, the fluid friction and total irreversibilities in the system. Furthermore, it is revealed that the nano-fluid always has a superior cooling performance as compared with the pure water. Finally, it is found that the best hydrothermal performance of the nano-fluid in the proposed heatsink occurs at Re = 1500 and φ = 1%, while the minimum total irreversibility occurs at Re = 500 and φ = 1%. [ABSTRACT FROM AUTHOR]