Boiling Mechanism Measurement:
Consecutive Photo Method
A new photographic measurement technique has been developed and is being used to quantify the vapor volume flow rate departing from a wire during boiling. The vapor flow rate is determined by measuring the volume of bubbles after departure from the boiling surface in consecutive frames of high-speed video. The volumetric flow rate data are used to calculate the latent heat and, indirectly, sensible heat mechanisms which comprise the nucleate boiling heat flux.
Volume Flow Rate Measurement
Based on this flattening phenomenon, the bubble volume was determined
from the 2-D image. First, the image processor mathematically transformed
the slightly irregular 2-D bubble shape into an equivalent-area, 2-D ellipse
with identical second moments about the center of gravity. The ellipse
had semi-major and semi-minor axes of a and b respectively. Then, based
on the flattening phenomenon, the 3-D bubble was assumed to resemble an
ellipsoid with semi-axes, a, a, and b, so that the bubble volume was calculated
as
When each bubble's spatially averaged velocity within the boundary bubbles is known, vapor volumetric flow rate can be computed for the length of the wire examined as follows:
