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 3.4 mm 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.
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September 2018
This article was originally published in
Journal of Heat Transfer
Research-Article
Convective Boiling of R-134a Near the Micro-Macroscale Transition Inside a Vertical Brazed Plate Heat Exchanger
Hyun Jin Kim,
Hyun Jin Kim
Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: hkim257@illinois.edu
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: hkim257@illinois.edu
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Leon Liebenberg,
Leon Liebenberg
Department of Mechanical Science
and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: leonl@illinois.edu
and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: leonl@illinois.edu
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Anthony M. Jacobi
Anthony M. Jacobi
Professor
Fellow ASME
Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: a-jacobi@illinois.edu
Fellow ASME
Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: a-jacobi@illinois.edu
Search for other works by this author on:
Hyun Jin Kim
Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: hkim257@illinois.edu
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: hkim257@illinois.edu
Leon Liebenberg
Department of Mechanical Science
and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: leonl@illinois.edu
and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: leonl@illinois.edu
Anthony M. Jacobi
Professor
Fellow ASME
Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: a-jacobi@illinois.edu
Fellow ASME
Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: a-jacobi@illinois.edu
1Corresponding author.
Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 11, 2017; final manuscript received February 5, 2018; published online May 7, 2018. Assoc. Editor: Amy Fleischer.
J. Heat Transfer. Sep 2018, 140(9): 091501 (10 pages)
Published Online: May 7, 2018
Article history
Received:
September 11, 2017
Revised:
February 5, 2018
Citation
Jin Kim, H., Liebenberg, L., and Jacobi, A. M. (May 7, 2018). "Convective Boiling of R-134a Near the Micro-Macroscale Transition Inside a Vertical Brazed Plate Heat Exchanger." ASME. J. Heat Transfer. September 2018; 140(9): 091501. https://doi.org/10.1115/1.4039397
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