Some basic terms and definitions

Some basic terms and definitions from two-phase flow theory are required for the description of heat transfer in boiling. For this we will consider the section of a channel shown in Fig. 4.48, in which the gas and liquid are flowing. An annular flow is shown in the picture for the sake of simplicity, but the following terms are 

The volume fraction of the vapour in the tube section under consideration is then 

The quantity e is called the volumetric vapour content. This is to be distinguished from the volumetric quality 

4 Convective heat and mass transfer. Flows with phase change 

The quality has to distinguished from the specific vapour content in thermodynamics, which is defined by x = MG/M. With the mass flow rates MG of the gas and Ml of the liquid the mean velocity of both phases in any cross section can be obtained 

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