Estimating the Thermal Effusivity for Coaxial Thermocouple Using a Quantified Aluminum Nitride Heater

Abstract

In this paper, a parameter estimation approach, based on a least-square method and a quantified heat flux source, is proposed for estimating the effective thermal effusivity of a co-axial thermocouple. The co-axial thermocouple is inserted in a through hole of a stainless steel 304 sample. From one-dimensional, constant-property, semi-infinite heat conduction theory, a direct integral relationship exists that connects probe temperature, source heat flux, and thermal effusivity. The effective thermal effusivity can be estimated using a highly accurate heat flux source and temperature measurement through a calibration study. This paper describes the calibration of the heat flux source, composed of an aluminum nitride heater with a tungsten heating trace, and the experimental and computational procedures used for estimating the effective thermal effusivity. Once obtained, this value is used in a series of experiments for reconstructing the surface heat flux. The estimated surface heat flux is then compared with the high-quality heat flux source. It is demonstrated that the effective thermal effusivity, when used in conjunction with the co-axial thermocouple temperature, produces an estimated source heat flux that compares favorably with the source heat flux.