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The current two-dimensional (2D) numerical study presents the melting phenomenon and heat transfer performance of the nanocomposite phase change material (NCPCM) based heat sink. Metallic nanoparticles (copper: Cu) of different volume fractions of 0.00, 0.01, 0.03, and 0.05 were dispersed in RT–28HC, used as a PCM. Transient simulations with conjugate heat transfer and melting/solidification schemes were formulated using finite–volume–method (FVM). The thermal performance and melting process of the NCPCM filled heat sink were evaluated through melting time, heat storage capacity, heat storage density, rate of heat transfer and rate of heat transfer density. The results showed that with the addition of Cu nanoparticles, the rate of heat transfer was increased and melting time was reduced. The reduction in melting time was obtained of − 1.36%, − 1.81%, and − 2.56% at 0.01, 0.03, and 0.05, respectively, compared with 0.00 NCPCM based heat sink. The higher heat storage capacity enhancement of 1.87% and lower reduction of − 7.23% in heat storage density was obtained with 0.01 volume fraction. The enhancement in rate of heat transfer was obtained of 2.86%, 2.19% and 1.63%; and reduction in rate of heat transfer density was obtained of − 6.33%, − 21.05% and − 31.82% with 0.01, 0.03, and 0.05 volume fraction of Cu nanoparticles, respectively. The results suggest that Cu nanoparticles of 0.01 volume fraction has the lower melting rate, higher heat storage capacity and heat transfer rate, lower heat storage density and heat transfer rate density which is preferable for passive cooling electronic components. [ABSTRACT FROM AUTHOR]

Researchers have attempted to improve heat transfer in mini/microchannel heat sinks by dispersing nano-encapsulated phase change (NPC) materials in base coolants. While NPC slurries have demonstrated improved heat transfer performance, their applications are limited by decreasing enhancement at increased flow rates. To address this challenge, the present study numerically investigates the effects of wavy channels on the performance of NPC slurries. Simulation results reveal that a wavy channel induces Dean vortices that intensify the mixing of the working fluid and enlarge the melting fractions of the NPC material, thus offering a significantly higher heat transfer efficiency than a straight channel. Moreover, heat transfer enhancement by NPC slurries varies with the imposed heat flux and flow rate. Interestingly, the maximum heat transfer enhancement obtained with the wavy channel not only exceeds the straight one, but also occurs at a higher heat flux and faster flow rate. This finding demonstrates the advantage of wavy channels in management of intensive heat fluxes with NPC slurries. The study also investigates wavy channels with varying amplitude and wavelength. Increasing the wave aspect ratio from 0.2 to 0.588 strengthens Dean vortices and consequently increases the Nusselt number, optimal heat flux, and overall thermal performance factor. [ABSTRACT FROM AUTHOR]

An ultra-thin vapor chamber (1.5 mm thick) has been developed for experimental investigation. Aqueous solutions of propanol exhibiting concentration and thermal Marangoni effects are investigated as potential vapor chamber charge fluids, and their impact on the thermal performance is investigated and compared against pure water and 2-propanol. The vapor chamber thermal resistance and evaporator temperature are lower at low charges with pure 2-propanol and 2.4 M and 4.2 M 2-propanol-water solutions compared to pure water. A 4.2 M propanol-water mixture shows an almost 4.5 X increase in the evaporator heat transfer coefficient compared to pure water. [ABSTRACT FROM AUTHOR]

As electronic device performance is enhanced, the amount of heat generation is also increased. Electrohydrodynamic (EHD) technology presents a promising alternative solution to address the cooling demands. The EHD flow is generated by a corona discharge, directly converting the electrical energy into kinetic energy, and offers unique advantages over traditional cooling methods. The use of a magnetic field can improve the efficiency of the EHD flow by enhancing the local energy conversion. Experimental results showed that a magnetic field deflected the local velocity distribution, and improved the ionic wind velocity. At a magnetic flux density of 78.1 mT, the energy conversion efficiency was improved by 66.8 %. The convective heat transfer on the surface of high-power light emitting diode (LED) was analyzed. The heat transfer coefficient also increased under the effect of the electromagnetic field. The potential of alternative cooling systems for electronic devices using EHD technology was confirmed. [ABSTRACT FROM AUTHOR]

In this paper, the authors present the design, operating principle, and results from the study of two-phase heat conductors intended for thermal regulation of heat-loaded equipment: ring thermosyphons with a horizontally located evaporator and condenser and a porous coating in the evaporator. Two modifications of thermosyphons—with a cylindrical evaporator and liquid cooling of the condenser and with a flat evaporator and air cooling of the condenser—were tested. The porous wick promotes uniform distribution of liquid and heat flow in the longitudinal and cross sections of the evaporator and equalization of the temperature field over the surface of the evaporator and, consequently, the cooled object. Thermosyphons are made of copper, and the operating fluids are water and freon R245fa. [ABSTRACT FROM AUTHOR]

This numerical research study focuses on impacts of using twisted rib geometry on the hydrothermal performance and entropy generation characteristics of biologically synthesized Ag/water nanofluid flowing in heat sink ‌minichannels. To this end, twelve different twisted rib geometries (Case 1 to 12) were designed where the double-row ribs were twisted at the bottom and top portions with twist angles between − 45° and + 45°. To elucidate the cooling performance comprehensively, four different Reynolds numbers (Re = 500, 1000, 1500, and 2000) and four different nanoparticle concentrations ( φ = 0%, 0.1%, 0.5%, and 1%) were included in the numerical computations. Results revealed that using twisted ribs significantly smoothen the fluid flow and reduces pressure drop remarkably depending on twist angles, nevertheless, it deteriorates the cooling performance. In Case 12, the convective heat transfer coefficient reduces by up to 15.8% at Re = 2000 and φ =1%, compared to the base case. However, pumping power requirement is decreased by 43.9% in this case. Nanoparticle incorporation contributes to enhancement of convective heat transfer coefficient by up to 13.5% at the lowest Re. Frictional entropy generation considerably decreases (up to 31%) when twisted ribs are utilized. However, thermal entropy generation can increase up to 36%, due to ineffective cooling with twisted ribs. This work can be regarded as a first study in the field concerning the effects of top and bottom twist angles on hydrothermal performance and entropy generation in nanofluid-cooled mini-channel heat sinks. [ABSTRACT FROM AUTHOR]

Oscillatory baffled flows (OBFs) provide a combined active and passive means of achieving convective heat transfer enhancement, and previous studies at large scale have demonstrated the heat transfer benefits of OBFs. To date, however, this technology has not been scaled down for the purpose of heat sink performance enhancement. Presented in this study is a numerical investigation of a single baffled channel with a hydraulic diameter of 2.8 mm, containing gate baffles, with a 50% open area, which are spaced 7.5 mm apart. Three net-flow rates were investigated while varying the oscillation conditions by varying the oscillation amplitude (3 mm to 7 mm) and by varying the oscillation frequency (0 to 8 Hz). Increasing the oscillation intensity had a greater impact on the Nusselt number compared to simply increasing the net-flow rate, with Nu enhancements of up to 330% observed when imposing oscillatory flow on a purely steady flow. Ideal operating conditions were identified by grouping the data by velocity ratio ( Ψ ) and graphing the theoretical pumping power against the thermal resistance of the channel. The highest Nu enhancement of 330% was achieved for a net-flow Reynolds number ( R e n ) of 165, oscillatory amplitude of 5 mm and a frequency of 8 Hz. Ideal operating conditions can be predicted by selecting conditions with Ψ > 1. A flow with a R e n of 46, Ψ of 7 and Nu = 12 required the same pumping power as a flow with a R e n of 165, Ψ of 0.65 and Nu = 6. [ABSTRACT FROM AUTHOR]

Micro-blower is an innovative device that is used for sensitive applications such as electronics cooling, avionics and the medical field. It features a piezoelectric disc (PED)-diaphragm assembly. A 3D computational model of micro-blower is developed and simulated using COMSOL Multiphysics and studied its characteristic parameters such as maximum displacement (w), average velocity (w̅’), maximum von Mises stress (Tv), total kinetic energy (EK), total elastic strain energy (EU) and total electric energy (EE). The frequency-dependent electric potential difference was supplied to the Lead Zirconate Titanate (PZT-5H) PED. Seven different square wave ultrasonic frequencies were used as input for the PED ranging from 22 to 28 kHz, a resonance frequency is proposed in the study. There were three peak-to-peak voltages, Vp-p, of 10, 15 and 20 V were used. The characteristic parameters were estimated for the diaphragm, PED and PED-diaphragm assembly. For a 20 Vp-p and at 27 kHz, the maximum w reached 1.987 µm. The maximum Tv on the diaphragm surface and EE developed in the PED were 29.925 MPa and 442.98 nJ, respectively. The present numerical results were validated with previous studies on a similar domain and were in good agreement.

Thermal management plays a crucial role in the performance of electronic devices. For devices operating at room temperatures, manifold microchannels (MMCs) are essential for heat dissipation in heat sinks due to their low thermal resistance and pressure drop. However, their application in cryogenic electronic devices to enhance thermal performance has been largely unexplored. Herein, we integrated manifold microchannels into the evaporator of a micromachined Joule-Thomson (MJT) cooler to improve its cooling performance. The results show a notable reduction in the minimum cooling temperature from 105.0 K to 95.3 K, accompanied by an approximate 20 % increase in maximum cooling power. Furthermore, the coefficient of performance (COP) exhibits a rise of over 20 %. These findings underscore the feasibility and effectiveness of using MMCs in cryogenic electronic devices.

There has been a growing demand for novel, highly efficient, power-saving cooling solutions in recent years. In many cases, standard cooling techniques offer only limited opportunities to prevent the overheating of circuits. Such issues concern high-speed Printed Circuit Board Assemblies (PCBA) in data centers and telecommunication racks, where the flow of the cooling medium is obstructed due to the lack of space. Size limitations can also be a serious problem when cooling high-power devices because the devices consume a large space. Since the heat sink-based cooling solutions and the sophisticated IC packages only deal with one possible heat flow path, we were given the idea of enhancing the secondary heat flow path towards the Printed Circuit Board (PCB). Led by this intention, the idea of creating an embedded minichannel system inside the circuit board and circulating the cooling agent was realized. Through this method, we could decrease the board-to-ambient thermal resistance significantly. This paper presents the demonstration and feasibility study of this method. One of the main aims of this study is to demonstrate the applicability of the proposed concept in PCBAs, where the primary concerns are the low-cost manufacturability and available space. The other goal is to create an adaptation of the standard thermal characterization methodologies to deal with the specific dissipating components in the PCBA demonstrators. In the first part, the manufacturing technology is elaborated on, and its efficiency is characterized by thermal transient testing and Computational Fluid Dynamics (CFD) simulations. For these use cases, it was noted that the cumulative thermal resistance decreased by approximately 60 % when a volumetric flow rate of 100 ccm was applied in the minichannels. In the second part, a more sophisticated technology demonstration is realized and characterized by adding the proposed embedded minichannel heat sink to an existing high-speed PCBA. A specific thermal transient testing was implemented specifically for this use case, and it was carried out on programmable logic devices by utilizing general-purpose programmable logic to construct the necessary measurement methods. In the future, this feature can be used in different logic circuit designs where it is not possible to determine the junction temperature directly.

Aluminum nitride (AlN), a versatile ceramic with high thermal conductivity, high electrical resistivity, and a coefficient of thermal expansion compatible with silicon, is well‐suited for direct‐to‐chip cooling applications of electronics, implementation in wide bandgap semiconductors, and for high‐temperature heat exchangers. Despite multiple advantages, AlN's implementation in liquid‐cooling applications is often hindered by surface‐degrading effects of working‐fluid‐induced hydrolysis. Herein, a scalable ‐but highly tunable‐ wettability engineering approach is introduced, that allows effective implementation of bulk AlN substrates in enhanced two‐phase cooling of electronics. The approach prevents hydrolysis of AlN by aqueous media and establishes control over surface roughness, all the while maintaining bulk integrity and material properties of the underlying substrate. Demonstration of the new approach is presented in spontaneous, pumpless, surface liquid transport, a necessity if such ceramics are to play an integral role as components of sealed, phase‐change, wickless thermal‐management devices (e.g., vapor chambers or heat pipes) that require rapid working‐fluid transport in their multi‐phase interior. The novelty of this work lies in establishing a scalable methodology for utilizing and further enhancing the properties of this non‐oxide ceramic material for phase‐change heat‐transfer hermetic devices, thereby paving the way toward the implementation of this intriguing material in next‐generation heat spreaders. [ABSTRACT FROM AUTHOR]

This paper harnesses the spectral approach to study electromagnetohydrodynamics (EMHD) flow through an undulating 2D microchannel for a Newtonian fluid. The present study aims to investigate EMHD flow through a periodically patterned channel for large values of corrugation amplitude (surface roughness) relative to the channel height, Hartmann number and a wide range of wavelengths. A mathematical model is developed for the hydraulic permeability and the velocity field using the Fourier approach. By imposing a small pattern amplitude constraint, asymptotic analysis was employed to investigate the model presented in the literature. In the present study, hydraulic permeability is shown to strongly depend on the Hartmann number, pattern amplitude and wavelength. The spectral method predicts a monotonic decrease in hydraulic permeability irrespective of pattern amplitude at a small dimensionless wavelength (λ = 1) and Hartmann number (Ha < 1). At large wavelengths (λ > 3), the hydraulic permeability demonstrates an augmentation corresponding to the pattern amplitude. At intermediate wavelength ( 2.5 < λ < 3 ), the permeability of the channel firstly decreases and then increases with pattern amplitude. For large Hartmann numbers (H a ≫ 1) , the prediction from the spectral model exhibits a similar trend as a function of wavelength. Across a range of wavelengths, the spectral model captured the permeability minima for various large Hartmann number values. The spectral model is significantly faster than the finite-element-based numerical simulation, with computational efficiency ranging from 150 to 250 times higher. The existence of a limited pattern amplitude and Hartmann number for small-large wavelength patterns, at which the permeability of the channel is minimized, is one example of a prediction from the spectral model that is beyond the resolution of currently accessible asymptotic theories. [ABSTRACT FROM AUTHOR]

AbstractThis article presents the results of numerical investigation on comparison between two different cooling techniques namely cross flow and jet impingement cooling techniques used in heat sinks for the electronic components. Pin fin heat sink with and without phase change material (PCM) are considered for the investigation. The main focus of this research is to reduce the peak operating temperature of electronic component and pressure drop and to increase the Nusselt number of the heat sinks. Computational fluid Dynamics (CFD) tool is used to model and investigate the heat transfer characteristics across the heat sink. It is found that the cross flow shows superior thermal characteristics compared to jet impingement method due to which the base temperatures of pin fins in cross flow is at an average temperature of 14.5° C lower than that of jet impingement. Furthermore, the use of PCM significantly reduces the operating temperature of the pin fins by an average temperature of 7.5 °C for cross flow and 6.1 °C for jet impingement flow techniques. [ABSTRACT FROM AUTHOR]

[Display omitted] Films with nanoengineered surfaces have found extensive utilization in versatile applications, such as freshwater harvesting, water purification, steam generation and thermal energy management. Herein, we develop a liquid metal (LM) nanoporous film on a copper substrate via a simple and scalable bubble-induced self-assembly method. The LM nanoporous film not only provides abundant nucleation sites of bubbles due to nanoscale pores, but also generates CuGa 2 intermetallic compound (IMC) as a thermal interface layer with low interfacial resistance due to in situ alloying with the copper substrate. When the film is used in ethanol-based boiling system, it shows a 172% enhanced heat transfer coefficient compared to the pristine copper. In addition, the metallic wetting force between the LM nanoporous film and CuGa 2 IMC results in a durable nanoporous film. When the LM nanoporous film is utilized for the phase-change thermal energy management of a high-power-density light emitting diode, it leads to a distinct decrease in temperature by 20.7 ℃ relative to the pristine copper. This work provides a strategy to combine nanoengineered surfaces with interface engineering to enhance phase-change heat transfer, which can result in efficient energy transport in various energy-related applications. [ABSTRACT FROM AUTHOR]

Localized boiling and enclosed condensation of a dielectric liquid in a thermosyphon can be used as an alternative to traditional air cooling for high performance microprocessors. A small quantity of dielectric fluid boils at the surface of the microprocessor and is condensed by a heat exchanger, which removes the heat from the system. Here, the heat exchanger was a water-fed cold plate cooling a round fins heat sink. Such a thermosyphon can remove large heat fluxes and increase the energy efficiency of data centers.An experimental setup was built to measure the impact of various operating parameters on the thermal resistances of the thermosyphon. The thermal resistances that were considered were the boiling resistance between the heater and the dielectric fluid, the condensation resistance between the dielectric fluid and the cold water feeding the cold plate, and their sum (the total thermal resistance). The operating parameters tested were the cold plate inlet flow rate (0.2 L/min and 1 L/min), the cold plate inlet temperature (15 °C and 24 °C) and the filling ratio of the enclosure (33 %, 66 % and 88 %).It was observed that changing the filling ratio did not have a significant impact on the thermal resistances of the thermosyphon. Increasing the cold plate inlet flow rate from 0.2 L/min to 1 L/min and decreasing the cold plate inlet temperature from 24 °C to 15 °C both led to significantly lower total thermal resistance. However, increasing the flow rate lowered the rate at which the pressure increased with the amount of heat removed from the system, while this rate did not change when decreasing the cold plate inlet temperature.These observations could be properly explained by a simple analytical model, with a single free parameter (increasing the thermal resistance of the heat sink for the lowest cold plate flow rates). With the free parameter adjusted to the data, the model had a root-mean square error of 1.8 °C and a maximum error of 6 °C, over all measured conditions.This study demonstrates how changing the filling ratio or the cold plate inlet temperature and flow rate have an impact on the pressure, the temperature and the thermal resistances inside the thermosyphon. This is a first step in evaluating the energetic and economic efficiency of the thermosyphon solution for its future integration in data centers.

A MEMS heat sink having straight microchannels integrating sidewall cavities in staggered pattern is conceptualized in this work and its thermal resistance and pumping power characterized for Reynolds number ranging from 100 to 750. Over this Reynolds number range, the thermal resistance and pumping power of the proposed MEMS heat sink are lower than that of a MEMS heat sink having straight microchannels. With increase in Reynolds number, the relative reduction of thermal resistance varied from 1.8% to 23.4% while the relative reduction of pumping power varied between 18.6% and 6.5%. The proposed MEMS heat sink achieves reduction in thermal resistance with reduced pumping power and this is its novelty. The Nusselt and Poiseuille numbers of the straight microchannel integrating sidewall cavities are higher and lower than that of a straight microchannel without sidewall cavities, respectively. With increase in Reynolds number, the relative increase of Nusselt number ranged between 6.6% and 46.5% while the relative reduction of Poiseuille number ranged from 18.6% to 6.5%. The influence of the geometric features of the MEMS heat sink having straight microchannels integrating sidewall cavities is examined in this study. It is identified that there is a threshold value for the length of the sidewall cavities below which sidewall cavities do not influence thermal resistance and pumping power; above this threshold value, increase in the length of the sidewall cavities lead to reduction in thermal resistance and pumping power as well as increase and decrease in Nusselt and Poiseuille numbers, respectively. Increase in length of sidewall cavities led to the relative reduction of thermal resistance and pumping power varied from 1% and 19% at the lowest Reynolds number to 23.2% and 7.3% at the highest Reynolds number. With increase in the length of sidewall cavities, the relative increase of Nusselt number and relative reduction of Poiseuille number ranged from 2.3% and 19%, for Reynolds number of 100, to 38.9% and 7.3%, for Reynolds number of 750. It is identified that for every Reynolds number there exists an optimal value for the width of the sidewall cavities at which thermal resistance and Nusselt number are minimum and maximum, respectively; similar observation is made regarding the relationship between hydraulic diameter and thermal resistance while Nusselt and Poiseuille numbers decrease and increase with hydraulic diameter, respectively. Also, increase in the number of sidewall cavities lead to reduction in thermal resistance and pumping power; increase in the number sidewall cavities leads to increase and decrease in both Nusselt and Poiseuille numbers, respectively. With increase in the number of sidewall cavities, the relative reduction of thermal resistance at the lowest and highest Reynolds numbers are 1.4% and 1.8%, respectively; the relative reduction of pumping power at the lowest and highest Reynolds numbers are 12.6% and 7.1%, respectively. The relative increase of Nusselt number at the lowest and highest Reynolds numbers are 29.2% and 23.6%, respectively; the relative reduction of Poiseuille number at the lowest and highest Reynolds numbers are 12.6% and 7.1%, respectively. The model is validated using data from literature.INDEX TERMS Electronics cooling, microfluidics, numerical simulation, thermal resistance.

Researchers have attempted to improve heat transfer in mini/microchannel heat sinks by dispersing nano-encapsulated phase change (NPC) materials in base coolants. While NPC slurries have demonstrated improved heat transfer performance, their applications are limited by decreasing enhancement at increased flow rates. To address this challenge, the present study numerically investigates the effects of wavy channels on the performance of NPC slurries. Simulation results reveal that a wavy channel induces Dean vortices that intensify the mixing of the working fluid and enlarge the melting fractions of the NPC material, thus offering a significantly higher heat transfer efficiency than a straight channel. Moreover, heat transfer enhancement by NPC slurries varies with the imposed heat flux and flow rate. Interestingly, the maximum heat transfer enhancement obtained with the wavy channel not only exceeds the straight one, but also occurs at a higher heat flux and faster flow rate. This finding demonstrates the advantage of wavy channels in management of intensive heat fluxes with NPC slurries. The study also investigates wavy channels with varying amplitude and wavelength. Increasing the wave aspect ratio from 0.2 to 0.588 strengthens Dean vortices and consequently increases the Nusselt number, optimal heat flux, and overall thermal performance factor.

The thermal reliability of two different high-power insulated gate bipolar transistor (IGBT) modules was studied under both conduction and switching regimes by experimental and numerical approaches. Indeed, the reliability of semiconductor devices is tightly linked to the junction temperatures reached in the IGBT, which is a function of the diode chips present in such devices and its operating condition. However, measurements of the semiconductor temperatures are often difficult to be done, thus requiring modeling and simulation tools to accurately evaluate the instantaneous temperature under different thermal loads. For this reason, a transient 3D heat transfer numerical model of two different IGBT power devices was proposed using the Finite Element Method, assuming that heat is dissipated on the IGBT by natural convection and radiation. These simulations were validated with experimental measurements, obtained through infrared thermography, performed for the IGBT modules either opened or enclosed, varying the heat source, the module orientation and under conduction or switching regime. For the switching regime, power losses due to the gate-closing and gate-opening transitions between conducting and non-conducting states were taken into consideration. The heat losses were modeled assuming the time-dependent heat dissipation obtained by previous electrical simulations, and it was compared with time-averaged heat source solutions. Results showed that averaging the heat source can significantly reduce the computational time, allowing quick design explorations. Overall, the numerical model led to deviations of less than 16% over the transient heating and at steady-state. Finally, the impact of a heat sink attached to the IGBT was studied, demonstrating that the proposed model can be used for accurate and quick investigations of potential failures and for the development of more efficient IGBT devices. [ABSTRACT FROM AUTHOR]

Miniaturized microelectronics or small modular reactors (SMRs) simultaneously undergo an increase in heat flux and a decrease in size with the enhancement of device functionalities. Therefore, efficient convection cooling is required to prevent the malfunctioning of electronic devices or small nuclear reactors. Herein, mesh-patterned copper pyramids were fabricated via supersonic spraying for surface cooling applications. Zinc oxide nanowires (ZnO NWs) were patterned on top of the copper pyramids to produce a highly efficient cooling system for a high-heat-flux surface by increasing the overall surface area of the pyramids. In addition, ZnO NW decoration imparted superhydrophilicity to the surface with firm anchoring and spreading of impacting spray liquid drops until complete evaporation. The effects of macroscale pyramid mesh resolution and introduction of ZnO NWs on the spray cooling efficiency were quantified and compared. Herein, the pyramids with coarse resolution and ZnO NWs yielded the highest heat flux during the drop impact heat transfer process and the lowest surface temperature under air and spray cooling conditions owing to the maximized surface area. The use of the pyramids and introduction of ZnO NWs increased the Leidenfrost temperature from 140 to 190 °C, thereby expanding the range of the evaporation cooling regime.

This paper investigates the thermal performance of straight microchannel heat sinks featuring square-shaped fins on the sidewalls using a CFD developed model. The study evaluates the performance of the heat sink in terms of the total thermal resistance (Rth) and pumping power (PPf). The results show that incorporating square-shaped fins improves thermal performance, however at the penalty of increased pressure drop. To combine heat transfer enhancement with increased pressure drop, the study uses the Figure of Merit (FOM) approach. The study finds that increasing the size of the fins reduces thermal resistance by an average of 53.5%, but Design 1, which has smaller fins, offers a higher FOM. Similarly, reducing the spacing between fins lowers thermal resistance by an average of 61.95%, but Design 5 with smaller spacing than Design 4 offers a higher FOM. Furthermore, smaller channel sizes reduce thermal resistance by an average of 51.43%, but Design 6, which has larger channel sizes than Design 7, provides a higher FOM. Additionally, reducing channel spacing reduces thermal resistance by an average of 62.2% without affecting the pumping power, and Design 8 with smaller spacing than Design 9 offers a higher FOM.

This case study experimentally investigates a R134a charged Vapor Compression Refrigeration (VCR) assisted liquid cooling of high-powered CPUs. In this hybrid system, water-based liquid cooling of the CPU is achieved in a pumped loop with a commercial cold plate affixed to the simulated CPU. The heat is then transferred to the evaporator heat exchanger of a miniature VCR system that rejects the energy to ambient air. Tests are performed at room temperature over a range of operating conditions, including CPU heat loads (12 W/cm2 - 75 W/cm2), liquid volumetric flow rates (0.5 Litre/min - 8 Litre/min), fan air speeds (2.1 m/s – 4.2 m/s), and compressor speeds (2540 rpm–6500 rpm). Both cooling performance and additional energy consumption implications are considered. Overall, it is shown that the miniature hybrid VCR system can cool the primary liquid to below ambient temperature, even at the highest tested heat load. As a result, cooling levels that far exceed both a conventional Fan-Fin Air Cooled heat exchanger and a Hybrid Liquid-Air Cooled system are achieved. Finally, optimal combinations of liquid flow rate and compressor speed are identified for minimum energy consumption of the cooling system to maintain a setpoint CPU die temperature. It is shown that management and control of pump, compressor and fan speeds can result in significant improvement in the overall system Coefficient of Performance (COP).

The performance and stability of laptop computers can be adversely affected by overheating, which, in turn, can result in hardware failure due to low performance and stability. The purpose of this study is to develop a blower fan impeller that will solve the problems of overheating and noise production in laptop computers as a result of overheating. This proposed impeller was tested both numerically and experimentally using a Lenovo ThinkPad Carbon X1 notebook for performance analysis. Using the revolutionary novel impeller and adding an airfoil between each adjacent blades demonstrated an improved airflow distribution and a resistance reduction. According to the results of the free air simulation, there was a performance improvement of 6 %. Additionally, there was a significant increase of around 20.1 % in the volumetric flow rate of air and a significant increase in static pressure by 20 % respectively in the experimental results. Lastly, even at high speeds, blade peak noise generated by blades is extremely low in terms of sound pressure level (SPL). This work has patented under patent No. TW202248538A, CN216009004U, and CN115419611A.

In many energy-related applications, components with high heat loads, such as power electronics, play an important role. Pulsating heat pipes (PHPs) are an effective solution to deal with the increasing heat load of these components. In many real-life applications, the PHP must work against gravity and still be able to operate efficiently. However, the majority of present flat-plate PHP designs do not perform well under this condition. Therefore, this paper presents a flat-plate PHP with a conventional channel design optimized for gravity-independent operation. The PHP was capable of transmitting a heat output of 754 watts in all orientations, while the testing heater in use never exceeded a temperature of 100 °C. No indications of dryout were observed, implying that the maximum thermal load the PHP can handle is even higher. Additionally, three different condenser zone sizes were tested with the PHP. Previously published results indicated that there is a specific range of suitable condenser zone sizes, and performance problems will occur if the condenser zone size falls outside of this range. The findings from this work point in the same direction. [ABSTRACT FROM AUTHOR]

Optimization algorithms have significantly evolved because of advancements in computational capacity. This increase aids in the availability of data to train various artificial intelligence models and can be used in optimizing solutions for electronic chip cooling. In the current study, such a microchannel heat sink (MCHS) is optimized using a Boron Nitride Nanotube (BNN)-based nanofluid as a coolant. Thermal resistance and pumping power are chosen as the objective functions, while geometric parameters such as the channel aspect and width ratio are used as the design variables. Multi-objective multiverse optimizer (MOMVO), an evolutionary algorithm, is used to optimize both objective functions, which are minimized simultaneously. The primary objective of this study is to study the applicability of such advanced multi-objective optimization algorithms, which have not previously been implemented for such a thermal design problem. Based on the study, it is found that the optimal results are obtained with a population size of only 50 and within 100 iterations. Using the MOMVO optimization, it is also observed that thermal resistance and pumping power do not vary significantly with respect to the channel aspect ratio, while pumping power varies linearly with the channel width ratio. An optimum thermal resistance of 0.0177 °C/W and pumping power of 10.65 W are obtained using the MOMVO algorithm. [ABSTRACT FROM AUTHOR]

Oscillatory baffled flows (OBFs) provide a combined active and passive means of achieving convective heat transfer enhancement, and previous studies at large scale have demonstrated the heat transfer benefits of OBFs. To date, however, this technology has not been scaled down for the purpose of heat sink performance enhancement. Presented in this study is a numerical investigation of a single baffled channel with a hydraulic diameter of 2.8 mm, containing gate baffles, with a 50% open area, which are spaced 7.5 mm apart. Three net-flow rates were investigated while varying the oscillation conditions by varying the oscillation amplitude (3 mm to 7 mm) and by varying the oscillation frequency (0 to 8 Hz). Increasing the oscillation intensity had a greater impact on the Nusselt number compared to simply increasing the net-flow rate, with Nu enhancements of up to 330% observed when imposing oscillatory flow on a purely steady flow. Ideal operating conditions were identified by grouping the data by velocity ratio (Ψ) and graphing the theoretical pumping power against the thermal resistance of the channel. The highest Nu enhancement of 330% was achieved for a net-flow Reynolds number (Ren) of 165, oscillatory amplitude of 5 mm and a frequency of 8 Hz. Ideal operating conditions can be predicted by selecting conditions with Ψ > 1. A flow with a Ren of 46, Ψ of 7 and Nu = 12 required the same pumping power as a flow with a Ren of 165, Ψ of 0.65 and Nu = 6.

MEMS heat sink having wavy microchannels integrating circular pin-fins for cooling of microelectronic chips is proposed and analyzed in this work; the pin-fins are placed at the valleys and peaks of the wavy structure. The pumping power and thermal resistance of the proposed MEMS heat sink is higher and lower than that of MEMS heat sink having straight microchannels. At Reynolds number of 250, the maximum temperature of the microelectronic chip, generating 106 W/m2, when using the proposed MEMS heat sink is only 0.77 of that when using MEMS heat sink having straight microchannels; this ratio lowers to 0.6 at Reynolds number of 1250. The thermal resistance of the proposed MEMS heat sink is only 0.72 and 0.43 of that of the MEMS heat sink having straight microchannels at Reynolds numbers of 250 and 1250, respectively. Regarding the pumping power of the proposed MEMS heat sink, it is higher than that of the MEMS heat sink having straight microchannels by 2 and 3.7 at the lowest and highest Reynolds numbers, respectively. This work also analyzes the contribution of geometric features on the behavior of the proposed MEMS heat sink in terms of maximum temperature of the microelectronic chip, thermal resistance, and pumping power as well as that of microchannel employed in the proposed MEMS heat sink in terms of Poiseuille and Nusselt numbers. Maximum temperature of the microelectronic chip and thermal resistance decrease along with increase in pumping power with increase in amplitude, diameter of pin-fins, and hydraulic diameter of microchannel as well as with decrease in wavelength. Poiseuille and Nusselt numbers increased with rise in amplitude, diameter of pin-fins, and hydraulic diameter as well as decrease in wavelength. In addition, experiments have been conducted on two designs of the proposed MEMS heat sink to generate data for purposes of validating the model. The experimental data are compared with data from simulations and the difference between the two are within the uncertainty of experimental data thereby validating the model.

Two-phase-based heat spreaders are highly sought electronics cooling solutions due to their superior thermal performance over conventional conduction plates. Along with good thermal performance, Pulsating Heat Pipes (PHPs) potentially have thickness, shape matching and cost benefits over Embedded Heat Pipe (EHP) heat spreader solutions. In this manuscript, the thermal performance of PHP charged with three different fluids-propylene, R245fa, and acetone was experimentally determined for different sink temperatures and compared to an EHP heat spreader. A mathematical model to predict the thermal performance of the PHP was developed and validated against experimental results. It was determined that at low sink temperatures, PHP charged with propylene performs better than or similar to an EHP heat spreader with up to 7.8 times higher effective thermal conductivity over a conduction plate. However, at moderate temperatures above >40 °C, propylene PHP dries out faster than the EHP plate. PHP performance with R245fa and acetone improves with increasing heater power. Effective thermal conductivity improved by 2.5 times with R245fa PHP and by 4 times with acetone PHP over the conventional plate but was lower than the EHP plate whose effective thermal conductivity was 17.3 times higher. However, weight comparison showed PHP to be lighter than the EHPs.

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

Effective natural-convection-cooled heat sinks are vital to the future of electronics cooling due to their low energy demand in the absence of an external pumping agency in comparison to other cooling methods. The present numerical study was carried out with ANSYS Fluent and aimed at identifying a more-effective fin design for enhancing heat transfer in natural convection applications for a fixed base-plate size of 100 mm × 100 mm under an applied heat flux of 4000 W/m2. The Rayleigh number used in the present study lied within the range of 2.6 × 106 to 4.5 × 106. Initially, a baseline case with rectangular fins was considered in the present study, and it was optimized with respect to fin spacing. This optimized baseline case was then validated against the semi-empirical correlation from the scientific literature. Upon good agreement, the validated model was used for comparative analysis of different heat sink configurations with rectangular, trapezoidal, curved, and angled fins by constraining the surface area of the heat transfer. The optimized fin spacing obtained for the baseline case was also used for the other heat sink configurations, and then, the fin designs were further optimized for better performance. However, for the angled fin case, the optimized configuration found in the scientific literature was adopted in the present study. The proposed novel curved fin design with a shroud showed a 4.1% decrease in the system's thermal resistance with an increase in the heat transfer coefficient of 4.4% when compared to the optimized baseline fin case. The obtained results were further non-dimensionalized with the proposed scaling in terms of the baseline case for the two novel heat sink cases (trapezoidal, curved). [ABSTRACT FROM AUTHOR]

Abstract This study proposes using novel ogive-shaped ribs and cavities to enhance the thermal performance of a microchannel heat sink (MCHS). A three-dimensional conjugate numerical model was employed to investigate the impact of these modifications, i.e., ogive shape ribs and cavities, on the hydro-thermal performance of MCHS in laminar flow regime (Reynolds number 100–1000). The results show that flow separation occurs on the trailing edge of ogive ribs, promoting convective heat transfer by disrupting the boundary layer and enhancing fluid mixing on the downside of ogive ribs due to the formation of recirculation zones. Conversely, stagnant zones are created inside the ogive cavity due to very low fluid local velocity which results in a decrease of local Nusselt number. The study reports a 41.34% maximum improvement in Nusselt number for MCHS with ogive ribs on side channel walls and a maximum thermal enhancement factor of 1.42 for MCHS with ogive ribs on the bottom channel wall. [ABSTRACT FROM AUTHOR]

An ultra-thin flattened heat pipe has been developed with a centered wick structure. This structure is essential to make the heat pipe thinner. However, the centered wick structure reduces the evaporation and condensation surface areas of the wick structure because it is sandwiched between heat pipe walls. In this study, because detailed discussion has not been made, heat transfer experiments were conducted for the wick structure sandwiched between two solid walls. This study focused on the evaporation heat transfer characteristics from the sandwiched wick structure. The experiments were conducted with three wick structures, that is, strip-shaped sintered copper powders with thicknesses of 0.5, 1.0, and 1.5 mm. Water was used as working fluid. The capillary pumping performance, that is, the liquid lifting velocities of the threewick structureswere the same. The experimental results of the three wick structures were compared regarding the relation between the evaporation heat transfer rate and the superheat of the working fluid. The heat transfer experiments were also conducted when one of the solid walls was removed from the wick structure. It was confirmed that even if the wick structure was sandwiched between the solid walls, sufficient evaporation of the working fluid occurred from the thin sides of the wick structure. [ABSTRACT FROM AUTHOR]

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

Vapor compression refrigeration is considered one promising technology for dissipating much higher heat fluxes from electronic devices at lower temperatures. The compressor, one key component, has a great effect on the overall size and performance of the system. One lightweight, miniature, hermetic Wankel compressor was developed to solve limited space cooling problems. The assembled Wankel compressor had a diameter of 65 mm, a length of 85 mm and a weight of 340.2 g, without a motor and housing. An experimental system for miniature refrigeration was set up to explore the optimal refrigerant charge and the performance of the compressor under changing rotational speeds and inlet temperatures of cooling water. The experimental results showed that the optimal refrigerant charge was 220 g and the coefficient of performance was approximately 2.8. The refrigeration coefficient of the system decreased with increases in rotational speed and inlet temperature of the cooling water at a stable cooling capacity of 100 W. The developed lightweight, miniature, hermetic Wankel compressor had reliable performance after running for 600 h, with a power consumption of 35 W and a high coefficient of performance (COP) of 2.63. [ABSTRACT FROM AUTHOR]

ObjectivesThis study seeks to improve the thermal management technology of electronic devices through constructal optimization design. MethodsFirst, the 3D flow and heat transfer numerical model of a hybrid microchannel heat sink is established, and the volume ratio and relative position of its single-sided internal fins are fixed. Constructal optimization is then performed, for which the height-to-width ratio h/w and spacing distribution of fins ε are taken as the design variables, and the minimization of the temperature gradient uniformity factor in the solid region of the heat sink is taken as the objective. The exhaustive method and genetic algorithm are subsequently performed. ResultsThe results show that both the exhaustive method and genetic algorithm can find the minimum value of the temperature gradient uniformity factor and corresponding optimal construct, and the temperature gradient uniformity is improved by up to 13.30% compared to that of the finless microchannel heat sink. The relative difference in the obtained minimum objective function value between the exhaustive method and ten genetic algorithm schemes is no more than 0.92%. ConclusionsThis study provides new optimization design results for the research and development of heat sinks for electronic devices.

An analytical model is developed to determine the thermal performance of a Loop Heat Pipe filled (LHP) with copper oxide–water and alumina–water nanofluids for battery thermal management in electric vehicles. The thermal performances of the LHP are predicted for different heat loads and nanoparticle concentrations. It is demonstrated that for fast charging operation corresponding to a heat load of 150 W, the LHP ensures evaporator temperatures of less than 60 °C for a heat sink temperature of 40 °C. The heat transport capacity of the LHP is enhanced and the evaporator temperature is deceased by augmenting the nanoparticle concentration. The water–CuO nanofluid-filled LHP performs better than the water–Al2O3 nanofluid-filled one. The addition of the nanoparticles increases the LHP total pressure drop and the driving capillary pressure. The capillary limit of the water–CuO nanofluid-filled LHP is hardly affected by CuO nanoparticle concentration until 6% beyond which the capillary limit starts decreasing. For the water–Al2O3 nanofluid-filled LHP, the capillary limit decreases when Al2O3 nanoparticle concentration increases. Beyond 6% Al2O3 nanoparticle concentration, the capillary limit of the Al2O3-filled LHP becomes lower than the water-filled one.