Implementation of a Water Heat Pipe at CETIAT

CETIAT’s calibration laboratory, accredited by COFRAC, is a secondary thermometry laboratory. It uses overflow and stirred calibration baths ((hbox {from} -,80,{^{circ }}hbox {C} hbox { up } hbox { to } +,215,{^{circ }}hbox {C})), dry blocks and furnaces ((hbox {from } +,100,{^{circ }}hbox {C} hbox { up } hbox { to } +,1050,{^{circ }}hbox {C})) and thermostatic chambers ((hbox {from } -,30,{^{circ }}hbox {C} hbox { up } hbox { to } +,160,{^{circ }}hbox {C})). Typical calibration uncertainties that can be reached for platinum resistance thermometers in a thermostatic bath are between (0.03,{^{circ }}hbox {C}) and (0.06,{^{circ }}hbox {C}). In order to improve its calibration capabilities, CETIAT is working on the implementation of a gas-controlled heat pipe (GCHP) temperature generator, used for industrial sensor calibrations. This article presents the results obtained during the characterization of water GCHP for industrial applications. This is a new approach to the use of a heat pipe as a temperature generator for industrial sensor calibrations. The objective of this work is to improve measurement uncertainties and daily productivity. Indeed, as has been shown in many studies (Dunn and Reay in Heat Pipes, Pergamon Press, Oxford, 1976; Merlone et al. 2012), the temperature of the system is pressure dependent and the response time, in temperature, follows the pressure accordingly. Thanks to this generator, it is possible to perform faster calibrations with smaller uncertainties. In collaboration with INRiM, the GCHP developed at CETIAT works with water and covers a temperature range from (+,30,{^{circ }}hbox {C}) up to (+,150,{^{circ }}hbox {C}). This device includes some improvements such as a removable cover, which allows us to have different sets of thermometric wells adjustable according to the probe to be calibrated, and a pressure controller based on a temperature sensor. This article presents the metrological characterization in terms of homogeneity and stability in temperature. A rough investigation of the response time of the system is also presented in order to evaluate the time for reaching thermal equilibrium. The results obtained in this study concern stability and thermal homogeneity. The homogeneity on 200 mm is better than 5 mK and with a calibration uncertainty reduced by a factor of three.