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Flow boiling heat transfer, pressure drop and dryout characteristics of low GWP refrigerants in a vertical mini-channel
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. (Two Phase flow in Mini-Channels)ORCID iD: 0000-0002-1403-758X
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two-phase heat transfer in mini/micro-channels is capable of meeting the high cooling demands of modern high heat flux applications. The phase change process ensures better temperature uniformity and control for local hot spots. Furthermore, these compact channels could be helpful in reducing the required charge and material inventories.Environmental concerns—mainly ozone depletion and global warming—have instigated a search for new alternatives in refrigeration industry. While new compounds are being developed to address stringent legislative demands, natural alternatives are also coming into prominence. A limited number of investigators have reported on thermal performance of such alternatives. The current study is therefore focused on saturated flow boiling heat transfer, pressure drop and dryout characteristics for three low global warming potential (GWP) refrigerants (R152a, R600a and R1234yf) in a vertical mini-channel.In this study experiments were carried out by uniformly heating a test section (stainless steel tube with 1.60 mm inside diameter and 245 mm heated length) at 27 and 32 oC saturation temperature with 50-500 kg/m2s mass velocities. The effects of various parameters of interest (like heat flux, mass flux, system pressure, vapor quality, operating media) on flow boiling heat transfer, frictional pressure drop and dryout characteristics were recorded. R134a, which has been widely used in several applications, is utilized as a reference case for comparison of thermal performance in this study.Experimental results for saturated boiling heat transfer showed strong influence of heat flux and system pressure with insignificant contributions from mass flux and vapor quality. Two phase frictional pressure drop increased with mass flux, vapor quality and with reduced operating pressure. The dryout heat flux remained unaffected with variation in saturation temperature, critical vapor quality in most cases was about 85%. The experimental results (boiling heat transfer, two-phase pressure drop and dryout heat flux) were compared with well-known macro and micro-scale correlations from the literature.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , 99 p.
Series
TRITA-REFR, ISSN 1102-0245 ; 14:03
Keyword [en]
Mini/micro-channels, R1234yf, R152a, R600a, R134a, Boiling heat transfer, Pressure drop, Dryout, Correlation
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-156056ISBN: 978-91-7595-389-2 (print)OAI: oai:DiVA.org:kth-156056DiVA: diva2:764344
Public defence
2014-12-17, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20141124

Available from: 2014-11-24 Created: 2014-11-18 Last updated: 2015-06-02Bibliographically approved
List of papers
1. Flow boiling heat transfer and dryout characteristics of R152a in a vertical mini-channel
Open this publication in new window or tab >>Flow boiling heat transfer and dryout characteristics of R152a in a vertical mini-channel
2014 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 53, 207-217 p.Article in journal (Refereed) Published
Abstract [en]

This article reports on flow boiling heat transfer and dryout characteristics of R152a in a vertical mini-channel. The experiments were carried out with a resistively heated stainless steel tube (1.60mm in diameter and 245mm heated length) at 27 and 32°C saturation temperature. Five mass fluxes in the range 100-500kg/m2s with heat fluxes from 5 to 245kW/m2 were tested. Under similar operating conditions experiments were repeated with R134a in the same setup to compare thermal performance of R152a. The results showed that the heat transfer was strongly influenced by the applied heat flux with insignificant convective contributions. The dryout heat flux increased with increasing mass flux but no effect of varying operating pressure was noticed. The experimental results for heat transfer and dryout heat flux were compared with well-known macro and micro-scale correlations from the literature.

Keyword
Dryout, Flow boiling, Heat flux, R152a, Vertical mini-channel
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-143005 (URN)10.1016/j.expthermflusci.2013.12.009 (DOI)000331422700023 ()2-s2.0-84892560102 (Scopus ID)
Note

QC 20140314

Available from: 2014-03-14 Created: 2014-03-14 Last updated: 2017-12-05Bibliographically approved
2. Flow boilingheat transfer and dryout characteristics of R600a in a vertical mini-channel
Open this publication in new window or tab >>Flow boilingheat transfer and dryout characteristics of R600a in a vertical mini-channel
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-156168 (URN)
Note

QS 2014

Available from: 2014-11-24 Created: 2014-11-24 Last updated: 2014-11-24Bibliographically approved
3. Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf: Experimental results and predictions
Open this publication in new window or tab >>Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf: Experimental results and predictions
2015 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 66, 137-149 p.Article in journal (Refereed) Published
Abstract [en]

Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf in a vertical stainless steel test section (1.60mm inside diameter and 245mm heated length) under upward flow conditions are reported in this article. The experiments were carried out at 27 and 32°C saturation temperatures with five mass fluxes in the range of 100-500kg/m2s while the applied heat flux was in the range of 5-130kW/m2. The experiments were carried out with gradual increase of the applied heat flux til completion of dryout. Under similar conditions, tests were repeated with R134a in the same test setup to compare thermal performance of these two refrigerants. The results showed that boiling heat transfer was strongly controlled by the applied heat flux and operating pressure with insignificant dependence on mass flux and vapor quality. The frictional pressure drop increased with mass flux and vapor quality and decreased with increasing saturation temperature as expected. Signs of dryout first appeared at vapor qualities of 85%, with the values generally increasing with increasing mass flux. The effect of varying system pressure was insignificant. The experimental results (boiling heat transfer, pressure drop and dryout heat flux) were compared with the predictions from well-known correlations (for macro and micro-scale channels) from the literature.

Keyword
Correlation, Dryout, Heat flux, Mini-channel, R1234yf, R134a, Correlation methods, Drops, Forecasting, Heat transfer, Pressure drop, Stainless steel, Boiling heat transfer, Dry-out, Flow boiling heat transfer, Frictional pressure drops, Mini channels, Saturation temperature
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-167685 (URN)10.1016/j.expthermflusci.2015.03.021 (DOI)000356129000015 ()2-s2.0-84926675760 (Scopus ID)
Note

QC 20150602

Available from: 2015-06-02 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved
4. Dryout characteristics of natural and synthetic refrigerants in vertical mini-channels
Open this publication in new window or tab >>Dryout characteristics of natural and synthetic refrigerants in vertical mini-channels
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-156170 (URN)
Note

QS 2014

Available from: 2014-11-24 Created: 2014-11-24 Last updated: 2014-11-24Bibliographically approved

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