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Experimental Investigation of an Evaporator Enhanced With a Micro-Porous Structure in a Two-Phase Thermosyphon Loop

[+] Author Affiliations
Richard Furberg, Rahmatollah Khodabandeh, Björn Palm, Shanghua Li, Muhammet Toprak, Mamoun Muhammed

Royal Institute of Technology, Stockholm, Sweden

Paper No. HT2008-56471, pp. 327-334; 8 pages
doi:10.1115/HT2008-56471
From:
  • ASME 2008 Heat Transfer Summer Conference collocated with the Fluids Engineering, Energy Sustainability, and 3rd Energy Nanotechnology Conferences
  • Heat Transfer: Volume 2
  • Jacksonville, Florida, USA, August 10–14, 2008
  • Conference Sponsors: Heat Transfer Division
  • ISBN: 978-0-7918-4848-7 | eISBN: 0-7918-3832-3
  • Copyright © 2008 by ASME

abstract

Following is an experimental study of six different evaporators in a closed two-phase thermosyphon loop system, where the influence of various evaporator dimensions and surfaces was investigated. The evaporators featured a 30 mm long rectangular channel with hydraulic diameters ranging from 1.2–2.7 mm. The heat transfer surface of one of the tested evaporators was enhanced with copper nano-particles, dendritically connected into an ordered micro-porous three dimensional network structure. To facilitate high speed video visualization of the two-phase flow in the evaporator channel, a transparent polycarbonate window was attached to the front of the evaporators. Refrigerant 134A was used as a working fluid and the tests were conducted at 6.5 bar. The tests showed that increasing channel diameters generally performed better. The three largest evaporator channels exhibited comparable performance, with a maximum heat transfer coefficient of about 2.2 W/(cm2 K) at a heat flux of 30–35 W/cm2 and a critical heat flux of around 50 W/cm2 . Isolated bubbles characterized the flow regime at peak performance for the large diameter channels, while confined bubbles and chaotic churn flow typified the evaporators with small diameters. In line with previous pool boiling experiments, the nucleate boiling mechanism was significantly enhanced, up to 4 times, by the nano- and micro-porous enhancement structure.

Copyright © 2008 by ASME

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