Flashing flow model for industrial energy applications

In this thesis, a reliable Computational Fluid Dynamics (CFD) modeling approach is developed for flashing flow. To account for phase change process inside throttling devices, an evaporation model, modified from Lee model, is performed that considers thermal non-equilibrium effect (boiling delay) by artificial coefficients. Two-phase stage of flow in evaporation process is described by mixture model with slip effect between two phases. Results of CFD approach are then validated by experimental benchmarks of flow without phase change (air-water flow) and with phase change phenomenon (flashing flow). Besides, sensitivity analysis of artificial coefficients, turbulence models and turbulence quantities is also performed to complete evaluation of model. Validation shows an agreement between CFD model and experimental data for both global and local results. On the other hand, sizing equation in case of two-phase flow inside control valve is established by adding downstream information into original formula of Leung developed for safety valve. This modification is acceptable due to outlet information is always available for sizing control valves. To validate developed sizing equation, the reliable CFD results for convergent-divergent nozzles from previous stage are used as input data for sizing equation. Convergent-divergent nozzles are used instead of a real control valve in this work due to (i) nozzle and control valve have singularity in geometry (ii) purpose of thesis is to develop a general two-phase sizing equation for all types of control valve so the usage of nozzle geometry is necessary. Finally, results of validation show a better accuracy of present sizing equation than the others in previous works. Besides, validation also confirms accuracy of semi-empirical sizing equations which is used in industry to size two-phase control valve.

In this thesis, a reliable Computational Fluid Dynamics (CFD) modeling approach is developed for flashing flow. To account for phase change process inside throttling devices, an evaporation model, modified from Lee model, is performed that considers thermal non-equilibrium effect (boiling delay) by artificial coefficients. Two-phase stage of flow in evaporation process is described by mixture model with slip effect between two phases. Results of CFD approach are then validated by experimental benchmarks of flow without phase change (air-water flow) and with phase change phenomenon (flashing flow). Besides, sensitivity analysis of artificial coefficients, turbulence models and turbulence quantities is also performed to complete evaluation of model. Validation shows an agreement between CFD model and experimental data for both global and local results. In this thesis, a reliable CFD modeling approach is developed for flashing flow. To account for phase change process inside throttling devices, an evaporation model, modified from Lee model, is performed that considers thermal non-equilibrium effect (boiling delay) by artificial coefficients. Two-phase stage of flow in evaporation process is described by mixture model with slip effect between two phases. Results of CFD approach are then validated by experimental benchmarks of flow without phase change (air-water flow) and with phase change phenomenon (flashing flow). Besides, sensitivity analysis of artificial coefficients, turbulence models and turbulence quantities is also performed to complete evaluation of model. Validation shows an agreement between CFD model and experimental data for both global and local results. On the other hand, sizing equation in case of two-phase flow inside control valve is established by adding downstream information into original formula of Leung developed for safety valve. This modification is acceptable due to outlet information is always available for sizing control valves. To validate developed sizing equation, the reliable CFD results for convergent-divergent nozzles from previous stage are used as input data for sizing equation. Convergent-divergent nozzles are used instead of a real control valve in this work due to (i) nozzle and control valve have singularity in geometry (ii) purpose of thesis is to develop a general two-phase sizing equation for all types of control valve so the usage of nozzle geometry is necessary. Finally, results of validation show a better accuracy of present sizing equation than the others in previous works. Besides, validation also confirms accuracy of semi-empirical sizing equations which is used in industry to size two-phase control valve.