Die Vermeidung eines Schutzringes bei der Messung der Wärmeleitfähigkeit plattenförmiger Körper
Avoiding the guard ring at heat conductivity measurements in plates: For measuring the heat conductivity of solid materials in form of plates the real heater has to be surrounded by a guard ring to obtain a parallel flow of heat and a constant gradient of temperature in the material. The guard ring has to be heated up to the same temperature as the heater by gradually altering the electric current until equality of temperature is attained. This is rather tedious and takes much time. If the guard ring is omitted the isothermes chanqe to curved surfaces, and the heat conductivity of the material can no more be determined in the simple way from the difference of temperature and the heat flow per unit area entering the material. By theoretical investigation it is shown, that also without a guard ring exact measurements of heat conductivity are possible if the curvature of the isothermes is determined by additional measurements of differences of temperature on the surface of the plate in contact with the heater. For this purpose a set of four thermocouples in serie is proposed to get a sufficient exactness of the small temperature difference occured.