Fluctuating temperature measurement by a fine-wire thermocouple probe: influences of physical properties and insulation coating on the frequency response

Abstract

Theoretical analysis of the frequency response of a fine-wire thermocouple probe has been further developed to investigate influences of the difference in physical properties between the two wires composing a butt-welded fine-wire thermocouple. The solution obtained demonstrates complex behaviour of the frequency response of the copper–constantan (type-T) thermocouple whose physical properties differ greatly between the two constitutive wires. It was also shown that, in an air flow, the frequency response is almost uniform in the cross-section of the thermocouple wire, but, in a water flow, it becomes remarkably nonuniform. The present theoretical analysis provides useful information for improving the reliability of fluctuating temperature measurement in high-temperature turbulent flows.