Spontaneous Condensation Process Research Articles

Numerical study on carbon dioxide removal from the hydrogen-rich stream by supersonic Laval nozzle

A hydrogen purification system with a supersonic nozzle pretreatment process is proposed to improve the performance of traditional CO2 removal processes from hydrogen-rich streams. A mathematical model of the H2–CO2 double-component condensation was established to investigate the feasibility of CO2 capture in a hydrogen-rich stream using a supersonic nozzle. Compared to the single-phase model, this model is more similar to the objective flow facts and can effectively correct the deviation of the single-phase flow model by 21.4%. Furthermore, the parameters in the H2–CO2 double-components spontaneous condensation process in the nozzle were analyzed, and the microscopic mechanism of CO2 spontaneous condensation was clarified. Finally, the effects of the inlet parameters on the carbon capture efficiency were analyzed. The results indicated that the nozzle is more suitable for purifying hydrogen-rich streams with low temperatures and high carbon content, confirming the possibility of using a supersonic nozzle as a carbon capture method.

Numerical study on the condensation characteristics of natural gas in the throttle valve

Due to the cooling effect of natural gas throttling, spontaneous condensation will occur in the throttle valve, which may affect pipeline system efficiency. However, the condensation characteristics (such as nucleation rate and condensation rate) remain unclear, and the traditional method based on the isenthalpic hypothesis can hardly solve this non-equilibrium issue. Based on the geometry differences between the throttle valve and the Laval nozzle, this paper explored the condensation parameters of the CH4–C2H6 binary mixture in the throttle valve and the Laval nozzle using CFD techniques (solving non-equilibrium condensation at a lower cost). This paper discussed the influence of the inlet pressure and inlet temperature on the spontaneous condensation process in the throttle valve as well. The findings are that the nucleation and droplet growth regions in the throttle valve are closer to the throat but narrower than that of the Laval nozzle, and the liquid mass fraction decreases after reaching the peak value. The onset of droplet nucleation and droplet growth is closer to the throat when increases inlet pressure or decreases inlet temperature. The condensation rate of ethane in the throttle valve is lower than that in the Laval nozzle, and the sensitivity of the nucleation rate and the Wilson point to the inlet parameters is higher and lower than that in the Laval nozzle, respectively.. The main innovation of the paper lies in revealing the differences in the condensation between the throttle valve and the Laval nozzle using the non-equilibrium method.

Large Eddy Simulation of a Condensing Wet Steam Turbine Cascade

Abstract The influence of turbulence modeling approach by means of (U)RANS and large eddy simulation (LES) on the overall modeling of turbulent condensing wet steam flows is investigated using the example of a low-pressure steam turbine cascade. For an accurate numerical treatment of turbulence in the presence of shock waves, necessary for predictive scale-resolving computations, a hybrid flux treatment switches between a baseline nondissipative central flux in energy consistent split form and a shock-capturing upwind flux in shocked regions based on a shock sensor. Condensation is realized by a monodispersed Euler–Euler source term model, the equation of state by the highly efficient and accurate spline based table lookup method (SBTL). The numerical treatment is validated with a decay of homogeneous isotropic turbulence test case containing eddy shocklets. The measurement results of the condensing wet steam cascade are overall much better matched by LES compared to RANS and URANS. Analysis shows that the LES is much better able to account for the inherently unsteady nature of the spontaneous condensation process and its interaction with the trailing edge shock wave structure.

Experimental and numerical research on the effect of the inlet steam superheat degree on the spontaneous condensation in the IWSEP nozzle

The spontaneous condensation process takes place in many power engineering machines and devices, such as steam turbines, supersonic separators, ejectors etc. In the paper, the effect of the inlet steam superheat degree in steam condensing flow through the IWSEP (International Wet Steam Experimental Project) nozzle was investigated experimentally and numerically. The experiment was conducted for the low inlet pressure values under different inlet superheat conditions. The static pressure on the nozzle walls as well as the liquid phase properties in the three positions along the nozzle centreline were measured. The paper delivers new experimental data desirable for validation of the numerical models. For the numerical simulations, a condensation model using the Benson surface tension model was employed, and its accuracy was checked by comparing with the experimental data of SUT. The results state clearly that the condensation model using the Benson surface tension model can predict the spontaneous condensation process accurately, and the error is less than 5%. With the inlet steam superheat degree increasing, the condensation process moves downstream and the condensation strength weakens, and the nucleation zone range increases about 36mm. The presented results provide a good reference for further research in the field of condensing steam flows and for the improvement of both experimental and numerical methods and models.

Effect of impeller blade profile on the cryogenic two-phase turbo-expander performance

Being the core-block of air separation and liquefaction plants, turbo-expanders should definitely be responsible for the most part of refrigeration capacity for the whole cryogenic system. The feasibility and economy of the whole cryogenic equipment can be prompted by achieving two-phase flow state at the turbo-expander outlet. A reasonable design of 3-D impeller blade has an important significance on the thermodynamic performance of turbo-expanders. In this paper, the influences of impeller blade profile on spontaneous condensation flow and thermodynamic performance are investigated. The non-equilibrium spontaneous condensation process in the flow passage is simulated based on Euler/Euler two-fluid models. Classical nucleation theory with non-isothermal correction and Gyarmathy droplet growth model are used for the prediction of the liquid droplets formation and growth. The definition of three-dimensional blade surfaces are determined by relative length of expansion section (RBe) and curvature of diversion section (Cur). The effects of the RBe and Cur values on the flow characteristics and thermodynamic performance are analyzed, such as velocity, nucleation rate, flow losses and exit kinetic energy. Based on results of the analysis, some theoretical guidance on the design of impeller blade profile for cryogenic two-phase turbo-expanders is obtained.

Numerical simulation of CO 2 condensation process from CH 4 -CO 2 binary gas mixture in supersonic nozzles

Supersonic separation technology is a technique potentially applicable in separating CO2 from natural gas. An Euler-Euler two-fluid model is developed to predict the spontaneous condensation process of CO2 in CH4-CO2 binary gas system during supersonic expansion using the nucleation theory and droplet growth model. The proposed model is validated by the experimental data obtained from literature and the effects of inlet temperature, pressure and gas composition on the condensation process are analyzed. The simulation results show that the homogeneous nucleation of CO2 occurs intensively within a short period in the diverging part of the nozzle and the mass fraction of condensed phase increases continuously until the nozzle outlet. The onset of the condensation occurs earlier and more CO2 can be condensed out of the gas mixture at lower inlet temperature, higher inlet pressure and bigger CO2 feed concentration.

Comprehensive investigations into thermal and flow phenomena occurring in the atmospheric air two-phase flow through nozzles

Atmospheric air always contains a certain amount of water vapour being an element of the Earth's hydrological cycle. This content, which can be defined by relative humidity for example, has a significant impact on the transonic flow field. What happens then is the water vapour rapid condensation, due to a non-equilibrium process of spontaneous condensation, followed by evaporation of the resulting liquid phase on shock waves arising in a transonic flow. These two phenomena, related to the moist air flow and the heat transfer between the gaseous and the liquid phase on the condensation wave and on the shock wave, are analysed numerically and experimentally. The analyses were conducted using in-house numerical methods and an in-house experimental facility for testing transonic flows. The investigations focused mainly on geometries of convergent-divergent nozzles, which best represent transonic, i.e. subsonic and supersonic, flows.

Numerical investigation of wet steam spontaneous condensing flow with considering the velocity slip

A new dual-fluid model was proposed considering the phase transition along with the velocity slip between phases. Based on this dual-fluid model, numerical simulations were conducted on the flow field in 2D Laval nozzle as well as in Bakhtar cascade. The simulated results were shown to be of high consistency with the experimental results, but the existing difference still implied that the simulation accuracy of droplets growing could be improved further. The research on the flow in nozzle showed that the degree of supercooling at the inlet has great impact on the process of spontaneous condensation, i.e. lower degree of supercooling at the inlet will bring lower intensity of condensing shock and in the meantime, the position where condensation occurred would be closer to the exit of nozzle as well. The study of the condensing flow in Bakhtar cascade then inferred that the expansion ratio of the passage had opposite effect on the condensation compared with the degree of supercooling at the inlet. Namely, the increase of the inlet degree of supercooling will bring the occurrence of the spontaneous condensation forwards, but the ascent of the expansion ratio then will postpone the condensation.

Influences of friction drag on spontaneous condensation in water vapor supersonic flows

A mathematical model was developed to investigate the water vapor spontaneous condensation under supersonic flow conditions. A numerical simulation was performed for the water vapor condensable supersonic flows through Laval nozzles under different flow friction conditions. The comparison between numerical and experimental results shows that the model is accurate enough to investigate the supersonic spontaneous condensation flow of water vapor inside Laval nozzles. The influences of flow friction drag on supersonic spontaneous condensation flow of water vapor inside Laval nozzles were investigated. It was found that the flow friction has a direct effect on the spontaneous condensation process and therefore it is important for an accurate friction prediction in designing this kind of Laval nozzles.

Effects of turbulence and inlet moisture on two-phase spontaneously condensing flows in transonic nozzles

The objective of the paper is to analyse the effects of flow turbulence and inlet moisture on the process of spontaneous condensation of supercooled steam. Calculations of steady and unsteady spontaneously condensing transonic turbulent flows in Laval nozzles are presented. Comparisons of model predictions with experimental data are discussed.

The effect of turbulence on spontaneously condensing wet-steam flow

This paper deals with the effects of flow turbulence and inlet wetness on the process of spontaneous condensation in Laval nozzles. Two-dimensional computations are presented and compared with experimental data for transonic flows in flat and round nozzles in the case of both the absence and the presence of initial wetness supplied to the nozzle inlet.

The Effect of Turbulence on the Flow of Spontaneously Condensing Moist Steam in Laval Nozzles

A transonic turbulent flow of supercooled steam under conditions of spontaneous condensation is treated. Analysis is made of the effect of flow turbulence at the nozzle inlet on the process of spontaneous condensation.

Theoretical and experimental investigation of condensation in a centered rarefaction wave

The analysis of the process of spontaneous condensation in one-dimensional formulation is dealt with adequately in many papers. However, in reality supersonic flows are not one-dimensional. The most striking effect of two-dimensionality is manifested in two-phase flows, for example in nozzles, inclined sections of jet turbine grills and rarefaction waves. The investigation of these flows, both in the experimental and theoretical aspect, is a complex problem for which a solution has been found only recently. The results are given in this paper of a theoretical and experimental investigation of spontaneous condensation of water vapor in a centered rarefaction wave formed by flow around a protuberant angle by a hypersonic stream.

A study of spontaneous condensation over a wide range of initial pressures

An experimental and theoretical study has been made concerning the flow of saturated vapor through a Laval nozzle with attendant spontaneous condensation, over the range of initial pressures from 2.35 to 29.40 bars. This study has shown that the initial pressure has an appreciable effect on the spontaneous condensation process.