Abstract
Summary Supersonic-swirling-separation technology is an innovative gasconditioning technology that separates heavy hydrocarbon and water vapor from natural gas. The Laval nozzle, where the condensation occurs, is used to generate supersonic flow and achieve a high degree of supersaturation in this natural-gas dehydration unit. Therefore, the nozzle shape has a strong impact on the nonequilibrium phase transition and plays a decisive role in distribution of nucleation and growth rate. To optimize the structure of the Laval nozzle and achieve higher separation efficiency, numerical simulation plays an important role in accelerating development cycles and cutting down the cost of experiment. To avoid the complexity of using the multiphase model and real-gas model, a quick and efficienct method is validated and used to determine the location of the nucleation zone and the droplet-growth zone in this paper. On the basis of the Fluent software, this paper presents a numerical-simulation method for condensing flow using user-defined function (UDF). This method itself is an extension of Fluent software for simulating condensing flow by adding a condensation model. The corrected internally-consistent-classical-theory (ICCT) model and Gyarmathy model (gya82) are employed to prescribe this phase transition. Actually, this problem is solved by coupling the Navier-Stokes (N-S) equation and condensate mass equation. Condensing flow in a Laval nozzle is simulated at different nozzle-pressure ratios (NPRs) and initial supersaturations. The results show that high cooling rate results in a high value of supersaturation and nucleation rate in a supersonic expansion Laval-nozzle flow. When condensation occurs, the flow is affected by the latent heat released and the total temperature is increased. This method can accurately predict the distribution of the condensing flow parameters, find an optimized flow state to obtain larger droplets, and ensure that the latent heat released is moderate to maintain a steady flow. Finally, this method is applied to the numerical simulation of a full-scale supersonic-swirling-separator flow field under different work conditions.
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