Mechanical Engineering Seminar

Thermal Lagging in Multi-Carrier Systems

Robert D. Tzou, Ph.D.

Department of Mechanical and Aerospace Engineering

University of Missouri

Abstract

Extending the microscopic two-step heating model where electrons and phonons are two main carriers, lagging behavior for heat transport in systems containing multiple carriers is explored. Targeted applications include ultrafast/microscale heat transport in biological/medical materials/tissues, energy dissipation across the interface between dissimilar materials, and energy redistributions among solid, liquid and vapor phases in heat pipes with wick structures.

Fundamental behavior of thermal lagging is outlined, emphasizing its perfect correlations to the existing macroscopic and microscopic models in the various limits. Diffusion-wave duality of heat propagation is illustrated in terms of the time-rate of change of temperature as well as the physical scale of the response time. Heat transfer with complicated microstructural interaction effects is lumped into their resulting delayed response; in time, characterized by the thermalization time and the relaxation time of the various orders.

It is shown, for the first time, that the system containing n carriers will display thermal lagging of the (n-1)th order, resulting in new energy equations that have not been seen before. Under the simplest possible mathematical content, an example is given to illustrate such high-order effects in thermal lagging. The excessively high temperature during the ultrafast transient in the heat affected zone, as well as the time constants characterizing the ultrafast response, are critical to the success of ultrafast thermal processing of materials/tissues employing the femtosecond lasers.

Tuesday, April 22, 2008, 10:30 am


3540 Engineering


Refreshments served at 10:15 am


Biography

Dr. Robert Tzou is James C. Dowell Professor of Engineering and Chairman of the Department of Mechanical and Aerospace Engineering at the University of Missouri, Columbia. He received his PhD from Lehigh University in 1987. He joined the University of New Mexico in Albuquerque in 1988 – 1996, and was recruited to the University of Missouri in 1996.

Dr. Tzou’s research is in the general area of ultrafast thermomechanics. Among the 143 papers that he has published in this area, milestones include his first book on Microscale Scale Transfer published in 1997, four reviewed articles invited by the ASME Journal of Heat Transfer, Journal of Thermal Stresses, Annual Review of Heat Transfer, and Journal of Engineering Mathematics. He has delivered several keynote lectures for the international conferences organized by the various professional societies, including ASME and SPIE, and is the Conference Chair of the 1st ASME International Conference on Micro/Nanoscale Heat Transfer, where a total of 17 Tracks were formed to address the uprising issues in Micro/Nanoscale Heat Transfer research.