An experimental and analytical investigation of thermoacoustic convection heat transfer in gravity and low-gravity environments

An experimental and analytical study of Thermoacoustic Convection (TAC) heat transfer in gravity and low-gravity environments is presented. The experimental apparatus consisted of a cylinder containing air as fluid. The side wall of the cylinder was insulated while the bottom wall was allowed to remain at the ambient temperature. The enclosed air was rapidly heated by the top surface which consisted of a thin stainless steel foil connected to a battery pack as the power source. Thermocouples were used to measure the transient temperature of the air on the axis of the cylinder. The output of the thermocouples were displayed on digital thermometers and the temperature displays were recorded on film using a high-speed movie camera. Temperature measurements were obtained in the low-gravity environment by dropping the apparatus in the 2-seconds Zero-Gravity Drop Tower Facilities of NASA Lewis Research Center. In addition, experiments were also performed in the gravity environment and the results are compared in detail with those obtained under zero-gravity conditions.

A conduction-only numerical heat transfer model was developed to compute the transient air temperature in the cylindrical geometry. For the purposes of comparison, the experimental geometry and boundary conditions were employed in this numerical model. The results are compared to the experimental data to determine the significance of the thermoacoustic convection heat transfer mechanism. It is observed that the rate of heat transfer to the air measured during the experiments is consistently higher than that obtained by the conduction-only solution.

A one-dimensional TAG numerical model was developed to determine the unsteady temperature distribution in the enclosed air. This numerical model is similar to those studied in earlier investigations of thermoacoustic convection heat transfer. The governing equations were numerically integrated employing the transient heater-surface temperature measured in the experiments. The numerical results show that the variations in the non-dimensional air temperature with time agree