Ph.D. Proposal Presentation by Camil-Daniel Ghiu
Monday, July 15, 2002

(Dr. S. M. Ghiaasiaan, advisor)

"Regimes of Pool Boiling from Transparent Microfabricated Enhanced Structures"


Enhanced boiling structures are used in the process, refrigeration and
electronics industries. Although the enhancement in heat transfer has been
demonstrated, there is still considerable lack of understanding about the
underlying physical mechanism behind the enhancement. An experimental and
analytical investigation of these effects is proposed.

The enhanced structure employed in the present study has a network of parallel
microchannels fabricated on the bottom surface. The top surface has a
microchannel network aligned 900 to those on the bottom surface. This resulted
in an array of pores at the intersections of the microchannels. The structures
are manufactured of quartz and the working fluid is a dielectric fluorocarbon
( PF 50-60 ). The present study investigates channel widths in the 70 ­ 200 mm
range and pore pitches between 0.5 ­ 1 mm. A high-speed camera operating at
1000 frames/s at full resolution (512 x 512 pixels) with attached magnifying
lens allows precise observation of the evaporation process in the bottom and
top tunnels.

This study has two main aims:
1) Developing a complete map of boiling regimes and
2) Modeling one of the boiling regimes

Three boiling regimes have been identified so far: slug formation (in either
top or bottom channels), slug migration between the top and bottom channels and
slug predominance (most of channels vapor filled).

A semi-analytical model for the slug predominance regime is being proposed. The
model takes into account the following parameters: bubble departure diameter,
frequency, nucleation site density and dissipated heat flux. The predictions
from the model will be compared with experimental data.