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RESEARCH PAPERS: Boiling and Condensation

A Control Volume Approach for Investigating Forces on a Departing Bubble Under Subcooled Flow Boiling

[+] Author and Article Information
S. G. Kandlikar, B. J. Stumm

Mechanical Engineering Department, Rochester Institute of Technology, Rochester, NY 14623

J. Heat Transfer 117(4), 990-997 (Nov 01, 1995) (8 pages) doi:10.1115/1.2836321 History: Received February 01, 1994; Revised February 01, 1995; Online January 23, 2008

Abstract

This paper presents the theoretical and experimental work conducted on nucleating vapor bubbles in subcooled flow boiling of water at atmospheric pressure and 60°C in a 3 mm × 50 mm × 400 mm long rectangular channel. A new model is developed for analyzing forces acting on the vapor bubble under pseudo-static conditions corresponding to the thermally controlled region of bubble growth. The model considers two separate control volumes for the front and rear regions of the bubble. The forces due to surface tension, buoyancy, drag, pressure difference, and momentum changes are considered, and the effects of different upstream and downstream contact angles are included. These angles and the departure bubble diameters are measured from the top and the side views of bubbles recorded on a video camera through a microscope. The new model and the experimental study confirm that the bubble removal in flow boiling for small diameter bubbles investigated in this study (less than 500 μm) is initiated at the front edge of the bubble through a sweep-removal mechanism. Previous models available in the literature consider a force balance on the entire bubble, and are therefore unable to address the effect of a significant reduction in the component of the surface tension force in the flow direction at the leading edge caused by an increase in the upstream contact angle.

Copyright © 1995 by The American Society of Mechanical Engineers
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