The flow of flashing water in conduits

The paper presents an interim report on some studies into the phenomena arising during the transport of flashing fluids which form part of a programme of research being conducted at the Heriot-Watt University. This programme is directed primarily towards the flash distillation process and is financed by a grant from the Science Research Council of the U.K. An analysis of flashing flow is presented in which the local rate of vapour formation is introduced since it is the finite value of this which determines the non-equilibrium character of flashing flow. Some discussion of the physical factors governing this rate of flashing is given which leads to the presentation of a simple semi-empirical expression {A figure is presented} where T is local liquid temperature, T_S is the local saturation temperature, x is the local vapour fraction, G is the specific mass flow. Equations are developed to describe flashing flow and analytical solutions are presented for the simple frictionless flow case. For the more general problem including friction effects numerical solutions are given. Experimental work on flashing flow in both horizontal and vertical tubes is described and measurements obtained of the pressure drop and liquid temperature are compared with those obtained from the theoretical model. It is shown that good agreement is obtained over the range of the experiments treating the parameters a₁ and a₂ in the above expression as constants. Turbulence promoters were introduced into the test sections to increase the equilibration and their effects are reported. Experiments using two-component air water mixtures made to check the slip between the phases and to determine the two-phase friction factors are reported. © 1967.