Non-equilibrium Condensation Phenomenon Research Articles

The bosonic skin effect: Boundary condensation in asymmetric transport

We study the incoherent transport of bosonic particles through a one dimensional lattice with different left and right hopping rates, as modelled by the asymmetric simple inclusion process (ASIP). Specifically, we show that as the current passing through this system increases, a transition occurs, which is signified by the appearance of a characteristic zigzag pattern in the stationary density profile near the boundary. In this highly unusual transport phase, the local particle distribution alternates on every site between a thermal distribution and a Bose-condensed state with broken U(1)U(1)-symmetry. Furthermore, we show that the onset of this phase is closely related to the so-called non-Hermitian skin effect and coincides with an exceptional point in the spectrum of density fluctuations. Therefore, this effect establishes a direct connection between quantum transport, non-equilibrium condensation phenomena and non-Hermitian topology, which can be probed in cold-atom experiments or in systems with long-lived photonic, polaritonic and plasmonic excitations.

Condensation characteristics of ammonia vapor during supersonic separation: A novel approach to ammonia-hydrogen separation

Ammonia has gained significant attention as a prospective hydrogen energy carrier. However, the effective separation of ammonia and hydrogen becomes a crucial aspect after the decomposition of ammonia into hydrogen. In this study, a novel method for ammonia separation is introduced, which leverages the phase transition behavior in supersonic flow. Consequently, this study presents the development of a mathematical model to elucidate the non-equilibrium condensation phenomenon of ammonia, and the accuracy of this model is validated. The simulation results reveal that, in comparison to classical nucleation theory (CNT) and internally consistent classical theory (ICCT), the Lothe-Pound (L-P) nucleation model more accurately characterizes the nucleation process of ammonia at low temperatures. Furthermore, numerical simulations demonstrated that increasing the inlet pressure from 1.2 bar to 1.8 bar led to a 2.66% enhancement in ammonia condensation efficiency. In contrast, raising the inlet temperature from 271 K to 283 K resulted in a decrease in condensation efficiency and a reduction in the radius of the exit droplets, potentially affecting subsequent separation efficiency. When the inlet ammonia molar fraction was elevated from 11% to 14%, the ammonia condensation efficiency increased from 13.7% to 14.5%, with only a minor decrease in outlet droplet radius (from 3.42 × 10−7 m to 3.39 × 10−7 m). These findings indicate that increasing pressure, decreasing temperature, and raising ammonia concentration can all stimulate ammonia condensation. These results have potential implications for the design and optimization of separators.

Supersonic nozzle performance prediction considering the homogeneous-heterogeneous coupling spontaneous non-equilibrium condensation

Supersonic nozzles are widely applied in steam turbines and other industrial fields. Condensation occurs due to rapid expansion of steam flowing through a sonic nozzle. The process is affected by the presence of steam impurities. The primary purpose of this study is to investigate the impact of different heterogeneous particles (solid particles, tiny droplets and NaCl particles) at different concentrations on the non-equilibrium condensing flow, and to classify and calculate condensation losses and total static isentropic efficiency resulting from the non-equilibrium condensation phenomenon. First, the proposed non-equilibrium condensation model is estimated numerically using the Barschdorff nozzle, and the model accuracy is validated by comparing the results with existing experimental data. Second, the effect of different particle concentrations on several condensing flows is studied using the Barschdorff nozzle. The results show that homogeneous condensation will get weaker with an increase in the particle concentration in the vapour condensing flow with solid particles and NaCl particles. Moreover, homogeneous condensation will be slightly enhanced first and then weakened with an increase in the particle concentration in the vapour condensing flow with tiny droplets. The steam condensing flow with different heterogeneous particles at the same particle concentration and the process of pure steam condensation are analysed. The results show that impurity particles in steam have a significant impeding effect on the process of homogeneous condensation. The losses are classified in the Barschdorff nozzle, and the magnitude of the losses and the flow total static isentropic efficiency are estimated. As the particle concentration increases from 1014[1/kg] to 1015[1/kg], the total static isentropic efficiency of solid particles and tiny droplets increases by 12.8 % and 9.6 %, respectively, while the total static isentropic efficiency of NaCl particles decreases by 27.2 %. This indicates that an appropriate increase in the particle concentration can effectively reduce condensation losses and improve total static isentropic efficiency. The paper describes the effect of heterogeneous particles on the steam condensing flow, providing a reference for future research on heterogeneous condensation processes.

Performance evaluation of condensing flow behavior considering magneto hydrodynamics field effects

In industrial equipment, the losses and damages due to the spontaneous non-equilibrium condensation phenomenon are one of the biggest concerns of industry managers. This study focused on wetness loss rate, condensation loss, erosion rate, and kinetic energy of condensing steam flow in industrial equipment (Moses Stein nozzle, IWSEP nozzle, Dykas/ Bakhtar laboratory stationary cascades of a steam turbine) with the magnetic field injecting through equipment walls. The mathematic modeling of condensing flow including the magneto hydrodynamics (MHD) equation, are combined with the non-equilibrium condensation model and k-wSST model, which were verified and established by theory and experiments on an Eulerian-Eulerian approach accounts. Wet steam model is used to investigate the flow behavior between the turbine blades, due to the sonication and non-equilibrium phenomena. At first, such model has been carefully validated against the available experimental data. Then, MHD injecting to flow through walls. At finally, the condensing flow field damage behaviors, such as condensation shock, liquid mass fraction, nucleation zone, wetness loss rate, and erosion rate, are controlled by MHD fields. Finally, each part of the losses is derived from the condensation and wetness loss, which were analyzed. The Findings show that MHD fields play an important role in the nucleation zone. The mass-averaged liquid mass fraction and the average radius of droplets at the outlet of industrial equipment drop sharply with MHD fields. The MHD field injection exhibits 34%, 10% and 25% reduction in condensation loss, the number of droplets due to nucleation phenomenon and the average radius of droplets at the outlet of the Bakhtar laboratory stationary cascades of a steam turbine, respectively. For other equipment the same trend has been predicted.

Applying machine learning for optimization of dehumidification strategy on the modified model for the non-equilibrium condensation in steam turbines

In this study, the dehumidification strategy has been used to reduce the damages caused by the non-equilibrium condensation flow. In the first stage, the non-equilibrium condensation phenomenon modeling has been performed after a sensitivity grid size test, and validated by an Eulerian-Eulerian approach for the machine learning (ML) initial data. In the next step, the location of nozzle have been evaluated for the ML to predict the non- equilibrium phenomenon. Then, the output data of the numerical method have been used as the initial data for the ML method. Finally, after accurately ensuring the prediction of the ML from the behavior of the non-equilibrium condensing flow compared to the experimental data, the dehumidification technique has been linked to the ML. By help of the ML approach, a performance optimization has been carried out to reduce the presence of water droplets on different locations of the blade surface. In this way, the numerical simulations result by applying the ML have been linked and the final optimized model according to the defined parameters has been developed. It is noteworthy to mention that the objective functions are defined according to the energy of flow and the corrosion rate. The outcomes from such optimization could lead the designers to find the best location for suction dehumidification technique for the turbine blades. The machine learning has been linked to three optimization algorithms, including drone squadron optimization, particle swarm optimization, and genetic algorithm. According to the obtained results of the employed machine learning and optimization methodology, for the optimum case compared to the original case, 99%, 1%, 18%, and 90% reductions have been achieved for the erosion rate, entropy, loss of moisture, and droplet sizes, respectively. It means that, by performing such research one could study some optimization parameters and link them by artificial intelligence to investigate the best place for the suction dehumidification technique.

Effect of Superheat Steam on Ejector in Distilled Water Preparation System for Medical Injection.

In this study, a wet steam model was used to investigate the effect of steam superheat on ejector performance and non-equilibrium condensation phenomena. The simulation data for the ejector were validated with experimental data. The simulations show that an increase in primary flow superheat will increase the entrainment ratio, while an increase in secondary flow superheat will decrease the entrainment ratio. The output fluid superheat has little effect on the entrainment ratio. As the primary flow superheat increases from 0 to 20 K, the starting position of non-equilibrium condensation moves backward by 5 mm, and the mass fraction of condensed droplets decreases by 20%. The higher the secondary flow superheat, the lower the mass fraction of liquid in the diffusion chamber. The superheat level of the output fluid has no influence on the non-equilibrium condensation phenomenon of the ejector.

Thermodynamics analysis of CO2 condensation in supersonic flows for the potential of clean offshore natural gas processing

The separation technology of carbon dioxide (CO2) is a key step to achieve high efficient carbon capture and storage targets. In the present study, we propose a new concept to remove CO2 from the offshore natural gas industry, which utilises the combined effect from nonequilibrium condensation phenomena in the supersonic flow and cyclonic separation process from swirling flows. The feasibility study of this concept is evaluated by using computational fluid dynamics modelling. The effect of thermodynamics properties on the phase change process in supersonic flows is analysed in detail. The results show that the supersonic flow can condense 28% CO2 in a liquid state from the main gas flow based on the real gas model. Nine orders of magnitude differences are observed between the mass generations due to the nucleation process and droplet growth process, which indicates that the droplet growth process contributes more significantly to the mass transfer during CO2 condensations. The ideal gas model both under-predicts the mass flow rate and the liquid fraction by 25% and 46% compared to the real gas model. This study demonstrates the potential application of the CO2 separation using the phase change behaviour in supersonic flows.

A Novel Dehumidification Strategy to Reduce Liquid Fraction and Condensation Loss in Steam Turbines.

Massive droplets can be generated to form two-phase flow in steam turbines, leading to erosion issues to the blades and reduces the reliability of the components. A condensing two-phase flow model was developed to assess the flow structure and loss considering the nonequilibrium condensation phenomenon due to the high expansion behaviour in the transonic flow in linear blade cascades. A novel dehumidification strategy was proposed by introducing turbulent disturbances on the suction side. The results show that the Wilson point of the nonequilibrium condensation process was delayed by increasing the inlet superheated level at the entrance of the blade cascade. With an increase in the inlet superheated level of 25 K, the liquid fraction and condensation loss significantly reduced by 79% and 73%, respectively. The newly designed turbine blades not only remarkably kept the liquid phase region away from the blade walls but also significantly reduced 28.1% averaged liquid fraction and 47.5% condensation loss compared to the original geometry. The results provide an insight to understand the formation and evaporation of the condensed droplets inside steam turbines.

Effects of surface roughness and temperature on non-equilibrium condensation and entrainment performance in a desalination-oriented steam ejector

• Wet steam model was built and effects of surface conditions were fully studied. • Increase of roughness reduces the ejector performance and condensation intensity. • The performance varies within 4% as the wall temperature changes from 30 to 150 °C. • The condensation droplets occur on the inner wall when it has poor adiabatic properties. Ejectors usually act as thermal compressors to recover the superfluous water vapor in multi-effect desalination systems. However, the influences of wall conditions on the steam ejector performances were not fully understood. To investigate the effects of the surface roughness and temperature on non-equilibrium condensation and entrainment performance in the steam ejector, a wet steam model was built by a computational fluid dynamics software. Simulation results indicate that the increase of roughness height reduces the ejector performance and attenuates the non-equilibrium condensation phenomenon significantly. Furthermore, as the wall temperature changes in the range of 30–150 °C, the ejector performance varies merely within 4%; however, condensation droplets which may cause erosion damage occurs on the internal surface when the wall has poor adiabatic properties. Therefore, the wall roughness and temperature should be fully considered to enhance the ejector performance and mitigate potential condensation on the wall.

Reduction entropy generation and condensation by NaCl particle injection in wet steam supersonic nozzle

The supersonic nozzle is very often used in many technical applications, such as fluid-flow machines or devices. If the medium flowing through a supersonic nozzle is a moist gas, moist air or wet steam, non-equilibrium condensation must occur. Such mediums usually contain impurities which affect the condensation phenomenon. The main purpose of this research is a numerical study on the effect of the content of impurities in steam on the non-equilibrium condensation phenomenon. In order to achieve this purpose, salt (NaCl) is used. Sodium chloride (NaCl) is a very common steam impurity. It may occur in a soluble or crystal form. Different concentrations of salt are considered as the input quantity. The results show that the process of steam condensation on salt particles has a significant impact on two-phase variables and flow parameters. In the presence of salt, steam condensation starts whenever the supersaturation ratio is above one. Latent heat of the condensation changes the flow pattern and reduces the nucleation rate and water droplet production. The presence of 1015 particles of salt reduces the outlet average liquid mass fraction and entropy generation by 14.5 % and 15.2 % respectively. The research results prove that steam impurities have a significant impact on non-equilibrium condensation.

Steam ejector performance considering phase transition for multi-effect distillation with thermal vapour compression (MED-TVC) desalination system

The multi-effect distillation with thermal vapour compression (MED-TVC) desalination system is efficient to produce freshwater. The steam ejector performance is not fully understood as the phase transition has been ignored in many studies. The present work develops a two-phase condensing flow model to assess the steam ejector performance considering nonequilibrium condensation phenomena. The transition of the flow structure from an under-expanded flow to an over-expanded flow in the steam ejector is investigated in detail. We present that the maximum Mach number can reach 4.02 in the under-expanded flow, which is weakened to 2.88 in the over-expanded flow. The steam undergoes several expansion-compression processes in the steam ejector in the under-expanded flow, which induces the formation and evaporation of massive droplets. In the over-expanded flow, the steam is compressed and then expanded after leaving the primary nozzle and the condensation process is not observed in mixing and constant sections. The increasing suction chamber pressure significantly improves the entrainment ratio while leading to an increasing entropy loss coefficient. The entrainment ratio is improved from 0.25 for the under-expanded flow to 1.69 for the over-expanded flow, while the entropy loss increases from 0.081 for the under-expanded flow to 0.29 for the over-expanded flow. This indicates that the transition of the flow structure from an under-expanded flow to an over-expanded flow can entrain more steam from the last effect while causes more entropy losses in a steam ejector for the MED-TVC desalination system.

Accurate condensing steam flow modeling in the ejector of the solar-driven refrigeration system

The ejectors are widely employed in power engineering installations, both refrigeration, and thermal ones. In the paper, a steam ejector of a solar-driven refrigeration system is investigated numerically, using different CFD models, to reveal the flow structures and evaluate its performance. A modified nucleation model adopting the Benson and Shuttleworth surface tension definition is proposed. The model composed by the modified nucleation model and Young's droplet growth equation demonstrates the superiority in predicting the non-equilibrium condensation phenomenon. An ejector experimental data is contrasted with three different numerical models, the results show that the effect of the non-equilibrium condensation (NEC) on the steam ejector performance cannot be ignored, and the modified model can accurately predict the ejector performance. An investigation of a steam ejector being a crucial part of a solar-driven refrigeration system is carried out employing different models. The internal flow structures and ejector performance are investigated, the difference of results predicted by three numerical models are compared and analyzed. The results show that the non-equilibrium condensation process reduces the entrainment ratio in critical mode, but it will enlarge the critical mode zone. Besides, the treatment of steam property has a certain impact on the calculation results.

Optimization of the primary nozzle based on a modified condensation model in a steam ejector

The beauty and complexity of steam ejectors have fascinated scientists for decade. A modified condensation model is presented to evaluate the steam ejector performance and to optimize the steam ejector geometry. Four models consisting of different nucleation models and droplet growth models are employed to predict the non-equilibrium condensation phenomenon in a nozzle and in a steam ejector. The results show that the modified condensation model is more appropriate than the other three models. The internal flow structures as well as p-h diagram are applied in the steam ejector performance analysis. The results show that the steam ejector entrainment ratio predicted by the modified condensation model is smaller than the value predicted by the dry gas model. Given that the nucleation process mainly occurs in the steam ejector primary nozzle, only the primary nozzle is optimized using the Multi-Objective Genetic Algorithm method based on the modified condensation model. The optimal results indicate that the entrainment ratio of the optimized steam ejector increases by about 27.5% against the original value. The findings are of fundamental and practical relevance. It hopes that experimenters will be motivated to check our predictions.

Feature Extraction of Oscillating Flow With Vapor Condensation of Moist Air in a Sonic Nozzle

The sonic nozzle is commonly used in flow measurement. However, the nonequilibrium condensation phenomenon of moist air in the nozzle has a negative effect on the measuring accuracy. To investigate this complex phenomenon, the experiments on the oscillating condensation flow of moist air were conducted by an adjustable humidification apparatus with different relative humidities (0%-100%), temperatures (30-50°C), and carrier gas pressures (1-6 bar), where the microsize pressure measuring system was designed by Bergh-Tijdeman (B-T) model. The accurate mathematical model of nonequilibrium condensation was also built and validated by the experimental data of time-averaged pressure distribution. Then, the frequency and intensity of pressure fluctuation of oscillating flow at a wide range of operation condition were obtained combining experimental data and physical simulation model. Importantly, a new semiempirical relation of dimensionless frequency deduced from dimensionless analysis was identified accurately by experimental data. Finally, the signal nonstationarity was also observed using the continuous wavelet transform (CWT). The instantaneous frequency saltation and the energy attenuation of pressure signals were observed in the condensation flow.

Annular supersonic swirling flows with heterogeneous condensation

In recent years, separating and extracting technologies of condensate gas have been developed by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow. The technology can reduce the size of the device and does not use chemicals. However, there are many unresolved problems for performance of the separation, extraction and operating principle. Therefore it is necessary to research further in order to improve the performance of the equipment. In the present study, the numerical study was carried out to clarify the effect of the heterogeneous condensation on the characteristics of the swirling flow field in a supersonic annular nozzle, and the differences between homogeneous condensation and heterogeneous condensation in the flow field. As the results, it is found that the condensation flow with a swirl affects the position of sonic line, the generating position of condensate and the radial distribution ratio of liquid phase.

CFD Modelling of the Condensation Inside a Supersonic Ejector Working with R134a

Abstract The present work is about CFD modelling of condensing flow inside a supersonic ejector. The geometry used for the simulations reproduces a small-scale prototype ejector chiller built at Georgia Institute of Technology (Atlanta). The working fluid is R134a, whose expansion inside the primary nozzle and mixing chamber can lead to non-equilibrium condensation phenomena. These alter the pressure and Mach profiles along the ejector, thus generating severe thermodynamic losses. The numerical analysis of non-equilibrium condensation requires modelling of the microscopic behaviour of the fluid with a high level of fidelity. In this study, the condensation of R134a is simulated by means of two in-house developed numerical models. The first considers equilibrium conditions between the phases whereas the latter reproduces the non-equilibrium behaviour of the phase transition. Comparisons are made to understand the limitations and advantages of both approaches.

Numerical Simulation of Compressible Two-Phase Condensing Flows

In the present paper, the hybrid AUSM-van Leer scheme is extended to solve the governing equations of twophase condensing flows. The method of moments with the classical homogeneous nucleation theory is used to model the non-equilibrium condensation phenomenon. Firstly, the hybrid method is validated using two test cases (i.e. Laval nozzle and rotor-tip cascade) and the results are compared with the MacCormack method. Then the hybrid method is used to solve two other problems (i.e. wavy channel and VKI stage). Based on the numerical results of the paper, the hybrid AUSM-van Leer scheme is an accurate method to simulate twophase transonic flows with nucleation. If the super cooling degree reaches to its maximum value, the nonequilibrium condensation begins and wetness fraction increases suddenly. Also across a shock the wetness fraction decreases due to evaporation of the droplets.

Effect of nozzle inlet shape on annular swirling flow with non-equilibrium condensation

Recently, by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow, a separating and extracting techniques of condensate gas have been developed. This technique can reduce the size of the device and don’t use chemicals. In the present study, by using a non-equilibrium condensation phenomenon of moist air occurred in the supersonic flow in the annular nozzle composed of an inner body and an outer nozzle with a swirl, the possibility of separation of the condensable gas and the effect of shape of nozzle inlet on the flow field were examined numerically.

Non-equilibrium condensation of water vapor in sonic nozzle

The non-equilibrium condensation phenomenon during the operation of sonic nozzle is very complicated, and will affect the flow measurement and control of sonic nozzle. Two-dimensional multi-fluid k–ε turbulence models for both homogeneous and heterogeneous nucleation of condensation were constructed to investigate the effect of vapor condensation on mass flow-rate of sonic nozzle. These models were validated by experimental data of homogeneous nucleation in the moist nitrogen flow through a convergent–divergent nozzle by Wyslouzil and the numerical solutions of heterogeneous nucleation in wet steam flow by Dykas respectively. Finally, both models above were applied to study the condensation flow in sonic nozzle. It was showed that the discharge coefficient of sonic nozzle is affected by both homogeneous and heterogeneous nucleation. When the flow is homogeneous, there is significant influence on discharge coefficient with high inlet relative humidity, which agrees with the thermal choking theory. The discharge coefficient deviation reaches 0.275% when the inlet relative humidity is 95%, which is close to the Lim's experimental data with accuracy of 0.15%. However, under low relative humidity condition, the experimental discharge coefficient deviation is larger, which is explained by the heterogeneous nucleation fortunately.

Time-dependent characteristics of the nonequilibrium condensation in subsonic flows

High-speed moist air or steam flow has long been of important subject in engineering and industrial applications. Of many complicated gas dynamics problems involved in moist air flows, the most challenging task is to understand the nonequilibrium condensation phenomenon when the moist air rapidly expands through a flow device. Many theoretical and experimental studies using supersonic wind tunnels have devoted to the understanding of the nonequilibrium condensation flow physics so far. However, the nonequilibrium condensation can be also generated in the subsonic flows induced by the unsteady expansion waves in shock tube. The major flow physics of the nonequilibrium condensation in this application may be different from those obtained in the supersonic wind tunnels. In the current study, the nonequilibrium condensation phenomenon caused by the unsteady expansion waves in a shock tube is analyzed by using the two-dimensional, unsteady, Navier-Stokes equations, which are fully coupled with a droplet growth equation. The third-order TVD MUSCL scheme is applied to solve the governing equation systems. The computational results are compared with the previous experimental data. The time-dependent behavior of nonequilibrium condensation of moist air in shock tube is investigated in details. The results show that the major characteristics of the nonequilibrium condensation phenomenon in shock tube are very different from those in the supersonic wind tunnels.