Dr. Amy Betz
Assistant Professor of Mechanical & Nuclear Engineering at Kansas State University
Enhancing Transport Phenomena in Microgeomtries
102 Cardwell Hall
October 29, 2012
4:30 p.m.
In microgeometries, interfacial forces dominate
over inertia due to the high surface area to volume ratio. Heat and mass
transfer can be controlled by manipulating these interfaces. This can be
achieved through the use of multiphase flows to create fluid-fluid
interfaces or through nano and micro-manufacturing to change the surface
properties at solid-fluid interfaces. I will go over two of my research
topics that show how interfaces can be manipulated to enhance heat transfer.
First, I will show how the generation of fluid-fluid interfaces can increase
convective heat transfer in microchannel heat sinks. Flow in microchannels
is usually laminar since the Reynolds number (Re = ρVd/μ) is small. When air
bubbles are injected into liquid filled channels they create recirculating
wakes because the air bubbles move faster than the liquid. When the bubbles
are longer than the channel width, a phenomenon known as segmented flow, the
recirculating wakes encompass the liquid filled channels and increase both
the heat and mass transfer rate over 100% at the fluid-wall interface.
Second, I will show how surfaces with heterogeneous wettability enhance heat
transfer. In pool boiling, the heat transfer coefficient is a function of
the bubble size and frequency at departure, and the number of active
nucleation sites. By selectively changing the surface properties using nano
and micro-manufacturing, the three parameters can be controlled. Using this
technique the heat transfer coefficient can be increased by over 300%.
Refreshments in CW 119 at 4:15 p.m.