Fast and Accurate Analysis of Steam Condensing Flows Using Ideal Gas Equation

Abstract When the steam is used in fluid machinery, the phase-transition can occur and it affects not only the flow fields but also the machine performance. Therefore, to achieve accurate prediction on steam condensing flow using computational fluid dynamics, the phase-transition phenomena should be considered and the proper model which can reflect the non-equilibrium characterisic is required. In the previous study of us, a non-equilibrium condensation model was implemented in T-flow, and several cases on nozzles and cascades were under the consideration. The model showed quite good predictions on the pressure variations including condensation shock. However, the pressure discrepancies in downstream regions were found in all nozzle cases, and the use of ideal gas law as equation of state seemed to be responsible for them. Therefore, IAPWS-95 or IF97 are usually adopted for wet-steam codes, but it entails highly increased computational costs. In this study, the wet-steam model is modified to ensure the accuracy of pressure in nozzle’s downstream region while maintaining the usage of ideal gas equation, which has a benefit to solve the problem quickly. The numerical results of the nozzles are compared with those of the previous wet-steam model, and the results of equilibrium condensation model are also appended. As a result, the accurate predictions are feasible by using the modified non-equilibrium condensation model. In addition, the corrections on liquid surface tension and droplet growth rate are carried out for underestimated droplet sizes and enthalpy, entropy changes throughout the nozzles are investigated.