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

2016 ◽  
Vol 78 (10-2) ◽  
Author(s):  
Nik Ahmad Faiz Nik Mazlam ◽  
Normah Mohd-Ghazali ◽  
Thierry Mare ◽  
Patrice Estelle ◽  
Salma Halelfadl
Keyword(s):  
Thermal Resistance ◽  
Heat Sink ◽  
Operating Temperature ◽  
Heat Removal ◽  
Hydrodynamic Performance ◽  
Spherical Particles ◽  
Microchannel Heat Sink ◽  
Pumping Power ◽  
Rectangular Microchannel ◽  
Aspect Ratios

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.  

scholarly journals Optimization of nanofluid-cooled microchannel heat sink

2016 ◽  
Vol 20 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Ahmed Adham ◽  
Normah Mohd-Ghazali ◽  
Robiah Ahmad
Keyword(s):  
Thermal Resistance ◽  
Heat Sink ◽  
Volume Fraction ◽  
Operating Conditions ◽  
Microchannel Heat Sink ◽  
Pumping Power ◽  
Nsga Ii ◽  
Rectangular Microchannel ◽  
Total Thermal Resistance ◽  
Overall Performance

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.

scholarly journals Constructal Optimization of Rectangular Microchannel Heat Sink with Porous Medium for Entropy Generation Minimization

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1528
Author(s):  
Wenlong Li ◽  
Zhihui Xie ◽  
Kun Xi ◽  
Shaojun Xia ◽  
Yanlin Ge
Keyword(s):  
Heat Flux ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Heat Sink ◽  
Width Ratio ◽  
Microchannel Heat Sink ◽  
Rectangular Microchannel ◽  
Entropy Generation Minimization ◽  
Aspect Ratios ◽  
Length Width

A model of rectangular microchannel heat sink (MCHS) with porous medium (PM) is developed. Aspect ratio of heat sink (HS) cell and length-width ratio of HS are optimized by numerical simulation method for entropy generation minimization (EGM) according to constructal theory. The effects of inlet Reynolds number (Re) of coolant, heat flux on bottom, porosity and volume proportion of PM on dimensionless entropy generation rate (DEGR) are analyzed. From the results, there are optimal aspect ratios to minimize DEGR. Given the initial condition, DEGR is 33.10% lower than its initial value after the aspect ratio is optimized. With the increase of Re, the optimal aspect ratio declines, and the minimum DEGR drops as well. DEGR gets larger and the optimal aspect ratio remains constant with the increasing of heat flux on bottom. For the different volume proportion of PM, the optimal aspect ratios are diverse, but the minimum DEGR almost stays unchanged. The twice minimized DEGR, which results from aspect ratio and length-width ratio optimized simultaneously, is 10.70% lower than the once minimized DEGR. For a rectangular bottom, a lower DEGR can be reached by choosing the proper direction of fluid flow.

PERFORMANCE OF A MULTI-STACK MICROCHANNEL HEAT SINK

2016 ◽  
Vol 78 (10-2) ◽  
Author(s):  
Nik Mohamad Sharif ◽  
Normah Mohd Ghazali
Keyword(s):  
Thermal Resistance ◽  
Heat Sink ◽  
Cooling System ◽  
Heat Fluxes ◽  
Width Ratio ◽  
Optimum Number ◽  
Microchannel Heat Sink ◽  
Objective Functions ◽  
Pumping Power ◽  
Total Thermal Resistance

The usage of a very large scale integrated circuits generate high heat fluxes and require an effective cooling system. A microchannel heat sink (MCHS) is one of the reliable cooling systems that had been applied. In terms of performance, a MCHS can be appraised by obtaining low total thermal resistance and pumping power. However, as the total thermal resistance decreases, the pumping power will increase. A few studies have been focused on the minimization of the thermal resistance and pumping power of a multi-stack MCHS. Optimization of two objective functions which are the total thermal resistance and pumping power has been done by using genetic algorithm. It is demonstrated that both objective functions can be minimized by optimizing two design variables which are the channel aspect ratio, , and wall width ratio, . It was found that the usage of a stacked configuration for the MCHS is able to reduce the total thermal resistance. From the optimization, it was found that the optimum number of stacks that can be implemented is three. With the three-stack configuration, the total thermal resistance found is 0.1180 K/W which is 21.8% less compared to the single-stack MCHS. However, the pumping power needed for the three-stack MCHS is increased by 0.17 % compared to single-stack which is 0.7535 W.

Numerical Investigation of Heat Transfer Characteristics of a Novel Wavy-Tapered Microchannel Heat Sink

2016 ◽  
Author(s):  
Ahmed Eltaweel ◽  
Abdulla Baobeid ◽  
Brian Tompkins ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Heat Sink ◽  
Substrate Surface ◽  
Microchannel Heat Sink ◽  
Aspect Ratios ◽  
Wavy Channels ◽  
Channel Configuration

In the present study, a multi-variable comparative study of the effect of microchannel heat sink configurations on their thermal performance is conducted by numerically simulating three-dimensional fluid flow and heat transfer in multiple microchannel heat sink configurations. Thermal analysis is performed to investigate a novel wavy-tapered channel configuration of microchannel heat sinks with directionally alternating coolant flow for high-end electronics cooling. Simulations were conducted at different tapering and aspect ratios, focusing on how effectively previously proven geometric enhancements combine with one another in novel ways. Results confirmed the superiority of wavy channels over straight channels due to the development of the secondary flow (Dean Vortices), which enhance the advection mixing and consequently the overall heat sink thermal performance. Moreover, width-tapering of the wavy channel showed improved channel performance in terms of thermal resistance compared to untapered wavy channels. Almost 10% improvement in thermal resistance is obtained with width tapering. Also, the thermal performance showed a strong dependency on channel aspect ratio. Overall performance suggests that optimum tapering and aspect ratio conditions exist. The numerical investigations are then extended to novel heat sink design includes wavy tapered microchannels with directionally alternating flow to improve heat sink thermal performance. A 15% reduction in thermal resistance and highly improved substrate surface temperature distribution uniformity are obtained using alternating flow compared to corresponding parallel flow channels.

Microchannel Heat Sink for Thermal Management of Concentrated Photovoltaic Cells

2021 ◽  
Author(s):  
Dinumol Varghese ◽  
Ahmed Sefelnasr ◽  
Mohsen Sherif ◽  
Fadi Alnaimat ◽  
Bobby Mathew
Keyword(s):  
Reynolds Number ◽  
Thermal Resistance ◽  
Thermal Management ◽  
Heat Sink ◽  
Stokes Equations ◽  
Photovoltaic Cells ◽  
Navier Stokes ◽  
Microchannel Heat Sink ◽  
Pumping Power ◽  
Energy Equations

Abstract This article conceptualizes a single-phase microchannel heat sink for thermal management of concentrated photovoltaic cells; details of the model-based parametric study that is carried out on the heat sink is also detailed in this article. The heat sink consists of multiple serpentine microchannels. The mathematical model consists of continuity equation, Navier-Stokes equations and energy equations. Fluent module of Ansys Workbench is used for solving the model. The performance of the device is quantified in terms two metrics such as thermal resistance and pumping power. Studies are done for Reynolds number ranging from 100 to 1250. It is observed that increase in Reynolds number decreases the thermal resistance while increasing the pumping power irrespective of the geometric parameters of the heat sink. Decrease in hydraulic diameter of the microchannel reduces the thermal resistance while increasing the pumping power. Increase in the length segment of the serpentine microchannel increases and decreases the thermal resistance and pumping power, respectively. With increase in the offset width of the serpentine microchannel the thermal resistance and pumping power decreases and increases, respectively.

Thermal Performance and Pressure Drop of Galinstan-Based Microchannel Heat-Sink for High Heat-Flux Thermal Management

2015 ◽  
Author(s):  
Yoshikazu Hayashi ◽  
Navid Saneie ◽  
Yoon Jo Kim ◽  
Jong-Hoon Kim
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Specific Heat ◽  
Thermal Management ◽  
Heat Sink ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Pumping Power

We numerically investigated a novel galinstan-based microfluidic heat-sink. Galinstan is an eutectic alloys of gallium, indium, and tin. The thermal conductivity of galinstan is ∼27 times that of water, while the dynamic viscosity is only twice of water. Thus, heat transfer coefficient can be remarkably enhanced with a small penalty of pumping power. However, the specific heat of galinstan is significantly lower than that of water, which will inevitably undermine the cooling capability by increasing fluid outlet temperature (i.e., increase of caloric thermal management) and/or flow rate. As an alternative, therefore, galinstan/water heterogeneous mixture was proposed as a working fluid and the cooling performance was numerically explored with varying volume composition of galinstan. Effective medium theory for heterogeneous medium was used to evaluate the thermal conductivity of the mixture. The viscosity change with respect to the volume composition was also predicted considering both the viscosity of dispersed phase and interaction between the droplets. Classical models were used for the mixture density and specific heat calculations. Heat transfer and pressure drop characteristics of laminar flow through a silicon microchannel heat-sink was simulated using Fluent. The length and width of the channel array are 10 mm and 9.5 mm, respectively. The cross-sectional area of each channel is 300 μm × 300 μm and the spacing between channels is 100 μm. The heat dissipation was 50 W and the pumping power was fixed at 5 mW for the comparison between the varying galinstan/water compositions. The results showed that more than 30% of the thermal resistance enhancement was attainable using the novel working fluid. Due to the compromise between the convective thermal resistance (effect of thermal conductivity) and the caloric thermal resistance (effect of viscosity and specific heat), the lowest junction temperature was marked at the galinstan composition of ∼35% by volume.

Thermodynamic Analysis of Microchannel Heat Sink With Cylindrical Ribs and Cavities

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Faraz Ahmad ◽  
Taqi Ahmad Cheema ◽  
M. Mohib Ur Rehman ◽  
Muhammad Ilyas ◽  
Cheol Woo Park
Keyword(s):  
Heat Sink ◽  
Side Wall ◽  
Second Law Of Thermodynamics ◽  
Hydrodynamic Performance ◽  
Performance Criteria ◽  
Microchannel Heat Sink ◽  
Transport Efficiency ◽  
Smooth Channel ◽  
Thermal Enhancement ◽  
Staggered Arrangement

Abstract Heat transfer improvement in microchannel heat sink (MCHS) has been a challenge, because it increases the power requirements for the fluid flow. In the present study, MCHS with different wall, geometric, and design configurations of cylindrical ribs and cavities are simulated to investigate their effect on thermal and hydrodynamic performance of MCHS using a laminar flow having Reynolds number in the range from 100 to 1000. The wall configurations include; base wall cylindrical ribs (BWCR), side wall cylindrical ribs (SWCR), and all wall cylindrical ribs (AWCR). Moreover, the geometric configurations involve different AWCR cases having rib spacings (Sfr) of 0.4 mm, 0.8 mm, 1.2 mm, and 0.4 mm staggered arrangement. Furthermore, the design configurations include; AWCR, all wall cylindrical cavities (AWCC), and all wall cylindrical ribs and cavities (AWCRC) with constant Sfr = 0.4 mm. The performance of various channels with flow disruptors is analyzed in terms of friction factor (f) and Nusselt number and then compared with smooth channel in terms of thermal enhancement factor (η). Based on the first law of thermodynamics, thermal resistance (Rth) is used to investigate the resistance of any configuration to flow of heat comparing at same pumping power. Moreover, the second law of thermodynamics is applied to quantify the rate of entropy generation (S˙gen) and transport efficiency (ηt) for MCHS. The results show that although the MCHS with all wall ribs has a lower value of η than the base wall and side wall ribs; however, it has the maximum value of  ηt and minimum value of Rth and S˙gen; thus, indicating that η is not the only performance criteria for the selection of MCHS.

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