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Title: The role of buoyancy orientation on bubble residence times and the related critical heat flux

Measurements of the effects of buoyancy orientation on the critical heat flux (CHF) in subcooled forced convection boiling of R113 are presented, examining the motion of the vapor above the heater surface and its possible influence on the feed of liquid to the surface. At the low flow velocity of 4 cm/s used, the buoyancy force acting on the vapor dominates over the flow inertia, and the measured CHF values show a strong dependence on the orientation of the heater surface with respect to gravity. The transient and time-averaged behavior of the vapor above the surface at heat flux levels close to the CHF is characterized using hot wire anemometry. Through this, a description of the behavior of the largest vapor bubbles is obtained, which is considered to be of primary importance to the processes by which liquid is fed to the heater surface at these high heat flux levels. The mean residence time of the largest bubbles above the heater surface at a given heater orientation is also determined from the hot wire data. The reciprocal of the mean residence time is found to correlate directly with the measured CHF values for the different orientations and subcoolings, showing thatmore » the amount of energy absorbed in the vapor formation process during the bubble residence time is constant for all heater orientations at a given subcooling, and demonstrates that the motion of the largest bubbles determines the CHF. This suggests that the relative effects of buoyancy orientation on the CHF can be modeled by considering only the motion of the largest bubbles in the immediate vicinity of the heater surface.« less
Authors:
; ;  [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Mechanical Engineering and Applied Mechanics
Publication Date:
OSTI Identifier:
516812
Report Number(s):
CONF-950828--
ISBN 0-7918-1704-0; TRN: IM9738%%122
Resource Type:
Book
Resource Relation:
Conference: 1995 National heat transfer conference, Portland, OR (United States), 5-9 Aug 1995; Other Information: PBD: 1995; Related Information: Is Part Of 1995 national heat transfer conference: Proceedings. Volume 3; HTD-Volume 305; Sadhal, S.S. [ed.] [Univ. of Southern California, Los Angeles, CA (United States)]; Gopinath, A. [ed.] [Naval Postgraduate School, Monterey, CA (United States)]; Oosthuizen, P.H. [ed.] [Queens Univ., Kingston, Ontario (Canada)]; Hashemi, A. [ed.]; PB: 199 p.
Publisher:
American Society of Mechanical Engineers, New York, NY (United States)
Sponsoring Org:
National Aeronautics and Space Administration, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING NOT INCLUDED IN OTHER CATEGORIES; CRITICAL HEAT FLUX; SUBCOOLED BOILING; TWO-PHASE FLOW; WEIGHTLESSNESS; BUBBLE GROWTH; FORCED CONVECTION; EXPERIMENTAL DATA