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Experimental comparison and visualization of in-tube continuous and pulsating flow boiling
Tech Univ Denmark, Dept Mech Engn, Nils Koppels Alle Bygn 403, DK-2800 Lyngby, Denmark..
Tech Univ Denmark, Dept Mech Engn, Nils Koppels Alle Bygn 403, DK-2800 Lyngby, Denmark..
Tech Univ Denmark, Dept Mech Engn, Nils Koppels Alle Bygn 403, DK-2800 Lyngby, Denmark..
Tech Univ Denmark, Dept Mech Engn, Nils Koppels Alle Bygn 403, DK-2800 Lyngby, Denmark..ORCID iD: 0000-0002-0503-6286
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2018 (English)In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 125, p. 229-242Article in journal (Refereed) Published
Abstract [en]

This experimental study investigated the application of fluid flow pulsations for in-tube flow boiling heat transfer enhancement in an 8 mm smooth round tube made of copper. The fluid flow pulsations were introduced by a flow modulating expansion device and were compared with continuous flow generated by a stepper-motor expansion valve in terms of the time-averaged heat transfer coefficient. The cycle time ranged from 1 s to 7 s for the pulsations, the time-averaged refrigerant mass flux ranged from 50 kg m(-2) s(-1) to 194 kg m(-2) and the time-averaged heat flux ranged from 1.1 kW m(-2) to 30.6 kW m(-2). The time-averaged heat transfer coefficients were reduced from transient measurements immediately downstream of the expansion valves with 2 K and 20 K subcooling upstream, resulting in inlet vapor qualities at 0.05 and 0.18, respectively, and covered the saturated flow boiling range up to the dry-out inception. Averaged results of the considered range of vapor qualities, refrigerant mass flux and heat flux showed that the pulsations at low cycle time (1 s) improved the time-averaged heat transfer coefficients by 5.6% and 2.2% for the low and high subcooling, respectively. However, the pulsations at high cycle time (7 s) reduced the time-averaged heat transfer coefficients by 1.8% and 2.3% for the low and high subcooling, respectively, due to significant dry-out when the flow-modulating expansion valve was closed. Furthermore, the flow pulsations were visualized by high-speed camera to assist in understanding the time-periodic flow regimes and the effect they had on the heat transfer performance.

Place, publisher, year, edition, pages
Pergamon Press, 2018. Vol. 125, p. 229-242
Keywords [en]
Flow boiling, Flow pulsation, Heat transfer enhancement, Visualization, Flow regime
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-233261DOI: 10.1016/j.ijheatmasstransfer.2018.04.060ISI: 000440118600019Scopus ID: 2-s2.0-85046355941OAI: oai:DiVA.org:kth-233261DiVA, id: diva2:1239414
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QC 20180816

Available from: 2018-08-16 Created: 2018-08-16 Last updated: 2018-08-16Bibliographically approved

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Palm, Björn

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