A Thermo-Fluid Model of Droplet Evaporation and Pressure Variation in Venturi Liquid-Gas Mixers

Abstract

An analytical model has been developed to determine how effectively the temperature of a flowing hot gas can be reduced through the introduction of cold liquid droplets. The hot gas flows through a venturi-shaped mixer where the cold liquid is introduced into the mixer at the throat, vaporizes, and mixes with the hot gas resulting in a cooler gas temperature at the exit of the mixer. The cold liquid droplet residence time, evaporation time, and mixing with the hot gas determine the extent to which the hot gas temperature can be reduced. The model is used to predict the achievable gas cooling of hot hydrogen, nitrogen, and oxygen with cryogenic droplet coolant of the same species. Temperature and pressure along the mixer for these different fluids are calculated, and trends are presented using a non-dimensional number analogous to the Damkohler number in reaction chemistry. The model can be used to predict the minimum mixer length required to achieve specified amount of hot gas cooling or to assess the cooling efficacy of a mixer of given length for various hot gas and cold liquid flow rates.