The main purpose of current study is to reduce the temperature gradient and pressure drop in the heat sinks by using a new double-layer mini/micro-channel stacked heat sink. In this numerical study, the conjugate heat dissipation characteristics of concurrent flow of pure water/water-based nano-emulsion through a mini- and micro-channel stacked double-layer heat sink is investigated. The potentials of pure water/phase change nanoemulsion in a mini- and micro-channel stacked double-layer heat sink for heat dissipation are compared with those for pure water in the single-layer microchannel heat sink. The effects of different parameters, such as flow rate ratio, total flow rate, heat flux, and concentration of the phase change nanoemulsion on the heating surface temperature suppression, pressure drop ratio, thermal resistance ratio, heating surface temperature uniformity index ratio, total heat transfer coefficient gain, and performance indexes are investigated. The three-dimensional velocity field in the channel is calculated by the pseudo-vorticity-velocity method, and the finite volume method is used to discrete the mathematical formulas. The numerical results showed that when the ratio of flow rate is 0.5, the total flow rate is 25.48 cm3/min, and the heat flux is 25 W/ cm2, the overall heat transfer coefficient of the mini- and micro-channel stacked double-layer heat sink with pure water/10 % mass fraction of phase change nanoemulsion as the coolants increases by 36.14 % compared with single-layer heat sink with pure water as the coolant. In addition, when the flow rate ratio is high and the total flow rate is low, the values of average and maximum thermal resistance ratios are greater than 1.

Multilayer ceramic capacitors (MLCCs) are essential passive elements for circuit boards and could be treated as metal/ceramic laminated structures. Due to thermo-mechanical mismatch and the high temperature experienced during fabrication, considerable stress could be induced. Consequently, structural failures such as delamination between layers or crack propagation in ceramics are frequently reported due to the brittle nature of materials. In this work, essential structural integrity assessment flow for characterizing fracture properties of MLCC are developed and the corresponding fracture properties characterization are conducted after different processing conditions in prior to serve for device longevity design based on indentation techniques. Elastic modulus and hardness, and consequently, the dependence of both fracture toughness and residual stress w.r.t. sintering temperatures are obtained. The results should be useful for optimizing processing parameters such as sintering temperatures and durations for both performance improvement and carbon emission reduction.

Enhancing convection heat transfer performance of internal flows have been a subject of interest relevant to thermal engineering applications. The present study aims to elucidate, via a novel thermal circuit modeling, the heat flow paths and the heat transport mechanisms of thermally developing forced convection of concurrent fluid flows through the outer annulus and inner tube of an externally iso-flux heated concentric double tube, which was demonstrated as an effective heat transfer enhancement configuration with respect to its parent single tube under identical operation conditions, including the inlet fluid temperature, the total volumetric flow rate, the length of heated section, as well as the wall heat flux imposed. To examine the validity of the model developed, corresponding numerical simulations based on the finite volume method were conducted to evaluate the local thermal resistance relationships. The resulting local total thermal resistance fully demonstrated the local convective effect of the fluid flows in managing the heated wall temperature at the outer-ring wall, from which the local heated wall temperature can be readily evaluated from the given imposed heat flux and the inlet fluid temperature.

To provide a feasible heat dissipation solution for a high heat flux, in this study, the internal flow and heat transfer characteristics of an externally heated concentric double tube were numerically studied via the implicit finite difference method. The outer ring and inner tube were filled with a phase change nanofluid and water, respectively. The parameter ranges were as follows: the mass fractions of the phase change material (PCM) emulsions were 2.04 %, 2.91 %, and 7.11 %, the relative flow ratio was 0.33-4.0, the heat power inputs were 70 W and 150 W, and the total tube flow rates were 304.83 cm(3)/min and 465.98 cm(3)/min. The results showed that incorporating PCM emulsions can effectively improve heat transfer performance; however, the PCM concentrations, heating conditions, and outer-annulus/inner-tube flow rates (relative flow ratios) must be properly matched so that the phase change of the working fluid occurs in the expected section. Within these parameter ranges, in the heated section, the latent heat utilization of the PCM emulsion is lower than that of the sensible heat, and only when the flow ratio is greater than 1 is the latent heat utilization of the 7.11 % PCM emulsion similar to that of the sensible heat.

This work uses artificial neural networks to evaluate heat transfer in a mini-channel heatsink using an alumina/water nanofluid. The multi-layer perceptron (MLP) and radial basis function (RBF) neural networks are employed for the modeling. To apply the artificial neural network analysis, 60 data of experimental works are utilized. The outcomes depicted that the simulated annealing (SA) technique significantly increased the performance of the RBF network, although the optimal MLP structure was discovered by trial and error. The optimized RBF network carried over more data with less than 2% errors as compared to the MLP. While the results of the MLP network showed that the average relative error for the test data set was 2.0496%, this value was 1.417% for the RBF network. The modeling time is a significant determining element when choosing the optimal technique. The RBF network optimization took longer than 60 minutes, even though all MLP structures were run 100 times in less than 15 minutes. In summary, artificial neural networks are effective instruments for simulating these kinds of processes, and their application can save a lot of time-consuming experimentation. Additionally, the RBF network outperforms the MLP in terms of precision while requiring less processing time.

The temperature of the cooling fluid in single-layer micro-channel heat sinks (SL-MCHHSs) increases along the flow direction that leads to non-uniform temperature distribution and high thermal stress. In addition, the corresponding pressure drop in SL-MCHHSs is also higher as compared to the traditional heat sinks. The main aim of this study is to solve the problems of high temperature gradient and pressure drop by using the novel double-layer mini/micro-channel stacked heat sink (DL-MMCHHSs). In the present investigation, an experimental study is performed on the heat dissipation efficacy of a DL-MMCHHS with H2O/nano-phase change emulsion (NPCE) as the coolant. NPCEs are popular coolants owing to their high storage capacity during phase change. The pressure drop and the heat dissipation efficacy of this design of heat sink with NPCE are important parameters, which should be obtained in this study. Compared with a SL-MCHHS, this design can effectively reduce the pressure drop and increase the heat dissipation efficacy. The results reveal that the DL-MMCHHS is dominated by the pressure drop of the micro-channel. When the NPCE with the mass fraction of 9.04% is used instead of H2O in the micro-channel, the heat transfer coefficient is enhanced by 112.4% at Re=1114.88 and Q*u/l = 0.50. The NPCE with higher mass fraction provides higher convection heat transfer coefficient defined by the inlet temperature. The wall temperature decreases with the decrease in the flow rate ratio. The maximum wall temperature depression of 67% can be achieved by using the NPCE as compared with H2O. Eventually, the uniformity index declines as the mass fraction of NPCE increases.

A trend toward high power and relatively small package sizes in electronic components has resulted in a dramatic increase in the corresponding heating flux; thus, the enhancement of internal convection has been a focus of attention. In this study, to improve the thermal efficiency of the internal flow, the forced-convection heat transfer of concurrent flows of functional working fluids through the outer annulus/inner tube of a concentric double tube was investigated experimentally and compared to that of an identical double tube filled with water, for which limited information is available. The fluids in the outer annulus/inner tube were 0.5% Al 2 O 3 -water nanofluid/pure water, 1.0% Al 2 O 3 -water nanofluid/pure water, and 1.0% Al 2 O 3 -water nanofluid/4.63% phase-change nanofluid. The nominal values of the main parameters were as follows: heating power = 120 W, 160 W, and 200 W; Reynolds number = 800, 1300, and 1700; and concurrent flow ratio = 0.1, 0.29, 0.45, 1.0, 1.6, and 2.38. The results indicated that when the outer annulus and the inner tube were filled with a 1.0% Al 2 O 3 -water nanofluid and a 4.63% PCM emulsion/or water, respectively, a high total flow rate and high flow ratio could suppress the rise in the wall temperature and increase the average heat transfer coefficients. Although using a functional working fluid may enhance heat transfer, this gain is considerably smaller than the increase in the pressure drop, resulting in the figures of merit for nearly all the considered cases being lower than 1.

Fan-out reconstitution process involves numerous thermal cycling and significant wafer warping would inevitable occur and full scale simulations are thus usually required for properly optimizing design and process parameters. However, the present nonlinear finite element approach of predicting wafer asymmetric warpage could result in extra computational cost and alternative approach might be worth to explore for performing efficient simulations. Thus, this work proposes a buckling/post-buckling scheme as a potential alternative for studying wafer warping problem and applies the schemes in real packaging process for demonstrating the feasibility and potentials of the approach. The simulation shows that the errors of bifurcation temperature and warpage of the two analyses are 14% and 6%, respectively w.r.t. nonlinear simulation thus the deviations are within acceptable range. Subsequently, process emulator with buckling/post-buckling analysis is established to predict warpage in the large deformation region. And compare with the nonlinear analysis, the error of warpage is within 3%. In the future, more numerical models are discussed to analyze the sensitivity of parameters thus the deformation behavior of actual process can be described more realistically.

By increasing demands for high thermal performance and energy efficiency, attentions to microchannel heat sinks (MCHSs) as the suitable method for heat flux dissipation from thermal systems have increased significantly. Microchannel heat sinks can be widely employed in electronic devices for higher heat re-moval rate and to provide best performance and durability for electronic systems. The critical issue as-sociated with MCHSs is their ability for integration of effective thermal performance. In this work, on the assessment of the thermal performance of microchannel heat sink with nanofluid is experimentally examined. The heat removal performance of the pure water and nanofluid through the MCHS is studied. Different im portant parameters, such as dimensionless wall temperature, pressure drop, mean convection heat transfer coefficient, thermal resistance, and uniformity index, are investigated. The results indicated that the maximum suppression value of the thermal resistance attained by employing the nanofluid is 12.61%. The uniformity index of the heating surface is increased as the Re number increases. More sup-pression in the wall temperature can be observed as the volume concentration of nanoparticles is in-creased. By increasing the total flow rate and using the nanofluid, the hot spots on the heating surface are suppressed. Finally, the maximum gain value of the nanofluid for the mean convection heat transfer coefficient is up to 14.43%.(c) 2022 Elsevier Ltd. All rights reserved.

Mini/micro-channel heat sinks are the advanced cooling method to fulfill the cooling demand of electronic equipment integrated with high-power circuit packages. Many designs are provided to enhance the thermal performance of micro-channel. In the present experimental study, the mini/micro-channel stacked double-layer heat sink is designed and tested for the first time. The mini/micro-channel stacked double-layer heat sink is composed of a single-layer micro-channel heat sink stacked with a mini-channel heat sink. The pure water and alumina-water nanofluid are considered as the coolant. A comparison is conducted between the heat dissipation performance of mini/micro-channel stacked double-layer heat sink and single-layer micro-channel heat sink. The results showed that as compared with the case of single-layer micro-channel heat sink, the pressure drop can be reduced considerably by using the mini/micro-channel stacked double-layer heat sink. For the flow rate ratio less than 2.0, the average convection heat transfer coefficient of the mini/micro-channel stacked double-layer heat sink is higher than that of the single-layer micro-channel heat sink. Finally, the FOM ratios are greater than unity for all cases. This indicates that the use of mini/micro-channel stacked double-layer heat sinks has more ad-vantages in engineering applications than the single-layer micro-channel heat sinks.

In energy storage, energy transfer and thermal management applications, phase change material (PCM) nanoemulsions are promising; however, supercooling has always been an important issue in the research and application of PCMs. When supercooling occurs, the efficiency of energy storage applications may possibly be reduced. In this study, n-octadecane and n-eicosane (as core materials), and nonionic surfactants (hydrophile-lipophile balance value = 8) were used to prepare n-octadecane and n-eicosane emulsions with a mass concentration of 1-9%. The effects of particle size and operation temperature on emulsion viscosity were investigated, and the relationships between supercooling and the PCM particle size, PCM concentration and process cooling rates were analyzed. The results showed that small PCM particles could form a 2(nd) freezing point far from the melting point, resulting in a large supercooling degree. As the process cooling rates increased, the supercooling became more pronounced. However, when the high-concentration emulsion was mainly composed of small particles and subjected to low cooling rates, the concentration effect was significant, thereby decreasing the supercooling effect.

In this work, the cooling effectiveness and entropy production of aluminum oxide–water nanofluid flow and heat transfer in the circular tube with the wall conduction effects are explored. All values of heat transfer effectiveness ratios are more than unity in this study. For a constant value of nanoparticles concentration, both heat transfer effectiveness ratios increase as the input temperature of fluid is increased. Both heat transfer effectiveness ratios are increased as the concentration of nanoparticles increases. Predictions show that all values of dimensionless local entropy production ratio are less than unity in this study except in the areas near the entrance of the heating part. This means that the usage of nanofluid is beneficial for decreasing the irreversibility of the system. The dimensionless local entropy production ratio decreases when the input temperature of fluid increases. The maximum value of Biw = 5 × 10-4 was reported for the Biot number in this study, which is far less than 0.1. As a consequence, the tube wall can be regarded as a Lumped system, and it is a reasonable assumption to ignore the radial thermal resistance.

The water-based microemulsion or nanoemulsion of phase change materials, that can be used as the dual functional thermal fluids for energy transport or/and energy storage, have received many attentions due to their practical applications in convective heat transfer improvement and thermal energy storage. This is owing to the advantages of these fluids in providing high effective specific heat resulted from latent heat release/absorption associated with freezing/melting behaviors within the phase change material particles. In general, it is important to evaluate the long-term overall energy efficiency of these fluids, used in thermal systems, under the practical and complex conditions. To address this issue, in the present study, the turbulent forced convective heat transfer of water-based nanoemulsion in a circular tube is experimentally investigated. The n-Eicosane, as a phase change material, with different mass fractions is suspended in the water by an ultrasonic-vibrator-aided emulsion process to prepare the nanoemulsion fluid. The circular tube is under a constant heat flux. The effects of different parameters, such as the Reynolds number, mass fraction of n-Eicosane particles, and heating power, on the dimensionless wall temperature, local convective heat transfer effectiveness, temperature control effectiveness, figure of merit (FOM), and pressure drop are studied. The experimental results reveal that the local convective heat transfer effectiveness decreases as the heating power increases. The use of n–Eicosane particles with smaller value of mass fraction can provide the convective heat transfer effectiveness larger than unity in the entire length of the heating section. The heating power has little effect on the pressure drop ratio. Increasing the heating power leads to a marginal decrease in the pressure drop ratio at larger values of the Reynolds number. The FOM index decreases as the mass fraction of n–Eicosane particles increases. The FOM index is decreased about 10% as the mass fraction of n–Eicosane particles increases in the range of 1% to 5% for the Reynolds number in the range of Re=4548∼4677. This decrease is 10.55% for the Reynolds number in the range of Re=5044∼5195. In addition, the FOM index is reduced with increasing the Reynolds number. The FOM index reduces about 1.3% as the range of Reynolds number increases from 4548∼4677 to 5044∼5195 for ωPCM=5%.

In this study, a tube with a smaller diameter was inserted in an isoflux heated circular tube to form a concentric double-tube duct. The forced convection heat transfer enhancement efficacy of using concurrent flows of Al2O3/PCM nanofluids through outer annulus/inner tube of this resulting double-tube duct to replace its parent single-tube (with water) was experimentally investigated. The results showed that a high total flow rate combined with a high concurrent flow ratio could effectively increase heat transfer effectiveness. When heating power = 200 W, Reynolds number = 1700, and the concurrent flow ratio = 2.38, for 1% Al2O3-water nanofluid in the outer annulus and 4.63% phase-change nanofluid in the inner tube, the convective heat transfer increased by 32%. Due to the excessive pressure drop, the figures of merit of the investigated objectives are all less than 1.

To effectively improve internal convection, in this study, the heat transfer enhancement using concurrent forced flows of phase change nanofluids/water through the outer ring/inner tube of a double tube was investigated experimentally and compared to that of an identical tube filled with water, for which limited information is available. The parameters are described as follows: heating powers of 70, 110, and 150 W; mass fractions of the phase change nanofluid of 2.04 %, 2.91 %, and 7.11 %; flow ratios of 0.33-4.0; and a total flow rate of 304 cm3/ min. The results indicated that the PCM concentration, flow ratio, and heating power must be correctly matched so that the phase change in the working fluid falls in the expected position and the effect of the latent heat can be fully realized. For a 2.04 % PCM emulsion, when the heating wattage is 70 W and the flow ratio is approximately intermediate (0.51), the local heat transfer effectiveness of the heated section is >1, indicating that using a PCM emulsion as the working fluid instead of water can effectively increase the heat transfer rate.

In this study, a numerical simulation is performed to explore oscillatory natural convection in a square enclosure with a phase change material (PCM) suspension using the implicit finite difference method. The following parameters are considered: aspect ratio of the physical model = 1; ratio of the buoyancies caused by temperature and concentration gradients = 1; Rayleigh number = 10(3)-10(6); initial mass fraction (or concentration) of PCM particles = 0-0.1; Stefan number = 0.005-0.1; and subcooling factor = 0-1.0. The results show that high Rayleigh numbers can easily cause oscillations in the flow field and temperature distribution. However, even under low Rayleigh number conditions, when the initial mass fraction or subcooling is increased or the Stefan number is decreased, oscillations occur.

In this work, experimental study is performed to explore the cooling performance of water-based hybrid nanofluid with PCM and graphene nanoparticles in a tube to enhance energy efficiency of heat exchanger. The forced convection experiments have been performed for the cases of pure water and the hybrid nanofluids. The experiments are conducted for the volumetric flow rates of Q˙ = 60, 90 and 180 cm3/min, the mass fractions of tetracosane PCM nanoparticles of ωpcm = 2, 5, and 10%, and the mass fractions of graphene nanoparticles of ωnp = 0 and 0.006%. The measured results show clearly that for the appropriate flow rate and heating power, using the nanoemulsion with the PCM nanoparticles as coolant can effectively reduce the wall temperature and enhance the heat dissipation effectiveness as compared with the case of pure water. However, the highly increased viscosity of the nanoemulsion with the PCM nanoparticles would drastically downgrade its highest figure of merit (FOM). The maximum average heat transfer effectiveness ratio of 1.044 can be achieved by using the PCM nanoparticles at lh+/(di+Pef) = 0.033, ωpcm[Stef∗(1+Sbf∗)]=0.0942, and Q˙ = 90 cm3/min. In addition, adding the graphene nanoparticles with the mass fraction of ωnp = 0.006% to the nanoemulsion to form the hybrid nanofluid leads to significant enhancement in the heat transfer.

In this work, experimental study was performed to measure the thermophysical properties of water-based nano-emulsion of phase change material (tricosane). The particle size distribution, the dynamic viscosity, the thermal conductivity and the specific heat of the emulsion in the different mass fraction of the phase change material (PCM) over the temperature range of 20–60 °C were measured. Based on the results, the thermophysical properties of the based fluid are strongly affected by the phase change progress of the PCM. Measured results show that the dynamic viscosity of the water-based PCM nano-emulsion in the heating process is lower than that in the cooling process. Besides, the higher the mass fraction of the PCM is, the larger the dynamic viscosity is. In the temperature ranges of 20–40 °C and 40–60 °C, the temperature change on the thermal conductivity is insignificant. However, in the phase change temperature range, the thermal conductivity increases considerably.

Research on using phase change material (PCM) suspension to improve the heat transfer and energy storage capabilities of thermal systems is booming; however, there are limited studies on the application of PCM suspension in transient natural convection. In this paper, the implicit finite difference method was used to numerically investigate the transient and steady-state natural convection heat transfer in a square enclosure containing a PCM suspension. The following parameters were included in the simulation: aspect ratio of the physical model = 1, ratio of the buoyancies caused by temperature and concentration gradients = 1, Raleigh number (RaT) = 103–105, Stefan number (Ste) = 0.005–0.1, subcooling factor (Sb) = 0–1.0, and initial mass fraction (or concentration) of PCM particles (ci) = 0–0.1. The results showed that the use of a PCM suspension can effectively enhance heat transfer by natural convection. For example, when RaT = 103, Ste = 0.01, ci = 0.1, and Sb = 1, the steady-state natural convection heat transfer rate inside the square enclosure can be improved by 70% compared with that of pure water. With increasing Sb, the Nusselt number can change nonlinearly, resulting in a local optimal value.

This study explores the effects of pipe wall properties (thermal conductivity k and wall thickness t(w)) on the heat transfer performance of a rectangular thermosyphon with a phase change material (PCM) suspension and a geometric configuration (aspect ratio = 1; dimensionless heating section length = 0.8; dimensionless relative elevation between the cooling and the heating sections = 2) that ensures the optimum heat transfer efficiency in the cooling section. The following parameter ranges are studied: the dimensionless loop wall thickness (0 to 0.5), wall-to-fluid thermal conductivity ratio (0.1 to 100), modified Rayleigh number (10(10) to 10(11)), and volumetric fraction of PCM particles (0 to 10%). The results show that appropriate selection of k and t(w) can lead to improved heat transfer effectiveness in the cooling section of the PCM suspension-containing rectangular thermosyphon.