Thermal Instabilities in Discharging Gas Reservoirs

The flow structure in a discharging gas reservoir has been studied using schlieren cinematography. Effects due to discharge orientation, gas species, and vessel wall vibration have been observed. Initially, the internal flow structure has been found to be controlled by the mass sink, with streamlines going in approximate straight lines from the vessel wall to the exit orifice. At later time, free convection dominates and recirculation patterns are established. Discharge orientation can have a dramatic effect on the free convection flow field as well as on the growth and stability of the wall thermal diffusion layer. A jet-like structure (initiated at very early time and believed to be caused by wave effects) was observed to extend from the vessel wall diametrically opposite the exit orifice. When the discharge was parallel to but in the opposite direction of the gravitational vector, this jet-like structure was found to cause an instability in the lower wall diffusion layer. Vessel wall vibration resulted in a standing cellular acoustic wave pattern in the gas which, depending on discharge orientation, caused a violent instability. A model for temperature variation in the thermal diffusion layer is discussed and a numerical solution is given. Results of the predicted thermal diffusion layer histories are compared to data. A discussion of vessel orientation effects on critical Rayleigh number is given.