Nanoscale Heat Transfer and Its Applications for Thermal Energy Conversion and Management

Dr. Renkun Chen
Department of Mechanical & Aerospace Engineering
University of California at San Diego

Thermal transport plays a very significant role in both energy production and consumption: More than 80% of the world’s total power is generated by heat engines and  more  than  60%  of  the  U.S.  primary  energy  is  used  in  the  form  of  heat.  The fundamental length scales associated with the transport of basic heat carriers, such as phonons, electrons and photons, generally fall in the range of 1-1000 nm. Therefore, exploring and exploiting basic heat transfer physics at micro and nanoscale hold the key for developing materials and devices for thermal energy conversion, storage and management. Despite its important applications, understanding of heat conduction at nanoscale is still in its infancy. For example, the range of thermal conductivities of natural materials only spans five orders of magnitude at room temperature, with air and diamond as the lower and upper bounds, respectively, and the theory for explaining the phonon transport in solids is still essentially the Drude model. In contrast, the range of  electrical  conductivities  spans  more  than  eighteen  orders  of  magnitude  at  room temperature  and  our  understanding  on  electron  transport  has  been  advanced significantly over the last century. In this seminar, I will discuss our prior and current work  on  using  nanostructures for  studying  nanoscale  heat transfer  and developing thermoelectric materials and thermal management devices. Examples include probing phonon  transport  in  nanowires  by  using  nanofabrication  technique,  50-fold enhancement in thermoelectric efficiency of Si nanowires over bulk Si, and more than three-fold  enhancement  of  critical  heat  flux of  boiling  heat  transfer  on  micro- and     nano-structured surfaces.

Renkun Chen received a B.S. in Thermo-physics from Tsinghua University in 2004,  and  a  Ph.D.  in  Mechanical  Engineering  from  the  University  of  California, Berkeley  in  2008,  for  research  conducted  in  the  laboratory  of  Professor  Arun Majumdar. Following a one year postdoctoral fellowship at Lawrence Berkeley National Laboratory,  he  began  his  faculty  appointment  as  an  assistant  professor  in  the department of Mechanical and Aerospace Engineering at UC San Diego in November 2009.