Abstract
Heat transfer between gas bubble and liquid bath has been studied by using cold models. The rising bubble diameter, velocity and the heat efficiency were measured to explain the mechanism of the heat exchange for various gas–liquid systems.
Preheated gas (N2, He, Ar–He mixture) was injected into the bath of volatile (water) or non-volatile (ethylene glycol, methyl carbitol and ethylene glycol–glycerin mixture) liquid. It is shown that liquid surface tension, gas density and gas temperature are of great importance in determining the bubble diameter. The heat efficiency increases as the bath depth increases and the gas flow rate decreases. The heat exchange is found to be controlled by the heat transfer within the gas bubble.
A model describing time variations in the average temperature and the vapor content inside the bubble has been developed. The computed and measured results reveal that the heat transfer is enhanced with thermal conductivity of gas in the case of gas injection into non-volatile liquid. However, when gas is injected into volatile liquid, the heat efficiency must be considered with accounting for the heat transfer and the vaporization proceeding concurrently.
