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.

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.

Heat Transfer and Pressure Loss Characteristics of Pin-Fins With Different Shapes in a Wide Channel

2017 ◽  
Author(s):  
Jin Xu ◽  
Jiaxu Yao ◽  
Pengfei Su ◽  
Jiang Lei ◽  
Junmei Wu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Bottom Surface ◽  
Number Range ◽  
Pin Fin ◽  
Nominal Diameter ◽  
Pin Fins

Convective heat transfer enhancement and pressure loss characteristics in a wide rectangular channel (AR = 4) with staggered pin fin arrays are investigated experimentally. Six sets of pin fins with the same nominal diameter (Dn = 8mm) are tested, including: Circular, Elliptic, Oblong, Dropform, NACA and Lancet. The relative spanwise pitch (S/Dn = 2) and streamwise pitch (X/Dn = 4.5) are kept the same for all six sets. Same nominal diameter and arrangement guarantee the same blockage area in the channel for each set. Reynolds number based on channel hydraulic diameter is from 10000 to 70000 with an increment of 10000. Using thermochromic liquid crystal (R40C20W), heat transfer coefficients on bottom surface of the channel are achieved. The obtained friction factor, Nusselt number and overall thermal performance are compared with the previously published data from other groups. The averaged Nusselt number of Circular pin fins is the largest in these six pin fins under different Re. Though Elliptic has a moderate level of Nusselt number, its pressure loss is next to the lowest. Elliptic pin fins have pretty good overall thermal performance in the tested Reynolds number range. When Re>40000, Lancet has a same level of performance as Circular, but its pressure loss is much lower than Circular. These two types are both promising alternative configuration to Circular pin fin used in gas turbine blade.

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.

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.

Heat Transfer Enhancement by Fins in the Microscale Regime

1999 ◽  
Vol 121 (4) ◽  
pp. 972-977 ◽  
Author(s):  
F.-C. Chou ◽  
J. R. Lukes ◽  
C.-L. Tien
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Size Effect ◽  
Heat Transfer Enhancement ◽  
Transfer Enhancement ◽  
Pin Fin ◽  
Pin Fins ◽  
Microscale Effect ◽  
Fin Thickness ◽  
Micro Pin Fins

The current literature contains many studies of microchannel and micro-pin-fin heat exchangers, but none of them consider the size effect on the thermal conductivity of channel and fin walls. The present study analyzes the effect of size (i.e., the microscale effect) on the microfin performance, particularly in the cryogenic regime where the microscale effect is often appreciable. The size effect reduces the thermal conductivity of microchannel and microfin walls and thus reduces the heat transfer rate. For this reason, heat transfer enhancement by microfins becomes even more important than for macroscale fins. The need for better understanding of heat transfer enhancement by microfins motivates the current study, which resolves three basic issues. First, it is found that the heat, flow choking can occur even in the case of simple plate fins or pin fins in the microscale regime, although choking is usually caused by the accommodation of a cluster of fins at the fin tip. Second, this paper shows that the use of micro-plate-fin arrays yields a higher heat transfer enhancement ratio than the use of the micro-pin-fin arrays due to the stronger reduction of thermal conductivity in micro-pin-fins. The third issue is how the size effect influences the fin thickness optimization. For convenience in design applications, an equation for the optimum fin thickness is established which generalizes the case without the size effect as first reported by Tuckerman and Pease.

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.

Pressure Drop and Heat Transfer Characteristics of Pin Fin Enhanced Microgaps in Single Phase Microfluidic Cooling

2013 ◽  
Author(s):  
Zhimin Wan ◽  
Yogendra K. Joshi
Keyword(s):  
Three Dimensional ◽  
Thermal Characteristics ◽  
Practical Interest ◽  
Electrical Performance ◽  
Signal Delay ◽  
Pin Fin ◽  
Dense Arrays ◽  
Pin Fins ◽  
3D Stacking ◽  
Semiconductor Chips

Three dimensional (3D) stacking of semiconductor chips is an emerging technology which promises improved electrical performance including improved bandwidth, reduced wire interconnection lengths, and reduced signal delay. However, due to the higher power density per unit volume of the stacking, it poses great challenge for thermal management. Inter-tier microfluidic cooling with microgaps with surface area enhancements such as pin fins can potentially achieve superior thermal performance. As such, the hydraulic and thermal characteristics of this configuration over parametric ranges of practical interest are important. Conventional correlations developed in the literature for macropin fins show large errors for dense arrays of micropins. In this work, the hydraulic and thermal characteristics of a microgap with pin fin were investigated for a large range of Reynolds number (Re) based on pin fin diameter (Dp) by numerical modeling. The effects of the pin fin dimensions including diameter, transversal spacing, longitudinal spacing, height and Re on the friction factor (f) and colburn j factor were studied. Correlations of the f and j for dense arrays of micro pins are developed based on parametric runs over 22< Re <357, pin fin diameter of 100 μm, pitch/ diameter ratios of 1.5 ∼ 2.25, and height/ diameter ratios of 1.5 ∼ 2.25. The validity of the correlations is confirmed by experiments. Lastly, a parametric optimization was done and the thermal resistance of the microgap with 150 W heat generation is reduced by 28.5% with the optimized dimensions for a given pumping power compared to an un-optimized pin fin configuration.

Thermal Resistance and Pressure Drop of Silicon Based Micro Pin Fin Heat Exchanger Under Cross Flow

2005 ◽  
Author(s):  
Ravi S. Prasher ◽  
John Dirner ◽  
Je-Young Chang ◽  
Alan Myers ◽  
David Chau ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Temperature Sensors ◽  
Test Chip ◽  
Pin Fin ◽  
Pin Fins ◽  
Silicon Based ◽  
Micro Pin Fins

We have performed a parametric study of the thermal and hydraulic performance of silicon-based micro pin fin heat exchangers with water as the fluid. Circular and square micro pin fins have been fabricated. The pin dimensions ranged from 50 μm to 150 μm. The test chip is unique because it has 20 micro temperature sensors of the size 75 μm × 75 μm to accurately capture the thermal resistance of the micro pin fin heat exchanger. Data shows that there is no difference in the hydraulic and the thermal resistance of circular and square pins. Conventional correlations for friction factor and Nusselt number match well with the data.

Experimental Study of Adiabatic Water Liquid-Vapor Two-Phase Pressure Drop Across an Array of Staggered Micro-Pin-Fins

2008 ◽  
Author(s):  
Christopher A. Konishi ◽  
Weilin Qu ◽  
Ben Jasperson ◽  
Frank E. Pfefferkorn ◽  
Kevin T. Turner
Keyword(s):  
Pressure Drop ◽  
Maximum Mass ◽  
Two Phase ◽  
Pin Fin ◽  
Pin Fins ◽  
Micro Pin Fins ◽  
Pin Fin Array ◽  
Test Module ◽  
Phase Pressure ◽  
Liquid Vapor

This study concerns pressure drop of adiabatic water liquid-vapor two-phase flow across an array of 1950 staggered square micro-pin-fins having a 200×200 micron cross-section by a 670 micron height. The ratios of longitudinal pitch and transverse pitch to pin-fin equivalent diameter are equal to 2. An inline immersion heater upstream of the micro-pin-fin test module was employed to produce liquid-vapor two-phase mixture, which flowed across the micro-pin-fin array. The test module was well insulated to maintain an adiabatic condition. Four maximum mass velocities of 184, 235, 337, and 391 kg/m2s, and a range of vapor qualities for each maximum mass velocity were tested. Measured pressure drop increases drastically with increasing vapor quality. Nine existing two-phase pressure drop models and correlations were assessed. The Lockhart-Martinelli correlation for laminar liquid-laminar vapor combination in conjunction with a single-phase friction factor correlation proposed for the present micro-pin-fin array provided the best agreement with the data.

A Study on Flow Patterns and Pressure Drop in Adiabatic Two-Phase Flow Across a Bank of Micro Pin Fins

2007 ◽  
Author(s):  
Santosh Krishnamurthy ◽  
Yoav Peles
Keyword(s):  
Pressure Drop ◽  
Mass Flux ◽  
Slug Flow ◽  
Flow Patterns ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Pin Fin ◽  
Scale Models ◽  
Pin Fins ◽  
Micro Pin Fins

Flow patterns, void fraction and pressure drop in adiabatic nitrogen-water two phase flows across a bank of micro pin fin were experimentally investigated for Reynolds number ranging from 5 to 50. Staggered cylindrical shaped micro pin fins with diameter and height of 100 μm were micro-fabricated into 1 cm long, 1.8 mm microchannel. Flow patterns were determined by flow visualization and classified as bubbly-slug flow, gas-slug flow, bridged flow and annular flow. The applicability of conventional scale models to predict two-phase frictional pressure drop was also assessed. The two-phase frictional multiplier was found to be a strong function of mass flux and flow patterns unlike the previous results observed in the microchannel studies. It was observed that models from conventional scale systems did not adequately predict the two-phase frictional multiplier at micro-scale and thus, a modified model accounting for mass flux and flow patterns have been developed in this work.

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