Single- and Two-Phase Flow in Microchannels With Heat Transfer and Driven by an EHD Conduction Pump

2011 ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Transport Process ◽  
Enhancement Effect ◽  
Phase Flow ◽  
Two Phase ◽  
Small Areas ◽  
Dielectric Liquids ◽  
Phase Loop ◽  
Two Phase Heat Transfer ◽  
Heat Transport Process

Microchannels have well-known applications in cooling because of their ability to handle large quantities of heat from small areas. Electrohydrodynamic (EHD) conduction pumping at the micro-scale has previously been demonstrated to effectively pump dielectric liquids through adiabatic microchannels by using electrodes that are flushed against the walls of the channel. In this study, an EHD micropump is used to pump liquid within a two-phase loop that contains a microchannel evaporator. Additional EHD electrodes are embedded within the evaporator, which can be energized separately from the adiabatic pump. The enhancement effect of these embedded electrodes on the heat transport process in the micro-evaporator and on the two-phase loop system is characterized. Single- and two-phase heat transfer regimes are both studied and the effect of applied voltage and heat flux are considered on the overall flow rate and the wall temperature of the microchannel.

Electrohydrodynamic Conduction Driven Single- and Two-Phase Flow in Microchannels With Heat Transfer

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Transport Process ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Reverse Effect ◽  
Two Phase ◽  
Small Areas ◽  
Dielectric Liquids ◽  
Phase Loop ◽  
Heat Transport Process

Microchannels have well-known applications in cooling because of their ability to handle large quantities of heat from small areas. Electrohydrodynamic (EHD) conduction pumping at the microscale has previously been demonstrated to effectively pump dielectric liquids through adiabatic microchannels by using electrodes that are flushed against the walls of the channel. In this study, an EHD micropump is used to pump liquid within a two-phase loop that contains a microchannel evaporator. Additional EHD electrodes are embedded within the evaporator, which can be energized separately from the adiabatic pump. The effect of these embedded electrodes on the heat transport process, flow rate, and pressure in the micro-evaporator and on the two-phase loop system is characterized. Local enhancements are found to be up to 30% at low heat fluxes. The reverse effect that phase-change has on the EHD conduction pumping phenomenon is also quantified.

IR Based Inverse Calculation of Two-Phase Heat Transfer Coefficients in Microgap Channels

2011 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Heat Fluxes ◽  
Heated Wall ◽  
Phase Flow ◽  
Ir Thermography ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Two Phase Heat Transfer

IR thermography of the heated wall for the two-phase flow of FC-72 in microgap channels provides explicit evidence of the quality-driven M-shaped variations in the two-phase microgap heat transfer coefficients. Data obtained from a 210μ microgap channel, operated with an FC-72 mass flux of 195 and 780 kg/m2-s and asymmetric heat fluxes of 28 W/cm2 to 35 W/cm2 are presented and discussed.

Experimental Investigation and Empirical Analysis of Non-Boiling Gas-Liquid Two Phase Heat Transfer in Vertical Downward Pipe Orientation

2012 ◽  
Author(s):  
Swanand M. Bhagwat ◽  
Mehmet Mollamahmutoglu ◽  
Afshin J. Ghajar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Annular Flow ◽  
Single Phase ◽  
Phase Flow ◽  
Upward Flow ◽  
Two Phase ◽  
Reynolds Analogy ◽  
Two Phase Heat Transfer

The non-boiling gas-liquid two phase flow is pertinent to industrial applications like the reduction of paraffin wax depositions in petroleum transport lines, air lift systems and the chemical processes such as ethanol-water fractionation seeking enhanced heat and mass transfer. The non-boiling two phase heat transfer mechanism in horizontal and vertical orientations has been investigated by many researchers. However, till date very little experimental work and investigation has been performed for vertical downward flow. In order to contribute more to this research and have a better understanding of the non-boiling two phase heat transfer phenomenon for this pipe orientation, experimental investigation is undertaken for a vertical downward oriented 0.01252 m I.D. schedule 10 S stainless steel pipe using air-water as fluid combination. The influence of different flow patterns on the two phase convective heat transfer coefficient is studied using experimental measurements of 165 data points for bubbly, slug, froth, falling film and annular flow patterns spanned over the entire range of the void fraction. In general the two phase heat transfer coefficients are found to be consistently higher than that of the single phase flow. This tendency is observed to increase with increase in the gas flow rate as the flow regime migrates from bubbly to the annular flow. The concept of Reynolds analogy as implemented by Tang and Ghajar [1] for horizontal and vertical upward flow is analyzed against the vertical downward flow data collected in the present study. Due to lack of correlations available for predicting the two phase heat transfer coefficient in vertical downward orientation it was decided to perform the quantitative analysis of the seventeen two phase heat transfer correlations available for vertical upward flow. This analysis is concluded by the recommendation of the top performing correlations in the literature for each flow pattern. Based on the pressure drop data and using Reynolds analogy, a simple equation is proposed to correlate the two phase heat transfer coefficient with the single phase heat transfer coefficient.

Modeling and Prediction of Two-Phase Refrigerant Flow Regimes and Heat Transfer Characteristics in Microgap Channels

2007 ◽  
Author(s):  
Avram Bar-Cohen ◽  
Emil Rahim
Keyword(s):  
Heat Transfer ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Channel Diameter ◽  
Dielectric Liquids ◽  
Transition Criteria

This keynote lecture will open with a brief review of the primary two-phase flow regimes and their impact on thermal transport phenomena in tubes and channels. The Taitel and Dukler flow regime mapping methodology will then be described and applied to the two-phase flow of refrigerants and dielectric liquids in microgap channels. The effects of channel diameter, as well as alternative transition criteria, on the prevailing flow regimes in microgaps will be explored along with available criteria for microchannel behavior. Available microgap data will then be shown to reflect the dominance of annular flow and to display a characteristic heat transfer coefficient curve in such configurations. It is found that the heat transfer coefficients in the low-quality annular flow segment of this locus can be predicted by available, microtube correlations, but that the moderate-quality transition to the axially-decreasing segment occurs at substantially.

Frictional Pressure Drop during Two-Phase Flow of Pure Fluids and Mixtures in Small Diameter Channels

2015 ◽  
Vol 13 (4) ◽  
pp. 493-502 ◽  
Author(s):  
Davide Del Col ◽  
Marco Azzolin ◽  
Alberto Bisetto ◽  
Stefano Bortolin
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Small Diameter ◽  
Mass Composition ◽  
Vapor Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Two Phase Heat Transfer

Abstract Two-phase flow is widely encountered in minichannels heat exchangers such as air-cooled condensers and evaporators for automotive, compact devices for electronic cooling and aluminum condenser for air-conditioning applications. In the present work, frictional pressure drop during adiabatic liquid-vapor flow is experimentally investigated inside a single 0.96 mm diameter minichannel. Tests have been run with three mixtures of R32/R1234ze(E) (23/77%, 50/50% and 75/25% by mass composition) at mass flux ranging between 200 and 600 kg m−2 s−1. Since pressure drop has a strong influence on the two-phase heat transfer, it is crucial to have reliable pressure drop prediction methods for two-phase heat transfer modeling and optimization. Therefore, with the aim of extending its validity range, a model to calculate the frictional pressure gradient during two-phase flow in small diameter channels is tested against the present two-phase pressure drop database. An assessment is also done with two low-GWP refrigerants: the halogenated olefin R1234ze(E) and the hydrocarbon R290. The present model accounts for the effect of internal surface roughness as a function of the liquid-only Reynolds number.

MICROSCALE TWO PHASE HEAT TRANSFER ENHANCEMENT IN POROUS STRUCTURES

Equipment ◽  
2006 ◽  
Author(s):  
Leonid L. Vasiliev ◽  
A. Zhuravlyov ◽  
A. Shapovalov ◽  
L. L. Vasiliev, Jr
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Porous Structures ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Two Phase Heat Transfer
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