Liquid Mixing and Heat Transfer in Submerged Combustion Apparatus

Abstract

Studies of both the gas-liquid mixing zone and of pulse response measurement were carried out to account for the mixing condition of combustion gas and liquid within a submerged combustion apparatus. It was found that the liquid in the apparatus was almost completely mixed and that contact of combustion gas with liquid was satisfactory.
A theoretical analysis of the heat transfer rate in the apparatus is developed to reveal a variation of combustion gas temperature and gas humidity with position. Furthermore, the relationship between volumetric heat transfer coefficient h_GA·α and combustion gas mass velocity in the downcomer tube is derived from experimental data.
The optimum depth of submergence, at which heat transfer between high-temperature combustion gas and liquid was completed, was about 25 cm under the following condition : diameter ratio of downcomer tube to airlift tube =1/2.
If the downcomer tube is lowered to a depth of 25 cm, the pressure drop can be controlled at the minimum value without losing heat transfer efficiency. The submerged combustion apparatus was found to be better suited for evaporation than for heating of liquid.