Parallel Microchannel Heat Sink Research Articles

Hydrothermal analysis of parallel and symmetric microchannels with phase change slurry and porous fin designs

The dynamic information of microchannel systems with parallel and symmetric configurations is insufficient, which limits our ability to compare and optimize these systems in all directions. In this study, thermal and hydraulic characteristics in parallel and symmetric microchannel heat sinks (MCHSs) with porous fins cooled by phase change slurry are investigated. A 3-D steady state conjugate model is adopted to compare the effects of fin configuration, coolant type and structural parameters on hydrothermal properties of wavy MCHS. The variations of dimensionless parameters involving Nu, f, η (temperature control effectiveness) and PEF (performance evaluation factor) are considered to demonstrate the effectiveness of combined design on overall performance enhancement of wavy MCHS. Results indicate that lower temperature increment and higher pressure loss appear in wavy configuration with porous fins than in straight mode, and lowest thermal resistance arises in parallel porous fin design. At the narrow position of symmetric channel, the fluid changes from the low-speed drop-shaped micelle to high-speed bullet-shaped one with increasing A, which leads to higher Nu with larger pressure drop penalty. Due to the extended flow route and improved fluid mixing, η increases with decreasing wavelength in all cases, and η of porous microchannels with both phase change slurry and parallel fins is much larger than that of symmetric one and the one with only base fluid. Compared with wavy fin configurations with small and large ε, lower temperature and its more uniform distribution happen in the mode with medium porosity. In comparison with basic configuration, the parallel configuration with slurry as cooling medium has the maximum PEF value when the pore size is 0.14 mm, up to 1.64. Larger f increase occurs in wavy channel with increasing N, and the space shortening between adjacent channel cavities in symmetric mode makes the adjoining Dean vortices easier to contact and repel, thus making it appear larger rise of f than parallel mode. Compared with other channel parameters, it is not effective to improve the overall performance of wavy MCHS with porous fins by adjusting α. Overall, the throat effect of symmetric MCHS significantly occurs in channel configuration with larger A, bigger λ, lower ε, smaller dp, more N, and lesser α, leading to higher f rise than the parallel mode.

Subcooled flow boiling in multiple parallel rectangular micro-channel heat sink: Development of heat transfer correlation

Subcooled flow boiling in multiple parallel rectangular micro-channel heat sink: Development of heat transfer correlation

Exploiting the flow maldistribution characteristics in parallel microchannel heat sinks of I, U, and Z configurations to tackle the nonuniform heat loads

This study aims to analyze the cooling performance of parallel microchannel heat sinks (PMCHS) under uneven heat flux distributions, taking into account different flow configurations including I, U, and Z. The objective is to demonstrate the potential of utilizing the flow maldistribution inherent in each configuration to effectively manage and mitigate the effects of uneven heat flux distributions. Four different heating arrangements have been considered, namely uniform, non-streamline, streamline, and across-streamline to generate the uneven heat flux distributions. A three-dimensional numerical simulation has been performed to analyze the combined effect of uneven heat flux distributions and flow maldistribution characteristics on the thermal performance of PMCHS. To assess the thermal performances; thermal resistance (Rth), Nusselt number (Nu), temperature nonuniformity (Ψ), and fin efficiency (ηfin) have been employed. The results show that all three flow configurations exhibit similar thermal performances for uniform heat load conditions (0.1 K/W for Rth, 5.5 kW for Nu, 0.3 for Ψ, and 0.98 for ηfin). However, in the case of uneven heat flux distributions, the thermal performance of each configuration is observed to be varying with respect to hotspot positions. This study reveals that each configuration has a huge discrepancy in terms of thermal performance with respect to uneven heat flux distributions. Also, the study concludes that a single flow configuration alone is insufficient to address the cooling challenges that arise due to uneven heat flux distributions. The cooling capability of any configuration to handle uneven heat distributions mainly depends upon the flow maldistribution characteristics of the respective configurations.

Topology optimization of laminated-sheet microchannel heat sinks based on a pseudo-three-dimensional method

Laminated-sheet microchannel heat sinks (LS-MHSs) have shown enormous potential in the thermal management of integrated chips due to their advantages of easy integration, high surface-to-volume ratio and high heat transfer efficiency. In this paper, a five-layer pseudo-3D (P3D) conjugated heat transfer model of the double-layer microchannel heat sink (DL-MHS) was established, and topology optimization (TO) was applied for optimal design of the DL-MHS. The effects of different inlet pressures and lamination methods on the optimal design were discussed, and then, the optimization results were compared with those obtained for a single-layer microchannel heat sink (SL-MHS) and conventional parallel microchannel heat sink (CP-MHS). A full-scale 3D conjugate heat transfer numerical model was also built to investigate the heat transfer and fluid flow performance of the topology optimized microchannel heat sink. The results showed that the topology optimized microchannel heat sink can enhance heat transfer and show a higher heat transfer and comprehensive performance compared to the conventional parallel microchannel heat sink. Under the same pumping power consumption, the topology optimization of the DL-MHS with parallel flow obtains the best heat transfer performance, which is 2.04 times that of the CP-MHSs and 1.09 times that of the SL-MHS. Under the same pumping power consumption, the topology optimization of the DL-MHS with counter flow achieves the best temperature uniformity and its maximum temperature difference is 5.0–16.9 K lower than that of the CP-MHSs and 1.6–3.4 K lower than that of the SL-MHS.

Efficient optimization of parallel micro-channel heat sinks based on flow resistance network model

Electronics cooling is a critical issue affecting technological development. Parallel micro-channel heat sink (PMCHS) is widely applied for electronics cooling. However, the existing optimization methods are incapable to perform efficient design of three-dimensional liquid-cooled PMCHSs, impeding the thermal management of high power and volume-shrinking electronics. In this study, a flow resistance network (FRN) model is developed for structural optimization of three-dimensional liquid-cooled PMCHSs. Based on the uniform flow rate distribution, the FRN model is used to determine the optimized parallel channel widths and the optimized inlet deflector shape of the PMCHS. With the optimized parallel channel widths, the maximum temperature (Tmax) of the PMCHS is decreased by 4.0 K and the temperature standard deviation (σT) is decreased by 20%. With the optimized inlet deflector shape, Tmax and σT are reduced by 4.8 K and 14% respectively. The optimization method based on the developed FRN model for structural design of PMCHSs avoids multiple iterations of system parameters in existing optimization methods, showing its potential in high efficient thermal management of electronics.

Influence of system pressure on flow boiling in microchannels

The effect of pressure on the flow boiling characteristics of HFE-7200 between 1.0 to 2.0 bar was investigated in a parallel microchannel heat sink (Dh = 0.48 mm, 44 channels). The mass flux and subcooling degree were kept constant at 200 kg/m2 s and 10 K respectively, while heat flux ranged from 26.1 – 160.7 kW/m2. Increasing system pressure decreased the vapour density ratio, thus leading to reduced pressure drop, increased bubble generation frequency and two-phase heat transfer coefficients in the system, though this may not be apparent at low superheat degrees at higher pressures. Smaller bubble diameters were observed at higher pressures and resulted in a delay in flow regime transition to slug flow, which is prone to flow reversal. The experimental work showed promising means to manage flow instabilities and enhance heat transfer performance in two-phase microchannel systems for HFE-7200.

Modeling of confined bubble growth and heat transfer characteristics in parallel microchannel heat sinks

The current study aims to present the modeling and numerical analysis of parallel microchannel heat sinks accounting for transient phenomena during confined bubble growth in one of the microchannels, considering dynamic aspects for the bubble growth and heat transfer characteristics to identify flow instabilities. The model incorporates the estimative of the inlet velocities and pressure drop due to parallel channels’ interaction. Therefore, the model can predict conditions that result in reversal flow, as well as the main trends and values of the main parameters during this process. A parametric analysis is performed numerically aiming to infer the effects of the number of channels, heat flux, inlet mass velocity, and location of the nucleation site on the occurrence of reversal flow.

Numerical study on thermal and hydraulic performance of a stacked-plate jet-impingement/microchannel heat sink

This paper presents a stacked-plate jet impingement microchannel (SP-JIMC) heat sink with highly-dense micro-fins and numerically investigates the thermal and hydraulic performance with single-phase water as coolant. Comparative analysis with the parallel microchannel heat sink and the micro-gap heat sink indicates that the SP-JIMC can achieve a better cooling performance and improve the temperature uniformity. With the inlet water temperature of 300 K and flow rate of 1 L/min, SP-JIMC has a thermal resistance of 0.45 cm2⋅K/W and a pressure drop of 208.2 Pa, and the maximum temperature difference is 2.2 K under 100 W/cm2 over a span of 35 mm. When the flow rate is increased to 10 L/min, the thermal resistance decreases to 0.21 cm2⋅K/W, and the pressure drop increases to 5085.9 Pa. The heat transfer analysis shows the micro-fins dissipate 77.5 % with a flow rate of 1 L/min. As the flow rate increases to 10 L/min, the jet impingement heat transfer is enhanced and the percentage of heat transfer over micro-fins drops to 56.2 %. Parametric study is performed to investigate the influence of structural parameters on the heat transfer characteristics. The results show the thermal performance is improved by increasing jet length and separator thickness, and reducing separator gap. The lowest thermal resistance is achieved at a jet width of 0.35 mm when the combined effects of jet impingement and micro-fins reach the optimum situation. In order to further improve the thermal performance of SP-JIMC, dual-side micro-fins and convex/concave impinged surfaces are simulated. The results show that adding the micro-fins on the out-flow plate can increase the heat transfer percentage over fins by 9.4 % and reduce the thermal resistance to 0.39 cm2⋅K/W under a flow rate of 1 L/min. The maximum heat transfer capacity is achieved when the inlet flow rate 35 L/min under 300 W/cm2 heat flux, the average temperature of the heating surface is 349.5 K, the pressure drop is 55.1 kPa and the thermal resistance is 0.165 cm2⋅K/W.

Flow Distribution in Parallel Rectangular Multi Microchannels in Single Phase

This study proposed newly designed inlet manifolds to manage non-uniformity in parallel multi microchannel heat sink by introducing edges with a curved shape were introduced in order to reduce flow-recirculation at the sharp edges. This resulted in a better flow distribution in the parallel channels. A comprehensible numerical study has been performed using ANSYS-Fluent and a three-dimensional computational domain, incorporating the effect of conjugated heat transfer, was employed in this study. R134a was used as the working fluid and copper was selected as the heat sink material. The dimensionless channel flow ratio and flow maldistribution factor were introduced to quantify the flow distribution inside individual channels and the uniformity of this flow distribution. A uniform flow distribution is achieved when the maldistribution factor value approaches 0.

Impact of pressure drop oscillations and parallel channel instabilities on microchannel flow boiling and critical heat flux

Microchannel flow boiling heat sinks that leverage the highly efficient heat transfer mechanisms associated with phase change are a primary candidate for cooling next-generation electronics in electric vehicles. In order to design flow boiling heat sinks for such practical applications, one key obstacle is an understanding of the conditions for occurrence of dynamic two-phase flow instabilities, to which microscale flow boiling is particularly susceptible, as well as their impact on heat transfer performance. While mapping the operational regimes of these instabilities has been well-studied, with numerous stability criteria available, their impact on the heat transfer performance of heat sinks in practical applications is not understood. This work seeks to assess the impact of pressure drop oscillations and parallel channel instabilities on the surface temperature and critical heat flux in parallel microchannel heat sinks. This is achieved through measurement of time-averaged steady-state temperatures and pressures, combined with high-frequency pressure signals and high-speed flow visualization. These data are compared across three controlled flow configurations that comprise a condition of stable flow boiling, a condition where only parallel channel instabilities can occur, and a third where both pressure drop oscillations and parallel channel instabilities can occur. Experiments are performed using the dielectric refrigerant HFE-7100 in 2 cm long parallel microchannel heat sinks with square-cross-section channels (0.25, 0.5, 0.75, and 1 mm widths) at three mass fluxes (100, 400, and 1600 kg/m2s). Across this range of conditions, the time-averaged surface temperature and critical heat flux were remarkably insensitive to the occurrence of these instabilities despite the significant hydrodynamic events and transient flow patterns observed.

Multi-objective optimization of parallel microchannel heat sink with inlet/outlet U, I, Z type manifold configuration by RSM and NSGA-II

Designing an effective parallel microchannel heat sink (PMCHS) is necessary for addressing the cooling challenges of high heat-dissipating electronics. This paper presents a shape optimization of PMCHS to minimize the thermal resistance and pressure drop for each U, I, and Z-type inlet/outlet manifold configuration with vertical intake and coolant delivery. The performance of PMCHS influencing design parameters, such as channel width, fin width, and channel height, is designed using the response surface methodology (RSM). In the present communications adopting the Artificial Neural Network (ANN) coupled NSGA-II method, a three-dimensional numerical simulation is executed to minimize the pressure drop and thermal resistance. Numerical simulation is performed using the finite volume method; the computational domain is taken as the entire microchannel system including the inlet/outlet plenum area, ports and microchannels. The overall analysis demonstrated that the pareto optimal design point has better hydraulic and thermal performances than the predefined design. The optimized design showed benchmark thermal resistance of 0.0306 ˚C/W, 0.0315 ˚C/W, 0.0316 ˚C/W and pressure drop of 3.1 kPa, 3.2 kPa, 3.19 kPa for U, I, Z configurations respectively.

Comparison of the parallel microchannel and Pin-Fin heat Sinks: An experimental study

The present study reports an experimental study for parallel microchannel and pin–fin heat sinks performance. Copper heat sinks are selected and used with DI water as a coolant at different flow rates. Both thermal and hydraulic characteristics are analyzed in terms of substrate temperature, pressure drop, pumping power, and thermal resistance. It is found that the thermal resistance reduces with increasing the pumping power for both the heat sinks however with different rates and magnitudes. Also, thermal resistance reduces and pressure drop increases with increasing Reynolds numbers for both the designs. Parallel microchannel heat sink performed better in comparison to the pin fin heat sink exhibiting lower thermal resistance pumping power under similar heat flux conditions. However, the pressure drop is more in the case of the parallel microchannel heat sink relative to the pin fin heat sink. The study demonstrated that the size of the parallel channels, the thickness of the pin fins, and the base remarkably affected the heat flux removed and temperature rise of the copper substrate.

Experimental investigation on critical heat flux measurement in parallel microchannel heat sink at low mass fluxes

Experimental investigation on critical heat flux measurement in parallel microchannel heat sink at low mass fluxes

Numerical investigation of inter-linked parallel micro-channel heat sinks

Parallel micro-channel heat sinks linked with a joint are investigated in this paper. Channels are analyzed for laminar flow (water) under constant heat flux. The considered channels with same hydraulic diameter (776 ) are investigated for two different dimensional variations of connecting link with parallel flow and the comparison of parallel and counter flow in the channels. It is found that the varying dimension of joining link has a little influence on the over-all thermal hydraulic performance. Performance index decreases in the cases of either increasing the height (J) or width (W) of the joint at higher Reynolds number (1000 and 1200). Convective heat transfer (Nu) marginally improves with the increasing J. Inter-linked micro-channels with counter flow has given improved convective heat transfer but with an increase in frictional factor. The Nu with counter flow is found almost 15% higher than that with parallel flow at Re = 1200. The design can be further explored based on present calculations for a positive addition of designing micro-channel heat sinks.

Minimizing the Effects of On-Chip Hotspots Using Multi-Objective Optimization of Flow Distribution in Water-Cooled Parallel Microchannel Heatsinks

Abstract The industry shift to multicore microprocessor architecture will likely cause higher temperature nonuniformity on chip surfaces, exacerbating the problem of chip reliability and lifespan. While advanced cooling technologies like two phase embedded cooling exist, the technological risks of such solutions make conventional cooling technologies more desirable. One such solution is remote cooling with heatsinks with sequential conduction resistance from chip to module. The objective of this work is to numerically demonstrate a novel concept to remotely cool chips with hotspots and maximize chip temperature uniformity using an optimized flow distribution under constrained geometric parameters for the heatsink. The optimally distributed flow conditions presented here are intended to maximize the heat transfer from a nonuniform chip power map by actively directing flow to a hotspot region. The hotspot-targeted parallel microchannel liquid cooling design is evaluated against a baseline uniform flow conventional liquid cooling design for the industry pressure drop limit of approximately 20 kPa. For an average steady-state heat flux of 145 W/cm2 on core areas (hotspots) and 18 W/cm2 on the remaining chip area (background), the chip temperature uniformity is improved by 10%. Moreover, the heatsink design has improved chip temperature uniformity without a need for any additional system level complexity, which also reduces reliability risks.

Optimization of Microchannel Heat Sink with Rhombus Fractal-like Units for Electronic Chip Cooling

Abstract Microchannel heat sink is commonly used as a high-efficiency heat exchanger type in electronic microchips cooling, and the parallel microchannels arranged on the heat sink not only enhance heat transfer area but also result in large pumping power. In this paper, a novel structure of microchannel heat sink with rhombus fractal-like units is proposed for improve the overall performance, and a geometry optimization approach is developed for the design of the new microchannel heat sink. The validation of the geometry optimization approach is performed, and the results show that the predicted pumping power can describe 93% of the experimental data within the deviation limit of ± 5% and the mean deviation is 1.95%. Compared to the conventional parallel microchannel heat sink, the microchannel heat sink with rhombus fractal-like units may increase the COP by 7.9%-68.7% under the same constrains of external size, specified heat flux and maximum temperature limitation, which indicates the rhombus fractal-like units may effectively improve the efficiency of microchannel heat sinks.

Combined effect of inlet restrictor and nanostructure on two-phase flow performance of parallel microchannel heat sinks

In this study, the combined effect of nanostructure and inlet restrictor on reducing the instabilities during flow boiling in parallel microchannel heat sinks is investigated experimentally. Four types of microchannel heat sinks are considered; plain microchannel, microchannel with inlet restrictor, nanostructured microchannel, and nanostructured microchannel with inlet restrictor. Different flow regimes such as bubbly flow, slug flow, annular flow, and partial dry out are observed with the variation in applied heat flux and mass flux. The fluctuations in pressure, temperature, and mass flux are characterised in each regime. It is found that the fluctuations increase with power input, which is primarily due to backflow of vapour in the upstream direction of flow. The microchannel with inlet restrictor is more effective in reducing fluctuations and result in less surface temperature compared to the baseline case of plain microchannel without restrictor at the same mass flux. Moreover, if the nanostructured surface is added to the plain microchannel with inlet restrictor, the effectiveness in reducing fluctuations increases at higher heat flux and also produces less surface temperature compared to other types of microchannels.

Experimental Investigation on Heat Spreader Integrated Microchannel Using Graphene Oxide Nanofluid

Thermal design consideration is highly essential for efficient heat dissipation in advanced microprocessors which are subjected to conjugate heat transfer under high heat flux with a minimal area for cooling. Generally, these multicore processors develop a localized high density heat flux referred to as hotspot. The effective use of microchannel in order to mitigate the hotspot is found in literature; however, the flow induced hotspot still exist due to maldistribution of flow inside the microchannel. Henceforth, the present study provides an experimental insight on laminar forced convection in a parallel microchannel heat sink accompanied with 1.2 mm thin copper heat spreader with a surface area of 30 mm2 to effectively migrate the maldistribution flow induced hot spot. The present experimental study provides a profound insight about the hotspot and migration of hotspot to safe zones; as a result, not only the performance of the multi core microprocessor is highly improved but also the reliability of neighboring components is well secured.

Numerical Study on Mitigation of Flow Maldistribution in Parallel Microchannel Heat Sink: Channels Variable Width Versus Variable Height Approach

Microchannel heat sink on one hand enjoys benefits of intensified several folds heat transfer performance but on the other hand has to suffer aggravated form of trifling limitations associated with imperfect hydrodynamics and heat transfer behavior. Flow maldistribution is one of such limitation that exaggerates temperature nonuniformity across parallel microchannels leading to increase in maximum base temperature. Recently, variable width channels approach had been proposed by the current authors to mitigate the flow maldistribution in parallel microchannels heat sinks (MCHS), and in the current numerical study, variable height approach is opted for flow maldistribution mitigation. It is found that variable height microchannels heat sinks (VHMCHS) approach mitigates flow maldistribution rapidly in comparison to variable width microchannels heat sinks (VWMCHS) approach, almost 50% computational time can be saved by VHMCHS approach. Average fluid–solid interface temperature fluctuation across parallel microchannels reduces 3.3 °C by VHMCHS in comparison to VWMCHS approach. The maximum and average temperatures of the base of the heat sink are further reduced by 5.1 °C and 2.7 °C, respectively, for the VHMCHS. It is found that overall heat transfer performance of the heat sink improves further by 3.8% and 5.1% for the VWMCHS and VHMCHS, respectively. The pressure drop penalty of the VHMCHS is found to be 7.2% higher than VWMCHS.

Mitigation of Flow Maldistribution in Parallel Microchannel Heat Sink

Flow rate nonuniformities (termed as maldistribution) among a stack of microchannels connected with each other through the inlet/outlet plenums of a microchannel heat sink (MCHS) are one of the major hindrances associated with effective and efficient operations. That induces many undesirable effects, including accentuation of lateral and flow direction nonuniformities in surface temperatures (for uniform heat flux loads). This can lead to feedback-induced lateral heat flow in the electronics underneath the MCHS, which is to be avoided. For the reported numerical study of single-phase liquid cooling, a new flow maldistribution mitigation technique—involving splitting of the single inlet port to the inlet manifold (conventional) into two separate inlet ports—is proposed, and the results are compared with the conventional method. The proposed scheme helps in reducing the flow maldistribution (its measure defined in this paper) problem. In the case of two ports, in the front of the inlet manifold, the reduction is about 26.2%, and in the case of one suitably placed port on each side of the inlet manifold, the flow rate maldistribution is reduced by about 68.5%, and in addition, the MCHS efficiency (defined as heat-carrying capacity per unit pumping power) is improved by 7.7%.