Convective boiling of R-134a near the micro-macroscale transition inside a vertical brazed plate heat exchanger

Hyun Jin Kim, Leon Liebenberg, Anthony M Jacobi

Research output: Contribution to journalArticle

Abstract

Heat transfer and pressure drop characteristics of R-134a boiling in a chevron-patterned brazed plate heat exchanger (BPHE) are studied experimentally. With corrugated BPHE channels having hydraulic diameter of 3.4mm and low refrigerant mass flux, boiling near the micro-macroscale transition is speculated. Heat exchanger performance is characterized with varying mass flux (30-50 kgm-2s-1), saturation pressure (675 kPa and 833 kPa), heat flux (0.8 and 2.5 kWm-2), and vapor quality (0.1-0.9). The two-phase refrigerant heat transfer coefficient increases with heat flux as often observed during nucleate boiling. It also weakly increases with saturation pressure and the associated lower latent heat during convective boiling; heat transfer is improved by the decreased liquid film thickness surrounding confined bubbles inside the narrow BPHE channels, which is the main characteristic of microscale boiling. As often observed in macroscale boiling, the inertial forces of the liquid and vapor phases cause an unsteady annular film, leading to premature partial dryout. The onset of dryout is accelerated at the lower saturation pressure, due to increased surface tension, another microscale-like characteristic. Higher surface tension retains liquid in sharp corners of the corrugated channel, leaving lateral surface areas of the wall dry. Two-phase pressure drop increases with mass flux and vapor quality, but with decreasing saturation pressure. Dryout decreases the friction factor due to the much lower viscosity of the gas phase in contact with the wall. Several semi-empirical transition criteria and correlations buttress the current analyses that the thermal-fluidic characteristics peculiar to BPHEs might be due to macro-microscale transition in boiling.

Original languageEnglish (US)
Article number091501
JournalJournal of Heat Transfer
Volume140
Issue number9
DOIs
StatePublished - Sep 1 2018

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norflurane
heat exchangers
boiling
Boiling liquids
Heat exchangers
microbalances
saturation
Mass transfer
refrigerants
Vapors
Refrigerants
pressure drop
Pressure drop
Surface tension
Heat flux
heat flux
interfacial tension
corrugated plates
heat transfer
vapors

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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Convective boiling of R-134a near the micro-macroscale transition inside a vertical brazed plate heat exchanger. / Kim, Hyun Jin; Liebenberg, Leon; Jacobi, Anthony M.

In: Journal of Heat Transfer, Vol. 140, No. 9, 091501, 01.09.2018.

Research output: Contribution to journalArticle

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