Design Of Microchannel Heat Sink Research Articles

Topology Optimization Design of Micro-Channel Heat Sink by Considering the Coupling of Fluid-Solid and Heat Transfer

To investigate the effect of the target weight coefficient on the structure design of the micro-channel heat sink, an innovative method for the topology optimization design of micro-channel structures with different bifurcation angles is adopted. In this study, the improved interpolation function, density filtering, and hyperbolic tangent projection methods are adopted to obtain a clear topological structure of the micro-channel heat sink. The heat transfer of the micro-channel heat sink under different bifurcation angles is compared. At the same time, the influence of the two different objective functions, heat transfer, and flow energy consumption, is analyzed in the topology optimization of micro-channel heat sinks. The results show that when the bifurcation angle is 135°, both the heat transfer and the average outlet temperature of the micro-channel heat sink obtain the maximum value, and the heat transfer effect is the best. With the increase of the heat transfer weighting coefficient, the distribution of solid heat sources in the main channel increases, and the refinement of the branch channels also increases. On the other hand, although the heat transfer effect of the micro-channel heat sink is the best, the corresponding flow energy consumption is larger.

Thermofluids performances on innovative design with multi-circuit nested loop applicable for double-layer microchannel heat sinks

This study numerically proposes a novel microchannel heat sink design named multi-circuit nested loop (ML) to strength the thermal performance of double-layer microchannel heat sinks (DMCHS). The ML is introduced into the DMCHS to enhance the thermal characteristics and is compared with the traditional straight DMCHS. Due to the complexity of the ML-DMCHS, 4 different working conditions on inlets and outlets are designed to find the optimal one. Based on the analysis of the thermal gradients on substrate, flow characteristics of coolant, overall thermal resistance and thermal performance factor, it is found that the novel ML-DMCHS not only can significantly reduce the peak temperature, but also offer better temperature uniformity on substrate. The peak temperature on substrate can be reduced up to 34 K when compared with traditional parallel straight double-layer microchannels (P-DMCHS). Furthermore, the inner cooling circuit in ML-DMCHS shows greater impact on the lowest temperature on substrate, while the outer cooling circuit affects more on the peak temperature.

A Numerical Investigation on Hydrothermal Performance of Micro Channel Heat Sink with Periodic Spatial Modification on Sidewalls.

Electronic gadgets have been designed to incorporating very small components such as microcontrollers, electronic chips, transistors, microprocessors, etc. These components are exceptionally heat sensitive and can be wrecked if heat is not released. As a result, the thermal control of such components is critical to their optimum performance and extended life. The use of a microchannel heat sink (MCHS) has shown promising solutions to remove the excess heat. In this paper, we have proposed a novel design of MCHS and investigated it numerically. Four different surface modifications on the sidewall of the passage, namely, extended triangular surface (ETS), extended circular surface (ECS), triangular groove surface (TGS), and the circular groove surface (CGS) in the passage of the microchannel have been exploited in the Reynolds number of 100-900. In the presence of geometrical modification, the cooling capacities have been enhanced. The results show that the Nusselt numbers of ETS-MCHS, ECS-MCHS, TGS-MCHS, and CGS-MCHS are increased by 4.30, 3.61, 1.62, and 1.41 times in comparison to the Nusselt number of MCHS with smooth passage, while the friction factor values are increased by 7.33, 6.03, 2.74, and 1.68 times, respectively. In addition, the thermohydraulic performance parameter (THPP) has been evaluated and discussed. The fact that MCHS have THPP values greater than unity demonstrates that the passage's geometries are a practical means of achieving effective thermal management.

Response Surface Methodology and Artificial Neural Network modellings on hydraulic and thermal performances of a disk-shaped heat sink with tree-like microchannels

To cope with the increasing heat generation resulting from increased power in micro-scale devices, an optimum design of a tree-like microchannel heat sink is suggested utilizing Artificial Neural Networks (ANN) and Response Surface Methodology (RSM). Based on the numerical finite volume model, both ANN and RSM models were trained, and their performances were assessed using four distinct performance criteria. The results showed that both of the models are reliable for the purpose of this study, showing a significantly high adjusted R2 for both performance control variables pressure drop (ΔP) and Nusselt number (Nu). The adjusted R2 values observed for the RSM were 0.987 and 0.997, respectively, for the Nu and ΔP. These values were calculated as high as 0.997 for Nu prediction and 0.997 for ΔP prediction using the ANN. Finally, utilizing the calibrated RSM and ANN models, three optimum design configurations for three different purposes given the priority requirements of the heat sink implementations were suggested. The minimum ΔP configuration is suitable for the longevity of the heat sink, and the maximum Nu configuration is suitable for applications where heat transfer performance is more critical. For a balanced optimum design, the efficiency index was maximized.

Pressure drop of R134a in mini channels with micro pin fins during flow boiling

Flow boiling in mini channel with micro pin fin arrays is a promising technology for thermal management in various fields such as microelectronics, energy utilization and national defence. Understanding its flow characteristics is the pave stone for further structure optimization of two-phase microchannel heat sinks. However, previous studies paid few attentions to the effect of different structural parameters on its flow performance, especially for the application with long channels for practical evaporators in aircraft environmental control systems. In this paper, an experimental system was set up to investigate the flow boiling pressure drops of refrigerant R134a in a 300 mm long channel with micro pin fin arrays. The flow characteristics of staggered diamond pin fin arrays with different channel widths of 1.0, 1.2 and 1.4 mm and fin angles of 30°, 60°and 90° were comprehensively investigated. The pin fins with a height of 0.5 mm were arranged in the rectangular channel through 3D printing. Two-phase pressure drops in the test section were then measured. The test range of vapor quality, mass flux, heat flux and saturation pressure were 0–1, 200–500 kg/m2s, 10.0–37.5 kW/m2 and 390–700 kPa respectively. Experimental results revealed that the smaller channel width and the greater diamond angle resulted in the greater two-phase pressure drops. The heat flux showed an insignificant influence on the two-phase pressure drops. The existing empirical correlations for pressure drops were evaluated and failed to predict the present experimental data. A new one with the consideration of pin fin structure parameters was then developed to improve the prediction accuracy with the maximum mean absolute deviation of 5.4 %. The proposed correlation can illuminate future study on flow boiling in mini channel with pin fin arrays and be beneficial for the practical design of two-phase microchannel heat sinks.

Parametric study for optimizing double-layer microchannel heat sink for solar panel thermal management

The most significant issue affecting the electric efficiency of solar panels is overheating. Concentration photovoltaic (CPV) modules work by converting approximately 80% of sunlight to heat; this may exceed the cell operating temperature limits. Therefore, thermal management is the best choice for keeping such panels working under specified conditions. Prior to producing an actual solar indoor unit, the current research primarily focuses on optimizing the heat sink dimensions that affect the cooling performance of the solar panel. Two parametric studies were employed to optimize the microchannel heat sink design. First, a two-dimensional numerical study was implemented to optimize the best channel height for more uniform flow inside a double-layer microchannel heat sink (DL-MCHS); the width of channels was kept as a constant value. Second, a three-dimensional conjugate heat transfer model for fluid flow in the optimized heat sink was used to optimize the inlet/outlet header length. To evaluate the overall CPV performance, a further numerical case study was carried out for the optimized designs at a wide range of inlet mass flow rates and steady-state heat flux. The findings indicated that a channel height of 0.5 mm and a header length of 20 mm were the best design points for the suggested heat sink. To assess the effectiveness of a solar/thermal module, the selected design points were applied to a 3D model. The maximum electricity efficiency measured was 17.45%, nearly 40% greater than the typical CPV/T system.

Numerical Investigation on the Heat and Mass Transfer in Microchannel with Discrete Heat Sources Considering the Soret and Dufour Effects.

Heat-transfer enhancement in microchannel heat sinks (MCHS) has been a hot topic in the last decade. However, most published works did not focus on the heat sources that are discrete, as in most microelectronic devices, and the enhancement of heat and mass transfer (HMT) due to the Soret and Dufour effects being ignored. Based on a heterogeneous two-phase model that takes into consideration the Soret and Dufour effects, numerical simulations have been performed for various geometries and heat sources. The numerical results demonstrate that the vortices induced by a heat source(s) can enhance the heat transfer efficiency up to 2665 W/m2·K from 2618 W/m2·K for a discrete heat source with a heat flux q = 106 W/m2. The Soret effect can affect the heat transfer much more than the Duffour effect. The integrated results for heat transfer due to the Soret and Dufour effects are not sampled superpositions. Discrete heat sources (DHS) arranged in microchannels can enhance heat transfer, especially when the inlet velocity of the forced flow is less than 0.01 m/s. This can provide a beneficial reference for the design of MCHS with DHS.

Analysis of Microchannel Heat Sink of Silicon Material with Right Triangular Groove on Sidewall of Passage.

Microchannel heat sink (MCHS) is a promising solution for removing the excess heat from an electronic component such as a microprocessor, electronic chip, etc. In order to increase the heat removal rate, the design of MCHS plays a vital role, and can avoid damaging heat-sensitive components. Therefore, the passage of the MCHS has been designed with a periodic right triangular groove in the flow passage. The motivation for this form of groove shape is taken from heat transfer enhancement techniques used in solar air heaters. In this paper, a numerical study of this new design of microchannel passage is presented. The microchannel design has five variable groove angles, ranging from 15° to 75°. Computational fluid dynamics (CFD) is used to simulate this unique microchannel. Based on the Navier–Stokes and energy equations, a 3D model of the microchannel heat sink was built, discretized, and laminar numerical solutions for heat transfer, pressure drop, and thermohydraulic performance were derived. It was found that Nusselt number and thermo-hydraulic performance are superior in the microchannel with a 15° groove angle. In addition, thermohydraulic performance parameters (THPP) were evaluated and discussed. THPP values were found to be more than unity for a designed microchannel that had all angles except 75°, which confirm that the proposed design of the microchannel is a viable solution for thermal management.

Interplay of wettability and confinement enhancing the performance of heat sinks

• Tapered Double layer heat sink performance is enhanced by modifying surfaces (slip). • Value of slip length has been obtained using Molecular Dynamics simulation. • Analysis has been done based on both the first law and the second law of thermodynamics. • Entropy generation rate due to changes in kinetic energy has been introduced. • The optimal design of a double-layer microchannel heat sink has been obtained. Engineering microchannel heat sinks can help to develop compact and highly efficient cooling systems for electronic devices. In the present study, we demonstrate the coupled effect of surface modification and confinement on the performance of Double Layered Microchannel Heat Sink (DL-MCHS). The effect of wettability is incorporated using interfacial slip obtained from Molecular Dynamics (MD) simulations performed for various wettabilities, and the effect of confinement, through varying tapering degrees, is directly embodied in the geometry. The coupled transport equations are solved using the Finite Element Method (FEM) to depict the thermo-hydraulic characteristics of DL-MCHS. We quantified the enhancement in hydraulic performance and thermal performance of DL-MCHS with varying degrees of surface modification and varying tapering. For the first time, we demonstrate a regime where thermal and hydraulic performances can be enhanced simultaneously in tapered DL-MCHS thereby, making the configuration a viable heat sink system. Also, for the first time, we perform an entropy generation rate analysis in tapered DL-MCHS and demonstrated ways to reduce irreversibility making it a thermodynamically advantageous system, and following that perform an all parameter optimization study. We show that by tuning the tapering factor and interfacial characteristics, the performance of the heat sink can be adjusted for the best performance. The present study will provide helpful guidelines in designing viable heat sinks or exchangers with smart surfaces for electronics cooling and associated applications.

Parametrized level set method for a coupled thermal–fluid problem using radial basis functions

This paper develops a parametric level set-based topology optimization method for the micro-channel heat sink design. In this study, the optimal objective functional is formulated as a bi-objective functional consisting of heat transfer maximization and pressure drop minimization based on the two- and three-dimensional steady-state Navier–Stokes and energy balance equations. The normal velocity of the interface propagation, which is derived from the steepest descent method and adjoint variable method, is used to drive the evolution of the level set function. Influence of the governing equations on the optimized heat sink structure and the distribution characteristics of adjoint variables are analysed through numerical experiments, which proved that governing equations can improve the heat dissipation capacity of the optimal structure. Based on Earth Mover’s Distance, the developed method is proved to have less dependence on initial structures compared with the density-based topology optimization method. Finally, through the experimental tests and numerical simulations, the effectiveness of the developed model is confirmed.

Heat transfer enhancement for microchannel heat sink by strengthening fluids mixing with backward right-angled trapezoidal grooves in channel sidewalls

To strengthen the fluids mixing in channels for enhancing heat transfer, a new design of microchannel heat sink with periodic gradual-expansion and sudden-constriction cross-sections was proposed by arranging backward right-angled trapezoidal grooves in channel sidewalls. The flow and heat transfer characteristics in the new design was numerically investigated and compared with those in two comparative microchannels, which have the same channel volume and the same or almost the same convective heat transfer area as the new design. The pressure and viscous resistances of channel walls were innovatively analyzed for explaining why grooves can maintain a lower pressure drop for microchannels. The results indicate that the new microchannel shows a significant improvement of heat transfer enhancement and overall performance although its pressure resistance and viscous resistance are much higher than those of other ones. The pressure drop and Nusselt number of the new microchannel are 1.02–1.45 and 1.31–2.14 times higher than those of the smooth straight microchannel, respectively. After an optimum process of the forward angle (θ) of grooves, the relative Nusselt number of the new microchannel can be achieved up to 2.23 at θ = 15°and Re = 737 while the overall heat transfer factor can be achieved up to 1.89 at θ = 18°and Re = 442.

Micro/nanoscale surface on enhancing the microchannel flow boiling performance: A Lattice Boltzmann simulation

Microchannel Heat Sink (MCHS) has been widely adopted in thermal engineering fields, such as refrigerators, chip cooling, battery packs, etc. To meet the ever-increasing demand for heat dissipation, surface modification methods adopting micro/nanoscale-modified surfaces have received considerable attention. In this paper, an advanced micro/nanoscale surface modification design is proposed based on a Lattice Boltzmann method (LBM) simulation study. Coupled boundary treatments at the inlet/outlet are developed with better numerical stability. The effects of surface wettability and micropillar on MCHS heat transfer performance are analyzed through bubbles' dynamic behaviors, Nusselt number, heat flux, and pressure drop. Design-based suggestions are proposed, and the enhancement mechanisms are explained. Results show that hydrophobic surface is more preferred for temperature-sensitive devices with low superheat requirement (Ja<0.1115), while the hydrophilic surface is more preferred for devices with a large heat dissipation requirement (Ja≥0.1286). Furthermore, the micropillar surfaces with pillar geometric factor Sp of 7 can yield the optimum heat transfer performance under a wide range of superheat conditions. Finally, an advanced design of a biphilic micropillar surface is proposed with superhydrophobic regions located at the top of the pillars, and other regions remain hydrophilic surfaces. An excellent heat transfer enhancement of 105.8% is achieved even compared with a pure hydrophilic micropillar surface. The enhancement is attributed to the superhydrophobic top regions efficiently blocking the bubbles merging process, which leads to more intense bubbles departure. These results provide a valuable guide for MCHS design and unravel the enhancement mechanism of the flow boiling process.

Pseudo 3D topology optimization of microchannel heat sink with an auxiliary objective

This paper investigated the application of pseudo 3D (P3D) variable-density topology optimization to the design of microchannel heat sink (MHS). To mitigate the grey-element issue and improve the precision of P3D model, outside surface viscous dissipation, adaptive equivalent heat transfer coefficient and auxiliary objective was introduced. The effects of adaptive equivalent heat transfer coefficient, auxiliary objective and its corresponding weight factor on the optimal design were analyzed. The results showed that the new proposed topological model can effectively mitigate intermediate density, improved accuracy and produced a well-defined structure. Furthermore, to validate the design of topology optimization, full 3D numerical simulations were adopted to investigate the fluid flow and heat transfer performance of the topological model and the results were compared with the conventional straight MHS. It is found that the increase of average inlet velocity and temperature uniformity of the topological MHS can be up to 305% and 69%, respectively, under the same inlet pressure. While under the same pumping power consumption, the average heat source temperature of the topological microchannel heat sink can be 9.3°C lower than the conventional one.

Experiment investigation on flow boiling heat transfer in a bidirectional counter-flow microchannel heat sink

Improving the critical heat flux (CHF) and avoiding dry out downstream are the keys to enhance the two-phase cooling performance of microchannel heat sinks. In this work, a novel type of bidirectional counter-flow (BCF) microchannels with 600 μm depth and 300μm width, giving a hydraulic diameter of 400μm, is fabricated in an oxygen-free copper base. Flow boiling experiments are conducted in bidirectional counter-flow microchannels and conventional unidirectional parallel-flow (UPF) microchannels, with the deionized water being used as the working fluid. Cases under six mass fluxes ranging from 118 kg/m2·s to 370 kg/m2·s and three inlet subcoolings of 30 ℃, 50 ℃, and 70 ℃ are tested. Two-phase flow behaviors in microchannels are simultaneously captured by a high-speed camera. It is found that, unlike conventional UPF microchannels, the location for the onset of nucleate boiling (ONB) in BCF microchannels is moved from downstream to the middle region. The downstream dry-out, which is usually occurred in UPF microchannels, can be well avoided in BCF microchannels due to the substantial feeding of liquid in adjacent microchannels. The CHF in BCF microchannels can be increased by 33.8∼57.2% compared with the conventional UPF microchannels. Under the combined effect of expanded nucleate boiling region and shortened subcooling region, the average heat transfer coefficient (HTC) in BCF microchannels can be increased by 36.6%∼56.7%. More interestingly, the improvement of heat transfer performance is found to be accompanied by a significant reduction in pressure drop for BCF microchannels in all the experiment cases. In addition, two-phase instabilities in terms of wall temperature and pressure drop oscillations can be significantly suppressed by using BCF microchannels instead of the conventional UPF microchannels. This study proposes a more efficient microchannel heat sink design scheme to deal with the microelectronic cooling challenges.

Numerical Study on Heat Transfer Characteristic of the Plate-Fin Microchannel Heat Sink for Water-Based Thermal Management of CPU Chip

For effective water-based thermal management of high heat generating CPU chip, a series of numerical simulation has been conducted to study the effects of heat flux, fin height and flow rate on convective thermal performance of the plate-fin microchannel heat sinks. The characteristics of heat transfer and flow resistance have been quantificationally discussed and <i>JF</i> factor is employed to evaluate the comprehensive efficiency of convective heat transfer of microchannel heat sink. Results show that the increase in fin height and flow rate of cooling water is helpful to decrease the maximum temperature of CPU chip. Large flow rate and heat flux and short fin height are benefit to improve Nusselt number <i>Nu</i>, but they lead to large resistance coefficient <i>fRe</i> simultaneously. Analysis of <i>JF</i> factor shows that the microchannel with short fins shows better convective thermal performance when the thermal power of the CPU chip is small. The fins should be heightened when the CPU is operating at higher thermal power. The employment of <i>JF</i> factor in the present work shows its pertinence and convenience in the application of design of microchannel heat sink.

Multi-objective optimization of thermal-hydraulic performance in a microchannel heat sink with offset ribs using the fuzzy grey approach

The effect of four geometrical parameters (width of the offset ribs, depth of the offset ribs, incline angle of the offset ribs, and distance between the adjacent offset ribs) on heat transfer enhancement, friction loss, and performance evaluation criteria is analyzed on the basis of the orthogonal experimental design (OED) method and fuzzy grey relational analysis (FGRA). Results of FGRA reveals that depth is the most influential factor in heat transfer enhancement, width affects the friction loss more than others, whereas incline angle is the most significant factor in the performance evaluation criteria (PEC) of microchannel heat sink (MHS). A series of S-shaped staggered triangular offset ribs (SSTOR) is proposed to strengthen the performance of MHS based on the results of FGRA. The MHSs with novel offset ribs are studied at different Reynolds numbers from 100 to 1000 to find the optimal offset ribs. The average Nusselt number, pressure drop, PEC, and maximum temperature at the bottom wall of the MHS with five different novel offset ribs are discussed. The result shows that the optimal offset rib structure, SSTOR-45, can significantly improve the behavior of MHS with PEC = 1.36 at Re = 1000. Furthermore, this work offers an excellent reference for MHS design in the electronic package heat dissipation field.

Achieving ultra-high coefficient of performance of two-phase microchannel heat sink with uniform void fraction

Thermal management of high-power electronics/devices has been a very challenging issue for data centers, flourishing electric vehicle revolution as well as cooling of the first wall of a Tokamak fusion reactor. As a prominent cooling strategy, two-phase flow in microchannels has received extensive research over decades. However, inherent defects such as relatively low critical heat flux due to the dry out of liquid film near the exit of the channel and relatively high two-phase flow pressure drop at high heat flux still hinder extensive commercial applications. The present work proposes a robust microchannel heat sink design toward uniform void fraction distribution along the flow direction. The two-phase flow pressure drop will not increase significantly with increase in heat flux. This is made possible by an innovative and unique combination of diverging microchannel and counter-flow manifold, which enables extensive channel-to-channel heat transfer, especially near the end or inlet of the channels. Moreover, flow visualization reveals that nearly uniform void fraction distribution along the channel with relatively high bubble slug ratio is possible. For a relatively large area of 12 cm2 and under the limitation of wall temperature of 140 °C, a heat flux as high as 3525 kW/m2 is achieved without sign of reaching the critical heat flux with nearly negligible pressure drop increment comparing to single-phase convection for a relatively low mass flux of 600 kg/m2s. An ultra-high coefficient of performance of 75,675 is attained under a low inlet temperature and low mass flux.

Optimization of permeable membrane microchannel heat sinks for additive manufacturing

The design freedom brought by additive manufacturing (AM) can be leveraged in the design of microchannel heat sinks to improve their cooling performance. The permeable membrane microchannel (PMM) heat sink geometry was inspired by the ability of powder bed AM processes to fabricate partially porous metal parts having small internal flow features on the order of the powder size. The design routes coolant through a parallel array of thin permeable membranes arranged in a single-layer-manifold configuration. The permeable membranes provide effective heat exchange surfaces and the manifold configuration yields a low flow resistance across the PMM heat sink, all incorporated in a single layer by the use of AM. Past work has introduced the PMM heat sink concept, but the optimal geometric feature sizes were not explored or identified. The n current study is first to explore design optimization of the PMM heat sink to identify target feature sizes for AM fabrication, assessment of the conditions under which the PMM geometry outperforms other standard microchannel heat sink designs, and inspection of the ability of metal 3D printing process to produce the optimal features. To this end, a reduced-order PMM heat sink model is developed, a gradient-based-multi-objective optimization is performed to identify the optimal feature sizes for different coolants (water and 48/52 water/ethylene glycol mixture) at different flow rates (100–500 mL/min), footprint areas (49–900 mm2), and channel heights (0.5–2.5 mm). The optimization results are benchmarked against an optimized straight microchannel (SMC) heat sink design. Optimized PMM designs offer up to 68% lower thermal resistance at a set pressure drop compared to optimized SMC designs. A pair of SMC and PMM heat sinks optimized for the same operating conditions are 3D printed using direct-metal-laser-sintering (DMLS) of AlSi10Mg. X-ray microtomography is used to characterize the geometry of the 3D-printed parts. The model identifies that optimal membrane gap sizes on the order of ~ 10 s μm are required for the PMM to realize performance advantages compared to SMC heat sinks under the same operating conditions. The performance is predicted to be highly sensitive to this pore size, and even though DMLS is shown to produce parts with gaps as small as 26.7 µm, morphological deviations between the design and as-printed part are shown to lead to noticeable performance differences. Albeit excellent performance potential reinforced by this work, these findings call for further AM process development to ensure reliable, as-predicted PMM heat sinks to realize this potential.

Research on modeling and parameter sensitivity of flow and heat transfer process in typical rectangular microchannels: From a data-driven perspective

With the miniaturized and high-powered development of power equipment and electronic devices, the microchannel heat sink is becoming an important device widely used in the modern cooling field. The heat transfer performance of the microchannel heat sink is affected by many influence factors, and amongst them there exists a complex coupling effect. So far, the mechanism of the microchannel heat sink has not been clearly elucidated. To figure out the dominant characteristics that affect the heat transfer performance of the microchannel heat sink and the interaction mechanism between relevant characteristics, this work carried out numerical simulations and parameter sensitivity analysis to investigate the key factors of the fluid flow and heat transfer performance in rectangular microchannels, and considered variables included key physical parameters of the fluids and dimensional parameters of the microchannels. To satisfy the enormous amount requirement of sample size in the parameter sensitivity analysis, a machine learning model, Gradient Boosting Tree (GBT), was constructed based on computational fluid dynamics (CFD) simulation results; then, the Sobel sensitivity analysis algorithm was coupled in to analyze the multi-parameter contribution of each input parameter. Results show that the number of channels N and Reynolds number Re have a greater impact on heat transfer performance under low Re conditions, and the cross-sectional area A and aspect ratio α have a much higher effect on the pumping power rather than Nusselt numbers Nu; N and A have a positive second-order interaction on Nu. When moving to the conditions with a higher Re, the number of channels N became the dominant factor that influenced both heat transfer and flow performance of the microchannel heat sink. This work also provides effective guidance for the design and optimization of high-efficiency microchannel heat sinks.

Investigation on the heat transfer enhancement by nanofluid under electric field considering electrophorestic and thermophoretic effect

Nanofluid as heat transfer medium in microchannel heat sink is very common. It is a promising approach to employ electrohydrodynamic(EHD) effect to improve the heat transfer efficiency. A modified Buongiorno’s model including EHD effect was established. And numerical simulations on flow and heat transfer for various electrode arrangements, various electric field intensity and frequencies were carried out. The numerical results show that, the main mechanisms to elevate the heat transfer in microchannel are chaotic convection induced by the electrophoretic effect and thermophoretic effect. The electrode-pair with top positive bottom negative arrangement and an alternating voltage are beneficial to the heat transfer enhancement. The heat transfer enhancement factor can be improved up to 10% and temperature on heated wall decreased up to 5 K for 1 V applied voltage. Besides, a moderate frequency of alternating electric field should be a good choice because about 20% increase in enhancement factor can be obtained. A promising approach can be provided for the design of microchannel heat sink based EHD effect.