| Abstract |
This paper questions the widely held view that expansion in the total flow nozzles takes place without significant thermodynamic disequilibrium between the phases. A simplified separate flow model of these two phase expansion is presented in which the liquid phase is considered as a population of size monodisperse droplets. The flow is taken to be homogeneous and driven by the sum of the enthalpy drop components from the liquid, the flashed vapor and the original vapor. The flashing is deemed to be quiescent and located at the interface and to be controlled by the rate of conductive heat transfer form the droplet core. The liquid is liable to become superheated whilst the vapor is likely to be supercool. The method of analysis is illustrated by an example in which expansion commences from 14 bar with initial dryness fractions of 0.1, 0.2 and 0.5 and a range of droplet diameters. The most significant finding is that deferred flashing and hence thermal disequilibrium is highly sensitive to droplet diameter, d. For d = 500 um less than 20% flashing occurs whereas with d = 100 um, 40-60% lahsing is secured. Attention is drawn to the uncertainties introduced by independent transients arising from the heat transfer rate form the droplet core, the initiation of flashing and the expansion rate through the nozzle. |