Method for Measuring Thermal Conductivity of Small Highly Insulating Specimens

A hot plate method for the measurement of thermal conductivity is described, which is unique in that it combines all the following capabilities: (1) Measurements of very small specimens, (2) measurements of specimens with thermal conductivity on the same order of that as air, and (3) the ability to use air as a reference material. As with other approaches, care is taken to ensure that the heat flow through the test specimen is essentially one-dimensional. However, unlike other approaches, no attempt is made to use heated guards to minimize the flow of heat from the hot plate to the surroundings. Results indicate that since large correction factors must be applied to account for guard imperfections when specimen dimensions are small, simply measuring and correcting for heat from the heater disk that does not flow into the specimen may be preferable. Extensive computational heat transfer modeling and experimental measurements taken in a prototype apparatus show that this approach is feasible. Suggestions are made for further improvements based on analyses of the generated data.