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Experimental Investigation of Two-phase Pressure Drop in a Microchannel
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0002-9902-2087
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
2011 (English)In: Heat Transfer Engineering, ISSN 0145-7632, E-ISSN 1521-0537, Vol. 32, no 13/14, 1126-1138 p.Article in journal (Refereed) Published
Abstract [en]

Experimental results of two-phase pressure drop in a horizontal circular microchannel are reported in this paper. A test tube was made of fused silica having an internal diameter of 781 mu m with a total length of 261 mm and a heated length of 191 mm. The outer surface of the test tube was coated with an electrically conductive thin layer of ITO (indium tin oxide) for direct heating of the test section. Refrigerants R134a and R245fa were used as the working fluids, and mass flux during the experiments was varied between 100 and 650 kg/m(2)-s. Experiments were performed at two different system pressures corresponding to saturation temperatures of 25 degrees C and 30 degrees C for R134a and at three different system pressures corresponding to saturation temperatures of 30 degrees C, 35 degrees C, and 40 degrees C for R245fa. Two-phase frictional pressure drop characteristics with variation of mass flux, vapor fraction, saturation temperature, and heat flux were explored in detail. Finally, the prediction capability of some well-known correlations available in the literature, some developed for macrochannels and others especially developed for microchannels, was assessed.

Place, publisher, year, edition, pages
2011. Vol. 32, no 13/14, 1126-1138 p.
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-27140DOI: 10.1080/01457632.2011.562463ISI: 000299957500005Scopus ID: 2-s2.0-79960485611OAI: oai:DiVA.org:kth-27140DiVA: diva2:374774
Note
Updated from accepted to published. QC 20120412Available from: 2010-12-06 Created: 2010-12-06 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Phase Change Phenomena During Fluid Flow in Microchannels
Open this publication in new window or tab >>Phase Change Phenomena During Fluid Flow in Microchannels
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phase change phenomena of a fluid flowing in a micro channel may be exploited to make the heat exchangers more compact and energy efficient. Compact heat exchangers offer several advantages such as light weight, low cost, energy efficiency, capability of removing high heat fluxes and charge reduction are a few to mention. Phase change phenomena in macro or conventional channels have been investigated since long but in case of micro channels, fewer studies of phase change have been conducted and underlying phenomena during two-phase flow in micro channels are not yet fully understood. It is clear from the literature that the two-phase flow models developed for conventional channels do not perform well when extrapolated to micro scale.

In the current thesis, the experimental flow boiling results for micro channels are reported. Experiments were conducted in circular, stainless steel and quartz tubes in both horizontal and vertical orientations. The internal diameters of steel tubes tested were 1.70 mm, 1.224 mm and the diameter of quartz tube tested was 0.781 mm. The quartz tube was coated with a thin, electrically conductive, transparent layer of Indium-Tin-Oxide (ITO) making simultaneous heating and visualization possible. Test tubes were heated electrically using DC power supply. Two refrigerants R134a and R245fa were used as working fluids during the tests. Experiments were conducted at a wide variety of operating conditions.

Flow visualization results obtained with quartz tube clearly showed the presence of confinement effects and consequently an early transition to annular flow for micro channels. Several flow pattern images were captured during flow boiling of R134a in quartz tube. Flow patterns recorded during the experiments were presented in the form of Reynolds number versus vapour quality and superficial liquid velocity versus superficial gas velocity plots. Experimental flow pattern maps so obtained were also compared with the other flow pattern maps available in the literature showing a poor agreement. Flow boiling heat transfer results for quartz and steel tubes indicate that the heat transfer coefficient increases with heat flux and system pressure but is independent on mass flux and vapour quality. Experimental flow boiling heat transfer coefficient results were compared with those obtained using different correlations from the literature. Heat transfer experiments with steel tubes were continued up to dryout condition and it was observed that dryout conditions always started close to the exit of the tube. The dryout heat flux increased with mass flux and decreased with exit vapour quality. The dryout data were compared with some well known CHF correlations available in the literature. Two-phase frictional pressure drop for the quartz tube was also obtained under different operating conditions. As expected, two-phase frictional pressure drop increased with mass flux and exit vapour quality.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xii, 141 p.
Series
Trita-REFR, ISSN 1102-0245
Keyword
Microchannels, Boiling, Heat Transfer
National Category
Energy Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-26796 (URN)978-91-7415-829-8 (ISBN)
Public defence
2010-12-17, M3, Brinellvägen 64, KTH, Stockholm, 20:35 (English)
Opponent
Supervisors
Funder
StandUp
Note
QC 20101206Available from: 2010-12-06 Created: 2010-11-28 Last updated: 2011-05-18Bibliographically approved

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