| dc.description.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 degrees C
in a 3 mm X 50 mm X 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
microns) 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. | en_US |
