CFD-Simulation of Bulk Condensation Considering the Finite Rate of Interphase Heat Transfer

Abstract

The work is devoted to simulation of the bulk condensation in a supersonic flow of a vapor-gas mixture through the Laval nozzle considering the finite rate of the interphase heat transfer. Numerical methods are examined for predicting the temperature of droplets using the improved VOF (Volume of Fluid) and Eulerian multiphase models. It has been demonstrated that, compared to the Eulerian model, the VOF model more accurately predicts the known experimental data and provides the numerical solution whose stability is less susceptible to the effect of high intensity source terms. Comparison of the predictions with the experimental data of other authors has revealed that the two-temperature model more accurately describes the flow with bulk condensation than the single-temperature model does. The application of a single-temperature approximation is justified when the impurity content in the mixture does not exceed 2% (by weight) since the zone of the active condensation onset is relocated considerably compared to its relocation in the case of the two-temperature approximation. However, the single-temperature approximation is recommended only for calculating the overall heat release level that could be beneficial, for example, for quick assessment of the effect of bulk condensation on turbine stage performance. The previously obtained estimates confirmed the applicability of the single-temperature formulation at an impurity content as high as 5 wt %, but solving this problem in 3D formulation improved the accuracy of these estimates. It has been revealed that the assumption about the flow homogeneity along the channel height (as one of the assumptions employed in one-dimensional calculations) during bulk condensation in a slot-type Laval nozzle is not valid on changing-over to a three-dimensional two-temperature formulation: supersaturation persists at the phase boundary, as a result of which the droplet growth process continues at the circumference of the flow.