Microchannel Heat Sink Research Articles

Effect of thermal capacitance on microchannel heat sink response to pressure drop oscillations

The efficient heat transfer resulting from flow boiling in microchannel heat sinks can help dissipate high heat fluxes from high-density electronic devices across a small temperature difference. However, practical implementation challenges unique to two-phase flow boiling, as compared to single-phase liquid cooling, have prevented its widespread adoption. A primary challenge is the occurrence of dynamic two-phase flow instabilities, such as pressure drop oscillations (PDO), that have the potential to degrade heat transfer performance or trigger premature critical heat flux (CHF) under some conditions. Under other conditions, PDOs are observed to have little to no impact on performance. One factor proposed by modeling studies to be responsible for this discrepancy in observations of the effect of dynamic instabilities on performance is the thermal capacitance of the heat sink, though this has not been confirmed by experiments. In this study, the effect of thermal capacitance on the transient thermal response of a heat sink experiencing PDOs is examined through use of a dynamic two-phase flow model and experiments. Flow boiling experiments are performed with a controlled compressible volume upstream of parallel-microchannel heat sinks having either a large or a small thermal capacitance. In accordance with the behavior predicted by our model, when thermal capacitance is reduced, the pressure drop oscillation frequency is found to decrease and temperature swings in the heat sink become more severe. Additionally, the experimentally measured CHF limit is diminished in the heat sink at smaller thermal capacitance. These results reveal thermal capacitance as a critical parameter that determines how much dynamic instabilities degrade flow boiling performance in a microchannel heat sink.

Multi-objective topology optimization and thermal performance of liquid-cooled microchannel heat sinks with pin fins

The optimized structures for the liquid-cooled microchannel heat sinks with different pin-fin arrays were designed via using the topology optimization method for the better performance, including minimization of the flow energy dissipation and the average temperature of the bottom surface, aiming to facilitate the more efficient design of microchannel heat sink for electronic chips’ cooling. The heat transfer and flowing performance was simulated with steady-state incompressible Navier-Stokes equation and the energy equation. Based on the rational approximation of material properties (RAMP) method, the mathematical optimization model for heat sink was established according to the multi-objective function. The Galerkin finite element method (GFEM) was employed to calculate the flow and heat transfer system. Furthermore, the globally convergent method of moving asymptotes (GCMMA) was adopted to deal with the mathematical optimization problem as the optimization method. The entropy generation analysis and comprehensive heat transfer factor were employed to evaluate the performance of the conjugate heat transfer problem of 3D microchannel heat sinks with various pin-fin structures. The calculation results reveal that the multi-objective optimal structure has good heat transfer performance, and the temperature distribution of the optimized structure is more uniform. As the same pumping power, the comprehensive heat transfer efficiency of the optimized inline and staggered pin-fin arrays increases by 31.20% and 32.18% compared to the smooth rectangular channel. Compared with the cylindrical pin-fin configuration with the same heat transfer area, the entropy generation rates of the optimized inline and staggered pin-fin configurations decrease by 4.67% and 4.25%, respectively. The results can provide theoretical basis and application support for the electronic chip cooling technology.

Multi-Level Embedded Three-Dimensional Manifold Microchannel Heat Sink of Aluminum Nitride Direct Bonded Copper for the High-Power Electronic Module

Abstract Better thermal management is a key enabler of higher power density in traction inverter power modules. For the first time, we successfully fabricated and tested a microchannel with a three-dimensional (3D) manifold cooler (MMC) using aluminum nitride (AlN)-based directed bonded copper (DBC) substrates. The microchannels (width ∼300 μm and height ∼450 μm) and 3D manifold fluidic passages (width ∼300 μm and height ∼600 μm) were fabricated in two DBC substrates using the femtosecond laser and subsequently bonded using transition liquid phase (TLP) bonding. In this study, the hydraulic and thermal performance of the 3D MMC is measured and validated with numerical simulation. The proposed 3D MMC is capable of removing heat at 600 W/cm2 with a 10 kPa pressured drop at the thermal thermal resistance of 0.2 cm2 K/W. The optimized designs via geometric and layout rearrangement were conducted, which indicates the pressure drop can be further reduced by 10× while maintaining the same thermal performance.

Hybrid concentrator photovoltaic/membrane distillation system for potable water production using new fabricated PS/ZIF_L membrane

A hybrid system is proposed to use solar energy as a heating source for the membrane distillation unit. Concentrating photovoltaic needs an efficient cooling system to manage the excess thermal load. Two microchannel heat sinks were proposed to keep the cells from thermal degradation and simultaneously transfer the excess thermal energy to the membrane distillation unit. The results showed a maximum coolant outlet temperature of 59 °C, which is adequate for the membrane distillation unit. A new composite electrospun nanofibrous membrane was successfully synthesized to reduce unfavorable membrane wettability. First, ZIF-L nanoparticles were synthesized and characterized to prove successful preparation, then used as a nanofiller with polystyrene as the polymer membrane matrix for the first time. SEM, XRD, FTIR, static water contact angle, membrane thickness, and porosity were introduced to prove nanofillers' successful preparation and encapsulation. The antiwetting phenomenon was proven by the measured contact angle of 160°. Furthermore, the fabricated membrane was tested experimentally on a lap scale direct contact membrane distillation unit with a productivity of about 4 kg/m2 h and 18 ppm water quality at 55 °C hot water temperature. Also, the introduced membrane outperformed the productivity of the commercial PVDF membrane at all examined operating conditions.

Numerical Investigation of the Hydrothermal Characteristics of Water Flow in Compound Microchannel Heat Sinks

In the present work, three-dimensional numerical simulations of laminar forced convection flow of water in unique compound microchannel heat sinks (MCHSs) were investigated using computational fluid dynamics (CFD) modeling. The newly proposed MCHS is made up of circular microchannels slotted from the top within a trapezoidal shape, and its cooling effectiveness was compared to that of traditional rectangular MCHS. Each MCHS under consideration has the same hydraulic diameter and heat transfer surface area. Water volumetric flow rates (Qin) with a wide range of values are used, ranging from 40 to 90 ml/min, with the fluid inlet temperature set to 20 oC. A constant heat flux boundary condition of 100 W/cm2 is supplied on the MCHS bottom. The results demonstrated that the inclusion of reentrant trapezoidal shapes can disrupt both hydrodynamic and thermal boundary layers, as well as accelerate fluid flow and mixing in the main flow, resulting in a significant heat transfer enhancement. Furthermore, at Qin=90 ml/min, the average Nusselt number (Nuavg) of compound MCHS increased by 2.16%, while total pressure drop and total thermal resistance decreased by 1.73% and 1.57%, respectively, when compared to the straight rectangular counterpart.

Optimization of brazing process and structure lightweight design for diamond microchannel

The application of diamond material significantly improves the heat dissipation capability of liquid cooling microchannels, solving the bottleneck problem of heat dissipation for highly integrated electronic components and thus promoting the development of a new generation of military electronic equipment. In this study, diamond microchannels with ultra-high heat flux density were reliably vacuum-brazed by using AgCuTi filler metal in a high vacuum furnace. Microstructure and properties of diamond brazing joints were studied and effect of brazing temperature and time was analyzed. The optimal brazing process parameters were obtained as follows: a vacuum level of <1×10−5 Pa, brazing temperature of 840°C, brazing pressure of 0.5–3 bars and holding time of 10 min. Following vacuum-brazing experiment, the brazing residual stress and working stress of the diamond microchannel were analyzed by finite element simulation. The wall thickness of the diamond microchannel was optimized. The minimum wall thickness, which was 0.4 mm, was obtained for the diamond microchannel with dimensions of 14 mm × 10 mm × 1.3 mm. On that basis, the influence of brazing pressure on the brazing filler overflow in the diamond microchannel brazing process was studied. It was showed that when the pressure was below 1 bar, the overflow of brazing filler from the brazing seam could be controlled to a minimum, especially suitable for brazing precision. The formation of residues in the diamond microchannel was thereby avoided basically, and a diamond microchannel heat sink with good performance was obtained.

Investigation on Embedded Microchannel Heatsink for 2.5-D Integrated Package

Investigation on Embedded Microchannel Heatsink for 2.5-D Integrated Package

Effects of micro-slots in fully interconnected microchannels on flow boiling heat transfer

This study introduced the experimental work to assess the effect of micro-slots on the flow boiling characteristics of HFE-7100 in a microchannel heat sink. In this work, fully interconnected microchannels with three different slot sizes of 10 μm, 20 μm and 40 μm, are designed as active nucleation sites to enhance flow boiling and thin film evaporation. The different slots sizes are defined the name as 135, 125 and 112 slots per inch (SPI), respectively. This new configuration is developed based on the experimental and theoretical study of half interconnected microchannel design. Results shows that compared to the plain wall microchannels, the heat transfer coefficient and critical heat flux of the fully interconnected microchannels with 135 SPI are significantly improved by up to 5.5 and 1.82 times, respectively. In addition, the transient study indicates that flow boiling in the present design is more stable than that in plain wall microchannels. Moreover, a visualization study was conducted to investigate the mechanism of high-frequency rewetting through micro slots. The study verified the importance of the micro-slots in microchannels with respect to the heat transfer rates and pressure drop.

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.

A comprehensive analysis of a rectangular microchannel heat sink furnished with a circular perforated cylindrical pinfin

In this study, a simulation has been performed to investigate the effect of circular perforated pinfins on the performance of microchannel heat sink by varying the number of holes and their locations on the pinfins. A total of ten configurations are considered in this work including a plain microchannel (without pinfin) and a solid pinfin case. The study was conducted on a single-phase flow using deionized water as coolant and the Reynolds numbers range from 150 to 350 when a constant heat flux of 100W/cm2 has been applied at the heated base wall of a heat sink. The results obtained indicate that the location, as well as the number of perforations, affects the heat transfer capacity and pressure drop that occurs in the microchannel. However, the outcomes of the present analysis contradict the findings for thermal airflows when identical cases have been applied to the micro heatsink. According to the present analysis case 1 (perforation at the underside of the pinfin) has the maximum Nusselt number followed by case 2 (perforation at the mid of the pinfin) and case 3 (perforation at the topside of the pinfin) whereas the minimum pressure drop is achieved by case 8 (four equidistant perforations) among pinfin configurations. The highest performance factor is achieved by case 1 at a low Reynolds number while case 6 (perforation at the underside and topside) performs best at a higher Reynolds number.

Local hydrothermal characteristics and temperature uniformity improvement of microchannel heat sink with non-uniformly distributed grooves

In order to improve the temperature uniformity of bottom walls, a novel design of microchannel heat sink with From-Sparse-To-Dense embowed grooves (MC-FSTD) was proposed as well as a comparative one with From-Dense-To-Sparse embowed grooves (MC-FDTS). The local hydrothermal characteristics and temperature distribution variance of bottom wall of microchannel heat sinks were numerically investigated for Reynolds number (Re) ranging from 100 to 800. The results showed that the denser grooves led to lower flow velocity, lower local friction factor and higher local pressure as well as the lower bottom wall temperature (Tw) and higher local Nusselt number (Nuz). The local Nusselt number and the bottom wall temperature of MC-FSTD were 2.17 times higher and 9.1K lower than that of MC-SC at z = 10 mm, respectively. MC-FSTD also had the most uniform temperature of the bottom wall and the corresponding temperature variance was 6.42 times lower than that of MC-SC at Re = 795.38. The heat transfer entropy generation rate and the total entropy generation rate of MC-FSTD were also the lowest with an acceptable friction entropy generation rate. Finally, the effects of the decreasing magnitude (Li) of the distance between two adjacent grooves on the local hydrothermal characteristics and temperature uniformity of MC-FSTD were explored and the total entropy generation rate was further reduced to 5.22 × 10−4 W/K at Li = 0.015 mm and Re = 795.38.

Study on the uneven flow distribution and non-uniform heat transfer in microchannels

The power module is one of the main heating sources with non-uniform heat flux in high-power electrical servo systems used for flight vehicles. Faults in the power module are usually caused by a high or a non-uniform temperature. Given the environment of heat dissipation during flight, a regenerative cooling method is typically used, and the cooling system is designed as a microchannel heat sink with supercritical fuel. This is an effective means of solving thermal problems in the flight vehicles. However, because of the high heating power and non-uniform heat distribution of the power module, it is necessary to optimize its heat sink to restrict the high temperature rise and suppress the non-uniform distribution of temperature. In light of these considerations, a 3D numerical model of the microchannel heat sink of a power module with non-uniform heat flux was established in this study to examine the heat transfer and the thermal performance of the cooling channels. Based on the validation of the mesh and numerical method, the simulations of the flow distributions of the channels were performed to assess the thermal performance of the heat sink. It included investigating the effects of the inlet location of the manifold and its injection angle on the flow distribution in the channels, and the influences of the flow distribution and the operational parameters on the thermal performance of the heat sink. The results revealed that the Z30 configuration provided the best location and injection angle of the inlet to match the non-uniform heat flux of the power module. In this case, the values of Stanton number and buoyancy parameter of channel 4 yielded the minimum values of all channels owing to its higher flow rate and gradual rise in temperature. The deviation in the rate of mass flow Φ changed slightly corresponding to the various operational parameters, only the total heat flux would bring a bigger fluctuation. The tiny difference in temperatures among the observation areas on the substrate verified the positive influence of the flow distribution in matching the non-uniform heat flux.

Study of the hot-pressing sintering process of diamond/copper composites and their thermal conductivity

Diamond/copper composites have been widely studied as high thermal conductivity (TC) materials for heat dissipation in electronic integrated devices. In this study, diamond/copper composites with fin structures were prepared by hot-pressing sintering. The relative density and TC of the composites were analyzed for different diamond particle sizes, diamond volume fractions, sintering temperatures and sintering pressures. The relative density of the composites decreases significantly with increasing diamond particle size and volume fraction. The TC of the composite was found to be a maximum of 564.2 W/m·K at 1400 N sintering pressure and 900 °C sintering temperature when the diamond particle size was 230 µm and the volume fraction was 60%. In addition, the coefficient of thermal expansion (CTE) of the diamond/copper composite was 7.01 × 10−6 K−1 at 1400 N sintering pressure and 900 °C sintering temperature, which meets the packaging requirements for electronic integrated devices. The heat dissipation experiment of the diamond/Cu microchannel heat sink (MCHS) showed that the surface temperature of the heat source can be controlled at 59.9 °C when the inlet velocity was 0.4 m/s, achieving a cooling of 40.1 °C.

Effects of Varying Volume Fractions of SiO2 and Al2O3 on the Performance of Concentrated Photovoltaic System

Highly concentrated triple-junction solar cells (HCTJSCs) are cells that have diverse applications for power generation. Their electrical efficiency is almost 45%, which may be increased to 50% by the end of the year 2030. Despite their overwhelming ability to generate power, their efficiency is lower when utilized in a concentrated manner, which introduces a high-temperature surge, leading to a sudden drop in output power. In this study, the efficiency of a 10 mm × 10 mm multijunction solar cell (MJSC) was increased to almost 42% under the climatic conditions in Lahore, Pakistan. Active cooling was selected, where SiO2–water- and Al2O3–water-based nanofluids with varying volume fractions, ranging from 5% to 15% by volume, were used with a 0.001 kg/s mass flow rate. In addition, two- and three-layer microchannel heat sinks (MCHSs) with squared microchannels were designed to perform thermal management. Regarding the concentration ratio, 1500 suns were considered for 15 August at noon, with 805 W/m2 and 110 W/m2 direct and indirect radiation, respectively. A complete model including a triple-junction solar cell and allied assemblies was modeled in Solidworks software, followed by temperature profile generation in steady-state thermal analyses (SSTA). Thereafter, a coupling of SSTA and Ansys Fluent was made, in combination with the thermal management of the entire model, where the temperature of the TJSC was found to be 991 °C without active cooling, resulting in a decrease in electrical output. At 0.001 kg/s, the optimum average surface temperature (44.5 °C), electrical efficiency (41.97%), and temperature uniformity (16.47 °C) were achieved in the of MJSC with SiO2–water nanofluid with three layers of MCHS at a 15% volume fraction. Furthermore, the average outlet temperature of the Al2O3–water nanofluid at all volume fractions was high, between 29.53 °C and 31.83 °C, using the two-layer configuration. For the three-layer arrangement, the input and output temperatures of the working fluid were found to be the same at 25 °C.

Examining the impact of inlet header configurations on wavy microchannel heat sinks

Examining the impact of inlet header configurations on wavy microchannel heat sinks

Flow and thermal modeling of liquid metal in expanded microchannel heat sink

Flow and thermal modeling of liquid metal in expanded microchannel heat sink

Thermal and hydrodynamic characteristics of single-phase flow in manifold microchannels with countercurrent regions

Manifold microchannel heat sink is promising to dissipate high heat fluxes for electronic devices due to its high surface to volume ratio. Traditional Z-type manifold encounters fluid flow maldistribution and a high temperature difference. In this work, two inlets and countercurrent flows are introduced into the manifold arrangement to alleviate these problems in the Z-type manifold microchannels. Six cases with different manifold arrangements are numerically investigated using single-phase HFE-7100 at mass flow rates ranging from 56.8 to 117.78 mg/s. The results show that the maximum temperature, average temperature, and temperature difference of the revised arrangements are all lower than these of the traditional Z-type manifold arrangement. The minimum temperature difference for an ideal multi inlet manifold arrangement can be less than 0.2 K, while the value is about 5.3 K for the traditional Z-type manifold arrangement. The revised arrangement can also improve the uniformity of mass flux distributions. The ratio of the maximum to the minimum mass flux within microchannels is 12.83 for the traditional Z-type manifold, while this value is about 5.82 for cases with two inlets and countercurrent zones. A longer flow path and a higher local pressure drop in the revised arrangements results in higher pressure drops than the traditional Z-type manifold microchannels. Compared with the traditional Z-type arrangement, heat transfer coefficients and performance evaluation criterion are higher for the improved cases. The presence of a countercurrent zone can improve the comprehensive performance of the manifold microchannel. New criterion based on the thermal resistance calculated at the maximum temperature is proposed to evaluate the cooling performance of electronics.

SiC Microchannel Heat Sinks for High Heat Flux Dissipation of 1 kW/cm2

Thermal management has become a major barrier in the development of high-power micro-devices. Microchannel heat sinks (MCHS) are a promising method to dissipate high heat fluxes from high power density devices. Reducing the thermal resistance will reduce the temperature increase of the electronic device, allowing for higher powers to be achieved while maintaining a safe operating temperature. This paper reports on the use of silicon carbide (SiC) microchannels to dissipate high heat fluxes up to 1 kW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> over a footprint of 0.25 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The use of high aspect ratio and decreased hydraulic diameter channels has allowed for very low thermal resistances to be achieved at higher heat duties compared to previous studies. The experiments performed resulted in heater temperatures of less than 60 °C and thermal resistances as low as 0.024 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> °C/W between the heater surface and fluid inlet temperature. The demonstrated thermal performance of the SiC MCHS is an encouraging means for dissipating heat from high power density microelectronic devices.

Diamond single crystal-polycrystalline hybrid microchannel heat sink strategy for directional heat dissipation of hot spots in power devices

Diamond single crystal-polycrystalline hybrid microchannel heat sink strategy for directional heat dissipation of hot spots in power devices

Comparison of cooling performance of nanofluid flows in mini/micro-channel stacked double-layer heat sink and single-layer micro-channel heat sink

Mini/micro-channel heat sinks are the advanced cooling method to fulfill the cooling demand of electronic equipment integrated with high-power circuit packages. Many designs are provided to enhance the thermal performance of micro-channel. In the present experimental study, the mini/micro-channel stacked double-layer heat sink is designed and tested for the first time. The mini/micro-channel stacked double-layer heat sink is composed of a single-layer micro-channel heat sink stacked with a mini-channel heat sink. The pure water and alumina-water nanofluid are considered as the coolant. A comparison is conducted between the heat dissipation performance of mini/micro-channel stacked double-layer heat sink and single-layer micro-channel heat sink. The results showed that as compared with the case of single-layer micro-channel heat sink, the pressure drop can be reduced considerably by using the mini/micro-channel stacked double-layer heat sink. For the flow rate ratio less than 2.0, the average convection heat transfer coefficient of the mini/micro-channel stacked double-layer heat sink is higher than that of the single-layer micro-channel heat sink. Finally, the FOM ratios are greater than unity for all cases. This indicates that the use of mini/micro-channel stacked double-layer heat sinks has more advantages in engineering applications than the single-layer micro-channel heat sinks.