Microchannel Heat Sink Research Articles

Experimental investigations on a novel instability suppression mechanism for subcooled flow boiling in microchannel heat sink

Flow boiling instability reduces the thermo-hydraulic performance of microchannel heat sink (MCHS) considerably. High rate of vapor bubble generation and their rapid growth block the confined flow passage of the microchannel and induce high flow resistance. Periodic changes in flow regimes and inefficient vapor venting lead to backflow. It increases dry out period and reduces overall heat transfer coefficient in MCHS. In this research, a novel instability suppression mechanism using Inlet Plenum Flow Restrictor (IPFR) is proposed. The subcooled flow boiling experiments are performed in a MCHS using degassed deionized-water (DI water). The inlet fluid temperature is maintained at 78 ± 1 °C (subcooling of 22 ± 1 °C). The results are reported for mass flux of 220, 320 and 416 kg/m2s and heat flux in the range of 21–88 W/cm2. The instability is observed to reduce by 76 % for surface temperature, 74 % for inlet plenum fluid temperature and 52 % for outlet plenum fluid temperature. Hence, the temperature instability is improved by 67 %. The heat transfer coefficient is increased by 13 % and pressure drop penalty is reduced by 34 % for stable operation of MCHS.

Optimal Design of Microchannel Heat Sink with Staggered Fan-Shaped Cavities and Ribs

In the present study, a three-dimensional numerical simulation is conducted to study the characteristics of fluid flow and heat transfer in a newly designed microchannel heat sink with fan-shaped cavities and ribs (MC-FCFR). The Reynolds number ranges from 147 to 736. A straight rectangular microchannel (MC-RC) is used as the baseline. The geometric parameters include the relative spacing θ, relative width α, and relative height β of the fan-shaped cavities and ribs. The overall performance index (OPI) of the MC-FCFR is evaluated in terms of the friction factor and Nusselt number. The OPI for the MC-FCFR with θ=3.56, α=1.63, and β=0.5 reaches 1.70.

Nanofluids in microchannel heat sinks for efficient flow cooling of power electronic devices

Nanofluids hold significant potential in the field of heat transfer intensification. The objective of this paper is to investigate the thermal-hydraulic characteristics of Ag, SiO2, and Al2O3 nanofluids in rectangular (MC-R), trapezoidal (MC-T), and omega-shaped (MC-O) microchannel heat sinks (MCHSs) through conjugate numerical simulations under a constant heat flux of 100 W/cm2. Water was used as the base fluid, and nanoparticle volume fraction ranged from 0 to 6 %. The average heat transfer coefficient (HTC), Nusselt number, thermal resistance, pressure drop, and pump power as a function of Reynolds number are studied for different nanofluids and cross-sectional shapes in microchannels. The overall performance is also characterized by thermal performance factor, coefficient of performance (COP), and entropy generation analysis. The simulation results show that adding Al2O3 nanoparticles with a volume fraction of 6 % in MC-R at a Reynolds number of 500 results in a substantial 12.3 % increase in the average HTC and an approximately 8 % reduction in total thermal resistance compared to pure water. For the same nanofluid, MC-O exhibits the highest convective HTC, the highest Nusselt number, and the lowest maximum heat sink temperature. The total entropy generation in the MCHSs decreases obviously with increasing Reynolds number. MC-O has the smallest total entropy generation, meaning it has the optimal flow and heat transfer irreversibility. These findings can not only provide valuable guidance for the rational design of MCHSs but also hold significant implications for the effective cooling of microelectronic components via nanofluid-based thermal management technology.

Multi-objective optimization of rectangular microchannel heat sink based on entropy generation and hydro-thermal performance using NSGA-II algorithm

In this study, multi-objective optimization of a rectangular microchannel heat sink is implemented based on two objective functions figure of merit (FOM) and entropy generation (Ṡgen). Decision variables are height ratio (α), width ratio (β) and number of channels (N). CFD simulations are conducted for different values of decision variables and the effects of each decision variable on hydro-thermal performance (FOM) and entropy generation are studied separately. To reduce the computational cost in multi-objective optimization process, a fourth-order multivariate polynomial regression model is used to predict the FOMαβ and Ṡgenαβ objective functions at each N. Non-Dominated Sorting Genetic Algorithm II coupled with predicted objective functions (FOM and Ṡgen) is implemented to maximize the FOM and minimize the Ṡgen at each N. Also, the decision variables related to the highest FOM are presented, which is 90% more than the reference point, and the hydrodynamic-thermal performance has improved. Decision variables related to the lowest Ṡgen are presented, which is 19% lower than the reference point. Finally, decision variables are presented to simultaneously satisfied the highest FOM and the lowest Ṡgen where FOM is 57% higher than the reference point and Ṡgen is 9.78% lower than the reference point.

Analysis of optimized combined microchannel and heat pipes for electronics cooling

In this work, innovative heat sink designs consisting of Microchannel Heat Sinks (MCHS) and Flat Plate Micro Heat Pipes (FPM-HP) are investigated to improve thermal management in electronic components. The three-dimensional finite volume method is used to analyze the fluid flow and heat transfer in the heat sinks. The validity of the numerical models is confirmed by comparison with pertinent experimental data. The thermal performances of the new heat sink designs are compared to that of double-layer microchannel heat sinks with parallel flow (DLPF MCHS) and counter flow (DLCF MCHS) configurations, as two of the more efficient heat sink designs in the industry. The investigated configuration of Silicon-Water Counter Dual MCHS with rectangular cross-section improves the temperature uniformity by 43–50 % and 26–31 % compared to DLPF and DLCF MCHSs, respectively, and the triangular cross-section configuration improves it by 38–47 % and 21–26 %, respectively. The thermal resistance of heat sinks is reduced by 10–15 % compared to DLPF MCHS and by 2–8 % compared to DLCF MCHS. Additionally, innovative hybrid heat sink designs combined with MCHS and FPM-HP are proposed to optimize hotspot management in electronics cooling applications that involve local high heat generation. The hybrid DLPF MCHS & FPM-HP reduces the maximum temperature and surface temperature gradient of the heat sink by 13–23 % and 20–49 %, while these are reduced by 16–40 % and 27–64 % for the hybrid DLCF MCHS & FPM-HP compared with the corresponding copper base (no heat pipe) designs. The hybrid Counter Dual Rectangular MCHS & FPM-HP reduces the maximum temperature and surface temperature gradient of the heat sink by 15–24 % and 29–65 % compared with the DLCF MCHS with copper base (no heat pipe) design, while these are reduced by 10–26 % and 24–63 % for the Counter Dual Triangular MCHS, respectively.

Numerical study of combined phase change material and water cooling in hybrid wavy microchannels for HCPV cell

HCPV cells are known for their high efficiency in converting sunlight into electricity. However, this increased efficiency also generates higher levels of heat, posing a risk of cell damage. Therefore, the study proposes the combination of a phase change material (CPCM) and liquid flow in hybrid wavy microchannels to ensure stable temperature within the high-concentration photovoltaic (HCPV) cells. A three-dimensional numerical model has been developed to capture the thermal behavior of PCM integrated with water cooling in a microchannel heat sink. The comparison and analysis involved contrasting cases with phase change material (PCM) and cases without PCM. The PCM cases were studied at Reynolds number (Re) 100, while the cases without PCM were investigated at Reynolds numbers of 100 and 200. Three distinct types of PCM were employed, specifically OM 32, Rt 35, and PA - SA/EG. The various microchannel geometries under consideration included Raccoon, wavy, and hybrid wavy microchannels. The results showed that using both PCM and water cooling in a microchannel is preferable over using only water cooling. The outcomes reveal that employing PCM 3 (CPCM) in conjunction with the raccoon wavy microchannel design, there is an 11.61% reduction in the maximum pressure drop, along with a decrease of 6.58% in the maximum solid substrate temperature. Moreover, this configuration attains the highest electrical efficiency, reaching 39.32%.

Jet Impingement Cooling of a Microchannel Heat Sink with Microgroove

The present study works on opportunities in improving the design of micro-channel heatsink (MCHS). The present study focuses on investigating numerically the effects of adding grooves at the MCHS which subject to jet impingement cooling. Commercial software ANSYS Fluent is used and realizable k-epsilon model is adopted to conduct a parametric study on the width and depth of rectangular longitudinal grooves at a constant heat flux of 250 W/cm2 applied at the base of MCHS. Two type of channel designs with grooves i.e. center-groove and side-groove were created and investigated numerically. Results show that addition of grooves generally give improvements in cooling performance and reducing the pressure drop. Some designs of side-grooved channels and center-grooved channels improve the temperature uniformity. The size of the groove affects the flow within the grooves and therefore affect the cooling performance.

A Study on the Responses Effect of the Flow Field and Temperature on Hybrid Micro-Channel Heat Sink (H-MCHS)

Research on the microchannel and its flow and heat transfer properties has received much attention. This study employed Autodesk Inventor software to build the model, and the Computational Fluid Dynamics software (Ansys Fluent 14) was used for numerical simulation. Taguchi analysis methods, ANOVA, and Minitab statistics testing were used. The results obtained for single response analysis for temperature, pressure, and velocity values are reasonable. With the optimal model for temperature difference () being W2H1S2 and the temperature difference across the model (), the pressure difference across the model (), maximum velocity in the channel (), and maximum outlet velocity () are W3H1S3, W1H1S3, W3H2S1, and W1H1S2, respectively. The analysis results for multi-response between the two values of velocity and pressure also achieved reasonable results with precisely defined parameters with response optimization for and , and the optimal model achieved is W(0.8mm), H(0.3mm), S(2.91), W(0.4mm), H (0.3mm), S(1.67), respectively. Analysis for , , , , and , the results are W(0.65mm), H(0.3mm), S(1), and W(0.4mm), H(0.3mm), S(1).

Enhanced thermo-hydraulic performance with two-phase flow boiling in wavy microchannel heat sink – A numerical investigation

This article demonstrates that using a wavy microchannel instead of a smooth microchannel can enhance thermal and hydraulic performance in both single and two-phase flow. Various performance parameters such as Nusselt number (Nu), friction factor (f), performance factor (PF), and enhancement factor (EF) are estimated for different wavy microchannels with varying waviness and amplitudes. The two-phase heat transfer coefficient (HTC) varies significantly with heat flux, particularly due to nucleate boiling. The heat transfer improvement with a wavy microchannel is evident with the highest values of the Nusselt number ratio (Nutp/Nusp = 2.35), PFwavy = 1.4, and EF = 1.88 achieved at specific operating conditions (heat flux = 100 W/cm2, mass flux = 188 kg/m2s, amplitude = 0.1 mm, wavelength = 1 mm). However, as mass flux, heat flux, and amplitude increase and wavelength decrease, the Nusselt number ratio Nutp/Nusp, PF, and EF decline due to the pressure drop penalty outweighing the benefits of heat transfer enhancement. The article also explores different designs of wavy microchannels for mitigating hot spots, including one with a decreasing wavelength along the flow direction and another with a shorter wavelength in the middle. However, these designs are more suitable for single-phase flow.

Thermal performance of microchannel heat sink integrated with porous medium, slip coefficient and phase change material and machine learning approach

In this study, the thermal performance (TP) of the microchannel heat sink (MCHS) under the influence of the slip coefficient on the microchannel wall, the use of porous medium (PM) and phase change material (PCM), and the changes in the geometrical parameters and the shape of the microchannel have been discussed. The flow and energy equations were solved using the finite volume method. The validation of the melting process, slip coefficient, and porous medium with the previous literature demonstrate the high accuracy of the numerical solution, with the difference between the results being <8 %. The results indicate that using a wavy microchannel can improve TP by approximately10.6 % and 5 % compared to smooth and converging microchannels. Additionally, using non-Newtonian fluids with a power characteristic of 0.53 leads to improved TP about 2.8 % by reducing shear stress compared to Newtonian fluids. Furthermore, the presence of slip on the microchannel wall influences the flow pattern, resulting in reduced convection resistance and improved TP about 3.2–3.8 %. The highest TP was observed at a slip coefficient of 0.00001. Incorporating PM in the microchannel (either in the center or around it) can enhance TP by approximately 8–15 % compared to the base state, with greater improvements observed when PM is placed around the microchannel. The type of PM material and the porosity coefficient significantly impact TP. Varying the cross-sectional shape of the microchannel (square, rhombus, and triangle) has a substantial effect on improving TP compared to a circular cross-section, with the highest TP (with a 71 % increase) observed in microchannels with a square cross-section. Lastly, the use of PCM and PM on the active surface leads to a significant TP improvement of over 80 % compared to the base state. Using the Group Method of Data Handling algorithm, thermal resistance was estimated with an R-square value of 0.94 to validate the available data.

Efficient Solutions for Electronic Chip Cooling: Multi-Objective Optimization Using Evolutionary Algorithms with Boron Nitride Nanotube-Based Nanofluid

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

Thermal-hydraulic characterization of manifold microchannel heat sink with diverging channels and uniform heating

This study presents the design and experimentation of a manifold microchannel heat sink with diverging channels, employing ammonia as the working fluid to evaluate its thermal–hydraulic performance under uniform heating conditions. The impact of heat flux, inlet subcooling, saturation temperature, and outlet thermodynamic quality were investigated. Under single-phase conditions, the heat sink exhibited low sensitivity to variations in heat flux with constant thermal resistance and pressure drop. However, with the onset of boiling, the heat transfer capability and pressure drop rapidly increased. A lower inlet subcooling boosted boiling inside the heat sink, leading to decreased thermal resistance and increased pressure drop. Under near-saturated inlet conditions, a higher saturation temperature enhanced heat transfer owing to smaller bubble nucleation and detachment size. The outlet thermodynamic quality for engineering applications should be moderately low because it provides a balance between high heat transfer capability and low pressure drop. Moreover, the results demonstrated excellent thermal–hydraulic performance, with a heat flux of up to 636.9 W/cm2 efficiently dissipated under uniform heating conditions while maintaining the heating surface temperature and pressure drop below 79.3 °C and 150.3 kPa, respectively.

Experimental study of flow boiling characteristics of open microchannels with elliptical cavities and elliptical ribs

Open microchannel heat sinks (O-MCHS) stand out among many thermal management technologies due to their extra open gaps that reduce pressure drop and mitigate flow instability. Recently, there has been a growing trend of incorporating microstructures onto microchannels in order to enhance the hydrothermal performance of heat sinks. However, the heat transfer characteristics and bubble behavior of O-MCHS with microstructures are still rarely studied. In this study, open copper-based microchannel heat sinks with elliptical cavities and elliptical central ribs (O-EC-ECR) and elliptical cavities and elliptical side ribs (O-EC-ESR) were designed and manufactured; the flow patterns, heat transfer performance and pressure drop were systematically studied and compared with those of rectangular open microchannel heat sink (R O-MCHS). The working fluid was degassed DI water and the experiments were performed with the inlet subcooling of 75 ℃ at efficient heat fluxes of 668.00–2416.16 kW/m2 under various mass fluxes ranging from 421 to 801 kg/m2·s. The experimental results demonstrated that the O-EC-ECR exhibited the best two-phase heat transfer performance among three structures at all mass fluxes. The average two-phase heat transfer coefficient of O-EC-ECR was increased by 12.2 % compared to R O-MCHS at the mass flux of 801 kg/m2·s. The average wall temperature of O-EC-ECR was found to be 10.1 ℃ lower than that of R-O-MCHS and 6.7 ℃ lower than that of O-EC-ESR at the mass flux of 801 kg/m2·s. This should be attributed to the dramatically increased convective heat transfer area as well as the separating and breaking effect of the central ribs on the bubbles, which was manifested by the increase in heat transfer coefficient and critical heat flux (CHF). In addition, the central ribs improved the flow boiling stability by effectively suppressing the generation of confined bubbles and the formation of slugs. The arrangement of the side ribs and cavities made bubbles easier to condense, which facilitated the mixing of hot and cold fluid. At low to medium mass fluxes, the O-EC-ESR only showed superior heat transfer performance during the bubbly flow dominated nucleate boiling regime. Whereas high mass flux can improve the boiling heat transfer performance; the average heat transfer coefficient of O-EC-ESR was increased by 6.1 % compared to R O-MCHS. The average pressure drop of O-EC-ESR was decreased by 21.8 % compared to R O-MCHS and 25.6 % compared to O-EC-ECR at the mass flux of 801 kg/m2·s.

A numerical investigation of the thermal–hydraulic performance during subcooled flow boiling in MMCs with different manifolds

Thermal management of high-heat-flux electronics has been a critical bottleneck for integrated circuit miniaturization and increased power density, and manifold microchannel (MMC) heat sinks are expected to be an efficient near-junction thermal solution. A numerical investigation based a self-developed solver has been conducted to explore the effects of manifold geometries on the thermal–hydraulic performance of MMC heat sinks during subcooled flow boiling, and phase, pressure, and mass distribution among microchannels are analyzed combined with temperature distribution. Heat flux makes little difference on the mass maldistribution among microchannels of MMCs regardless of single-phase and flow boiling, and flow patterns in the outlet manifolds of Z-type MMCs changes from bubbly flow, slug flow to vapor columns with segmented bubbles with increasing heat fluxes. As for the effect of manifold numbers, both the maximum temperature and the pressure drop decrease with increasing manifold numbers, and a relatively uniform distribution of mass and void fraction has been found for all cases of HU-type MMCs regardless of heat fluxes with the best thermal–hydraulic performance at N = 10. However, the thermal performance of Z-type MMCs would improve firstly and then flatten out with increasing manifold number, while the pressure drop presents an opposite trend. The differences in thermal–hydraulic performance are attributed to the longer flow path in Z-type manifolds, and the increasing manifold number presents a higher manifold pressure drop and thus would worsen the mass maldistribution. As for tapered manifolds, a tapered ratio of 0.33 could provide a slightly lower base temperature than the original case with a pressure drop decreased by over 25 %, and the pressure drop fluctuation at high heat fluxes could be suppressed by 70 % with significantly improved flow boiling stability. This work can serve as a basis for the further optimization of subcooled flow boiling in MMC heat sinks, and the results indicate that both an even mass distribution among microchannels and a desirable inlet/outlet port ratio for improved flow field are of great importance for the manifold design applied in MMC heat sinks for two-phase heat dissipation.

Effects of elastic micropillar array on the hydrothermal characteristics of a microchannel heat sink

The numerical study of a microchannel's flow and heat transfer characteristics with an elastic micropillar array. In addition, the effects of elastic micropillar dynamic properties, aspect ratio, spacing, and modulus of elasticity on fluid heat transfer performance, hydrodynamic friction factor, and overall hydrothermal efficiency are investigated. The results indicate that elastic micropillars in flapping mode can generate periodic vortices more conducive to disrupting the boundary layer and mixing heated and cold fluids, thereby enhancing heat transfer. The heat transfer effect of the elastic micropillar is enhanced by 10.84% compared to rigid ones. The elastic micropillar array has the best aspect ratio of 11 and the best spacing of 1.9D. Under the optimum working condition, at the expense of high mechanical loss, the heat transfer performance of the fluid can be improved by 59.35%, and the total hydrothermal efficiency can be increased by 17.7%.

On the flow field and heat transfer characteristics of a supercritical CO2-cooled microchannel heat sink under high heat flux conditions

Supercritical CO2 (sCO2) is a suitable choice as a coolant due to its favorable thermodynamic characteristics (lower density and viscosity, and higher specific heat) compared to water. In the current investigation, sCO2 is considered a coolant in a micro heat sink under high heat fluxes 75, 100, 125, and 150 W/cm2 and the operating pressure 8 MPa. The effects of the operating conditions, including the change in coolant mass flux (1250–3125 kg/s-m2), the change in the inlet temperature (305-308 K) under the mentioned heat fluxes on the heat transfer coefficient, thermal resistance, pressure drop, pumping power, and performance evaluation criteria (PEC) are investigated numerically using the finite volume method. Results indicated that thermohydraulic performance of the sCO2-cooled heat sink depends on the inlet coolant temperature and the applied heat flux due to the dramatic variation of the local thermophysical properties. It was found that increase in the heat flux from 75 to 150 W/cm2 results in increase of the pumping power by 48%, diminishing the PEC from 2.35 to 0.5. Overall, sCO2-cooled heat sink performs better than water-cooled heat sink if the mass flow rate is high and the inlet temperature is below the pseudocritical temperature. Otherwise, using sCO2 is not beneficial, especially under higher heat flux conditions.

Heat transfer enhancement using combined microchannel with vertical rectangular micro fins

This paper focuses on the numerical optimisation of a combined hybrid microchannel heat sink with rectangular solid fins. The axial length and volume are fixed, and external structure is allowed to vary. The simulation was performed on an elemental unit cell of the microchannel heat sink . The purpose of the optimisation is to discover an optimal geometric arrangement in internal and external configurations that minimises peak temperature in the microchannel heat sink. A high-density uniform heat flux of 250 W/cm2 is assumed to be dissipated on the bottom wall of the unit cell by microelectronics circuit boards devices. Computational fluid dynamic code was used to discretized the fluid domain and solve a set of governing equations. The influence of hydraulic diameter, external structural shape and fluid velocity on peak temperature and global thermal resistance, is discussed. Coolant or water of Reynolds number range 400 to 500 in a forced convection laminar flow is introduced through the inlet of the computational domain to remove the heat at the bottom of the rectangular block microchannel. The results show that when the fluid velocity is increased from 9.8 to 12.3 m/s across the axial length of the micro heat sink, more heat is removed from the bottom of the combined heat sink. The results revealed that the pump power increased by 37.1% in combined microchannels with fins and from by 27.2% in finless micro heat sink. The result of the study is validated with what is documented in open literature for a traditional micro heat sink with circular flow channel and the trends agree.

Numerical study on infrared detectors cooling by multi-stage thermoelectric cooler combined with microchannel heat sink

Lightweight, noiseless, and constant low-temperature refrigeration is crucial for cooled infrared (IR) detectors, especially short-wave-infrared (SWIR) detectors. However, some SWIR detectors, such as HgCdTe photovoltaic detectors are working below 210 K. For this application, multi-stage thermoelectric coolers (TEC) are preferable to single-stage thermoelectric coolers because they can generate larger temperature differences. This paper presents a refrigeration design that integrates SWIR and TEC into a vacuum Dewar package and combines them with a microchannel heat sink (MHS) to improve the detection performance and better responsiveness of SWIR. Two different refrigeration models, SWIR + TEC + AHS (air-cooled heat sink) and SWIR + TEC + MHS, were established to evaluate the refrigeration performance of the proposed SWIR + TEC + MHS scheme using the finite element method. The influences of multi-stage TEC leg length and current, inlet water temperature, and water velocity on the refrigeration performance of the TEC are analyzed. The results show that the SWIR + TEC + MHS design scheme has the best comprehensive performance and minimum volume. The influences of all the factors are obvious while the current has the most important effect on the performance. The temperature of SWIR reached 201.69 K at standard working conditions. It shows that the cooling scheme can not only meet the needs of flexible deployment of SWIR but also provide better thermal security. The proposed cooling design has an excellent prospect for short-wave-infrared detectors.

Influence of restrictor on the thermal-hydraulic performance in manifold microchannel heat sink

Manifold microchannel heat sinks (MMCHSs) are essential in thermal management. Conventional Z-type MMCHS encounter flow maldistribution and large temperature gradients on the heating surface. This work proposes an innovative MMCHS with restrictors to reduce flow maldistribution and compared with other optimization schemes. Through the numerical simulation, we optimize three dimensionless parameters (the width ratio α and length ratio β of the restrictor and inlet-to-outlet width ratio of manifold γ). Introducing the restrictor into the MMCHS can reduce flow maldistribution. In the research scope, the maximum mass flux discrepancy of MMCHS with α = 0.3 decreased from 327.17% to 64.51% compared to MMCHS with α = 1 when the volumetric flow rate is 8.51 mL/min. The reason is that restrictors increase the ratio between pressure drop in microchannels and total pressure drop(Δpc/Δp). Additionally, the coupling effect of the restrictor and γ on thermal-hydraulic in MMCHS are complicated. Therefore, the thermal resistance ratio (Rt/Rt,0), the pumping power ratio (Pp/Pp,0) and performance evaluation criteria (PEC) are taken as references to consider the thermal-hydraulic performance of MMCHS comprehensively. The results display that the MMCHS with α = 0.5– 0.6, β = 0.4 and γ = 0.8– 1 can further control the synchronization of Rt/Rt,0 and Pp/Pp,0 at about 0.75. The PEC values are all greater than 1.59.

An Optimization of Grooves Structure for Thermal Performance Enhancement in Microchannel Heat Sink

In the current work, the thermal performance of a grooved microchannel heat sink is evaluated at different offset positions inside the channel. For this purpose, the Eulerian–Eulerian approach-based mathematical model is developed and is numerically solved using the finite volume approach. Water is the base fluid to which alumina nanoparticles were added to enhance heat transfer. The effect of the Reynolds number (100–1,000), particle diameter (10–50 nm), the number of grooves (10–80), offset between the grooves (0–1), and particle volume fraction (0–5%) on the dimensionless pressure drop, Nusselt number, and coefficient of performance are investigated, and their impact on the microchannel’s thermal characteristics is quantified. Most importantly, the microchannels with symmetric (Offset = 0) and asymmetric grooves (Offset ≠ 0) were compared, and it was found that offsetting the grooves has an insignificant effect on the microchannel performance. Furthermore, an empirical correlation is proposed to evaluate the coefficient of performance of both symmetric and asymmetric microchannels as a function of the output variables.