Subject index of volume 91

Abstract

The flow characteristics and performance of a vertical liquid jet system having downcomers in an air-water system have been studied in relation to those having no downcomer. In order to obtain the basic data which are necessary for comparing the characteristics between the two systems with and without the downcomer, flow characteristics such as the bubble penetration depth and the gas entrainment rate which change depending on variables such as the nozzle diameter, the jet velocity and the nozzle height were first investigated experimentally. After evaluating the effects of these operating variables on such flow characteristics, empirical equations which may be used to predict the bubble penetration depth and the gas entrainment rate over the range of conditions tested in this ordinary liquid jet system were obtained. For the jet system having the downcomer, the effects of operating variables such as the nozzle diameter, the jet velocity, the downcomer diameter and height, etc. on the flow behaviour or on flow characteristics such as the bubble penetration depth, the gas entrainment rate, the gas holdup, etc. were then investigated, and the empirical correlations useful for predicting the boundary of flow regions, the gas entrainment rate, the gas holdup, etc. in this downcomer device were also presented. Furthermore, a comparison of flow characteristics such as the bubble penetration depth and the gas entrainment rate, which are the factors of importance as indices to evaluate the performance of plunging jet systems, between the two liquid jet systems with and without the downcomer was carried out, based on the results obtained above. As a result, it was ascertained that inserting a downcomer of small size in the gas entrainment region has the effect of markedly increasing the penetration depth of the entrained bubbles compared to that under corresponding conditions in the ordinary liquid jet system having no downcomer without any anxiety over a decrease in performance of gas entrainment and it also produces a much longer gas-liquid contacting section.