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 owrate, 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 con gurations, and the effects of liquid owrate, 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, de ned 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 K 2 . For the range of conditions investigated, reasonable agreement between the experimental results and the theoretical solutions were obtained with a value of K 2ˆ2 £ 10 ¡5 .

A study of transient processes in a closed vessel due to injection of hot liquid sprays

“…A selection of experimental results is presented in Figs. 2-5 in the form of spray chamber absolute pressure p against the injection time t. Further experimental results are given in the previous study [4].…”

“…The initial droplet velocity was then calculated as 35 m/s. Further details are given in the previous study [4].…”

“…The data were captured on a computer, which was also used to control the experimental work. Further details were given previously [4,8]. A selection of experimental results is presented in Figs.…”

“…6, is considered. The energy balance for a droplet can be written as [4] where m D is the mass of the droplet, T D is the droplet temperature, T G is the temperature of the gas/vapour control volume surrounding a single droplet, S D is the droplet surface area, t is time, c D is the specific heat of the droplet, h is the droplet-gas heat transfer coefficient and h fg is the specific enthalpy of evaporation. The energy balance for the gas/vapour control volume surrounding a single droplet is…”

“…This problem was also considered in a previous study [4]. The aim of the previous investigation was to present new experimental data and to understand the basic mechanism of heat and mass transfer from hot water spray droplets into the surrounding gas.…”