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.

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.

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.

Experimental Study and Numerical Analysis of Water Single-Phase Pressure Drop Across an Array of Circular Micro-Pin-Fins

2011 ◽  
Author(s):  
Jonathan R. Mita ◽  
Weilin Qu ◽  
Marcelo H. Kobayashi ◽  
Frank E. Pfefferkorn
Keyword(s):  
Numerical Analysis ◽  
Pressure Drop ◽  
Cross Section ◽  
Single Phase ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Experimental Results ◽  
Inlet Temperature ◽  
Pin Fins ◽  
Micro Pin Fins

This study investigates pressure drop associated with water liquid single-phase flow across an array of staggered micro-pin-fins having circular cross-section. The micro-pin-fins are micro-end milled out of oxygen free copper and have the following dimensions: 180 micron diameter and 683 micron height. The longitudinal pitch and transverse pitch are equal to 400 microns. Seven water inlet temperatures from 22 to 80 °C, and seventeen maximum mass velocities for each inlet temperature, ranging from 159 to 1475 kg/m2s, were tested. The test module was well insulated to maintain adiabatic conditions. The experimental results were compared to those from a micro-pin-fin array having similar size and geometrical arrangement but a square cross-section. The circular micro-pin-fins were seen to yield a significantly lower pressure drop than the square micro-pin-fins. The present experimental results were also compared with the predictions of several friction factor correlations as well as the results from a three-dimensional numerical analysis. Neither was able to accurately predict the experimental 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.

Liquid Single-Phase Flow in an Array of Micro-Pin-Fins—Part II: Pressure Drop Characteristics

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Weilin Qu ◽  
Abel Siu-Ho
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Friction Factor ◽  
Single Phase ◽  
Cast Aluminum ◽  
Pin Fin ◽  
Pin Fins ◽  
Friction Factor Correlation ◽  
Micro Pin Fins ◽  
Pin Fin Arrays

This Technical Brief is Part II of a two-part study concerning water single-phase pressure drop and heat transfer in an array of staggered micro-pin-fins. This brief reports the pressure drop results. Both adiabatic and diabatic tests were conducted. Six previous friction factor correlations for low Reynolds number (Re<1000) flow in conventional and micro-pin-fin arrays were examined and found underpredicting the adiabatic data except the correlation by Short et al. (2002, “Performance of Pin Fin Cast Aluminum Coldwalls, Part 1: Friction Factor Correlation,” J. Thermophys. Heat Transfer, 16(3), pp. 389–396), which overpredicts the data. A new power-law type of correlation was developed, which showed good agreement with both adiabatic and diabatic data.

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