Experimental Methods in Air Cooling of Electronics

Abstract

This short course deals mainly with aircooling situations and has three main parts: (1) Error and uncertainty analysis, (2) Experimental methods, and (3) Heat transfer measurements and Thermal characterization of electronic components. The first part introduces the Sources and Signatures of Error and Uncertainty Analysis as a tool for Planning and Executing experiments. The Experimental Methods part covers techniques of temperature, pressure, flow, and heat flux measurements as well as some elements of flow visualization. Thermocouples, thermistors, resistance detectors, and optical techniques (liquid crystal and infrared) are covered. Special attention is given to the environmental errors present in gas temperature, surface temperature, and solid temperature measurements. Several techniques are discussed for measuring heat transfer rates and heat transfer coefficients including energy balance methods, analogue methods, and heat flux transducers. The heat transfer part will summarize what we know about heat transfer in air cooling of electronics from more than fifteen years of research at Stanford University and the University of Arizona. We will particularly emphasize the interpretation and use of the heat transfer data in the literature and its bearing on thermal characterization of electronic components. We will discuss and interpret the sources of errors inherent in the measurement and use of junction to ambient and junction to case thermal resistance. Forced convection, free convection, and mixed convection situations will be discussed, aiming at the solution to the general problem of cooling of components on circuit cards.