Proposed Heat Sink Research Articles

Performance of new hybrid heat sink with trimmed fins and microchannels for thermal control of a triple-junction concentrator photovoltaic cell

An efficient and low-cost cooling method for high concentrator photovoltaic systems is essential to improve the overall performance and prolong their lifetime. Therefore, a new cost-effective hybrid heat sink with trimmed fins and microchannels was developed to harvest the benefits of active and passive cooling techniques. Unlike the traditional heat sink designs, adopting trimmed fins saves the heat sink weight and cost without affecting its cooling performance. Thus, three different heat sink configurations, including (A) heat sink with trimmed fins, (B) microchannel heat sink, and (C) hybrid heat sink with trimmed fins and microchannels, were compared. A comprehensive three-dimensional model for the proposed heat sink designs coupled with the triple-junction cell was numerically simulated and solved using ANSYS FLUENT software to predict the cell temperature distribution, temperature uniformity, electrical efficiency, and net output power. Compared to the other trimming angles, the fin trimming angle (α) achieves a 20 % reduction in the heat sink weight and cost with no noticeable effect on its cooling performance. The new hybrid heat sink efficiently controls the cell temperature below 110 ˚C up to a high concentration ratio of 3600 suns, compared to 1220 suns and 3010 suns for configurations A and B, respectively. Furthermore, using the hybrid heat sink improves the electrical efficiency by 3 % and 3.2 % compared to configurations A and B, respectively. Generally, the hybrid heat sink achieves the maximum generated power of 123.7 W compared to 41.9 W and 103.4 W for configurations A and B, respectively.

Experimental and numerical investigation on thermal characteristics of the heat sink integrating 3D vapor chamber heat spreader and liquid cooling fins

The traditional vapor chamber/ heat pipe heat sink in high-power chip heat dissipation structures consists of two separate parts. The contact thermal resistance between these parts leads to an increase in thermal resistance during the heat transfer process. To mitigate the contact thermal resistance and improve the heat dissipation performance of vapor chamber heat sinks, this paper proposes a heat sink integrating a 3D vapor chamber heat spreader and liquid cooling fins. Experiments and simulations were carried out to analyze the heat transfer characteristics under different heating powers. The pressure drop and thermal resistance were calculated to analyze the internal phase-change heat transfer process and capillary heat transfer limit. The simulation results were in close agreement with the experimental data for heating powers ranging from 397 to 795 W, with the thermal resistance of the proposed heat sink of about 0.04℃/W. Compared to three traditional vapor chamber heat sinks operating under the same heat flux, the proposed type exhibited a noteworthy enhancement in the heat transfer performance, leading to a reduction in thermal resistance by approximately 44% to 67%.

Numerical analysis on the cooling and electrical performances of photovoltaic noise barrier

A photovoltaic noise barrier (PVNB) is a useful device for installing PV systems on a noise barrier, which can save the space and cost associated with the installation of PV systems. Since a noise barrier usually consists of porous materials with low thermal conductivities, investigation on the cooling performance of the PVNBs is essential because the temperature of the PV module has a significant impact on its electrical performance. In this study, the cooling and electrical performances of a PVNB were numerically investigated using four different models: PV module-only, PVNB model without a heat sink, PVNB model with a conventional heat sink, and PVNB model with the proposed heat sink configuration. The simulation was validated by comparing the predicted and measured cell temperatures of the PV module at different heat fluxes, and the results showed good agreement. The average cell temperature in the PVNB model without a heat sink significantly increased by 42.2% from 86.98 ℃ to 123.66 ℃ because of the low thermal conductivity of the noise absorber, compared to the PV module only case. In the case of proposed heat sink configuration, the average cell temperature decreased by 42.7% from 123.66 ℃ to 70.90 ℃, compared with the PVNB model without a heat sink, owing to the additional injection of the cold ambient temperature air to the heat sink channel as well as natural convection and stack effect. The electrical performance of the PVs in the tested PVNBs was analyzed, and the results indicated that the maximum output power and voltage in the PVNB with the proposed heat sink configuration increased by 26.6% and 19.0%, respectively, compared to the PVNB model without a heat sink. The results of this study provide useful fundamentals regarding natural convection and the stack effect for optimizing heat sink designs for PVNB.

Investigation of Fluid Flow and Heat Transfer Characteristics in Wavy Mini-Channel Heat Sink With Interconnectors

Abstract In this paper, a novel sinusoidal wavy mini-channel heat sink (MCHS) with interconnectors (IC w-MCHS) has been introduced, and the effectiveness of the proposed heat sink over conventional mini-channel heat sink (s-MCHS) has been numerically investigated. Different parameters, i.e., wavelengths, wave amplitudes, and phase shifts of the proposed sinusoidal wavy MCHS, were varied to study its effect on thermal and hydraulic performance. This study used three different wavelengths, three different amplitudes, and two different phase shifts, and Reynolds number (Re) varied from 300 to 800. The Nusselt number (Nu) of IC w-MCHS increased as the wave amplitude ratio (α) and Re increased, whereas it increased with the decrement of the wavelength ratio (β). Nu of the IC w-MCHS was also found to depend on phase shift (θp); for θp = π, the chaotic advection and increment of flow reversal were observed in the IC w-MCHS compared to θp = 0, resulting in higher Nu and higher pressure drop penalty. Nu of the IC w-MCHS was found to be 115% higher compared to s-MCHS at Re 550, θp = π, and α = 0.3, whereas it was found 77% higher for θp = 0. The maximum temperature of the IC w-MCHS heat sink was also found to decrease compared to that of the s-MCHS due to enhanced coolant mixing. A maximum 26% decrease in the heat sink temperature was observed for the IC w-MCHS at Re 800 compared to the s-MCHS.

Thermal-hydraulic performance of ammonia in manifold microchannel heat sink

With the increasing miniaturisation of electronic devices, the demand for cooling technologies with high efficiency has increased. Therefore, in this study, a manifold microchannel heat sink was designed and fabricated to enhance the dissipating capability of high-heat-flux hotspots. Owing to its excellent thermophysical properties, ammonia was selected as the working fluid, and its thermal–hydraulic characteristics were evaluated. In addition, the effects of flow rate, heat flux, saturation temperature, and inlet conditions were investigated through experiments. High-subcooled inlet experiments revealed that the thermal resistance decreased and pressure drop increased with increasing flow rate. Moreover, localised subcooled boiling was observed near the heated region. In near-saturated inlet experiments, jet impingement and microchannel cooling were identified as the dominant heat transfer mechanisms over different flow ranges. Notably, the higher heat flux, lower saturation temperature, and two-phase inlet condition reduced the thermal resistance under the operating conditions of the study. The proposed heat sink dissipated the heat flux (up to 1542 W/cm2) from the heat source (1 mm × 6 mm) with a pressure drop of 10.6 kPa, and the corresponding heating surface temperature and thermal resistance were 68.05 ℃ and 0.450 K/W, respectively.

Heat transfer characteristics of thermally and hydrodynamically developing flows in multi-layer mini-channel heat sinks

In this study, a novel type of air-cooled heat sink is proposed, which consists of several layers of mini-channels. In this design, the hydraulic diameter is smaller than in conventional types of heat sinks, such as plate-fin heat sinks, and consequently, the achievable heat transfer rates are higher. To predict the cooling performance of this heat sink, an innovative analytical method is proposed, results from which are complemented by an extensive number of numerical simulations of the simultaneously developing flows, thermally and hydrodynamically, inside a rectangular channel of the heat sink. The results of the analytical method are compared against two- and three-dimensional simulations and good agreement is found, while from the simulations, correlations are proposed for the Nusselt number in these flows. Finally, the performance of the proposed heat sink is compared to a plate-fin heat sink. This comparison reveals that entropy generation in the latter is around 27% higher than in the former, and suggests a promising advantage of the proposed heat sink design.

Experimental study on the thermal characteristics of a 3D thermosyphon heat sink

Phase change heat transfer has received extensive attention in the thermal management of electronic devices. Most studies of heat pipe or vapor chamber were limited to one- or two-dimensional heat transfer mode. Enhancing the phase change heat transfer to three-dimensional mode in heat sinks and exploring the thermal behavior of the heat sinks deserve a dedicated study. In this paper, a three-dimensional thermosyphon (3D-TS) heat sink combining the superiorities of the vapor chamber, thermosyphon and folded fins was experimentally investigated. The experimental reliability was validated and consolidated by the heat loss analysis, and an iteration method was proposed to estimate the saturation temperature to facilitate the in-depth analysis of the results. The coupling characteristics of the air forced convection and phase change heat transfer, and the effects of the heating power and air volume flow rate on the thermal resistance of 3D-TS were involved in the discussion. The main results indicate that the overall thermal resistance exhibits a negative correlation with the heating power and the air volume flow rate. The lowest thermal resistance of 0.14 K·W−1 was achieved with Qtotal = 300 W and 100 CFM air volume flow rate. High temperature on the folded fins indicates that the phase change heat transfer extends from the flat vapor chamber to the vertical thermosyphon tubes. It is also found that for a small heating power, a relatively large air volume flow rate is not able to further reduce the overall thermal resistance due to inadequate phase change intensity. The proposed heat sink is expected to solve the heat dissipation problems for densely packed electronic devices, which can produce favorable performance according to the input heating power and appropriate air volume flow rate.

Investigation of the hydrothermal phenomena in a wavy microchannel with secondary flow passages through mid-wall inflection points

Advancement in manufacturing processeshas fuelled research in microchannel heat sinks to meet the demands of modern microelectronics. The heat sink design in the present study considers longitudinally wavy microchannels incorporating secondary flow passages. The secondary flow has been investigated for abrupt flow bifurcation (at 60° angle) and smooth flow bifurcation (at 30° angle). Further, these geometries were tested with different inlet–outlet configurations. The main objective of the paper is to study how a secondary flow would affect the flow profile and thermal performance of a wavy microchannel heat sink. The flow profile, pressure drop, temperature profiles, and average Nusselt number for a wide range of flow rates have been obtained and compared with those for the conventional design, and associated trends have been explored. Furthermore, the overall performance of the heat sink designs has been quantified by plotting the thermal enhancement factor (TEF) against a wide range of Reynolds numbers. The heat sink with flow bifurcation of 30° attains the highest value of Nuselt number below the flow rate of 1.8 × 10-6 m3/s, whereas above this flow rate, the Nusselt number value of the conventional wavy heat sink dominates the proposed heat sink designs. The study corresponds to the demands of modern microchips such as the 13th Gen Intel® Core™ processor and serves as a guideline for manufacturing heat sinks with wavy microchannels incorporating secondary flow passages.

Passive thermal control of a triple-junction solar cell at high concentrations using various finned heat sink configurations

Designing an effective heat sink that is light, inexpensive, and simple to manufacture and install, is crucial in developing a heat control strategy for high concentrated triple-junction (TJ) solar cells to maintain the cell operating temperature below the maximum allowed limit. Such heat sinks ensure better electrical output power and efficiency at a cheaper cost. Thus, the present research focuses on the passive thermal regulation of a triple-junction solar cell utilizing four different finned heat sink configurations; (A) flat plate, (B) straight fins, (C) pin fins, and (D) flared fins heat sink. A comprehensive 3D thermal and electrical model is developed and computationally simulated, incorporating the cell module layers coupled with the aluminium heat sink. The performance of the proposed system with different heat sink designs is investigated at various concentration ratios (CR) of the solar irradiance ranging from 50 suns to 1250 suns, air temperatures ranging from 25 °C to 40 °C, and wind speeds ranging from 1 m/s to 5 m/s. In hot climatic conditions (40 °C and 1 m/s), the integration of the proposed heat sink configurations A, B, C, and D enables the cell to operate safely (below 110 °C) at high concentration ratios of 440 suns, 1435 suns, 1250 suns, and 1775 suns, respectively, and produce large electric power of 15.2 W/cm2, 49.7 W/cm2, 43.3 W/cm2, and 61.4 W/cm2. In contrast, the maximum permissible concentration ratio of an uncooled cell operating in the same conditions is limited to 77 suns with an electrical output of 2.7 W/cm2. Although the flared fins heat sink is the heaviest, weighing about 0.6 kg, and the flat plate one is the lightest with 0.05 kg, the environmental analysis revealed that utilizing the former for cooling concentrated photovoltaic systems could reduce annual CO2 emissions by 1475.2 tons/m2 compared to 364.5 tons/m2 for the latter if both are operated at the maximum permissible solar concentration ratio.

Performance improvement of heat sink with vapor chamber base and heat pipe

The heat sink with vapor chamber heat spreader has been the emerging design as it offers tremendous reduction in spreading resistance. However, this type of heat sinks suffer from the fin side temperature non-homogeneity, which hinders the heat transfer enhancement. The present study aimed to develop parallelogram fins integrated with heat pipes to increase the heat transfer performance of the heat sink with the vapor chamber heat spreader. The experimental and numerical investigations were performed on different heat sinks with different heat spreaders, including flat plate, vapor chamber, and vapor chamber combined with heat pipe. The air-cooled heat sink features a parallelogram fin configuration is proposed to tailor the temperature non-uniformity alongside the fins. The results showed that the overall thermal resistance of the heat sink with the vapor chamber and the vapor chamber combined with heat pipe spreader (no-cut fins) is about 50% and 55% lower than in the flat plate case. The proposed heat sink with vapor chamber combined with heat pipe spreader having a parallelogram fin structure offered about 61% reduction in thermal resistance and 45–50 °C reduction in chip temperature over the heat sink with flat plate heat spreader.

Thermal management system for high, dense, and compact power electronics

Modern microelectronics requires more sophisticated and uniform thermal management practices to sustain the device's reliability and performance. The current work reports a new heat sink configuration that manipulates the heat by dividing the microchannel heat sink into four distinct symmetrical areas and multi-bifurcation channels. Additionally, cutting-edge carbon-based thermal interface materials (TIM) with high thermal conductivity anisotropy were applied. Two inlet and outlet cases (In case 1, the channel width is decreased with the flow stream and versa; in Case 2) were studied for water and Ethanol. Computational Fluid Dynamics (CFD) modeling and experimental setup were conducted to investigate the proposed heat sink. A multi-objective genetic algorithm and new user-defined functions (UDF) are utilized to determine the TIM's optimum thermal conductivity anisotropy values.The results show that the numerical and experimental results match with an average deviation less than 1% under the same conditions. Furthermore, the heat sink's geometry significantly influenced the device's non-uniformity. Comparing Case 1 to Case 2, at the highest flow rate, Case 1 showed 55% and 42% better uniform cooling for Ethanol and water, respectively. Water showed about 3% enhancement on the average wall temperature for both Case1 and 2. However, Ethanol offered better temperature uniformity, where the moderate enhancement in temperature uniformity was about 3.6% in Case 1 compared to water. Involving the TIM broke up any potential for creating local hotspots. Finally, the optimization shows that the optimum in-plane and through-plane thermal conductivity values were about 1170 W/m k and 1 W/m k, respectively.

Thermal management of solar photovoltaic module by using drilled cylindrical rods integrated with phase change materials

Solar photovoltaic panels are designed to generate electrical voltage when exposed to sunlight. The temperature of the photovoltaic cell surface rises as a result of sunlight striking the active portion of the panel. The output voltage of the PV cell decreases as the surface temperature of the PV cell rises, resulting in a drop in the PV module's output power. To reduce the operating temperature of the PV module different types of a heat sink having PCM are used in already published studies. This research work aims to enhance the performance of the heat sink by attaching an alternative and novel kind of heat sink to the rear side of the PV module. The proposed heat sink is composed of an array of drilled cylindrical rods with extended geometry like pin fins filled with phase change material. The proposed thermal management model is investigated both experimentally and by numerical simulations. Using experimental data, the thermal and electrical performances of the modified PV module are compared to the original PV module. Fins absorb heat from the rear surface of the PV panel through conduction heat transfer and increase the heat transfer area. The PCM absorbs the heat from the PV module in the form of latent heat transfer by shifting its phase. In the trials, the temperature of the PV module decreased by 5.18 °C. The output voltage is raised by 0.53 V, and the PV-PCM efficiency is increased by 2.9% to the efficiency of the PV module without a heat sink. Moreover, a comprehensive parametric sensitivity analysis is conducted using the validated numerical model to investigate the impact of wind speed and incidence angle on the PCM-integrated modified PV module. The numerical results show an increase of 0.4 m/s in wind speed decreases the temperature of the Tedlar wall to 0.4196 °C and the temperature of the solar module decreases by increasing the Iincidence angle of wind from 30°–90°. The results indicate that the PCM-integrated modified solar module is successful in optimizing the PV module's output power.

Thermo-hydraulic and entropy generation investigation of nano-encapsulated phase change material (NEPCM) slurry in hybrid wavy microchannel

PurposeThis study aims to capture the heat transfer and entropy generation characteristics of temperature-dependent nano-encapsulated phase change material (NEPCM) slurry in a hybrid wavy microchannel. In addition, the effect of substrate material combined with NEPCM slurry on conjugate heat transfer condition is captured for different microchannel heat sinks.Design/methodology/approachA novel “hybrid wavy microchannel” is proposed to enhance the overall heat transfer and reduce the pressure drop by combining wavy and raccoon geometry. NEPCM–water slurry is implied in the hybrid wavy, conventional wavy and raccoon microchannel. A user-defined function (UDF) is used to observe the effect of phase-change of paraffin material in thermophysical properties of NEPCM–water nanofluid. All three (hybrid, wavy, raccoon) microchannels are engraved on a rectangular substrate of 1.8 mm width (ωs) and 30 mm length (L), respectively. For hybrid, wavy and raccoon microchannel, waviness (γ) of 0.067 is selected for the investigation.FindingsThe result shows that NEPCM particle presence reduces the fluid domain temperature. The thermal performance of proposed Heat sink 2 is found better than the Heat sink 1. The effect of the geometrical modification, wall thermal conductivity, different volumetric concentrations of nanoparticles (ϕ ∼ 1 – 5%) and Reynolds number (Re ∼ 100 – 500) on thermodynamic irreversibility is also observed. Additionally, the effect of thermal and frictional entropy generation is reduced with a combination of NEPCM slurry and higher conductive material for all heat sinks.Practical implicationsA combination of NEPCM slurry with laminar flow microchannel cooling system emerged as a better alternative over other cooling techniques for higher power density devices such as microprocessors, electronic radar systems, aerospace applications, semiconductors, power electronics in modern electronic vehicles, high power lasers, etc.Originality/valueThe phase-change process of the NEPCM slurry is tracked under conjugate heat transfer in a hybrid wavy microchannel. Furthermore, the phase-change process of NEPCM slurry is captured with different heat sink materials (SS316, silicon and copper) under conjugate heat transfer situation for different heat sinks and concentrations (ϕ ∼ 1–5) of NEPCM.

Thermal analysis of proposed heat sink design under natural convection for the thermal management of electronics

The rapid development in the field of electronics has led to high power densities and miniaturization of electronic packages. Because of the compact size of electronic devices, the rate of heat dissipation has increased drastically. Due to this reason, the air-cooling system with a conventional heat sink is insufficient to remove large quantity of heat. A novel macro-channel ?L-shaped heat sink? is pro-posed and analyzed to overcome this problem. The thermal resistance and fluid-flow behavior under natural convection, of the novel and conventional air-cooled heat sink designs, are analyzed. Governing equations are discretized and solved across the computational domain of the heat sink, with 3-D conjugate heat transfer model. Numerical results are validated through experimentation. The effect of parameters i.e., fin height, number of fins and heat sink size, on the thermal resistance and fluid-flow are reported. Examination of these parameters provide a better physical understanding from energy conservation and management view point. Substantial increase in the thermal performance is noted for the novel ?L-shaped heat sink? compared to the conventional design.

Thermal analysis and optimization of L-shape fin heat sink under natural convection using ANOVA and Taguchi

Advancement in electronic systems resulted in miniaturization and high-power densities. Therefore, the rate of heat generation in circuit board increased dramatically. To overcome the problem of overheating, numerous heat sink designs are proposed including L-shape fins heat sink. The thermo-fluidic flow behavior and temperature difference are analyzed to get better understanding of heat transfer from the sink to ambient air. Governing equations for the model of conjugate heat transfer in 3-D environment are solved and discretized across the computational domain. Numerous experiments are carried out to validate the numerical results. The effect of fin numbers, height, and heat sink size at three different input power is reported. Furthermore, ANOVA and Taguchi statistical methods are used to predict parameters that affect the heat transfer. The study revealed that fin height affects the heat transfer rate the most, and accounts for 25.3% increase in heat transfer rate. Optimization of the heat sink is carried out to ensure better efficiency of the proposed heat sink. The optimized conditions for the sink are observed to be heat sink size of 90 mm, 9 number of fins, and 33 mm of fin height.

Optimization of semi-interlocking heat sinks for hotspot thermal management using multi-objective genetic algorithm

A semi-interlocking heat sink that operates based on the effect of flow acceleration in a curved channel is proposed to mitigate local heat fluxes from power electronics. The proposed heat sink offers easy manufacturability owing to its simple structure. A computational fluid dynamics simulation is developed and validated experimentally. The simulation is conducted based on periodic boundary conditions. The design of experiment method and the Kriging meta-modeling are used to optimize the heat sink. Furthermore, a multi-objective genetic algorithm is used to minimize thermal resistance and pressure drop. Based on the optimization results, the thermal and hydraulic characteristics are analyzed according to geometric changes. The analysis shows that the proposed heat sink affords a 30.4%–34.7% lower thermal resistance than plate-finned heat sinks at the same pumping power.

Experimental study on single-phase convective heat transfer of interlocking double-layer counterflow mini-channel heat sink

This study proposes an interlocking double-layer mini-channel heat sink that can realize counterflow in which the flow direction is opposite in the adjacent channel. The heat sink consists of two-channel layers and a header/plenum structure serving as a pre-flow path for counterflow into the channels. The novelty and significance of the current study are that the counterflow multi-channel heat sink was first experimentally implemented through the design of a new internal flow distribution structure. The test data are obtained from the experimental evaluation of the single-phase flow cooling performance of the heat sink. The heat transfer characteristics of the heat sink are analyzed by separating the change in the single channel heat transfer coefficient increased by the counterflow channel effect. The thermal resistance representing the overall cooling performance of the proposed heat sink shows a significantly small value of 10-4 K-m2/W order, which indicates the heat transfer performance advantage of the new heat sink. The beneficial effect of counterflow is verified by comparing the heat transfer coefficient obtained from the proposed heat sink and the prediction using the previous correlation for unidirectional single-phase flow heat transfer coefficient. The measured heat transfer coefficients are much larger than the predicted values by all kinds of past correlations. The difference between the measured value and the predicted value is much greater at low flow conditions where the temperature gradient increases more significantly with the flow direction. It can be concluded that this indirectly implies the fact that temperature gradient mitigation by counterflow results in an additional heat transfer improvement that is unpredictable in the previous unidirectional flow correlations. A new correlation is proposed to predict the heat transfer coefficient affected by the counterflow. This study is the first to experimentally implement a counterflow heat sink, confirming the distinct advantage of improved cooling performance over conventional heatsinks. In addition, this study is meaningful in that it presents a performance prediction model that can be used in design for the practical application of counterflow heat sinks.

Heat Sink Design for WBG Power Modules Based on Fourier Series and Evolutionary Multi-Objective Multi-Physics Optimization

Optimal heat dissipation in power modules can significantly increase their power density. Removing the generated heat is critical for capturing the benefits of advanced semiconductor materials and improving the reliability of the device operation. This study proposes a design optimization method for liquid-cooled heat sinks that use a Fourier analysis--based tool and an evolutionary optimization algorithm to optimize the heat sink geometry for specified objectives. The optimized heat sink geometry was compared with state-of-the-art solutions in the literature based on finite element analysis of different designs. The proposed methodology can develop complex geometries that outperform conventional heat sink geometries. Optimized heat sink design from the proposed method was fabricated and tested in an experimental setup under representative operating conditions. The experimental setup was also modeled in the finite element model that was used for the proposed heat sink optimization method. The experimental results show that developed finite element models can predict the thermal and flow performance of the complex design with high fidelity, and the results validate the proposed design approach.

Performance of displaced fin heatsink in natural convection subject to upward and downward arrangement

In this study, a heat sink with a displaced fin arrangement is proposed to enhance the thermal performance in natural convection. To demonstrate the competence of the proposed heat sink design, an experimental investigation was carried out for the upward and downward configurations for the heat flux range of 30–470 Wm-2. The experimental results suggest that the proposed heat sink with the fin displacement distance of 20 mm can reduce the total thermal resistance by 11% and 14% for the upward and downward configurations, respectively. The parametric study was conducted with the Definitive Screening Designs (DSDs) method, and it suggested thirteen optimized test conditions. The outcome of the parametric study implies that the fin spacing plays a vital role in determining the heat sink performance, followed by the fin height and fin length; and the effect of heat flux is insignificant. For the thirteen test conditions suggested by the DSDs method, the numerical investigation was conducted. The numerical results show that for the same volume, when compared to the regular rectangular heat sink the proposed heat sink can provide an 11% performance enhancement with a 28.7% reduction in mass.

Gradient wick channels for enhanced flow boiling HTC and delayed CHF

Liquid supply to wick structures of flow boiling surfaces is fundamentally restricted by the capillary limit at which the pressure drop of the wicked liquid surpasses texture-amplified capillary forces. Gradient wick structures partially decouple permeability and capillary pressure, thereby delaying the capillary limit. In this study, gradient wick channels facilitating out-of-plane liquid delivery are introduced to postpone the capillary limit and thus enhance the two-phase flow boiling heat transfer coefficient (HTC) and delay critical heat flux (CHF). Here, the permeability of the gradient wick channels is augmented by large-pore-size meshes employed near the bulk fluid while capillary pressure is maximized by small-pore-size meshes utilized near the hot boiling surface. This combination of wick structures enables to preferentially guide the cooling liquid, deionized water, from the far-field cold liquid toward the bottom hot substrate. The spatial distribution of individual gradient wick channels promotes separate liquid-vapor pathways, thus facilitating the vapor escape process. Experiments conducted here reveal that the flow boiling performance metrics of the proposed heat sink leveraging the gradient wick channels outperform those of the homogenous wick channels and solid fin channels. The proposed heat sink demonstrates a strong liquid mass flux dependency due to a combination of convective boiling and amplified wickability effects. The enhanced convective boiling could be related to surface roughness, a high number of active nucleation sites, and a large surface area available through tortuous passages of wick channels. At higher mass flow rates, effective capillary pressure available for out-of-plane wicking action also increases, thereby further boosting the wickability effect and associated heat transfer processes. This could meaningfully delay the CHF. In fact, the CHF limit was not observed on the gradient wick channel surfaces in the mass flux and wall superheat range studied. The experimental results indicated a maximum heat flux of 870 W/cm2 with a gradient wick channel heat sink, a 60% improvement compared with a plain copper surface. Furthermore, a maximum HTC of 1000 kW/m2-K at a wall superheat of 3 °C was observed, a three-fold enhancement compared with that of the plain surface. The proposed gradient wick channel topology offers new pathways for designing innovative surface technologies with high heat removal capabilities, thereby potentially improving the energy economy in myriad modern energy applications.