Rectangular Microchannel Heat Sink Research Articles

Geometric optimization of an enhanced microchannel heat sink with superhydrophobic walls

This paper compares the optimal geometry of a rectangular microchannel heat sink (MCHS) for different channel wall surfaces, namely, conventional (uncoated and smooth), hydrophobic, and superhydrophobic. For this purpose, the three-dimensional Navier-Stokes and energy equations with the slip boundary conditions are numerically solved using the finite volume method. Shape optimization is then carried out based on the response surface methodology and the desirability function approach. The optimal channel width ratio (β) and the number of channels (N), that yield the lowest thermal resistance of the heat sink for a fixed pumping power (Ω), are reported. The results show that as the wall hydrophobicity increases, the optimal β decreases, whereas the optimal N increases. For instance, the optimal N increases from 80 for an MCHS with hydrophobic walls to 140 for its counterpart with superhydrophobic walls. This trend is attributed to the strengthening effect of interfacial slip as channel width shrinks. It is also found that the overall thermal resistance of hydrophobic and superhydrophobic MCHS is reduced by 5 and 20%, respectively, compared with that of conventional one. The results also show that the beneficial effect of increasing wall hydrophobicity on the thermal performance weakens with an increase in Ω, and almost vanishes for Ω > 2 Watts.

Design of Microelectronic Cooling Systems Using a Thermodynamic Optimization Strategy Based on Cuckoo Search

This paper proposes a conceptual design strategy for an optimal cooling system, typically used in several microelectronic devices. The methodology was implemented using the entropy generation minimization (EGM) criterion, powered by the cuckoo search (CS) algorithm. EGM-CS methodology was addressed to design rectangular microchannel heat sinks, utilizing high thermal conductive graphite as build material and a water-based colloid as coolant. This strategy was implemented under different hydrodynamic conditions, where it showed strong capability to achieve optimal designs with flowing nanofluids in either laminar or turbulent regimes. In addition, two types of nanoparticles were considered, i.e., Al and TiO2, with several values of volume fraction, as a passive mechanism for enhancing overall system performance. It was corroborated that all considered flowing colloids in laminar regime improve the thermal efficiency of the system. Moreover, an additional enhancement of this performance was observed with smaller nanoparticle concentrations (e.g., 0.01 wt/wt%), which also reduces the side effects due to nanoclustering. Furthermore, fluids with titanium dioxide nanoparticles showed slightly better thermal performance enhancement compared to aluminum particles.

NUMERICAL STUDY OF PRESSURE DROP AND HEAT TRANSFER IN A STRAIGHT RECTANGULAR AND SEMI CYLINDRICAL PROJECTIONS MICROCHANNEL HEAT SINK

The heat transfer and pressure drop characteristics of a straight rectangular and semi cylindrical projections microchannel heat sink were investigated. The heat sinks, made of copper, were aligned in row as a cluster of 21 microchannels, 231 µm wide and 713 µm deep. Water was used as cooling fluid and was made to flow through the channels. A three dimensional analysis was done for Reynolds number ranging between 200 to 1000 with constant heat flux of 10 6 W/m 2 defined relative to the platform area of the heat sink. The temperature rise and pressure drop of the fluid in straight microchannel heat sink was evaluated using ANSYS-CFX package and was validated using experimental data. Similar analysis was done for semi cylindrical projections microchannel heat sink by solving the conjugate heat transfer problem. A comparison of heat transfer and pressure drop between rectangular and semi cylindrical projections microchannel was done and the results were laid out. Results shows that heat transfer increases with the use of semi cylindrical projections microchannel heat sink.

Numerical investigation on laminar flow and heat transfer in rectangular microchannel heat sink with wire coil inserts

A numerical investigation is carried out to study the laminar liquid flow and coupled heat transfer performance in rectangular microchannel heat sink (MCHS) equipped with wire coil inserts. Distilled water with temperature-dependent thermophysical properties is employed to perform this simulation. The effects of the length and arrangement of wire coil inserts on flow and heat transfer characteristics, and the mechanism of heat transfer enhancement in wire coil inserted MCHSs were analyzed using the first and second law of thermodynamics. This study is also to propose the frication factor and heat transfer correlations for MCHSs with wire coils. The results show that the heat transfer performance in the MCHS is enhanced effectively due to the longitudinal vortexes caused by the wire coils, but the flow resistance is increased simultaneously. The MCHS with long wire coil placed at the center line of microchannel shows the best heat transfer performance with enhancement factor of 1.4–1.8 at a heat flux 400kW/m2. Its overall performance is the best among five configurations using the principle of entropy generation minimization, but using the performance evaluation criteria (PEC), the best performance is only limited to the low Reynolds number. The best overall performance using PEC at the high Reynolds is the MCHS with three segments of short wire coil placed at the center line of microchannel.

Analysis of Interrupted Rectangular Microchannel Heat Sink with High Aspect Ratio

Analysis of Interrupted Rectangular Microchannel Heat Sink with High Aspect Ratio

THERMAL AND HYDRODYNAMIC PERFORMANCE OF A MICROCHANNEL HEAT SINK COOLED WITH CARBON NANOTUBES NANOFLUID

The microchannel heat sink (MCHS) has been established as an effective heat removal system in electronic chip packaging. With increasing power demand, research has advanced beyond the conventional coolants of air and water towards nanofluids with their enhanced heat transfer capabilities. This research had been carried out on the optimization of the thermal and hydrodynamic performance of a rectangular microchannel heat sink (MCHS) cooled with carbon nanotube (CNT) nanofluid, a coolant that has recently been discovered with improved thermal conductivity. Unlike the common nanofluids with spherical particles, nanotubes generally come in cylindrical structure characterized with different aspect ratios. A volume concentration of 0.1% of the CNT nanofluid is used here; the nanotubes have an average diameter and length of 9.2 nm and 1.5 mm respectively. The nanofluid has a density of 1800 kg/m3 with carbon purity 90% by weight having lignin as the surfactant. The approach used for the optimization process is based on the thermal resistance model and it is analyzed by using the non-dominated sorting multi-objective genetic algorithm. Optimized outcomes include the channel aspect ratio and the channel wall ratio at the optimal values of thermal resistance and pumping power. The optimized results show that, at high operating temperature of 40°C the use of CNT nanofluid reduces the total thermal resistance by 3% compared to at 20°C and consequently improve the thermal performance of the fluid. In terms of the hydrodynamic performance, the pumping power is also being reduced significantly by 35% at 40°C compared to the lower operating temperature.

Effect of geometrical and temperature-dependence parameters on forced convection of a nanofluid in a micro-channel heat sink

Purpose The purpose of this study is the numerical prediction of the thermal and hydraulic characteristics (Nusselt number and shear stress) of a forced convection laminar flow through a rectangular micro-channel heat sink, using constant and temperature-dependent thermo-physical properties. The effects of the solids volume fraction and the size of the micro-channel on heat transfer enhancement have also been investigated. Design/methodology/approach The authors use the flow of a water-Al2O3 nanofluid and a single-phase approach. The equations are solved using the commercial code Fluent Version 6.3. This code uses the finite volume approach to solve the equations subject to the boundary conditions, which govern three-dimensional conjugate convection-conduction heat transfer model. The physical domain was meshed using the code GAMBIT. The mesh used is non-uniform and was obtained by sweeping in the Z direction an X-Y surface meshed with QUAD/pave type cells. Findings The results clearly show that the inclusion of nanoparticles produces a considerable increase in the heat transfer. Also, the temperature-dependent models present higher values of local and average Nusselt number than in the case of constant thermo-physical properties, and an increase in the channel dimensions leads to an important increase in heat transfer. Consequently, we ensure a better cooling of the base of the micro-channel heat sink. Research limitations/implications Because of the settling of nanoparticles, the research results may not be generalized to high values of solids volume fraction. Therefore, researchers are encouraged to find other techniques of cooling when the heat loads exceed values that cannot be dissipated using nanonofluids. Practical implications The paper includes implications for the miniaturization of electronic devices such as in microprocessors or those used in robotics and automotive industries, where continually increasing power densities are requiring more innovative techniques of heat dissipation from a small area and small coolant requirements. Originality/value This paper shows the implementation of variable property nanofluid models in CFD commercial codes.

Thermal performance and structure optimization for slotted microchannel heat sink

Aiming at developing the structures of microchannel heat sinks for chip cooling techniques, three types of slotted microchannel heat sinks with metal-foam inlet header were numerically studied on flow and heat transfer characteristics, which were respectively Rectangular Parallel-Slot Microchannel Heat Sink (RP-Slot MCHS), Rectangular Stagger-Slot Microchannel Heat Sink (RS-Slot MCHS), and Trapezoidal Stagger-Slot Microchannel Heat Sink (TS-Slot MCHS). The rectangular slot width d and the base angle α of trapezoidal slot was studied respectively ranging from 0.2 to 1mm and 66° to 87°. Numerical results show that the heat transfer performance in microchannel heat sink could be improved after slot structure was set up. Besides, the value of rectangular slot size and trapezoidal base angle has great effects on flow and heat transfer characteristics. RS-Slot MCHS generally holds slightly better cooling capacity than RP-Slot MCHS under the same flow flux. In terms of hear transfer capability and thermal performance with constant pumping power, TS-Slot MCHS turns out the best, which holds both the lowest pressure drop and best heat transfer characteristic. Finally, combined with field coordination analysis, RS-Slot MCHS and TS-Slot MCHS are two kinds of structures with potential development for improving the performance of microchannel heat sink.

Experimental investigation for sequential triangular double-layered microchannel heat sink with nanofluids

This study examined new innovative design of aluminum rectangular and triangular double-layered microchannel heat sink (RDLMCHS) and (TDLMCHS), respectively, using Al2O3–H2O and SiO2–H2O nanofluids. A series of experimental runs for different channel dimensions, different nanoparticles concentrations and types and several pumping powers showed excellent hydrothermal performance for DLMCHS over traditional single-layer (SLMCHS). The results showed that the sequential TDLMCHS provided a 27.4% reduction in the wall temperature comparing with RDLMCHS and has better temperature uniformity across the channel length with less than 2°C. Sequential TDLMCHS provided 16.6% total thermal resistance lesser than the RDLMCHS at low pumping power and the given geometry parameters. Pressure drop observation showed no significant differences between the two designs. In addition, larger number of channels and smaller fin thickness referred less thermal resistance rather than only increasing the pumping power. Higher nanoparticle concentration showed better thermal stability for both nanofluids than pure water. The Al2O3–H2O nanofluid (0.9vol.%) showed best performance with the temperature difference of 1.6°C and lowest thermal resistance of 0.13°C/W·m2.

The characteristics of convective heat transfer in microchannel heat sinks using Al2O3 and TiO2 nanofluids

The present study aims to provide an overall analysis about nanofluids flowing through microchannel heat sinks. Al2O3 and TiO2 nanofluids based on deionized water with particle volume fractions of 0%, 0.1%, 0.5%, 1.0% were prepared by the two-step dispersion method. Nonionic surfactant polyvinylpyrrolidone (PVP) was added into the nanofluids to avoid particle aggregation and enhance stability. An ImageIR 3350 was used to get the temperature distribution on the substrate of microchannel heat sinks. The results reveal that the thermal conductivity and dynamic viscosity of Al2O3 and TiO2 nanofluids are both improved with the increase of particle volume fraction. Compared with a rectangular microchannel heat sink, the performance of heat transfer in fan-shaped microchannel heat sink is more strengthened using Al2O3 nanofluids. The thermal motion of nanoparticles could promote the interruption of laminar flow and intensify the heat transfer between fluids and channel walls. The cyclical change with a fixed period on equivalent diameter could also help destroy the boundary layers.

Heat transfer and entropy generation in a microchannel with longitudinal vortex generators using nanofluids

Conjugated heat transfer and hydraulic performance for nanofluid flow in a rectangular microchannel heat sink with LVGs (longitudinal vortex generators) are numerically investigated using at different ranges of Reynolds numbers. Three-dimensional simulations are performed on a microchannel heated by a constant heat flux with a hydraulic diameter of 160 μm and six pairs of LVGs using a single-phase model. Coolants are selected to be nanofluids containing low volume-fractions (0.5%–3.0%) of Al2O3 or CuO nanoparticles with different particle sizes dispersed in pure water. The employed model is validated and compared by published experimental, and single-phase and two-phase numerical data for various geometries and nanoparticle sizes. The results demonstrate that heat transfer is enhanced by 2.29–30.63% and 9.44%–53.06% for water-Al2O3 and water-CuO nanofluids, respectively, in expense of increasing the pressure drop with respect to pure-water by 3.49%–16.85% and 6.5%–17.70%, respectively. We have also observed that the overall efficiency is improved by 2.55%–29.05% and 9.78%–50.64% for water-Al2O3 and water-CuO nanofluids, respectively. The results are also analyzed in terms of entropy generation, leading to the important conclusion that using nanofluids as the working fluid could reduce the irreversibility level in the rectangular microchannel heat sinks with LVGs. No exterma (minimums) is found for total entropy generation for the ranges of parameters studied.

Designing a microchannel heat sink with colloidal coolants through the entropy generation minimisation criterion and global optimisation algorithms

This article presents an alternative approach for the design of a heat sink as a solution of the thermal management problem in microelectronic components. The design was carried out based on the entropy generation minimisation criterion and it was optimised through three different non-conventional methods, such as: Unified Particle Swarm Optimisation, Spiral Optimisation and Cuckoo Search. A rectangular microchannel heat sink manufactured from a High Thermal Conductive Graphite was considered and a colloid of H2O–TiO2 was used as working fluid. The performance of this nanofluid was compared against traditional fluids like air and ammonia gas. Also, nanoparticles were considered and studied at different volume fractions. Moreover, the performance solving the thermal problem was compared for the implemented global optimisation techniques. It was noticed that nanofluids represent a good alternative for designs with lower volume flow rates, requiring a lower nanoparticle volume fraction. Furthermore, the Cuckoo Search algorithm was more accurate and faster than the other two methods.

Optimization of nanofluid-cooled microchannel heat sink

The optimization of a nanofluid-cooled rectangular microchannel heat sink is reported. Two nanofluids with volume fraction of 1 %, 3 %, 5 %, 7 % and 9 % are employed to enhance the overall performance of the system. An optimization scheme is applied consisting of a systematic thermal resistance model as an analysis method and the elitist non-dominated sorting genetic algorithm (NSGA-II). The optimized results showed that the increase in the particles volume fraction results in a decrease in the total thermal resistance and an increase in the pumping power. For volume fractions of 1 %, 3 %, 5 %, 7 % and 9 %, the thermal resistances were 0.072, 0.07151, 0.07075, 0.07024 and 0.070 [oK W-1] for the SiC-H2O while, they were 0.0705, 0.0697, 0.0694, 0.0692 and 0.069 [oK W-1] for the TiO2-H2O. The associated pumping power were 0.633, 0.638, 0.704, 0.757 and 0.807 [W] for the SiC-H2O while they were 0.645, 0.675, 0.724, 0.755 and 0.798 [W] for the TiO2-H2O. In addition, for the same operating conditions, the nanofluid-cooled system outperformed the water-cooled system in terms of the total thermal resistance (0.069 and 0.11 for nanofluid-cooled and water-cooled systems, respectively). Based on the results observed in this study, nanofluids should be considered as the future coolant for electronic devices cooling systems.

Influence of moist air in copper heat sinks: Analysis through the entropy generation minimization criterion

Many factors affect heat transfer during the cooling of modern electronic devices. Today, knowledge accrues from modeling, simu-lation, and experimentation. This allows predicting and calculating features of heat transfer phenomena, to some extent. Examples include the amount of heat generated and removed, the required physical properties of the working fluid, and the required material properties of the heat sink, among other parameters. This article describes some simulation results of using air with a given relative humidity (10 %, 50 % and 90 %). Its influence on the heat transfer process was also analyzed. Results show a measurable effect of using humidified air instead of dry air and copper as a bulk material. The heat transfer rate increased about 20 % when using air with 90 % relative humidity passing through a rectangular microchannel heat sink made of copper.

Experimental Investigation of Heat Transfer in Coated Microchannels for MEMS Applications

The microchannel cooling technique appears to be a viable solution to high heat rejection requirements of today’s high-power electronic devices. The thermal design of the small electronics cooling devices is a key issue that needs to be optimized in order to keep the system temperatures at certain levels. Thus the need of microchannel became vital. This present work investigates the experimental work conducted in a coated rectangular microchannel heat sink of hydraulic diameter of 0.763 mm for a heat input of 250 to 1020 Watt with water to study the heat transfer characteristics with two types of header arrangement such as rectangular header and trapezoidal header. The header plays a significant role in distributing the water in to the channels. The uniform distribution of water leads to uniform heat transfer in microchannels. From the experimental results carried with two types of header arrangements, it was found that coated rectangular microchannel with trapezoidal header gives better heat transfer characteristics for the range of heat inputs.

Hydrodynamics and heat transfer prior to onset of nucleate boiling in a rectangular microchannel heat sink

The conjugate heat transfer of flow boiling in a rectangular microchannel heat sink (MCHS) was modelled numerically to investigate the hydrodynamics and thermal responses of flow prior to the onset of nucleate boiling (ONB). Local hydrodynamics and thermal conditions leading to ONB are analysed numerically for different heat flux. The flow patterns of different modes of microconvection and mixed convective flows including the circulating flow, wavy flow and seeping flow were demonstrated and discussed. The numerical study proposes the mechanism leading to the first bubble nucleation which cover the initiation of fluid instability until the ONB. This work provides better understanding of the superheat induced flow instability and the progressive fluid convection under transient heating.

Performance optimization of a microchannel heat sink using the Improved Strength Pareto Evolutionary Algorithm (SPEA2)

In this paper, a feasible optimization scheme for rectangular microchannel heat sinks, which incorporates the thermal resistance model and the Improved Strength Pareto Evolutionary Algorithm (SPEA2), is reported. An alternative coolant, namely, ammonia gas, is used to improve the overall thermal and hydrodynamic performances of the considered system. Results from the optimization showed significant reduction in the total thermal resistance compared to the conventional air-cooled systems up to 35% for the same allowable pumping power. The SPEA2 exhibited excellent performance when it was compared to another multiobjective algorithm, NSGA2. The results reported in this study open the door for the incorporation of some other algorithms, which have not been used in the optimization of microchannel heat sinks. Finally, the outcome of this paper predicts a promising future for the usage of ammonia gas in the area of electronics cooling.

Numerical Analysis of Constructal Water-Cooled Microchannel Heat Sinks with Multiple Bifurcations in the Entrance Region

The Constructal Theory is applied to obtain better thermal performance from a type of microchannel heat sink. Based on a smooth, straight, rectangular microchannel heat sink (Case 1), three different configurations of constructal multiple bifurcation are designed for the entrance region of each microchannel. These types are one bifurcation (Case 2), two bifurcations with the second placed in the front part (Case 3), and two bifurcations with the second bifurcation placed in the front part (Case 4). The corresponding laminar flow and heat transfer fields are investigated numerically by means of computational fluid dynamics. The effects of the bifurcation number and length ratio on pressure drop and overall thermal resistance are observed. The overall thermal resistance for the four microchannel heat sinks is compared when subjected to pumping power. It is found that designing one or two bifurcations (Cases 2, 3, 4) in the entrance region can improve thermal performance effectively. It is also recommended to place the second bifurcation in the back part (Case 4) of the microchannel heat sinks to obtain good overall thermal performance by proper design of the bifurcation position and number of channels.

Optimization of a Rectangular Microchannel Heat Sink Using Entropy Generation Minimization (EGM) and Genetic Algorithm (GA)

In this paper, the entropy generation minimization (EGM) is treated as a single-objective function and its minimization was the goal of the current study. Genetic algorithm (GA) is invoked to perform the minimization, and it showed an extraordinary performance. The effective combination between EGM and GA presented in this paper is used to examine the overall performance of a rectangular microchannel heat sink under the conditions of laminar and turbulent flows which has never been reported before. For volumetric flow rate values of 0.005 and 0.007 and 0.009 m3/s, the entropy generation rate reached its optimal minimum values after 12, 8 and 13 generation, respectively. In addition, significant reduction in the total thermal resistance is observed in the turbulent flow region. Finally, a parametric study is conducted in which the effects of the channel aspect ratio, fin spacing ratio, Reynolds number and different materials on the overall performance of the system is investigated and showed some promising results.

Experimental investigation of CuO–water nanofluid flow and heat transfer inside a microchannel heat sink

This paper presents an experimental investigation of the hydraulic and thermal fields of a 29 nm CuO nanoparticle–water nanofluid with various volume fractions, 0.24%, 1.03% and 4.5% flowing inside a rectangular microchannel heat sink under both laminar and turbulent conditions. The isothermal and heated tests are conducted for Reynolds number up to ≈5000 and to ≈2500, respectively. For a given fluid flow rate experimental results show an increase of the pressure drop and the friction factor with respect to water. This increase can be as high as 70%, 25%, and 0–30%, respectively, for the 4.5%, 1.03%, and 0.24% particle volume fractions. Although the laminar-to-turbulent transition was observed at nearly the same critical Reynolds number Rec ≈ 1000 for water and the tested nanofluids, this value of Rec is clearly lower than that corresponding to a smooth surface microchannel. Results show a slight heat transfer enhancement with respect to water for nanofluids with low particle volume fractions, 0.24% and 1.03%, while for the 4.5% fraction a clear decrease of heat transfer was found. In general, the nanofluid overall energetic performance, defined by the heat transferred/pumping power ratio, remains lower than that of water for a given Reynolds number. This ratio decreases with an augmentation of the particle volume fraction.