Paper 32: Errors in the Measurement of Surface Temperature Caused by Perturbations of the Heat Flux

Abstract

The work reported in this paper was done in connection with heat transfer experiments on reactor fuel elements. Tubes in which heat was generated by an electric current were cooled on the outside by a gas flow. To avoid disturbing the flow, taking the thermocouple leads through a steep temperature gradient and exposing them to gas forces, the thermocouples were secured in holes in the tube walls and led away inside the tubes. An insert of a different material in the tube wall disturbs the uniformity of electrical heat generation. The paper presents a theoretical solution for the disturbed heat generation pattern, and that is followed by a derivation of the temperature distribution allowing for conduction in the tube and insert. Experiments were made with thermocouples secured by braze and by a copper oxide cement. The temperature disturbance was found to be unacceptable with the cement owing to its poor thermal conductivity. With the brazed attachment the disturbance was fairly small but a second source of error is pick-up by the thermocouples of the tube potential gradient. Methods of reducing pick-up are discussed.