Copper Microchannel Heat Sink Research Articles

Experimental study on flow boiling in ultrahigh-aspect-ratio copper microchannel heat sink

One ultrahigh-aspect-ratio copper microchannel heat sink (AR = 25) was fabricated with wire electrical discharge machining technique, in which the flow boiling heat transfer of deionized water was experimentally investigated. The results show the present heat sink has a superior performance in the critical heat flux and a low thermal resistance compared to other ones (AR = 1, 5 and 15), even though its mass flux is around ten times lower than that in regular one (AR = 1). The largest improvement of critical heat flux and the maximum difference of thermal resistance are 40.95 % and 40.28 %, respectively, for the ultrahigh-aspect-ratio channel compared to those for the channel with AR = 1. It is found that the nucleate bubbles between the elongated bubbles can make full use of the remaining heat transfer area of the ultrahigh-aspect-ratio microchannel, which significantly improves its flow boiling thermal performance at a low heat flux. At a high heat flux, the nucleate bubbles generated in the deformed liquid film enhance the evaporative heat transfer process. The coexisting heat transfer mode in the ultrahigh-aspect-ratio microchannel can prolong the nucleate boiling period, which contributes to the heat transfer enhancement of the present heat sink.

Development of a mathematical model for prediction of heat transfer coefficient in micro-channel heat sink

The advancement of miniaturization and high-density manufacturing of electronic devices necessitates lightweight and high-performance heat dissipation components. As a result, traditional coolants and cooling technologies are rapidly unable to satisfy the ever conditioning problems and requirements of specific high temperature generated electronic devices. A microchannel heat sink (MCHS) has been extensively researched and commonly used in electronics cooling as a novel system that is highly suitable for applications with high power and small heat dissipation space. This research presents a mathematical model focused on dimension analysis to determine the heat transfer coefficient of a microchannel heat sink in electronics cooling. Buckingham Pi (π)theorem with dimensional analysis was used to determine a functional correlation between the heat transfer coefficient and independent variables. Independent variables comprise; thermal conductivity (copper MCHS), hydraulic diameter (MCHS), length (MCHS), a mass flow rate of nanofluid, the density of nanofluid, inlet temperature of nanofluid, heat flux, % by volume concentration of nanoparticle and thermal conductivity of nanofluid. The established relationship between dependent and independent variables concerning various operating conditions is helpful for analyzing behaviour.

Flow boiling characteristics in plain and porous coated microchannel heat sinks

Flow boiling heat transfer enhancement using porous coatings in microchannels has been experimentally investigated with HFE-7200. Results of the coated microchannel heat sink were compared to baseline results in a plain, micro-milled copper microchannel heat sink at similar operating conditions, namely inlet pressure of 1 bar, mass flux of 200 – 400 kg/m2 s and inlet subcooling of 10 K at wall heat fluxes between 24.5 kW/m2 to 206.6 kW/m2. Flow visualisation results and SEM surface analysis are presented. The coated surface was densely populated with well-defined cavities between 0.6 µm to 3.3 µm wide. The plain channels had fewer cavities for a given area and these were larger, i.e. up to 6 µm. Bubble generation frequency in the coated channels is significantly higher than in the plain channels due to the presence of more favourable nucleation sites on the coated surface. Flow pattern development occurred similarly in both heat sinks, namely bubbly to slug, churn and annular flow with increasing heat flux, with earlier flow pattern transitions in the coated heat sink. Enhancement in microchannel flow boiling heat transfer was shown to be influenced by mass velocity and may reach up to 44% at low heat fluxes, where the nucleate boiling mechanism is dominant. It diminishes with increasing heat flux, corresponding to nucleate boiling suppression following flow regime transition. Pressure drop increase posed by the coated heat sink is relatively small in terms of overall system power consumption but appears to be influenced by mass flux, pressure oscillations as well as channel rewetting behaviour.

Design and characterization of a copper microchannel heat sink for SiP cooling

With the increasing flourishing of miniaturized, multifunctional, and heterogeneously integrated system in package (SiP), heating problem is becoming more and more serious. In this paper, to meet the heat dissipation needs of the chips thus assembled and to achieve effective thermal management, linear, serpent and spiral shaped microchannel heat sinks were designed and fabricated into copper substrate by electrical discharge machining (EDM) and precision machining technology, acting both as the cooler and mounting base for passive and active SiP interposers. A test platform was set up to characterize the heat dissipation performance of the copper-based microchannel heat sink. The experimental and simulation results show that heat dissipation rate increases with the increasing heat flux density in the range 5–30 W/cm2 for the three microchannel designs, and the peak temperature can all be kept below 340 K (67[Formula: see text]C) even for the highest heat flux. The three designs are compared from the perspective of peak temperature, temperature distribution uniformity and pressure drop. In all, the solution proposed hereby provides a new and optimal option for in-situ cooling for densely integrated electronic hardware.

Enhanced flow boiling of HFE-7100 in picosecond laser fabricated copper microchannel heat sink

The enhanced flow boiling heat transfer of HFE-7100 in wavy copper microchannel heat sink was experimentally studied, which was fabricated with the picosecond laser technique. The micro porous structures were naturally formed on the sidewall and bottom of microchannel during the laser fabrication process, which increase the wall surface roughness. In single-phase flow region, the evaluation of performance evaluation criteria (PEC) proves the heat transfer enhancement overcomes the pressure-drop penalty in present wavy microchannel. In two-phase flow region, the flow patterns including bubbly flow, slug flow and annular flow were captured with the visualization technique, three heat transfer modes including heat convection, nucleate boiling and thin film evaporation were analyzed in detail. In wavy microchannel, the nucleate bubble on concave channel sidewall has a different apparent shape with a larger growth rate compared to that on convex one. In the thin film evaporation stage, the thickness of liquid film varies and it depends on the difference in curvatures between bubbles and sinusoidal channel sidewall. Compared to the straight channel, an increase of 28.89% for CHF can be achieved in wavy one, and the heat transfer coefficient enhancements of 60.76% and 52.71% are obtained in wavy one at the nucleate boiling stage and thin film evaporation stage, respectively.

Hybrid microchannel/multi-jet two-phase heat sink: A benchmark and geometry optimization study of commercial product

In this paper, an experimental study of two-phase cooling heat sink using the dielectric working fluid Novec/HFE-7000 is performed. The liquid flow is directed into microchannel fins through multiple impinging jets. A copper microchannel heat sink with a fin height of 3mm, fin thickness of 0.1 mm and channel width of 0.1 mm was used for removing heat flux from the heated surface. A copper block was used to mimic computer chip with a surface area of 1” x 1” (6.45 cm2). The experiment was performed at heat flux from 5 W/cm2 to 80 W/cm2, subcooling of 5 °C, 15 °C, 25 °C, and flow rates 1, 1.25 and 1.75 lpm. The results in the two-phase regime for high heat fluxes are compared with analytical correlations. Reduced subcooling can results in enhancement of heat transfer coefficient by 25 % but will increase the pressure drop through the heat sink. Heat transfer coefficient increases with flow rate in the single-phase region and in the convective boiling region. In nucleate boiling region, heat transfer coefficient increases with heat flux rather than flow rate. Geometry optimization of heat sink was carried out considering effects of fin height on thermal and hydraulic performance. It is found that thermal resistance variation with fin height shows a parabolic trend and an improvement of 46 % in thermal performance can be obtained. A new correlation was also developed to predict results of experimental data with mean absolute error of 7 %. The inclusion of Reynolds number and hydraulic diameter was found to considerably reduce error when compared to values obtained with the previously available correlation, in which only the subcooling and heat flux were the parameters for modelling the heat transfer.

CFD Simulation and Analytical Validation of Rectangular and Square microchannel heat sink with liquid water as cooling medium

In present work, both analytical and CFD investigation was performed to check the microchannel heat sink cooling performance, made up of copper with two different microchannel cross sections with shape of rectangle and square. CFD analysis is conducted with water as working fluid for both of the cross sections and Reynolds number ranging from 600 to 1000. A copper microchannel heat sink with bottom size of 25.4mm×25.4mm and height of 2.384mm is selected and CFD analysis was carried out and at bottom constant heat flux boundary condition is assumed. For comparison between two cross sections, the hydraulic diameter used is same for both. Rectangular cross section microchannel showed better cooling performance as compared to square cross section microchannel. Both analytical and CFD simulation results of pressure drop in rectangular microchannel heat sink are in good agreement with a difference of 18.9%.

Microembossed copper microchannel heat sink for high‐density cooling in electronics

A microembossed copper microchannel heat sink was designed and fabricated for high-density cooling in electronics. The microchannel width and aspect ratio were investigated to find out the optimised channel size for microembossing. The fabrication method was based on bulk copper forming including tungsten die inductively coupled plasma etching, hot copper microembossing, inlet/outlet ports punching and sealing. The heat dissipation performances were tested by ceramic heater. The maximum temperature decreased to ∼37°C under different heat fluxes, with the maximum temperature decreased by 69.2% at 50 W/cm2 heat flux. The equivalent heat transfer coefficient reached the value of 6492 W/m2 K. High-power chip was used as heat source too. The maximum heat flux reached 304.8 W/cm2 when the chip can still function properly at 90.5°C. High cooling performance with the micro-heat sink proves that microembossing by tungsten die is an alternative process for microchannel heat sink fabrication with batch production and low cost. Taking advantages of simple fabrication process and reutilisation of tungsten die, the technology shows promising potentials in high-density microcooling systems.

Heat transfer performance of a porous copper micro-channel heat sink

A novel porous copper micro-channel heat sink based on the high thermal conductivity and structural stability of porous copper micro-channel material is proposed in this study. A circular cross-sectional and a multi-layer staggered arrangement are the main characteristics of the micro-channel heat sink. Additionally, a heat dissipation model is produced for porous copper micro-channel heat sink by analyzing the heat transfer process. Further, the theoretical heat transfer coefficient is calculated using MATLAB, and the experimental heat transfer coefficient is determined based on an experimental platform. The heat dissipation model is verified by comparing the theoretical and experimental heat transfer coefficients. The relation between the porous copper micro-channel heat sink parameters and the heat transfer coefficient that is obtained based on the heat dissipation model of the porous copper micro-channel heat sink is analyzed. The results exhibit that variations in pore diameter, porosity, porous copper length, porous copper width, porous copper height, and volume flow significantly affect the heat transfer performance.

Analytical, experimental, and numerical analysis of a microchannel cooling system for high-concentration photovoltaic cells

In this work, we present the results of an analytical, numerical, and experimental analysis on the performance of a heat sink system designed as a parallel arrangement of microchannels for cooling a high-concentration photovoltaic (HCPV) cell. The analysis considered the worst-case scenario where no electricity is generated, and the solar incidence is maximum on the northwest region of the Sao Paulo State in Brazil. For the experimental, analytical, and numerical analysis, the considered HCPV cell has a geometrical concentration ratio of 500×, a maximum efficiency of 40% at cell’s operating temperature of 41.0 °C, and a cell base area of 100 mm2. The numerical analysis adopts the finite volume method implemented in ANSYS Fluent v15 to solve flow and energy equations with second-order upwind schemes, and the steady-state, incompressible, and laminar flow. In the experimental apparatus, the copper microchannel heat sink consists of 33 parallel rectangular channels of 10 mm in length, 200 μm in width, and 500 μm in height for each microchannel. A cartridge heater was used to simulate the on-sun test, i.e., it simulates the total heat rate supplied to the microchannel heat sink. The microchannel heat sink is capable of keeping the operating temperature of the cell below the maximum cell’s operating temperature (41.0 °C). In addition, the pressure drops are slightly higher than the predicted models, but not exceeding 34%. Moreover, the energy spent in the pumping in the microchannel represents < 1% of the energy generated by the photovoltaic cell.

Numerical simulation of nanofluids for improved cooling efficiency in a 3D copper microchannel heat sink (MCHS)

ABSTRACTIn this paper, laminar nanofluid flow in 3D copper microchannel heat sink (MCHS) with rectangular cross section, and a constant heat flux, has been treated numerically using the computational fluid dynamics software (FLUENT). Results for the temperature and velocity distributions in the investigated MCHS are presented. In addition, experimental and numerical values are compared in terms of friction factors, convective heat transfer coefficients, wall temperature and pressure drops, for various particle volume concentrations and Reynolds numbers. The numerical results show that enhancing the heat flux has a very weak effect on the heat transfer coefficient for pure water, but an appreciable effect for the case of a nanofluid. For all considered volume fractions, the sink friction factor decreases by increasing the Reynolds number and slightly increases by increasing the volume fractions, and, with increasing the volume fractions and the Reynolds number, the pressure drop increases.

An experimental investigation of flow boiling heat transfer of R-141b and R-1234yf in microchannels

This study presents experimental results of flow boiling heat transfer of refrigerants R-141b and R-1234yf in a horizontal microchannel heat sink. The copper microchannel heat sink contains 21 microchannels with 335×930 μm cross-section. Distribution of local heat transfer coefficients along the length and width of the microchannel plate were measured in the range of external heat fluxes from 50 to 550 kW/m 2 . Finally, comparisons with predictions according to the model of flow boiling heat transfer are reported for the data sets.

Flow Boiling Heat Transfer of Refrigerant R-134a in Copper Microchannel Heat Sink

In this paper we present experimental data on heat transfer and pressure drop characteristics at flow boiling of refrigerant R-134a in a horizontal microchannel heat sink. The primary objective of this study was to experimentally establish how the local heat transfer coefficient and pressure drop correlate with the heat flux, mass flux, and vapor quality. The copper microchannel heat sink contains 21 microchannels with 335 × 930 μm2 cross section. The microchannel plate and heating block were divided by the partition wall for the local heat flux measurements. Distribution of local heat transfer coefficients along the length and width of the microchannel plate was measured in the range of external heat fluxes from 50 to 500 kW/m2; the mass flux varied within 200–600 kg/m2-s, and pressure varied within 6–16 bar. The obvious impact of heat flux on the magnitude of heat transfer coefficient was observed. It showed that nucleate boiling is the dominant mechanism for heat transfer. A new model of flow boiling heat transfer, considering nucleate boiling suppression and liquid film evaporation, was proposed and verified experimentally in this paper.

Investigation of On-Chip Hot Spot Cooling Using Microchannel Heat Sink

With the increase of performance demands, the nonuniformity of on-chip power dissipation becomes greater, causing localized high heat flux hot spots that can degrade the processor performance and reliability. In this paper, a three-dimensional model of the copper microchannel heat sink, with hot spot heating and background heating on the back, was developed and used for numerical simulation to predict the hot spot cooling performance. The hot spot is cooled by localized cross channels. The pressure drop, thermal resistance and effects of hot spot heat flux and fluid flow velocity on the cooling of on-chip hot spots, are investigated in detail.

Heat Transfer Performance of Lotus-Type Porous Copper Micro-Channel Heat Sink

Lotus-type porous structure is a new kind of micro-channel structure and can be used as heat sink for heat elimination of high powered electronic devices. Numerical analysis based on the simple fin model was used to predict the equivalent heat transfer coefficient of lotus-type porous copper micro-channel heat sink. Compared with the water, GaInSn working fluid could further promote the heat transfer performance of the heat sink. According to the theoretical analysis, a heat transfer coefficient as high as 14W/(cm2K) was attainable when the pressure drop was 50 KPa and an appropriate structure parameters: 0.4 mm in pore diameter, 0.4 in porosity and 4mm in height of porous copper were achieved.

Investigating the heat transfer performance and thermophysical properties of nanofluids in a circular micro-channel

In this paper, the thermal performance of a circular shaped copper microchannel heat sink using three types of nanofluids is discussed analytically. Al2O3–Water, TiO2–water and CuO–water nanofluids were used in this analysis and the comparative thermal performance of these three nanofluids is also discussed. The hydraulic diameter of the circular channel is 400μm and the total block dimension is 10mm×10mm×4mm. A steady, laminar and incompressible flow with constant heat flux is assumed in the circular channel. The analyses are done at various volume fractions ranging from 0.5vol.% to 4vol.% and at a constant inlet velocity of 1.5m/s. The results showed that the thermal performance can be increased significantly by using CuO–water nanofluid as a coolant for cooling of electronic heat sink when Al2O3–water and TiO2–water nanofluids showed less improvement. Compared to pure water, the highest improvement (13.15%) in the heat flux occurred for 4vol.% CuO–water nanofluid when Al2O3–water and TiO2–water nanofluids showed 6.80% and 6.20% improvements respectively. This improvement in heat flux is calculated without considering the additional required pumping power due to the increased viscosity of nanofluids. Therefore, CuO–water nanofluid can be recommended to obtain maximum heat transfer performance in a circular microchannel heat sink.

Correlation between Flow Pattern and Refrigerant Flow Boiling Heat Transfer in Microchannel Heat Sinks

Flow boiling in microchannel heat sinks is significantly influenced by capillary forces and by boundary constrains affecting the flow pattern and the heat transfer. In the present work, some characteristics of flow boiling heat transfer are explained using measurements of statistical parameters of gas-liquid two-phase flow in a rectangular microchannel. Such statistical characteristics of the flow as length distributions of elongated bubbles and liquid plugs, and also velocity distribution of the elongated bubbles are determined by dual laser scanning of the horizontal adiabatic nitrogen-water flow in a microchannel with the cross-section of 370×217 μm. Pressure gradients in gas-liquid flow are measured, and the results found well matching the predictions that account for capillary pressure on the gas-liquid interface. Heat transfer coefficients are measured for a horizontal copper microchannel heat sink with refrigerant R-21 as the working fluid. The heat sink contains 21 channels with cross section dimensions 930×335-μm. Distribution of local heat transfer coefficients along the length and the width of the microchannel plate is measured in the range of heat fluxes from 14 to 63 kW/m2; vapour quality was varied within 0.05-0.8, and pressure was about 1.6 bar. For flow boiling of R-21 refrigerant, contributions of nucleate boiling and forced convection are comparable. This allows us to examine the heat transfer mechanism for these complex conditions.

Enhanced Thermal Transport in Microchannel Using Oblique Fins

Sectional oblique fins are employed, in contrast to continuous fins in order to modulate the flow in microchannel heat sinks. The breakage of a continuous fin into oblique sections leads to the reinitialization of the thermal boundary layer at the leading edge of each oblique fin, effectively reducing the boundary layer thickness. This regeneration of entrance effects causes the flow to always be in a developing state, thus resulting in better heat transfer. In addition, the presence of smaller oblique channels diverts a small fraction of the flow into adjacent main channels. The secondary flows created improve fluid mixing, which serves to further enhance heat transfer. Both numerical simulations and experimental investigations of copper-based oblique finned microchannel heat sinks demonstrated that a highly augmented and uniform heat transfer performance, relative to the conventional microchannel, is achievable with such a passive technique. The average Nusselt number, Nuave, for the copper microchannel heat sink which uses water as the working fluid can increase as much as 103%, from 11.3 to 22.9. Besides, the augmented convective heat transfer leads to a reduction in maximum temperature rise by 12.6 °C. The associated pressure drop penalty is much smaller than the achieved heat transfer enhancement, rendering it as an effective heat transfer enhancement scheme for a single-phase microchannel heat sink.

KW级光纤耦合输出二极管激光器模块

The fiber coupled system based on mini-bars is an effective way of avoiding complex beam shaping to reduce costs and improve brightness. Forty mini-bars mounted on copper microchannel heatsink are arranged in two stacks to collimate the output beam of the stacks with the aspherical cylindrical lens and cylindrical lens array in fast and slow axis directions in this paper. For increasing the fill factor of the beams of the stacks, the beams are combined spatially in the fast axis direction. The combined beam could be coupled into the fiber of 800 m core diameter and 0.22 numerical aperture. The opto-optical efficiency of the fiber coupled module is about 58% and the maximum output power is 1360 W with the power density of 1.73105 W/cm2 at fiber output facet.

3D Numerical Geometric Optimization of Copper and Aluminum Microchannel Heat Sink

3D Numerical Geometric Optimization of Copper and Aluminum Microchannel Heat Sink