Micro-heat Sink Research Articles

OPTIMIZATION OF MICRO HEAT SINK WITH REPETITIVE PATTERN OF OBSTACLES FOR ELECTRONIC COOLING APPLICATIONS

Micro heat sinks (MHS) are becoming integral part of microelectronics nowadays because of their ability to cool the tiny components which generate high heat flux. In this study, an electronic chip with a high heat flux of 100 W/cm<sup>2</sup> is cooled with the help of an MHS device which has repetitive patterns of obstacles of various shapes in the flow of cooling medium. Numerical modelling of all MHSs were performed using a computational fluid dynamics (CFD) solver and the pattern, which gives better thermohydraulic performance, was selected for optimization. A parametric study was performed with various obstacle sizes, distances between obstacles, and flow rates of cooling medium for maximum temperature of chip and pressure drop. Regression analysis was carried out with response surface method (RSM) between these three design variables and two objective functions, viz. thermal resistance (R<sub>th</sub>) and pumping power (P<sub>p</sub>). A multi-objective optimization of the MHS was performed using genetic algorithm (GA) and Pareto-optimal solutions were obtained. An optimal design was fabricated and the cooling experiment was carried out under optimal flow conditions. The repetitive pattern of obstacles increases the conjugate heat transfer area and helps in improving thermal performance.

Numerical evaluation of doubly clamped self-adaptive fins acting as vortex generators inside micro heat sinks (MHS)

The continuous increase in the power density of integrated circuits (ICs) has placed thermal management as a key focus for the ICT community. Current liquid cooling systems are usually not optimized for the real operating conditions of advanced electronics, which have heat loads that can vary in time and space. Hence, conventional cooling devices lead to non-uniform temperature patterns at the package level and overcooled systems. This work proposes the use of thermally adaptive actuators, based on doubly clamped fins able to change its shape with temperature, to improve the performance of micro heat sinks with an optimized adaptation to temporal and spatially variable thermal parameters. The effect of this thermally responsive bistable fins on the efficiency of two different micro heat sinks (MHS), one based on microchannels and other on a matrix of microfluidic cells, is numerically evaluated. Results demonstrated a maximum heat transfer enhancement of 40% when adding the clamped-clamped fins within a microchannel and 20% when the fins were placed inside a microfluidic cell. Additionally, savings on hydraulic pumping power have been quantified between 8% and 11%.

Effect of a new type staggered pin fin configuration on flow boiling characteristics of micro-heat sinks

Effect of a new type staggered pin fin configuration on flow boiling characteristics of micro-heat sinks

Investigation into the effects of hydrophobicity on thermohydraulic characteristics and entropy generation of hybrid nanofluid with the magnetic property in a micro-heat sink under a magnetic field

The cooling of devices is a big challenge in the electronics industry, and most process units (graphical are central process units) experience defects under harsh temperature conditions, so dissipating generated heat under various working conditions should be studied seriously. This study investigates the magnetohydrodynamics of hybrid ferro-nanofluids in the presence of hydrophobic surfaces in a micro-heat sink. To scrutinize this study, a finite volume method (FVM) is applied. The ferro-nanofluid includes water as a base fluid and multiwall carbon nanotubes (MWCNTs) and Fe3O4 as nanoadditives, which are used in three concentrations (0, 1, and 3%). Other parameters such as the Reynolds number (5–120), Hartmann number (magnitude of the magnetic field from 0 to 6), and hydrophobicity of surfaces are scrutinized for their impacts on heat transfer and hydraulic variables as well as entropy generation variables. The outcomes indicate that increasing the level of hydrophobicity in surfaces leads simultaneously to improved heat exchange and reduced pressure drop. Likewise, it decreases the frictional and thermal types of entropy generation. Intensifying the magnitude of the magnetic field enhances the heat exchange as much as the pressure drop. It can also decrease the thermal term in entropy generation equations for the fluid, but increase the frictional entropy generation and adds a new term, magnetic entropy generation. Incrementing the Reynolds number improves the convection heat transfer parameters, although it intensifies the pressure drop in the length of the channel. Also, the thermal entropy generation and frictional entropy generation decrease and increase with an increasing flow rate (Reynolds number).

Numerical Analysis of the Effect of Nanoparticles Size and Shape on the Efficiency of a Micro Heatsink.

In this paper, two novel micro heat sinks (MHSs) were designed and subjected to thermal analysis using a numerical method. The fluid used was Boehmite alumina-water nanofluid (NFs) with high volume fractions (VOFs). Studies were conducted to determine the influence of a variety of nanoparticle (NP) shapes, such as platelet brick, blade, cylinder, and Os. The heatsink (HS) was made of copper, and the NFs entered it through the middle and exited via four outlets at the side of the HS. The finite element method was used to simulate the NFs flow and heat transfer in the HSs. For this purpose, Multi Physics COMSOL software was used. The maximum and middle values of HS temperature (T-MAX and T-Mid), thermal resistance (TH-R), heat transfer coefficient (h), FOM, etc., were studied for different NP shapes, and with Reynolds numbers (Re) of 300, 1000, and 1700, and VOFs of 0, 3, and 6%. One of the important outcomes of this work was the better thermal efficiency of the HS with rectangular fins. Moreover, it was discovered that a rise in Re increased the heat transfer. In general, adding NPs with high VOFs to MHSs is not appropriate in terms of heat. The Os shape was the best NP shape, and the platelet shape was the worst NP shape for high NPVOF. When NPs were added to an MHS, the temperature of the MHS dropped by an average of 2.8 or 2.19 K, depending on the form of the pin-fins contained inside the MHS (circular or square). The addition of NPs in the MHS with circular and square pin-fins enhanced the pressure drop by 13.5% and 13.3%, respectively, when the Re = 1700.

Investigation of thermal entropy generation and nanofluid flow in a new heatsink with effect of nanoparticles shape

In this paper, the entropy generation (ENT) in two novel micro heatsinks (MHSs) is investigated numerically. The HSs are two types of octagonal ones with circular and rectangular fins. Water/alumina boehmite nanofluid (NF) is used as a cooling fluid for HSs, which enters from the middle of the heatsink (HS) and exits from four side outputs. The Reynolds number (Re) varies from 300 to 1700 and the concentration of nanoparticles (NPs) changes from 0 to 6%. The shapes of NPs include platelet brick, blade, cylinder, and Oblate Spheroid (OS). A heat flux due to the operation of a microprocessor is applied to the bottom of the HSs made of copper. The finite element method is used for the simulations. The variables include pumping power (PP), ENT, ENT due to fluid friction, thermal ENT, temperature gradient contours, etc. The results of this study show that less ENT occurs in the HS with rectangular fins and less PP occurs in the HS with circular ones. Increasing the Re reduces the amount of ENT and increases the PP. The results demonstrate that the addition of NPs with high volume percentages is not suitable in terms of ENT and PP.

Micro-heat sink based on silicon nanowires formed by metal-assisted chemical etching for heat dissipation enhancement to improve performance of micro-thermoelectric generator

This work demonstrates the micro-heat sink based on silicon nanowires formed by metal-assisted chemical etching (MACE) for heat dissipation enhancement to improve the performance of the micro-thermoelectric generator (µ-TEG). The heat dissipation through the micro-heat sink is enhanced by increasing the surface-to-volume ratio, which can be achieved by combining deep reactive ion etching (RIE) and MACE. Silicon nanowires with a diameter of 100 nm and a height of 9 µm are successfully formed in both horizontal and vertical surface directions. The micro-heat sink effectiveness is 8.3 times better than that of without employing the micro-heat sink. In addition, the performance of the µ-TEG has been significantly enhanced by utilizing the micro-heat sink. The maximum output power of the µ-TEG with and without the micro-heat sink are 93 µW and 18.5 µW, respectively, under the same evaluation conditions. The findings in this work may be useful not only for the µ-TEG, but also other applications such as micro-supercapacitors, micro-sensors, chemical analysis, and biological processes, which require a large surface-to-volume ratio.

Simulation of Nanofluid Flow in a Micro-Heat Sink With Corrugated Walls Considering the Effect of Nanoparticle Diameter on Heat Sink Efficiency

In this numerical work, the cooling performance of water–Al2O3 nanofluid (NF) in a novel microchannel heat sink with wavy walls (WMH-S) is investigated. The focus of this article is on the effect of NP diameter on the cooling efficiency of the heat sink. The heat sink has four inlets and four outlets, and it receives a constant heat flux from the bottom. CATIA and CAMSOL software were used to design the model and simulate the NF flow and heat transfer, respectively. The effects of the Reynolds number (Re) and volume percentage of nanoparticles (Fi) on the outcomes are investigated. One of the most significant results of this work was the reduction in the maximum and average temperatures of the H-S by increasing both the Re and Fi. In addition, the lowest Tmax and pumping power belong to the state of low NP diameter and higher Fi. The addition of nanoparticles reduces the heat sink maximum temperature by 3.8 and 2.5% at the Reynolds numbers of 300 and 1800, respectively. Furthermore, the highest figure of merit (FOM) was approximately 1.25, which occurred at Re=1800 and Fi = 5%. Eventually, it was revealed that the best performance of the WMH-S was observed in the case of Re=807.87, volume percentage of 0.0437%, and NP diameter of 20 nm.

A Computational Fluid Dynamic Study on Efficiency of a Wavy Microchannel/Heat Sink Containing Various Nanoparticles.

In this paper, a common and widely used micro-heat sink (H/S) was redesigned and simulated using computational fluid dynamics methods. This H/S has a large number of microchannels in which the walls are wavy (wavy microchannel heat sink: WMCHS). To improve cooling, two ( and ) water-based nanofluids (NFs) were used as cooling fluids, and their performance was compared. For this purpose, studies were carried out at three Reynolds numbers (Re) of 500, 1000, and 1500 when the volume percent (φ) of the nanoparticles (NPs) was increased to 2%. The mixture two-phase (T-P) model was utilized to simulate the NFs. Results showed that using the designed WMCHS compared to the common H/S reduces the average and maximum temperatures (T-Max) up to 2 °C. Moreover, using the NF is more suitable in terms of WMCHS temperature uniformity as well as its thermal resistance compared to the NF. Increasing the φ is desirable in terms of temperature, but it enhances the pumping power (PP). Besides, the Figure of Merit (FOM) was investigated, and it was found that the value is greater at a higher volume percentage.

Nanoparticles shape effect on the efficiency of microheat sinks with tightly packed pin-fins

In this paper, the effects of the nanoparticles shape on thermal efficiency, entropy generation for the application of a /boehmite alumina nanofluid in a microheat sink (MHS) are studied. The MHS is composed of a number of microchannels, the walls of which consist of circular pin-fins attached together. A constant heat flux enters the HS from the bottom and heat it up. On the other hand, the nanofluid is responsible for cooling the HS. To study the thermal efficiency and entropy, a simulation using the control volume method has been performed in Fluent software. The effect of the NP size has been reported in this research. The simulation results showed that the average HS temperature strongly depends on the inlet fluid velocity, and an increase in the nanofluid velocity decreases it. Moreover, the addition of NPs reduces the average temperature of the HS, but its impact is smaller than that of the fluid velocity. Adding 5% of the cylindrical nanoparticles reduces the average temperature of the heatsink by 0.72 K. In addition, increasing the velocity and volume fraction of NPs decreases the thermal resistance () and increases the pumping power. The addition of 5% platelet-shaped nanoparticles increases the pumping power required by up to 80%. Using cylindrical NPs leads to the best temperature uniformity and least thermal resistance in the HS. Adding NPs decreases entropy generation. Application of blade NPs in high volume fractions, as well as brick NPs in average volume fractions, leads the highest Figure of Merit (FOM).

An investigation of the exergy and first and second laws by two-phase numerical simulation of various nanopowders with different diameter on the performance of zigzag-wall micro-heat sink (ZZW-MHS)

An investigation of the exergy and first and second laws by two-phase numerical simulation of various nanopowders with different diameter on the performance of zigzag-wall micro-heat sink (ZZW-MHS)

Evaluating the efficiency of pin–fin micro-heat sink considering different shapes of nanoparticle based on exergy analysis

Evaluating the efficiency of pin–fin micro-heat sink considering different shapes of nanoparticle based on exergy analysis

Energetic and exergetic analysis of a new circular micro-heat sink containing nanofluid: applicable for cooling electronic equipment

In this paper, an exergy analysis is performed on the nanofluid stream of alumina water in a novel heat sink. The study heat sink has a new circular design. A constant heat flux from the work of an electrical component is applied to a part of the heat sink bottom. Nanofluid enters this heat sink in the range of 0–1% with Reynolds 500–1500. The heat sink has two separate entries and is made of aluminum. The maximum and mean temperatures of the electronic device and the output nanofluid temperature of the heat sink were studied. Also out exergy, gain exergy, loss exergy and second thermodynamic law were studied. The results of this paper showed that increasing the amount of Reynolds in the flow input decreases the maximum value and the average temperature of heat sink. With the addition of nanoparticles, this has also occurred. The temperature value of the output is also lowered by increasing the Reynolds number and the volume percentage of nanoparticles. The addition of nanoparticles to the base fluid decreases the amount of exergy at the output and also reduces by around 0.3 percent the efficiency of the second thermodynamics law. By adding nanoparticles to the fluid in the heat sink, the amount of loss exergy is minimized.

Thermal-hydraulic analysis and irreversibility of the MWCNTs-SiO2/EG-H2O non-Newtonian hybrid nanofluids inside a zigzag micro-channels heat sink

This study aims to investigate a micro-heat sink (MHS) with zigzag micro-channels subjected to constant heat flux. The MWCNTs – SiO2/EG – H2O hybrid nanofluids (HNFs) is used to cool the MHS. The HNFs properties of experimental models are used for this study for the conduction heat transfer coefficient and the rheological behavior of the HNFs as a power-law non-Newtonian (PL-nN) model. The present study also investigates the effective parameters on the thermal hydraulic and irreversibility. The effect of HNF velocity (1–2 m/s), the volume concentration of HNF (0–0.5%) and the zigzag height (0 to 10 mm) on the performance metrics are investigated. In addition, the obtained results and various parameters including heat transfer improvement, pressure drop (∆P), and maximum temperature (TMax) of the MHS are investigated in each section. Eventually, the results revealed that increasing the velocity increases the heat dissipation from the MHS. On the other hand, increasing the zigzag length of the channel increases heat transfer from the MHS's surface, and thus, improves heat transfer, which is associated with an increase in the ∆P of the passing fluid. The increase in the concentration of nanoparticles and MWCNTs cause to a considerable increase in viscosity, which dramatically increases the pumping power inside the MHS. Increasing the height of zigzags increases the collision of fluid to the walls of the micro-channels and increases the total entropy generation.

Numerical study of thermal enhancement in a micro-heat sink with ribbed pin-fin arrays

Targeted at improving comprehensive hydro-thermal performance of microfluidic cooling, a new type of ribbed pin-fin arrays heat sink is proposed. To reveal the mechanism of heat transfer enhancement in inline ribbed pin-fin arrays heat sink (RPHS), the comparisons among smooth microchannel heat sink (MCHS), inline cylinder pin-fin arrays heat sink (CPHS) and RPHS with coolant of deionized water are studied by numerical simulation with laminar flow (360 ≤ Re ≤ 780). Due to the flow disturbance and destroying of boundary layer, RPHS shows the best performance in heat dissipation and uniformity of temperature distribution among the three configurations. The average Nusselt number of RPHS reaches up to 23.1 which is almost twice of CPHS and three times of MCHS when Re number is 780. Meanwhile, the non-dimensional parameter He is proposed to evaluate the temperature distribution of bottom baseplate. RPHS has the lowest total thermal resistance under the same pumping power. Moreover, the entropy generation of RPHS is lower than MCHS and CPHS under the same operating condition. Conclusively, RPHS exerts the best comprehensive hydro-thermal performance.

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.

Optimization of micro-heat sink based on theory of entropy generation in laminar forced convection

The entropy generation (S˙gen) due to fluid friction and convective heat transfer is studied en-route the microscale. The S˙gen for water-flow through a circular tube for the constant wall heat flux boundary condition is estimated. The number of tubes (N) en-route the microscale is increased by correspondingly decreasing each tube diameter, for fixed total mass flow rate and the total heat flow rate is also kept constant. There exists an optimum tube diameter (DN,opt) and a corresponding optimum natural number N (Nopt) at which, the sum-total S˙gen is minimum. Criterion for DN,opt is obtained in terms of Reynolds number and a modified Brinkman number, which shows that DN,opt depends only on the total heat flow rate. Unlike other reported studies, the fluid temperature in the denominator of the entropy generation terms is considered as local and variable. The difference in S˙gen based on reported studies and this investigation increases significantly especially towards the microscale.

Hydrodynamic and Thermal Performance of Microchannels With Different Staggered Arrangements of Cylindrical Micro Pin Fins

This study focuses on microheat sinks with different staggered arrangements of micro pin fins (MPFs). A rectangular microchannel with the dimensions of 5000 × 1500 × 100 μm3 (l′ × w′ × h′) was considered for all the configurations while different MPF diameters, height over diameter ratio (H/D), and longitudinal and transversal pitch ratios (SL/D and ST/D) were considered in different arrangements. Using the ansys fluent 14.5 commercial software, the simulations were done for different Reynolds numbers between 20 and 160. A constant heat flux of 30 W/cm2 was applied through the bottom heating section. The performances of the microheat sinks were evaluated using design parameters, namely pressure drop, friction factor, Nusselt number, and thermal-hydraulic performance index (TPI). The effect of each geometrical parameter as well as wake-pin fin interaction patterns were carefully studied using the streamline patterns and temperature profiles of each configuration. The results reveal a great dependency of trends in pressure drops and Nusselt numbers on the wake region lengths as well as the local velocity and pressure gradients. Moreover, the wake region lengths mostly contribute to the increase in obtained pressure drop and Nusselt number with Reynolds number. Although an increase in the H/D and SL/D ratios results in an increase and a decrease in pressure drop, respectively, the effect on the Nusselt number depends on other geometrical parameters and Reynolds number. A larger ST/D ratio generally results in a decrease in the pressure drop and Nusselt number. Finally, while the friction factor decreases with Reynolds number, two different trends are seen for the TPI values of configurations with the H/D ratio of 1 and 2 (D = 100 and 50 μm). While the trend in the TPIs is increasing for Reynolds numbers between 20 and 40, it reverses for higher Reynolds numbers with a steeper slope in the configurations with the ST/D ratio of 1.5.

The water based Al2O3 nanofluid flow and heat transfer in tangential microtube heat sink with multiple inlets

Micro thermal systems are convenient cooling devices for high heat flux applications. Besides, the nanofluids are used to improve the cooling capabilities. The suspended nanoparticles in the base fluid increase the thermal conductivity, fluid viscosity and fluid density but decrease the effective heat capacity. To analyze the suitability of using the nanofluids for cooling applications, the numerical simulations are made for nanofluid heat transfer and fluid flow in micro-heat sink with straight microtubes and multiple tangential inlet jets. The configurations with five inlet jets is considered and numerical simulations are based on a finite volume method. The Al2O3 water based nanofluid was used in simulations. The heat flux spread through the bottom surface of the heat sink was q=50W/cm2. Re from 15 to 100 was considered to simulate the laminar fluid flow. The analysis is based on thermal and hydrodynamic results obtained for nanofluid and compared with results obtained for water. The results are analyzed on a fixed pumping power, Re or mass flow rate basis. It is observed that the conclusions are strongly dependent on the analysis constraint. Moreover the surface temperature difference is not very much improved by using the nanofluid.

Analysis of entropy generation and convective heat transfer of Al2O3 nanofluid flow in a tangential micro heat sink

Effect of using Al2O3–water nanofluids with different volume fractions and particle diameters on generated entropy, hydrodynamic performance and heat transfer characteristics of a tangential micro-heat sink (TMHS) was numerically investigated in this research. Results indicated that considerable heat transfer enhancement is possible when using Al2O3–water nanofluids as coolant and clearly the enhancement improves with increasing particles concentration and decreasing particles size. However, using nanofluid has also induced drastic effects on the pumping power that increases with particles volume fraction and Reynolds number. Finally, it was found that generated total entropy decreases with increasing volume fraction and Reynolds number and decreasing particles size.