ABSTRACT
Spacecraft are increasingly using CFRP thin sheets in honeycomb sandwiches and other components. The in-plane temperature dependent thermal conductivity (TDTC) of these thin sheets is challenging to evaluate experimentally. The radiating fin technique is often used to estimate the thermal conductivity of such sheets.
The radiating fin technique is used for conducting experiments in a vacuum chamber wherein the shroud is often cooled with liquid nitrogen. This can be very expensive. This paper investigates the possibility of obtaining the TDTC of thin sheets by conducting experiments using the radiating and convecting fin approach in ambient conditions. In this paper a formula for a radiating and convecting fin is derived that relates the heat supplied to the fin with the base temperature, tip temperature, temperature dependent emittance of the surface coating and the (unknown) TDTC. The TDTC is assumed to be a polynomial that is linear in the (unknown) coefficients. Linear regression (using the above formula) in conjunction with different heat loads and the corresponding measured tip and base temperatures is used to estimate the unknown parameters.
To validate this model, experiments were conducted on a thin sheet of Ti-6Al-4V both in ambient and under vacuum. The TDTC estimates of Ti-6Al-4V in ambient and under vacuum are compared with data from the open literature. Experiments were also conducted on a Carbon Fibre Reinforced Plastics (CFRP) sheet (43090/M18, bi-directional with 25 layers) to estimate the TDTC in ambient and under vacuum respectively. Uncertainties are observed to be higher when the experiments are conducted in air compared to vacuum. . It is also observed that the estimated TDTC is very sensitive to the base temperature. Further research is needed to improve this technique.
