Analysis of surrounding gas temperature influence on thermocouple measurement temperature

Abstract

When thermocouple is used to measure high temperature gas flow, the measured temperature, i.e., the thermocouple bead temperature is not exactly the gas temperature. The bead temperature results from the bead energy balance including the convection with the gas flow, the radiation with the environment and the gas, the conduction with the thermocouple wire near the bead. The wire temperature is determined by its own energy balance relating to the gas temperature contacting the wire. Through the wire conduction, the bead temperature is related to the gas temperature around the wire near the bead. The one-dimensional thermocouple heat transfer simulation code was developed and validated by the elaborate experiment. In the current study, this code is used to study the influence of the surrounding gas temperature on the bead temperature. Of course, the gas temperature far away from the bead will not influence the bead temperature. The size of the surrounding region which could influence the bead temperature is identified and its relation with the flow condition and the thermocouple size is analyzed. The quantitative bead temperature variation with the temperature gradient inside this region is studied.