Microchannel Heat Sink Research Articles

Insight into porous fin microchannel heat sinks with improved thermo-hydraulic performance

The escalating demand for enhanced cooling systems, particularly in high-power computer processors, necessitates innovative solutions within the spatial constraints of computing environments. This paper introduces a design modification that strategically diverts a portion of the main flow toward and through the porous fin region, creating a “cross flow.” The novel approach aims to maximize heat transfer through the fins, harnessing both conduction and convection heat transfer mechanisms. The realization of these flow patterns is achieved through interdigitated blocking of the inlet and outlet reigns of the microchannel, coupled with the utilization of converging and diverging microchannel porous fins in distinct elbow and zigzag geometrical configurations. Numerical simulations using computational fluid dynamics are employed to assess the proposed microchannel heat sink's thermo-hydraulic performance. The proposed design innovation significantly enhances heat dissipation efficiency by augmenting the convection heat transfer mechanism within the porous fins, resulting in a remarkable 17% improvement in Nusselt number compared to conventional parallel microchannel heat sinks with porous fins. This study provides valuable insight into the thermal and hydraulic performance of the proposed design, offering promising prospects for addressing the escalating demand for enhanced cooling systems in high-power computing environments.

Numerical study of the use of shear-thinning nanofluids in a microchannel heat sink with different pin densities and including vortex generator

This article numerically investigates the thermal and hydraulic performance of shear-thinning nanofluids when used as heat-conducting fluids in a microchannel heat sink device. Five geometries are evaluated: four with different pin densities and one with vortex generators. Six Reynolds numbers are studied, ranging between 200 and 1200. Numerical experiments show a comparison of using a water/ethylene-glycol mixture with and without alumina nanoparticles and multiwalled carbon nanotubes. Two different concentrations of nanoparticles were evaluated, both given shear-thinning nanofluid behavior. The viscous properties of the fluids are fitted from previously reported experimental data. The other thermophysical properties are modeled using single-phase expressions adjusted to consider hybrid nanofluids. Numerical results show that the heat transfer rates and pressure drop increase when the pin density increases, resulting in thermal blocking in the case of higher pin density. These key findings are a result of the increase in the heat transfer of shear-thinning nanofluids and the reduction of the pressure drop when compared with Newtonian fluids. Apparent viscosity contours are used to understand the thermal and hydraulic performance. Between the two nanofluids studied, the one with the lowest power-law index was the best in terms of heat extraction and pressure drop, indicating that fluids with thinning rheology may be recommended for heat transport in microchannel heat sink devices.

Multimodal machine learning for predicting heat transfer characteristics in micro-pin fin heat sinks

As three-dimensional integrated circuit (3D-IC) chip technology advances, thermal management has become increasingly important because of increasing heat flux from thermal stacking. Micro-pin fin-embedded cooling has emerged as a promising solution for 3D-ICs, offering better thermal and hydraulic performance than conventional microchannel heat sinks. It is also easy to integrate into existing 3D-IC structures, such as through-silicon vias between stacks. The utilization of two-phase flow in micro-pin fins further enhances temperature uniformity and improves the heat transfer coefficient by leveraging latent heat. Nevertheless, predicting thermal performance in micro-pin fin heat sinks under boiling conditions remains challenging owing to intricate geometric shapes and diverse operating conditions. The present lack of correlation or theoretical models poses a significant obstacle. To address this problem, our study employed a Multimodal machine-learning (ML) approach, combining image data capturing boiling patterns of two-phase flow and information about geometric shape and operating conditions, to predict heat transfer characteristics in micro-pin fin heat sinks. We utilized experimental data comprising 155 types of boiling heat transfer data with the dielectric fluid FC-72 in two micro-fin shapes directly etched on Si. Four ML algorithms (XGBoost, LightGBM, Multilayer perceptron (MLP), and Multimodal ML) were employed to predict thermal performance. The correlation coefficient analysis before learning revealed the influence of each type of measurement data on the heater surface temperature during two-phase flow. Prediction accuracy was measured using mean absolute percent error (MAPE), and the results were compared in terms of maximum and average temperature depending on the characteristics of each ML algorithm. Overall, the Multimodal approach demonstrated superior capability in predicting temperature distributions with spatial details, surpassing conventional decision-tree algorithms and MLP in performance. When trained with boiling images, the Multimodal ML model achieved remarkable precision, evidenced by a MAPE of 1.81% for the maximum temperature and 0.84% for the average temperature, highlighting its exceptional accuracy in mapping the heated surface temperature profile. By contrast, the traditional MLP model, which lacked training on boiling images, showed diminished accuracy, with a MAPE of 2.54% for the maximum temperature and 1.77% for the average temperature, indicating a comparative shortfall against the Multimodal model results.

The influence of micro-channel shape filled by nanofluid on heat transfer characteristics: Numerical and experimental study

The integration of nanofluid effects and channel shape effects in a heat sink, which exhibits both variable and constant cross-section, has gained significant traction as an efficient cooling method for thermal devices, particularly microelectronic devices. This research presents an experimental and numerical analysis to compare the performance of microchannel heat sink designs (straight, zigzag, wavy, and circular cavities). In addition, the study dealt with the use of pure water and nanofluid (CuO-H2O) with volumetric concentrations of (0.01, 0.02, and 0.03) as coolants. COMSOL Multiphysics was used for numerical analysis to simulate and solve the problem of fluid and heat flow in 3D. The bottom wall of the four microchannels is subjected to a steady heat flux of 170 kW/m2. The simulations were only performed within the laminar domain, encompassing a spectrum of Reynolds numbers ranging from 50 to 150. The influence on the microchannel's wall temperature, thermal resistance, pressure drop, and friction factor is exhibited. According to the findings, the wavy and zigzag microchannel heat sink cooled by nanofluid displays higher performance in terms of heat transmission and dissipation in comparison to the heat sink that was cooled by distilled water. as evidenced by a 12% increase in mussel number at volume concentrations of 0.03%.

Thermo-hydraulic characteristics and structural optimization of supercritical CO2-cooled microchannel heat sink

Supercritical carbon dioxide (sCO2) serves as an efficient working fluid in microchannel heat sinks (MCHS), effectively mitigating heat dissipation challenges in high heat flux microelectronic devices. Nonetheless, the issue of flow acceleration affecting micro-scale heat transfer, especially in channels with diameters <0.2 mm, warrants additional investigation. Flow acceleration exacerbates temperature non-uniformity, consequently diminishing heat transfer efficiency. Numerical simulations were conducted to examine the thermo-hydraulic characteristics of sCO2 in microchannels featuring complex structures including ribs and cavities. The channel had a diameter of 0.133 mm, with heat flux to mass flow rate (q/G) ranging from 0.1 to 0.5 kJ/kg. Three-dimensional entropy production rate (Sg) maps and corresponding heat maps were utilized to establish boundary conditions and evaluate heat transfer optimization. Additionally, structural optimizations were performed to rectify temperature non-uniformity in sCO2 within MCHS. The results indicate that the entropy production rate (Sg) of sCO2 initially decreased and then increased with the increase in q/G and dimensionless enthalpy (h*). The optimized MCHS demonstrated enhanced temperature uniformity, with a maximum temperature difference of 1.8 K, notably lower than that of the non-optimized MCHS (5.3 K). This study offers a theoretical basis for the design and implementation of sCO2 in micro-scale MCHS.

Experimental study of embedded manifold staggered pin-fin microchannel heat sink

High-heat-flux thermal management of high-power chips in electronic devices is becoming more and more critical. Manifold microchannel heat sink is one of the effective choices. In order to improve the heat dissipation capacity of manifold microchannel heat sink, a silicon-based thermal test chip including staggered pin-fin microchannels is designed and fabricated. Staggered pin-fin microchannels and rectangular microchannels with the same area size are embedded on the opposite side of the silicon-based thermal test chip for liquid-cooled heat dissipation. The experiments are conducted using HFE7100 as the working fluid. The heat transfer performance and the flow characteristic of two distinct microchannel structures are evaluated. It is found that the differences in temperature, convection heat transfer coefficient and pressure drop caused by different microchannel structures are greatly related to the mass flow rate. The heat transfer performance of the staggered pin-fin microchannel heat sink is better than that of the rectangular microchannel heat sink at a larger mass flow rate, but it also brings greater flow pressure drop. The bubble effect caused by the transition from single-phase to two-phase flow in microchannels makes the monotonicity of the convection heat transfer coefficient decrease significantly and the monotonicity of the pressure drop increase significantly. Compared to rectangular microchannel heat sinks, staggered pin-fin microchannel heat sinks reach the two-phase flow at higher heat flux. At the mass flow rate of 5 mL/s and the heat flux of 700 W/cm2, the staggered pin-fin microchannel heat sink can reduce the chip surface temperature by 8 K compared with the chip surface temperature of the rectangular microchannel heat sink.

Effect of curvature ratio on curved microchannel heat sinks

This work studies the influence of curvature ratio on flow and heat transfer in curved microchannel heat sinks, and introduces an innovative thermal test method that can be integrated into the micro heat sink and other micro-devices. The thermal performance was rigorously evaluated using a comprehensive set of parameters, including Reynolds number, Nusselt number, Poiseuille number. Within the scope of the study, microchannel heat sink with larger curvatures exhibit superior comprehensive thermal performance, but this also leads to an increase in flow resistance within a controllable range. However, larger curvatures are also constrained by machining precision, mechanical stability, and fabrication costs.

Enhanced heat transfer study of microchannel heat sink with periodically arranged triangular cavities and arc‐shaped ribs

AbstractThe microchannel heat sink with periodically arranged triangular cavities and arc‐shaped ribs (MC‐ARTC) is investigated numerically under the conditions of Reynolds number 147–736. The effects of triangular cavities and arc‐shaped ribs on velocity, pressure, and temperature distribution in the channel are analyzed in comparison with a rectangular microchannel heat sink, microchannel heat sink with arc‐shaped ribs, and microchannel heat sink with triangular cavities. The results show that the triangular cavity and the arc‐shaped rib have important effects on the flow and heat transfer characteristics in the microchannel heat sink. Both rib and cavity can cause a change in fluid flow direction and disturb the development of the flow boundary layer. The fluid flow and heat transfer characteristics of microchannels are improved. Among the four microchannels, the MC‐ARTC has the optimum comprehensive performance for the combined effect of the rib and cavity. Relative cavity width () and relative rib height () are also defined to study the effects of cavity width ( = 89–200 μm) and rib height ( = 8.9–28.9 μm) on the flow and heat transfer characteristics. It is found that the heat transfer of MC‐ARTC is enhanced with increasing and , while lead to higher pressure drop. When and are 252 and 249 μm, respectively, the comprehensive performance factor () of MC‐ARTC reaches 1.76.

Thermal stress analysis in pin fin microchannel heat sink

The conjugate heat transfer and the thermal stresses produced within a pin-fin microchannel heat sink are investigated numerically. The pin-fin microchannel heat sink is subjected to a constant heat flux from the bottom surface and cooled by water flow through the channel across the pin fins. Rectangular cross-section microchannel incorporating one raw of square pin fins are considered. The water flowing through the microchannel at Reynolds number varies from 200 to 800. The heat sink dissipates constant heat flux in the range of 75-175 kW/m2. The selected materials used for the solid substrate are Copper, Aluminium, Titanium, and Structural steel. The results are presented as contour plots for the temperature, thermal stress, and deformation distribution. It is found that the heat dissipation and the Nusselt number are increased with increasing Reynolds number, increasing the thermal conductivity of the mate-rial but remain constant throughout various heat fluxes. Thermal stresses are increased with decreasing Reynolds number, increasing heat flux, and increasing Youngs’ Modulus of the substrate material. The total deformation is increased with decreasing Reynolds number, in-creasing heat flux, and increasing the thermal expansion coefficient of the substrate material.

Effect of flow pulsation on heat transfer performance of biomimetic bark microchannel heat sink

Pumping coolant or using pulse flow through microchannels with novel structures on microelectronic devices is suitable for high heat flux dissipation and sensor development. This study proposes a novel microchannel designed as a series of biomimetic bark channel networks. Simulation and experimental testing of temperature distribution and heat transfer performance are conducted under different working conditions, including various fluid parameters. The results show that combining biomimetic bar microchannel and pulsation flow can improve heat transfer performance. The effect of pulsating flow frequency on the temperature is only evident outside the range of 10 mm from the inlet. Compared with non-slip boundaries, the boundary slip of pulsating flow slightly enhances heat transfer. Pulsating flow has an optimal frequency, minimizing thermal resistance for different inlet temperatures.

Multi-scale CuS-rGO pyramidal photothermal structure for highly efficient solar-driven water evaporation and thermoelectric power generation

Integrated water evaporation and thermoelectric power generation system (IWETPGS) has been recognized to be a promising strategy for the utilization of solar energy. Herein, we developed a new type of IWETPGS with multi-scale pyramidal photothermal structures. They featured three-dimensional pyramidal structures with microscale gradient porous copper foams, as well as micro/nanoscale CuS nanowires and reduced graphene oxide (rGO) composite materials. They combined the merits of efficient multiple refraction and absorption of light, broad-spectrum absorption capabilities of rGO and high near-infrared extinction coefficient of CuS, as well as fast water transportation by gradient porous matrix. These photothermal structures induced a photothermal conversion efficiency of 97.6%. An IWETPGS integrating these structures with a thermoelectric generator (TEG) and microchannel heat sink was developed, and outstanding evaporation and output power performance were obtained simultaneously with an evaporation rate of 2.29 kg/m2h and maximum output power of 1.32 W/m2 under 1 sun illumination. Outdoor tests showed that an average daily water production of 12.1 kg/m2 and a maximum power generation of 5.55 W/m2 was obtained. This work provides a high-performance multi-scale CuS-rGO pyramidal photothermal structure to achieve freshwater and thermoelectric power co-generation, which provides potential opportunities for freshwater and electricity supply in remote areas.

Artificial neural network prediction and multi-objective genetic algorithm optimization of the microchannel heat sink with trapezoidal ribs

Trapezoidal rib microchannel heat sinks (TR-MCHS) are widely used for efficient heat dissipation in electronic integrated devices. To enhance the heat transfer and hydraulic performance of TR-MCHS, an optimization method using neural network prediction combined with multi-objective genetic algorithm NSGA-II is proposed. First, the effects of trapezoidal rib geometry parameters and inlet velocity (V) on the Nusselt number (Nu¯) and pressure drop (ΔP) of TR-MCHS are investigated using numerical simulation and Sobol sensitivity analysis. The results show that the trapezoidal rib height (ht) and inlet V have the most significant effect on the TR-MCHS, and the interaction effect between the parameters can be neglected. Then, optimization is performed with Nu¯ and ΔP as objectives. On the obtained Pareto solution set, Nu¯ can be improved by 7.3 % compared to the unoptimized TR-MCHS without consuming additional pumping power. In addition, if the same Nu¯ is obtained as the unoptimized TR-MCHS, the ΔP can be reduced to 223 Pa. On this basis, the TOPSIS method based on entropy weight is developed to solve the optimal compromise solution. The best compromise solution has the Nu¯ of 50.9 and the ΔP of only 184.6 Pa, which is 87.9 Pa lower than that of the unoptimized TR-MCHS. These results have important implications for the design of TR-MCHS for electronics cooling.

Multi-objective optimization of a hybrid nanofluid jet impinging on a microchannel heat sink with semi-airfoil ribs based on field synergy principle

With the increasing power density of electronic devices, improving the cooling performance of their heat sinks is an important aspect of heat transfer enhancement research. A novel jet impinging microchannel heat sink with semi-airfoil ribs (JIMCHS-SAR) is proposed. Hybrid Cu-Al2O3/H2O nanofluid is adopted as the coolant. Using the field synergy principle, the flow and heat-transfer characteristics of the hybrid nanofluid impinging on the JIMCHS-SAR are investigated by both single-factor analysis and multi-objective optimization. The effects of jet Reynolds number and hybrid nanoparticle concentration on the optimized JIMCHS-SAR are also evaluated. The results show that a bilateral symmetrical arrangement of the semi-airfoil ribs provides the best thermal resistance and the smallest field synergy angle. Using the optimal structural parameters of the JIMCHS-SAR obtained from multi-objective optimization can significantly improve its overall performance. The thermal resistance and pump power of the optimal JIMCHS-SAR are 1.080 K/W and 0.387 W, respectively. The maximum temperature of the JIMCHS-SAR bottom surface is 8.1 K less than that for a jet impingement microchannel flat plate heat sink. As Reynolds number increases from 6000 to 14,000 and hybrid nanofluid volume fraction increases from 0 to 2.0 %, the thermal resistance decreases from 1.185 K/W to 0.908 K/W, a decrease of 23.4 %, while the pump power increases from 0.22 W to 2.1 W, a nearly 10-fold increase.

Thermal analysis and structure optimization of wavy microchannel with combining ribs of porous layer and solid wall in multi objective genetic algorithm

The combining rib of porous layer and solid wall is set in wavy microchannel heat sink to enlarge heat transfer area and convection with smaller increase in flow resistance, in which the consumption of pump power relates to the ratios of wave amplitude to length or to width and the thickness of porous layer due to vortices generation while coolant passing through channel. The local thermal equilibrium occurs in porous layer, and the Forchheimer-Brinkman-Darcy relations were used to describe the flow inside porous ribs. The effects of channel-to-pitch width ratio, width ratio of porous layer to pitch and microchannel height on its cooling performance are investigated, and the parameter of figure of merit (FOM) is defined to evaluate thermo-hydraulic performance in wavy microchannel. Besides, the multi objective genetic algorithm method is employed to optimize structure parameters in wavy microchannel to obtain better performances, in which the increase in thermal resistance from 0.062 K/W to 0.166 K/W together with consumption of pump power decreasing from 0.00416 W to 0.00185 W can be obtained in the Pareto front set, and it relates to the heat dissipation in convection between coolant and bottom surface or vertical side ribs. Compared to wavy microchannel with solid rib, the 37.61% and 16.67% decreases respectively in thermal resistance and consumption of pump power occur in the case with optimal combining rib of porous layer and solid wall.

Field synergy analysis on thermal-hydraulic behavior of phase change slurry in porous microchannel heat sink with graded porosity configuration

In this study, a novel design of porous microchannel heat sink (MCHS) with graded porosity configuration is proposed in the hope of attaining lower flow and thermal resistances than constant porosity (CP) configuration. The efficacy of new scheme is validated by utilizing a three-dimensional solid-fluid conjugate model based on the finite volume method, which considers the flow and heat transfer of microencapsulated phase change material slurry (MPCMS) inside the porous fins. It is reported that the thermal performance of porous MCHS with constant and graded porosity configurations is significantly better than that of non-porous MCHS. The feasibility of new design is verified by comparing the hydrothermal behavior of multiple graded porosity MCHSs and CP configuration for different fin designs (involving the number of graded equidistant fins N, graded length ratio R, and fin-to-pitch width ratio β) and operating conditions (including Reynolds number Re, mass fraction cm, and inlet velocity uin). The comprehensive performance improvement mechanism of MPCMS in graded porosity microchannels is discussed through the analysis of flow and thermal details, field synergy angle (θ) and field synergy number (Fc), and the overall performance of new design is evaluated by performance evaluation factor (PEF). Results indicate that the six types of porous MCHS with stepwise varying porosity exhibit lower thermal resistance than CP mode, and better thermal behavior and larger PEF can be obtained at N = 2 and β = 0.7. Smaller and larger R should be chosen for stepwise increasing porosity (SIP) and stepwise decreasing porosity (SDP) modes, respectively, to achieve higher heat transfer enhancement while avoiding greater friction losses. The Fc value of porous MCHS with various porosity configurations is about two orders of magnitude less than 1 and shows a monotonically reducing trend with Re, and the synergistic effect deteriorates at high Re. Compared to the CP mode, a low-θ “drift” toward the low porosity region of porous fin occurs within the graded porosity MCHS, which decreases and increases in the downstream and upstream directions of the “drift”, respectively. Among the novel MCHS designs, the z-directional SIP mode acquires the best overall performance due to the excellent synergy between the velocity and temperature fields, and its PEF consistently exceeds 1.13 and reaches up to 1.33. Generally speaking, the fin porosity of graded porosity MCHS near the channel cavity, channel top, and channel inlet should be greater for superior comprehensive performance.

Numerical analysis of flow and heat transfer characteristics of double-layer heterogeneous single crystal diamond microchannel heat sinks

In order to solve the heat dissipation problems associated with highly integrated and high heat flux microelectronic devices, in this work, a novel type double-layer heterogeneous single crystal diamond microchannel heat sink (DLH-SCD-MCHS) is designed and numerically analyzed, in which the upper channel is rectangular and the lower channel consists of various cavities and rib combinations. The comprehensive performance of the DLH-SCD-MCHS was analyzed by the correlation with pumping power and thermal resistance, and the enhanced heat transfer factor (η). The outcome shows that the DLH-SCD-MCHS significantly enhances the heat transfer while appropriately sacrificing part of the pressure drop. Compared with the traditional double-layer microchannel heat sink (DL-MCHS), the pressure drop of DLH-SCD-MCHS is increased by 23.8–43.5 %, the heat transfer coefficient is enhanced by 74.5–117.1 %, and the η is improved by 62.5–87.4 %. The DLH-SCD-MCHS can reduce the irreversible loss, and the minimum augmentation entropy generation number is 0.64 for the DLH-SCD-MCHS with rectangular cavity and rectangular rib (Model V). As Re = 874, the relative rib width, the relative rib length and the relative position of the ribs of the Model V are 0.5, 0.571 and 0.5, respectively, the maximum η is 1.97. The DLH-SCD-MCHS provides new insights for the management of the heat transfer system of microelectronic devices.

Thermal-Hydraulic performance of microchannel heat sink designed with counter-flow and different groove shape

Microchannel heat sink is a potential procedure for scatter heat as a result of its little size and high effectiveness. Thermal resistance and pumping power are two significant parameters to assess the behavior of microchannel heat sink. In this review, heat transfer and fluid behavior have been concentrated mathematically in a microchannel heat sink with the counter stream and different shape of the groove. Four unique cases are discussed in this paper, microchannel heat sink with rectangular groove (R-MCHS), microchannel heat sink with circular groove (C-MCHS), microchannel heat sink with triangular groove (T-MCHS), and straight microchannel heat sink (S-MCHS). Three-dimensional numerical simulation is conducted with the Reynolds number, Re, shifting from 100 to 500 with expanding 100 for each step. As the coolant, Single-stage fluid water streams in the heat sink. The thermal and hydraulic performance of these cases are evaluated by comparing the average temperature of the solid domain, Nusselt number, Thermal Resistance, and Pumping Power. Contrasted with the S-MCHS, the thermal performance of MCHSs with grooves is increased, and the Nusselt number increased at the furrow area. Likewise, the pumping power is bigger for all cases with grooves contrasted and S-MCHS. In all grooved cases, R-MCHS has the lowest average temperature on the bottom surface and the highest average temperature in the solid domain. The C-MCHS has the least thermal resistance for all Re between 100 to 500. In light of the component, the plan standards to move toward the presentation of inclination are proposed.

Pressure drop correlation for subcooled flow boiling in micro-channel heat sink

This study experimentally explores the subcooled flow boiling pressure drop of FC-72 in a multiple parallel rectangular micro-channel heat sink with a channel hydraulic diameter of 666 µm (width 400 µm and height 2000 µm). Detailed experimental procedures and data reduction methodology are presented. The study analyzes and reports the impact of inlet subcooling on the total pressure drop during subcooled flow boiling of FC-72 in rectangular micro-channels heat sink. Additionally, a consolidated subcooled flow boiling pressure drop database is created by incorporating the additional data points assimilated from the study of Lee and Mudawar (2008), which used HFE-7100 as the coolant fluid. The consolidated database is methodically reviewed and evaluated using the seminal pressure drop correlations described in the literature for pressure drop during subcooled flow boiling. For the micro-channels heat sink adopted in this study, existing subcooled flow boiling pressure drop correlations fail to predict the consolidated database. Based on the consolidated pressure drop data points, a new subcooled flow boiling pressure drop correlation for the rectangular micro-channels heat sink is suggested. The new pressure drop correlation well predicts the consolidated subcooled flow boiling pressure drop database with a mean absolute error of 16.6 % and 86.3 % of data points predicted inside ±30 %.

An Experimental and Numerical Study of the Effect of Microchannels Geometry on Heat Transfer of Nanofluids

The use of micro-channel heat exchangers is widespread across a variety of different industrial sectors. This study presents both an experimental and a numerical analysis to compare the performance of four different designs of microchannel heat sinks. The study dealt with using pure water and nanofluid (Al2O3, CuO, and TiO2–H2O) with volumetric concentrations of (0.01- 0.03) as coolants. The software Comsol Multiphysics was employed for conducting numerical analysis in order to simulate and resolve the issue pertaining to fluid and heat flow in a three-dimensional domain. A constant heat flux of 170 kW/m2 is applied to the lower wall of the four microchannels. The simulations were exclusively conducted within the laminar regime, covering a range of Reynolds numbers spanning from 50 to 150. The impact on the temperature of the microchannel's wall, thermal resistance, pressure drop, and friction factor is demonstrated. Based on the results obtained, it is evident that the utilization of nanofluid in the cooling process of a wavy and zigzag microchannel heat sink yields superior performance in terms of both heat transfer and dissipation, as compared to the implementation of pure water as the cooling medium for the heat sink.

Bubby behavior and heat transfer characteristics of bionic microchannels in the subcooled flow boiling process

Microstructures on the sidewall or bottom wall, have shown excellent heat transfer performance in the single-phase convective heat transfer of microchannel heat sinks. For increasing the heat flux, phase-change heat transfer was highlighted as an effective approach. However, more complicated mechanisms of boiling heat transfer make less study focused on the microchannel with microstructure. In this work, a bionic microchannel with concave cavities and bionic ribs was proposed to enhance the boiling heat transfer. Numerical simulations, along with the volume of fluid (VOF) analysis combined with a phase-change model, were used to investigate the effect of the microstructure on the behavior of bubbles in the subcooled flow boiling. The results showed that the microstructure promotes bubble nucleation and the occurrence of more small bubbles around big bubbles. Thus, it enhances boiling heat transfer. Meanwhile, the microstructure was found to be beneficial in maintaining a stable liquid film evaporation under annular flow and suppressing boiling instability. Ultimately, compared with rectangular microchannels, the reported wall temperature and inlet pressure are more stable in the proposed bionic microchannel, the heat transfer coefficient and critical heat flux of the bionic microchannel were found to be 1.45 times higher, with mass flux G of 498 kg/(m2·s) and heat flux q w of 600 kW/m2.