Development of a novel transient calorimeter

Abstract

Thermal protection has always been the key technology in hypersonic vehicles development. Accurate prediction of aerodynamic thermal environment is an important basis for thermal protection structure design and material selection. The existing transient heat flux sensors include thin film thermometer and coaxial thermocouple. Thin film gages are brittle in hot flow, which is its main disadvantage. Besides, large corrections are needed to account for the variation of substrate thermal properties with temperature. Hot flow will damage the coaxial thermocouple, hence re-machining is required between two shots. The polish process will affect the physical parameters of the junction, thus introducing measurement uncertainties. The accuracy and reliability of heat flux measurements are affected by the above uncertainties. In this paper, a novel transient calorimeter is proposed. The temperature on reverse side of the calorimeter is measured by a thin film thermometer. The principle of the calorimeter is analyzed by one-dimensional infinite heat conduction calculation. With the influences of the sensor base and heat dissipation on back substrate being taken into account, numerical calculations are carried out with 2D heat conduction model. Error factors are analyzed, and key parameters of the calorimeter are designed and optimized. Wind tunnel experiments with wedge model are carried out. Results verified its accuracy and reliability. This type of calorimeter has a strong anti-erosion ability and high signal sensitivity. In addition, the diamond sheet is a non-metallic material, which can prevent the gas charge from interfering measurements. Therefore, the novel transient calorimeter has a wide range of applications.