The heat transfer analysis of a microinsulation for nuclear microbatteries

Microelectromechanical Systems (MEMS) have not gained wide use because they lack the on-device power required by many important applications. Numerous studies have been carried out regarding technologies for providing electrical power to MEMS devices. Compared with solar or chemical energies, radioisotope sources have the advantage of large energy density and long lifetime. The radioisotope decay heat could be directly converted to electricity using thermoelectric or thermionic techniques. As a crucial part of this process, a microinsulation concept has been designed to maintain the radioisotope source temperature high in order to obtain good conversion efficiency.; This paper reviews thermionic energy conversion technology and creates heat transfer models for a Micro Heat Barrier (MHB) and radioisotope powered thermionic microbattery developed by Sandia National Laboratory. The computed results indicate that the MHB has apparent thermal conductivity on the order of 10-4 W/mK at vacuum and is capable of providing sufficient thermal resistance to produce a high conversion efficiency for a thermionic microbattery. A new microinsulation concept using photo resist SU-8 is designed and the photolithography fabrication process is described. The microinsulation sample's apparent thermal conductivity is measured and compared with theoretical results. The experimental results show that a typical design has apparent thermal conductivity on the order of 10-4 W/mK at vacuum and have a good agreement with what the model predicts.