Hydrodynamic Characteristics of Micro Heat Sinks With In-Line and Staggered Arrangements of Cylindrical Micro Pin Fins

2017 ◽  
Author(s):  
Ali Mohammadi ◽  
Ali Koşar
Keyword(s):  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Heat Sinks ◽  
Hydrodynamic Characteristics ◽  
Bottom Surface ◽  
Ansys Fluent ◽  
Phase Study ◽  
Pin Fins ◽  
Interacting Surfaces ◽  
Micro Pin Fins

This study compares the hydraulic performance of rectangular micro heat sinks (MHS) with different in-line and staggered arrangements of micro pin fins (MPF). With fixed MHS dimensions of 50 × 1.5 × 0.1 mm3 (1 × w × h), the height (H) and diameter (D) of MPFs are both set to be 0.1 mm which corresponds to a fixed H/D ratio of 1 in all cases. Four in-line and four staggered arrangements of MPFs with alternative horizontal and vertical pitch ratios (SL/D and ST/D) of 1.5 and 3 are considered. Streamline profiles are used to illustrate the flow patterns and wake regions. Using ANSYS FLUENT v.14.5 for this single phase study, the simulations are done at five Reynolds numbers of 20, 40, 80, 120 and 150, ensuring the flow remains in the laminar flow regime. Considering water as the coolant, a constant heat flux of 30 W/cm2 is applied through the bottom surface of the MHS and the MPFs liquid interacting surfaces. The results show a great dependency of the evaluating parameters on the arrangement type, geometrical specification and Reynolds numbers. For pressure drop, clear comparison could be made regarding each of the geometrical specifications. However, the trends with friction factor depend on geometrical specification and Reynolds number at the same time.

Hydoroil-Based Micro Pin Fin Heat Sink

2006 ◽  
Author(s):  
Ali Kosar ◽  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Sink ◽  
Hydraulic Performance ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Pin Fins ◽  
Micro Pin Fins

An experimental study on thermal-hydraulic performance of de-ionized water over a bank of shrouded NACA 66-021 hydrofoil micro pin fins with wetted perimeter of 1030-μm and chord thickness of 100 μm has been performed. Average heat transfer coefficients have been obtained over effective heat fluxes ranging from 4.0 to 308 W/cm2 and mass velocities from 134 to 6600 kg/m2s. The experimental data is reduced to the Nusselt numbers, Reynolds numbers, total thermal resistances, and friction factors in order to determine the thermal-hydraulic performance of the heat sink. It has been found that prodigious hydrodynamic improvement can be obtained with the hydrofoil-based micro pin fin heat sink compared to the circular pin fin device. Fluid flow over pin fin heat sinks comprised from hydrofoils yielded radically lower thermal resistances than circular pin fins for a similar pressure drop.

Hydrodynamic and Thermal Characteristics of the Flow Inside a Rectangular Microchannel With Different Cylindrical Micro Pin Fins

2016 ◽  
Author(s):  
Ali Mohammadi ◽  
Ali Koşar
Keyword(s):  
Computational Study ◽  
Thermal Characteristics ◽  
3D Models ◽  
Operating Conditions ◽  
Bottom Surface ◽  
Liquid Form ◽  
Rectangular Microchannel ◽  
Pin Fin ◽  
Pin Fins ◽  
Micro Pin Fins

This article presents a computational study to investigate the hydrodynamic and thermal characteristics of the flow inside a rectangular microchannel with the dimensions of 5000 × 1500 × 100 μm3 (l × w × h’) with different inline arrangements of cylindrical micro pin fins. A parametric study is performed on the effect of different geometrical specifications of micro pin fins on the wake-pin fin interaction. Three values of (50, 100 and 200 μm) are considered for the pin fin diameters (D) while the overall height (H) of the system is set to be constant (100 μm). For the first two cases, two longitudinal and vertical pitch ratios (SL/D and ST/D) of 1.5 and 3 are considered while for H/D ratio of 0.5, only ST/D ratio of 1.5 and SL/D ratios of 1.5 and 3 are considered. As a result, a total number of ten different geometries are analyzed in five different Reynolds numbers of 20, 40, 80, 120 and 160. A constant heat flux is applied through the bottom surface of the microchannel as well as the micro pin fins surfaces. All other surfaces are assumed to be thermally isolated. Thermodynamic properties of water are set to vary with temperature and it is assumed that the working flow remains in the liquid form in all operating conditions. ANSYS commercial package v14.5 with an academic license is utilized to generate the 3D models, applying the appropriate grid networks and simulating the flow fields for each configuration. Results show major dependencies of pressure drops, friction factors, Nusselt numbers and Thermal Performance Index values on ST/D ratio and Reynolds number while minor dependencies of these parameters on SL/D and H/D ratios are observed.

Numerical Study of the Endwall Effects on Water Single-Phase Pressure Drop Across a Circular Micro-Pin-Fin Array

2011 ◽  
Author(s):  
Jonathan R. Mita ◽  
Weilin Qu ◽  
Frank E. Pfefferkorn
Keyword(s):  
Pressure Drop ◽  
Single Phase ◽  
Numerical Study ◽  
Circular Cross Section ◽  
Reynolds Numbers ◽  
Pin Fin ◽  
Pin Fins ◽  
Micron Diameter ◽  
Micro Pin Fins ◽  
Pin Fin Array

This paper presents a numerical study of pressure drop associated with water liquid single-phase flow across an array of staggered micro-pin-fins having circular cross-section. The numerical simulations were validated against previously obtained experimental results using an array of staggered circular micro-pin-fins having the following dimensions: 180 micron diameter and 683 micron height. The longitudinal pitch and transverse pitch of the micro-pin-fins are equal to 399 microns. The effects of endwalls on pressure drop characteristics were then explored numerically. Six different micro-pin-fin height to diameter ratios were studied with seven different Reynolds numbers. All simulations were performed at room temperature (23°C). It was seen that for any given Reynolds number, as the pin height to diameter ratio increased, the pressure drop and resulting non-dimensional friction factor decreased.

Single-Phase Heat Transfer in Mems-Based Pin Fin Heat Sink

2005 ◽  
Author(s):  
Ali Kosar ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Pin Fins ◽  
Micro Pin Fins

An experimental study has been performed on single-phase heat transfer of de-ionized water over a bank of shrouded micro pin fins 243-μm long with hydraulic diameter of 99.5-μm. Heat transfer coefficients and Nusselt numbers have been obtained over effective heat fluxes ranging from 3.8 to 167 W/cm2 and Reynolds numbers from 14 to 112. The results were used to derive the Nusselt numbers and total thermal resistances. It has been found that endwalls effects are significant at low Reynolds numbers and diminish at higher Reynolds numbers.

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

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Ali Mohammadi ◽  
Ali Koşar
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Design Parameters ◽  
Interaction Patterns ◽  
Wake Region ◽  
Pin Fins ◽  
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.

Hydrodynamic Characteristics of Crossflow Over MEMS-Based Pillars

2008 ◽  
Author(s):  
Ali Kos¸ar ◽  
Brandon R. Schneider ◽  
Yoav Peles
Keyword(s):  
Pressure Drop ◽  
Dna Analysis ◽  
Microelectromechanical Systems ◽  
Hydrodynamic Characteristics ◽  
Hydrodynamic Drag ◽  
Heat Engines ◽  
Pin Fins ◽  
Micro Pin Fins ◽  
Characteristic Pressure ◽  
Careful Design

Great advancements are currently being made in diverse technological disciplines due to the prodigious advancement in microfluidic systems. Careful design of mass transfer has proven to be essential to the successful realization of numerous microelectromechanical systems, (MEMS) such as heat exchangers for IC chip cooling, micro rockets, micro combustors, micro chemical reactors, micro heat engines, and bioMEMS devices. Micro pin fins pillars are often placed in these systems to enhance chemical reactions, heat transfer, DNA sieving, DNA analysis, and mixing. Since objects in crossflow perturb the flow field and generate excess hydrodynamic drag, the pressure drop required to propel the flow in the systems elevates. It is therefore of prime importance to develop parametric knowledge and correlations of the characteristic pressure drop and friction factor in crossflow over micro scale pin fins under various hydrodynamic conditions.

CFD Analysis of an Air-Cooled Planar Heat Sink With Cross-Connected Alternating Converging-Diverging Channels

2015 ◽  
Author(s):  
Omer Bugra Kanargi ◽  
Christopher Yap ◽  
Poh Seng Lee
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Sink ◽  
Thermal Boundary Layer ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Heat Sinks ◽  
Ansys Fluent ◽  
Diverging Channel ◽  
The Cross

In this study, the thermal and hydraulic performances of an air-cooled planar heat sink with cross-connected alternating converging-diverging channels were investigated. The commercial CFD solver ANSYS Fluent was used to solve the fluid flow and heat transfer from the fins to the air flow for a range of converging-diverging channel expansion ratios, heat generation rates and Reynolds numbers. The converging and diverging channel sections create high and low pressure zones, respectively, in the flow domain and this pressure difference induces secondary flows from the converging channel sections to the diverging channel sections through the cross connections. The observed heat transfer enhancement results from two different phenomena: (1) thermal boundary layer disruption and re-initialization at the cross connections and (2) fluid mixing; where the former reduces the convection resistance in the vicinity of the fin walls by reducing the thermal boundary layer thickness, while the latter allows a more uniform temperature build-up of air in the streamwise direction. Despite the fact that the pressure drop penalty increases due to flow restriction compared to the straight channel heat sinks, it is possible to enhance the Nusselt number for up to 100% with the proposed heat sink design.

Single-Phase Capillary Effects in Rectangular Microchannels Heat Sinks

2007 ◽  
Author(s):  
Carlos A. Rubio-Jime´nez ◽  
Jesu´s Garci´a-Gonza´lez ◽  
Abel Herna´ndez-Guerrero ◽  
Daniela Popescu
Keyword(s):  
Fluid Flow ◽  
Rectangular Cross Section ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Heat Sinks ◽  
High Tech ◽  
Cooling Fluid ◽  
Capillary Effects ◽  
Channel Water ◽  
Necessary And Sufficient

In this work a steady state numerical analysis of the capillary effects in channels of a microscopic scale with rectangular cross section is presented. The diameter range under analysis falls on the microchannels classification. The velocities of the fluid flow satisfy the condition We<<Re, necessary and sufficient condition to guarantee that the capillary effects are present in the fluid flow in the channel. Water is used as the cooling fluid. A constant heat flux is applied at the heat sink bottom wall with a rating typical of the generated heat flow in current electronics high-tech devices. The results of thermal resistance are compared with the experimental results of Tuckerman, and the friction coefficient is compared with Peng and Peterson experiments, showing a good approximation when the capillary effects are considered in the numerical solution at lower Reynolds numbers.

Computational Fluid Dynamics Based Investigation of the Performance of Hybrid Heat Sinks

2021 ◽  
Author(s):  
Anas Alkhazaleh ◽  
Mohamed Younes El-Saghir Selim ◽  
Fadi Alnaimat ◽  
Bobby Mathew
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Heat Sinks ◽  
Geometrical Parameters ◽  
Microchannel Heat Sink ◽  
Liquid Cooling ◽  
Pin Fins

Abstract This article discusses the mathematical modeling of a straight microchannel heat sink, embedded with pin-fins, for purposes of liquid cooling of microelectronic chips. The influence of three different geometrical parameters, pin fins’ diameter, pitch, and hydraulic diameter, on the heat sinks performance is studied. The studies are performed for Reynolds numbers varying from 250 to 2000, and the results are quantified based on thermal resistance and pressure drop. The heat sinks embedded with pin fins have better performance in terms of thermal resistance but at the same time have higher pressure drop. Studies revealed that increasing the pin fins’ diameter, pitch, and hydraulic diameter have an influence on the thermal resistance; the thermal resistance is found to be decreasing with increasing these parameters for the same Reynolds number. For the cases studied, the reduction in thermal resistance of straight microchannels embedded with pin fins varied from 18% to 60% compared with that of traditional straight microchannels for different heat sinks configurations and Reynolds number. On the other hand, the pressure drop is increasing with an increase in pin fins’ diameter and pitch, while it is found to be decreasing with increasing the hydraulic diameter.

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