The focus of this Small Grant for Exploratory Research (SGER) project is on the development of a novel Stirling micro- refrigerator for cold electronics. This silicon and glass machine is to be batch fabricated by micromachining techniques developed in the silicon sensor industry. Despite its small size (approximately one cubic centimeter), the micro- refrigerator will pump practical amounts of heat by operating at much higher frequencies than previously thought possible for Stirling cycle machines. Heat transfer and losses in Stirling cycle machines, like those in other fluid dynamic systems, depend not on individual operating quantities such as frequency or speed, but rather on dimensionless groups of quantities, such as Reynold's number and Valensi number. These dimensionless groups permit losses to be controlled by compensating for high frequencies by means of small dimensions. Our analysis of a preliminary design describes a machine that is 30 times smaller with 100 times more heat lifting capacity than the most advanced miniature Stirling cryocooler yet described in the scientific literature. In this research, two theoretical and practical feasibility issues will be addressed. We will identify fundamental limitations and opportunities by analyzing the complex heat transfer and friction factor coefficients at high frequencies and small dimensions, and we will examine the extent to which the proposed micro-refrigerator can be manufactured by existing processes employed in the commercial silicon sensor industry. We will also design a thermally and fluid- dynamically "similar" Stirling refrigerator in larger dimensions and in conventional materials for later experimental verification of analyses with conventional instrumentation.
