Wetness loss prediction for a wet-type cryogenic turbo-expander based on 3-D numerical simulation

With growing demand for the high-efficiency cryogenic liquid plants, it becomes more and more attractive to develop wet-type cryogenic turbo-expander for high cooling capacity. Spontaneous condensation has significant influence on the thermal efficiency of the wet-type turbo-expander. In this study, the Baumann method is used to calculate the wetness loss in the cryogenic turbo-expander. Two reference expansions, including dry and equilibrium condensation, are modeled with the help of computational fluid dynamics (CFD) method. The model is verified by the experiment measurements on an air turbo-expander. The numerical results show that a uniform value of Baumann factor is unable to accurately predict the loss for certain wetness fractions, especially leading to an underestimation at low wetness fraction. Hence, Baumann factors are determined as a function of wetness fraction based on the experimental data and CFD results. Quantitative analysis on the losses in dry and wet expansions is presented. The proposed 3-D numerical method with wetness-loss-correction Baumann factors has been demonstrated for predicting the wetness loss of the cryogenic turbo-expander.