• Energy Research

This is the final version. Available from Elsevier via the DOI in this record. ; Data availability: Data will be made available on request. ; Carbon capture and storage is recognized as one of the most promising solutions to mitigate climate change. Compared to conventional separation technologies, supersonic separation is considered a new generation of technology for gas separation and carbon capture thanks to its advantages of cleaning and efficient processes which are achieved using energy conversion in supersonic flows. The supersonic separation works on two principles which both occur in supersonic flows: the energy conversion to generate microdroplets and supersonic swirling flows to remove the generated droplets. This review seeks to offer a detailed examination of the cuttingedge technology for gas separation and carbon dioxide removal in the new-generation supersonic separation technology, which plays a role in carbon capture and storage. The evaluation discusses the design, performance, financial feasibility, and practical uses of supersonic separators, emphasizing the most recent progress in the industry. Theoretical analysis, experiments, and numerical simulations are reviewed to examine in detail the advances in the nucleation and condensation characteristics and the mechanisms of supersonic separation, as well as new applications of this technology including the liquefaction of natural gas. We also provide the perspective of the challenges and opportunities for further development of supersonic separation. This survey contributes to an improved understanding of sustainable gas removal and carbon capture by using the new-generation supersonic separation technology to mitigate climate change. ; Ministry of Science and ICT ; National Research Foundation of Korea ; Engineering and Physical Sciences Research Council (EPSRC)

Abstract The present study evaluates the potential of clean natural gas dehydration using nonequilibrium condensations in high-pressure supersonic flows. A computational fluid dynamics model is developed to study the formation of massive nanodroplets due to the phase change process. The impact of thermodynamic models on nonequilibrium condensations in supersonic flows is analysed based on the ideal gas and real gas equations of state. The sensitivity of high-pressure supersonic separations under different inlet temperatures is discussed in detail, including the influences on gas processing capacities and nonequilibrium condensation processes. The results show that an ideal gas modelling not only predicts the earlier onset of nonequilibrium condensations but also under-predicts the liquid fraction by 61% compared to the real gas model. The decreasing inlet temperatures improve gas processing capacities and predict the earlier condensing onset inside high-pressure supersonic flows. The liquid fraction can be enhanced by 21% with a decrease of 10 K inlet temperature from 593 K and 583 K. It suggests that the decreasing inlet temperature could improve high-pressure supersonic separations from the view of the processing capacity and separation performance.

Supersonic separation is a novel technology. A multi-fluid slip model for swirling flow with homogenous/heterogenous condensation and evaporation processes in the supersonic separator was built to estimate the separation efficiency. This model solves the governing equations of compressible turbulent gas phase and dispersed homogenous/heterogenous liquid phase considering droplet coalescence and interphase force. Its prediction accuracy for condensation and swirling flows was validated. Then, the flow field, slip velocity and droplet trajectory inside the separators with different swirl strengths were investigated. The maximum values of radial slip velocity are 29.2 and 8.26 m/s for inlet foreign droplet radius of 1.0 and 0.4 micron. It means the larger foreign droplet has a better condensation rate. However, the residence time of larger foreign droplet in core flow is shorten. Thus, the inlet radius of foreign droplet has to be moderate for best separation efficiency. Finally, the dehydration performances of separator were evaluated. The optimal radius of inlet foreign droplet to maximize the dehumidification and efficiency was found. For the separator with swirl strength of 22%, the optimal radius is 0.85 micron at inlet pressure of 250 kPa, where the maximum dew point depression is 42.41 °C and the water removal rate is 87.82%.

Supersonic swirling separation plays an important role in the separation of the water vapor and heavy hydrocarbons in natural gas processing. A viscous flow solver with slip model was developed to predict the non-equilibrium condensation phenomenon in supersonic separator. Several sets of experiments were conducted to validate the accuracy of numerical models. The detailed introduction of the experimental device was discussed. Then, to investigate the behavior of gas-droplet two-phase flow with strong swirls, the tangential velocity and centrifugal acceleration were simulated. Moreover, the distributions of droplet number density and bulk density of dispersed droplet phase in the supersonic separator were discussed in detail.

Abstract The occurrence of non-equilibrium process of steam condensation has a significant effect on the efficiency of low pressure part steam turbine. To investigate the phenomenon of non-equilibrium condensation of supersonic nozzle including several self-excited oscillating modes, a full Navier-Stokes viscous laminar model for non-equilibrium condensing steam flow was established and validated by experiments and theory. The flow characteristics of pressure oscillation and velocity phase diagrams of different self-excited oscillating modes were analyzed. Finally, the distinct distributions of mass fluxes for both core flow field and viscous boundary layer of the condensing steam flow were discussed further. The results showed the relative variation of the displacement thickness of throat boundary layer is up to 55.73% which is significant.

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record ; Data Availability Statement: The research data supporting this publication are provided within this paper. ; Supersonic separator is a kind of natural gas dehydration device with great potential, but its internal mass and heat transfer process has not been fully studied. In this study, a novel three-field two-fluid model described by Eulerian-Eulerian approach for supersonic separator considering the heat and mass transfer between gas, liquid droplets, and liquid film was developed and validated. The interphase slip, latent heat, film heat flux, and film phase change rate were studied. It revealed that the maximum centrifugal slip velocity of droplets can reach 24.9 m s−1. The maximum latent heat is 5.3 × 108 J m−3 from droplets to gas phase during condensation, and the minimum latent heat is -3.4 × 108 J m−3 during evaporation. The thickness of swirling liquid film at wet gas outlet is 21 μm, 47 μm, 74 μm and 89 μm, respectively. The liquid film temperature decreases to a minimum 304.1 K due to droplets deposition, where the maximum heat flux is 0.74 MW m−2. Besides, the frequency and velocity of the interfacial wave of liquid film were obtained by using the cross-correlation algorithm, and their maximum values was 11.07 Hz and 1.49 m s−1, respectively. In addition, for achieving higher dehydration efficiency, the optimal value of the foreign droplet mass concentration should be 0.01 kg m−3. The maximum separation efficiency and dew point depression of separator A are 85.11% and 40.32 °C, respectively. The model without considering the liquid film over-predicts the separation efficiency. ; National Natural Science Foundation of China

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record ; Data Availability Statement: The research data supporting this publication are provided within this paper. ; The multi-effect distillation with thermal vapour compression (TVC) seawater desalination system provides an excellent energy-saving scheme by escalating the low-level energy. The internal mass and heat transfer in ejectors is an important element to improve efficiency. In this study, a visual mass transfer simulation model considering real thermodynamic properties is used to observe the inner-mixing process. The assessment is from the perspective of visible mixing layer growth and the effect on entrainment ratio. As shown in the mass percentage distribution graph, there is an inescapable phase change on mixing layer boundary, where the wetness of wet steam can reach to 16.0%. Meanwhile, the mixing layer length predicted by dry model is 25.1% higher than wet model. The condensation weakens the mixing process and leads to shorter length. Under subcritical mode, the cross-sectional area of the entrained flow is deducted and the mixing layer cannot develop completely. The critical pressure range predicted without condensation is 18.5% lower, which causes a misjudgment in entrainment ratio because overvaluing the influence of outlet pressure on entrained flow. Thus, mass transfer during development of the two-phase mixing layer has great impact for MED-TVC system. ; National Natural Science Foundation of China ; National Natural Science Foundation of China

This is the final version. Available from Elsevier via the DOI in this record. ; Data availability: No data was used for the research described in the article. ; The phase change in supersonic flows is of great interest in many industrial applications including steam turbines, nozzles, ejectors and aircraft. However, the phase change phenomenon is still not fully understood due to the completed flow behavior including nucleation, condensation, film generation and shock waves in supersonic flows. In the present study, we proposed a modified Euler-Lagrange-Euler model to explore the internal flow mechanism within supersonic separators. The mutual heat and mass transfer of the gaseous phase, droplets, and liquid film were simulated in supersonic flows. The homogeneous nucleation and growth model was innovatively added to ensure the model’s comprehensiveness. The feasibility of the proposed model was validated by experiments. Then, the interaction of heterogeneous and homogeneous condensation in supersonic condensation flow was excavated for the first time. The results show the heterogeneous droplet diameter’s decrease or concentration’s increase had a significant inhibitory effect on homogeneous condensation. Subsequently, the supersonic swirl field’s generation, the dynamic evolution of the homogeneous/heterogeneous droplet condensation and deposition, the liquid film development, and the heat-mass transfer between them in the supersonic separator were analyzed using the proposed model. Furthermore, the separation capacity of the supersonic separator was evaluated considering the co-action of homogeneous and heterogeneous condensation. Results show that increasing inlet droplet concentration from 0.0001 kg/s to 0.0025 kg/s can increase vapor separation efficiency and dew point depression from 61.39 % to 84.74 % and 19.03 K to 28.28 K, respectively. ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China

The supersonic separation offers an opportunity for natural gas processing. The problem is that the phase change of water vapour in the supersonic flow is not fully understood in the presence of shock waves in a supersonic separator. This study aims to evaluate the performance of the supersonic separation with the phase change process and shock waves. The condensing flow model is developed to accurately predict the energy conversion within the supersonic separator. The computational results show that the single-phase flow model over-estimates the vapour expansions by 12.43% higher Mach number than the condensing flow model. The liquid fraction of 8.2% is predicted by the condensing flow model during the phase change process in supersonic separators. The supersonic separator is optimised via combining the diverging part of the supersonic nozzle and constant cyclonic separation tube as a long diverging part of the newly designed nozzle. The optimised supersonic separator reduces the energy loss by eliminating the oblique and expansion waves in the newly designed nozzle, which improves the energy efficiency for natural gas processing.