Transient processes in a closed vessel due to injection of hot liquid sprays

Abstract

An experimental and theoretical study has been made to investigate the transient processes which occur when hot liquid spray droplets are suddenly injected into a gas contained in a closed chamber. A novel experimental apparatus was employed in which hot water is injected via commercial solid cone spray nozzles into air enclosed in a cylindrical spray chamber, of 121 mm diameter and 190 mm height, at a pre-determined constant flowrate, and for a set duration, under computer control. Measurements were made of the spray chamber pressure rise with time due to the combined effects of liquid—gas heat transfer, droplet evaporation and liquid accumulation in the chamber. The experimental results reported in the paper cover a range of nozzle sizes, in both single-nozzle and multi-nozzle configurations, and the effects of liquid flowrate, initial gas pressure and initial liquid—gas temperature difference are considered. A simple analytical model has been developed which subdivides the chamber volume into three zones: a liquid zone, a transfer zone where heat and mass transfer occurs, defined by the spray cone angle, and a still zone outside the spray cone. The analysis gathers the important parameters governing droplet heat transfer in a single dimensionless group, denoted by K2. For the range of conditions investigated, reasonable agreement between the experimental results and the theoretical solutions were obtained with a value of K2 = 2 × 10−5.