Data on the upwards annular flow of air-water mixtures

Abstract

Data are presented for film thickness, film flowrate and pressure gradient for upwards co-current air-water annular two-phase flow in a 1 1 4 in. bore perspex tube using two types of injector, a multijet type and an annular slot. Film flowrates, film thicknesses and pressure gradients were all observed to be lower with the multijet injector than with the annular slot. The results for pressure drop were compared with the Lockhart and Martinelli correlations and with correlations based on homogeneous flow; the former was found to predict the values closest. The Lockhart and Martinelli hold-up correlation generally overpredicted the film thickness—this is due to the presence of entrainment. Very different patterns of entrainment were observed for the two injectors. For higher liquid rates the entrainment results were found to agree with the correlating line obtained previously for vertical flow using the correlation method of Wicks and Dukler, provided the appropriate “critical Weber numbers” were used for the two types of injector. As in earlier work, at lower liquid rates the entrainment is less than that predicted by the correlating line extrapolated from high liquid rates, and is a function of the gas flowrates. It transpired that the point where the entrainment curve joins the line of the correlation occurs at values of y i + of 16–18 and may be related to the formation of large roll waves on the film surface. The inter-relation of film thickness, pressure drop and film flow rate by velocity profile theories has been studied and is discussed; systematic deviations from theory are found.