New Vacuum Blackbody Cavity for Heat Flux Meter Calibration

Abstract

In the field of thermal radiation measurements, blackbody cavities are commonly used as reference standards for the calibration of heat flux meters. Applying the energy balance equation to the closed system including the cavity and the sensor, it is possible to predict the heat flux density absorbed by the heat flux meter. Calibration procedures developed at Laboratoire National de Métrologie et d'Essais (LNE) in recent years have allowed us to propose practical solutions for heat flux meters working below 100 kW · m −2 . The best relative uncertainties (k = 2) over the range of (10-100) kW · m −2 vary from 1.7 % to 3 %. During previous studies, three major facilities were constructed, each one with the objective to respond to different technical problems considering the measuring principle of these heat flux sensors. Following this approach, the sensitivity of these meters to radiation, the sensitivity to radiation and convection, and also the influence of the size of the source or of the positioning of the sensor (horizontally, vertically, etc.) have been investigated. As an outcome of this recent experience, a new vacuum blackbody cavity has been set up. As well as the possibility to calibrate at very low irradiance, there are also some substantive improvements in heating, thermal performance, and calibration methodology. After a summary of the state of the art of calibration methods and their limits, the article presents the preliminary results of the characterization obtained with this new facility for which the objective is to reduce the uncertainties by at least a factor of two for heat flux densities lower than 20 kW · m −2 .

A method to measure heat flux in convection using Gardon gauge

“…The Gardon gauges are commonly calibrated by the standard blackbody source [45][46][47]. The gauges are irradiated by the known radiative heat flux from the blackbody source.…”

“…The gauges are irradiated by the known radiative heat flux from the blackbody source. The measurement sensitivity, r L , is then experimentally obtained by the ratio of the gauge voltage output to the irradiative heat flux value which is calculated by the Stefan-Boltzmann law using measured blackbody temperature [45][46][47].…”