Seminars

ME/IE 8773-8774
THERMODYNAMICS AND HEAT TRANSFER SERIES
Topic: Heat Transfer and the Environment
Host: Terrence W. Simon

Gravity Effects on Boiling Heat Transfer: Investigations Using a Microheater Array
by

Jungho Kim
Associate Professor
Department of Mechanical Engineering
University of Maryland
College Park, MD 20742

Wednesday, February 2, 2005
3:30-5:00 p.m.
Room 1130 ME
Coffee and cookies will be available at 3:15 p.m. in Room 1130 ME before and after the seminar

Abstract: The use of two-phase thermal systems on spacecraft has been greatly hampered by the inability to predict with sufficient confidence their performance at various gravity levels (Earth, Mars, and lunar gravity and microgravity). The limited number of experiments to date have shown that stable, subcooled boiling on flat plates in microgravity environments is possible with some alteration in heat transfer coefficients, but almost all of the research has been either of a qualitative nature (photographic studies) with some wall heat flux/wall temperature measurements, analytical work, or numerical simulations. In the studies where heat transfer coefficients were measured, the heated surfaces were always comparable to or larger than the bubbles, so only average heat transfer rates over the entire heated surface were obtained. Very little experimental data is available regarding the local heat transfer rates under and around bubbles as they grow and depart from the surface. Better understanding of the boiling heat transfer mechanisms can be attained by pinpointing when and where in the bubble departure cycle large amounts of heat are removed from the wall, and correlating this information to visual observations of the state of the bubble at those times. Such information can provide much needed data regarding the important heat transfer mechanisms during the bubble departure cycle, and can serve as benchmarks to validate many of the analytical and numerical models used to simulate boiling. We have designed and built a microheater array that provides time and space resolved heat transfer under individual bubbles, and we are slowly gaining an understanding of the true boiling heat transfer mechanisms in various gravity environments.

Bio: Jungho Kim received his BSME from the University of California, Berkeley (1982), and his MSME (1986) and Ph.D (1990) from the University of Minnesota, all in Mechanical Engineering. Between 1990-1992, he joined Arvin/Calspan Corporation in Buffalo, NY where he performed research in gas turbine heat transfer. Between 1992-1998, he taught at the University of Denver where he started research on gravity effects on boiling heat transfer using a microheater array. He joined the faculty at the University of Maryland in 1998. His current research interests are phase change heat transfer for electronic cooling, radiation absorption measurements of fuels at high temperatures, emissivity measurements, inverse heat conduction methods, and instrumentation. He has published over 70 technical papers.

Informal Faculty Luncheon: Wednesday, February 2, 2005, 12:00 noon. Meet in 1100 ME and walk to lunch with other faculty. Prof. Jungho Kim will be able to attend.