Wet Steam Research Articles

Parametric analysis on parallel flash cogeneration cycle for enhancing heat source utilization

ABSTRACT Demand for electricity and cooling is increasing due to population growth, which in turn increases pollution. Renewable energy sources are gaining popularity due to their lower levels of pollution. Resource utilisation efficiency is an important factor in maximising the efficiency of low-temperature heat sources. In this study, a vapour absorption cooling cycle and a Kalina power cycle were merged. At the economiser, heat is recovered from the heat exchanger and divided into two basic solution streams. The high-pressure flow passes through the boiler evaporator to produce wet steam, while another stream is throttled to an intermediate pressure. The thermal efficiency of the cycle improves with increasing separator temperature, separator pressure, concentration, and heat recovery temperature, but there is an optimal separator temperature for resource utilisation capacity. Increasing separator pressure and heat recovery temperatures improves resource utilisation efficiency. The proposed cycle has a better temperature match in the heating process. The resource utilisation efficiency of the present cycle is 31.13%, which is 90.63% higher than the reference study.

Numerical study on the three-dimensional flow of water film on the outer surface of the hollow stationary blade

In order to figure out the influence of water film on the performance of the turbomachinery, understand the mechanism of the interaction between the high-speed airflow and the water film in turbomachinery, and provide a reference for the design of the subsequent experiments and hollow stationary blade water removal by heating. The commercial software FLUENT with the Eulerian Wall Films model is used to establish a solution method for simulating the flow of water film on the blade. The accuracy of the solution method is verified by comparing it with the results of the water film thickness experiment on the surface of the plate. The distribution of the water film on the outer surface of the vane as well as the influence of the water film on the mainstream field are numerically studied in the condition of the wet steam mainstream. The results show that the gradient of water film thickness on the pressure surface is relatively gentle and is along the radial direction. The gradient of water film thickness on the suction side is along the axial direction, and the value is larger; There is a V-shaped water film agglomeration area on the suction surface near the trailing edge where the water film thickness is greater than 45.7 μm; The top areas on both the suction side and pressure side produce a local water film agglomeration area with the dual effect of the secondary flow and the centrifugal force of the mainstream; The water film flow on the blade surface has little influence of the steam velocity and the speed of the mainstream. The increase of local pressure on the surface leads to an increase in the pressure of the adjacent mainstream areas.

Impact of inlet steam state on ejector internal flow and performance considering non-equilibrium condensation

Most of the numerical studies adopted dry gas model to predict transonic and supersonic flow in steam ejectors, but it cannot accurately reflect flow characteristics in ejectors, since the condensation and evaporation of wet steam is ignored. The current work develops and validates a CFD model describing spontaneous condensation to simulate complicated flow behaviors and phase transition inside an ejector, and illustrates the impact of initial state of primary fluid including wet, saturated and superheated state on flow characteristics, mass and heat exchange and ejector performance. It is found that the initial steam wetness obviously impacts the average liquid fraction in the ejector. Both the superheated and wet initial primary steam suppress the process of mass and heat exchange during nucleation, and the position and intensity of nucleation are influenced by the inlet steam state. Compared with the case of dry saturated inlet steam, the superheated inlet steam improves entrainment ratio by 3.7%, and decreases compression ratio by 2.5%.

A study of the application of wet steam modeling for thermocompressor simulation in TVC desalination

Recently, the wet steam model, grounded in classical nucleation theory, has been utilized for computational fluid dynamics (CFD) simulations of thermocompressors and steam ejectors. However, this model, which accounts for the formation of liquid droplets in a homogeneous non-equilibrium condensation process, presents computational challenges due to its complexity. Unlike the ideal gas model, it involves solving multiple equations concurrently with the Navier-Stokes equations, rendering it computationally intensive and difficult to converge. The primary objective of this study is to evaluate the feasibility and efficacy of employing this intricate wet-steam model for modeling steam thermocompressors, specifically analyzing its impact on pressure, temperature, and Mach number contours. This paper aims to investigate the influence of modeling non-equilibrium condensation on various parameters affecting ejector performance. Utilizing numerical simulations conducted via ANSYS Fluent software, employing both 2-D axisymmetric wet steam and ideal gas models, our study reveals that non-equilibrium condensation leads to a higher entrainment ratio and critical back pressure. Additionally, our findings indicate that while the wet steam model notably affects temperature contours, its effect on pressure and velocity contours is comparatively minimal. The CFD analysis found that pathline trajectories were similar with both ideal gas and wet steam models. Droplet formation and evaporation within the thermocompressor revealed a gradual evaporation up to the midpoint of the constant area section, followed by a rise in liquid mass fraction due to droplet formation. However, after the constant area section, a shock wave led to a sudden pressure increase and decrease in liquid mass fraction of wet steam. These changes persist through the diffuser section of the ejector.Furthermore, to enhance the reliability of our results, this research integrates a robust validation methodology. We compare experimental results obtained from ejector studies in the literature with our simulations. Moreover, we introduce an experimental section in our research, specifically addressing zero suction mass flow rate conditions, thereby offering a practical validation approach.

A New Distribution Method for Wet Steam Injection Optimization

A New Distribution Method for Wet Steam Injection Optimization

Optimization of operating conditions in the steam turbine blade cascade using the black-box method

Water droplets cause corrosion and erosion, condensation loss, and thermal efficiency reduction in low-pressure steam turbines. In this study, multi-objective optimization was carried out using the black-box method through the automatic linking of a genetic algorithm (GA) and a computational fluid dynamics (CFD) code to find the optimal values of two design variables (inlet stagnation temperature and cascade pressure ratio) to reduce wetness in the last stages of turbines. The wet steam flow numerical model was used to calculate the optimization parameters, including wetness fraction rate, mean droplet radius, erosion rate, condensation loss rate, kinetic energy rate, and mass flow rate. Examining the validation results showed a good agreement between the experimental data and the numerical outcomes. According to the optimization results, the inlet stagnation temperature and the cascade pressure ratio were proposed to be 388.67 (K) and 0.55 (−), respectively. In particular, the suggested optimal temperature and pressure ratio improved the liquid mass fraction and mean droplet radius by about 32% and 29%, respectively. Also, in the identified optimal operating state, the ratios of erosion, condensation loss, and kinetic energy fell by 76%, 32.7%, and 15.85%, respectively, while the mass flow rate ratio rose by 0.68%.

Application of Regional Gravity and Magnetic Data in Yambajan and Gudui Geothermal Fields, Tibet

Yambajan geothermal field is the first wet steam field developed in the Chinese mainland. It is also the geothermal power station with the highest elevation in the world. It is rich in geothermal resources and its exploration and development level is relatively high. The Gudui geothermal field is the second largest geothermal display area in Tibet. It is rich in geothermal resources, second only to Yambajan Geothermal field, but its energy construction is relatively backward. In this paper, satellite gravity and aeromagnetic data are used to make a comprehensive comparative analysis of the two regions. The results show that they are both low gravity value areas and weak magnetic, and both of which are located on the fault zone. There is a very obvious relationship between the regional tectonic characteristics and the distribution law of hydrothermal activities, and the tectonic activities provide favorable conditions for the formation of hydrothermal activities. The fault depth in the south of the study area is deeper than that in the north, which is inferred to be caused by plate movement.

Thermodynamic analysis of high temperature cascade heat pump with R718 (high stage) and six different low-GWP refrigerants (low stage)

Decarbonizing industrial heating globally is a significant challenge, driving the integration of high-temperature heat pumps for heat recovery and electrification in the industrial sector. However, current high-temperature heat pumps with low global warming potential refrigerants face limitations in delivering high-temperature heat due to their restricted compressor discharge temperature or require several compressors/intercoolers. To address these issues, a novel high-temperature cascade heat pump system is proposed, utilizing water (R718) in the high stage, while selecting one among six low GWP refrigerants (R1234ze(Z), R1233zd(E), R1336mzz(Z), R600, R600a, R601) in the low stage, with single compressor at each stage. To manage high discharge temperatures of high stage, liquid water injection is applied during high stage compression, modeled for both wet and dry steam. The model is validated against available experimental data with maximum error less than 5 %. Further, the effectiveness of the internal heat exchanger in low stage cycle is assessed for all investigated low stage refrigerants. Results reveal that R718 + R600 offers the optimal refrigerant working pair, achieving a maximum COP × VHC of 2895.1 kJ m−3 for delivering high temperature heat at water condensation temperature of 190 °C and recovering heat from low temperature waste energy of 50 °C.

A new optimization strategy for wet steam effect minimization in steam turbine using combined 2D non-equilibrium wet steam flow and mean-line analysis

Wet steam flow in the low-pressure stage of a steam turbine reduces efficiency and causes blade erosion due to the formation of water droplets. To enhance efficiency and lifetime, shape optimization is a suitable method, but it requires computationally expensive numerical simulations of non-equilibrium condensation in 3D viscous flow. This study introduces a new and effective approach for shape optimization, which employs a mean-line method for two objectives: firstly, to calculate the aerodynamic losses without resorting to computationally expensive 3D viscous CFD simulation; secondly, to filter out the airfoils with high loss values before performing simulation in the optimization process. Instead of a 3D viscous simulation, a 2D inviscid one is employed that can estimate the wet steam loss and liquid droplet radius, which are beyond the capability of the mean-line method. The mean-line method is verified with experimental results of a steam turbine and the 2D inviscid flow simulation is validated with experimental results. The mean-line method and the 2D computational code are coupled with an airfoil generator code and integrated into a genetic algorithm. Moreover, the optimization process proposed in this study ensures that the mean-line method maintains the inlet and outlet flow of the blade under constant conditions, without affecting the other stages of the turbine. The cascade of a steam turbine serves as a test case for the optimization strategy, demonstrating its capability to decrease wet steam loss by 10 % and potentially reduce the erosion rate. This is achieved while being over ten times quicker than 3D optimization.

Numerical Investigation on the Effect of Wet Steam and Ideal Gas Models for Steam Ejector Driven by Ship Waste Heat

Steam ejectors could improve the energy efficiency of ships by efficiently utilizing low-grade waste heat from ships for seawater desalination or cooling. The internal flow characteristics of steam ejectors can be deeply analyzed through numerical simulation, which is of great significance for improving their performance. Due to the influence of the nonequilibrium phase change, the results of the wet steam model and the ideal gas model are significantly different. In this paper, the flow field characteristics of the wet steam model and the ideal gas model under different primary flow pressures (Pm) are compared and analyzed. The results show that the structures of the shock wave train for the wet steam model and the ideal gas model are different under different Pm. When the first shock wave of the shock wave train changes from a compression shock wave to an expansion shock wave, the Pm for the ideal gas model is 75,000 Pa and that for the wet steam model is 55,000 Pa. The phase change reduces the energy loss of the shock wave. With the increase in the Pm, the variation in the length of the shock wave train for the wet steam model decreases by 61%, the variation of the primary temperature at the nozzle exit increases by 60% and the variation in the choke temperature decreases by 50% compared with the ideal gas model. The investigation in this paper provides guidance for the design theory of a ship waste heat steam ejector.

An investigation comparing various numerical approaches for simulating the behaviour of condensing flows in steam nozzles and turbine cascades

The process of condensation takes place within the low-pressure stages of the steam turbine when undergoing rapid expansion. The dry supercooled steam turns into very tiny liquid droplets, and the resulting wet steam mixture causes additional losses and maintenance problems. Accurate simulation of steam condensing flows helps to obtain accurate information about the thermodynamics of such flows and use this information in the design of highly efficient steam turbine stages. In this study, by using the available numerical models in commercial CFD codes, seven cases are considered for simulating steam condensing flows. The important difference between these cases is the use of different condensation models and different equations of state to calculate the thermodynamic properties of wet steam. The objective of this research is to identify an appropriate model that can be used to simulate the flow of steam condensation effectively. In recent studies, it is still necessary for further improvement of the modelling methods because the numerical results did not fully match the experimental findings, underscoring the persisting uncertainties within this domain. The current study explores various condensation models and equations of state for calculating the thermodynamic properties of wet steam. This diversity of approaches is novel and allows for the comparison of different models to determine the most suitable one for effective flow simulation. The geometries of the IWSEP nozzle (International Wet Steam Experimental Project) and linear cascade of the last-stage rotor blades were considered. To identify the most appropriate model for the simulation of steam condensing flows, the numerical results are validated against in-house experiments. The results indicate that combining the Young droplet growth model with the Vukalovich and Young equations in cases 1 and 2 is not a suitable method for modelling steam condensing flows. However, cases 3 & 4, which are the combination of Gyarmathy and Fuchs-Sutugin droplet growth models with NIST real gas models, are the most appropriate ones. The findings of this research confirm the high sensitivity of the modelling of such flows, and emphasize that the necessary care should be taken in choosing the appropriate numerical model.

Enhancing low-pressure stage steam turbine using the TDLD criterion and the TOPSIS analysis

The liquid phase in the wet steam flow causes thermodynamics losses and affects steam turbine blade durability. The main objective of the present research is the design of the rotor stagger angle and different operating conditions in the low-pressure stage of the steam turbine. A two-phase Eulerian-Eulerian model and the SST k − ω model are used to simulate the viscous wet steam flow inside the steam turbine stage. Frozen rotor methodology is employed for modeling the stator-rotor interaction. The effects of different rotor stagger angles and different outlet pressure levels on the wet steam flow parameters are studied to introduce an improved case. The turbine stage efficiency, droplet average radius, liquid mass fraction, and degree of reaction (TDLD) are considered as design criteria. The search for the improved value of pressure ratio and rotor stagger angle is performed using the TDLD criterion by TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution). The improved case is selected with a rotor stagger angle of 64 degrees and outlet pressure of 6.5 kPa, at which the turbine stage efficiency (TSE) is increased by 21.3% compared to [Formula: see text]. Also, the liquid mass fraction (LMF) and the degree of reaction (DOR) reduced by 39.53 and 26% relative to [Formula: see text], and [Formula: see text], respectively. In addition, droplet average radius (DAR) increases by 26.14% compared to [Formula: see text].

Performance of supercritical carbon dioxide (sCO2) centrifugal compressors in the Brayton cycle considering non-equilibrium condensation and exergy efficiency

The Brayton cycle, with supercritical carbon dioxide (sCO2) centrifugal compressors at its core, has received widespread attention for its high efficiency and energy savings. Therefore, the in-depth exploration of the internal flow field behaviour of sCO2 centrifugal compressors becomes especially critical. In the present study, we develop a mathematical model to evaluate the performance of a sCO2 compressor considering non-equilibrium condensation in transonic flows. It is validated that the model can well predict the sCO2 phase change and is a reliable vehicle for the performance analysis in this study. Further, by incorporating the cubic spline curve extrapolation method, the model can handle the complex thermodynamic properties of CO2 under a metastable state. Then, this study presents a series of analyses for the effects under different conditions, such as different inlet temperatures and rotational speeds, on the flow field characteristics and performance of the compressor. It’s further found that with an increase in inlet temperature, the condensation intensity is suppressed and the condensation position moves backwards. At the 50% blade span, the liquid phase fraction decreases from 5.15% at 306 K to 1.32% at 325 K. Finally, from an energy perspective, this study implements a quantitative analysis of the exergy destruction and exergy efficiency of the compressor. The results show that the exergy efficiency under the wet steam model is quite different when the inlet temperature changes. With the decrease of rotating speeds, the exergy efficiency will decrease. The exergy efficiency reaches 81.35% at 20,000 rpm, which is 51.02% higher than that at 10,000 rpm.

CRITERIA AND CONDITIONS OF THE INTER-CIRCUIT THERMODYNAMIC INSTABILITY OF THE NPP’S MODERNIZED TURBINE SYSTEM

The original method of determining the criteria and conditions of inter-circuit thermodynamic instability in the modernized system "steam turbine - regeneration system with absorption heat pumps" is presented. This was developed through a thermodynamic analysis of the effect of independent fluctuating deviations from equilibrium in both the wet vapor flow at the absorption heat pump inlet and the measured pressure in the absorption heat pump/low pressure mixing heaters. Unlike known approaches to modeling thermodynamic processes, the thermodynamic model of the developed method takes into account the influence of fluctuating deviations from the equilibrium state of thermodynamic parameters, which determine the criteria and conditions of interloop thermodynamic instability. Based on the analysis of the received criteria and conditions, it was established that the main cause of inter-circuit thermodynamic instability in the modernized system "steam turbine unit — a regeneration system with absorption heat pumps" is determined by the incompleteness (inertia) of heat-mass exchange and hydrodynamic processes during fluctuating deviations from the equilibrium state of thermodynamic parameters. Prevention of the conditions for inter-loop thermodynamic instability in the modernized system "steam turbine unit — a regeneration system with absorption heat pumps" can be ensured by installing flow controllers in the wet steam supply circuits from the high-pressure cylinder of the turbine to the absorption heat pumps, and absorption heat pumps in mixing heaters low pressure to maintain a constant pressure in absorption heat pumps and low pressure mixing heaters. It is also necessary to consider that the modernization of the "steam turbine unit — a regeneration system with absorption heat pumps" system can affect the performance and conditions of inter-loop thermodynamic instability of "neighboring" systems. These issues determine the need for further analysis of the validity of the modernization of the "steam turbine unit — a regeneration system with absorption heat pumps" systems.

Wet steam flow in 1100 MW turbine

Wet steam flow in 1100 MW turbine

Energy and exergy analysis of primary steam superheating effects on the steam ejector applied in the solar renewable refrigeration cycle in the presence of spontaneous nucleation

Abstract The generator energy consumption in the renewable refrigeration cycles is supplied by solar energy, geothermal energy and waste heat. The thermal energy of low grade can be utilized to superheat the vapour in a generator of the refrigeration cycle. The effect of primary flow superheating was examined on the renewable refrigeration cycle performance using the wet steam model in the ejector. The vapour’s degree of superheating was selected in the 0–100 K range. The superheating level effects were investigated on parameters (wet steam, entrainment ratio, energy consumption, COP, second law efficiency and exergy destruction). The aim of this study is a comprehensive evaluation of the effect of superheat on the ejector refrigeration cycle and the flow behavior in the steam ejector simultaneously. The results represented that superheating the inlet steam in the primary nozzle weakens the spontaneous condensation intensity and delays the condensation shock, the combining process between the secondary flow and the primary flow is improved, and the entrainment ratio is increased, the generator energy consumption and the efficiency of the second law are decreased, the exergy destruction in the ejector is reduced, and the total exergy destruction of the refrigeration cycle is increased. Considering the second law efficiency, COP, the entrainment ratio and the energy consumption, a temperature of 40° of the superheat was achieved as the best degree of the superheat in this cycle that in comparison to the state without superheating, the entrainment ratio and COP are increased by 4.4 % and 1 %, the second law efficiency and the generator energy consumption are reduced by 19.5 % and 1.6 %, respectively.

Calculation of Thermodynamic Wetness Loss in Steam Turbines Using Computational Fluid Dynamics Simulation

Abstract In the paper, the behavior of wet steam flow is described in three different steam turbines. The first one is the 1100 MW turbine in the nuclear power plant with the pressurized water reactor. The second one is the 660 MW turbine in the fossil fuel power plant with ultrasupercritical steam parameters at the turbine inlet. The last turbine has a nominal output of 34 MW and operates in the municipal waste-to-energy plant. However, this turbine can often also operate even at 2 MW or higher. In all three turbines in the last stage area passages are made for an optical probe to measure steam wetness and primary droplets size, and for a pneumatic probe to determine the pressures, velocities and flow directions. Based on experimentally obtained data, analyses of thermodynamic wetness loss for all three turbines are performed using numerical flow simulations considering equilibrium and nonequilibrium steam. The condensation model that includes the nucleation rate and droplet growth velocity used in ansyscfx is calibrated based on experimentally obtained data. It is evident that the obtained loss patterns depend fundamentally on the turbine type and operating parameters.

Numerical investigation of the effects of dry gas model and wet steam model in solar-driven refrigeration ejector system

Abstract Nowadays, the use of equipment with little pollution is essential due to the increase in the planet’s temperature. Ejectors are considered one of the equipment with no pollution, and their failure rate is low due to the lack of moving parts. Also, scholars have recently focused on improving the efficiency of industrial equipment. The use of accurate modeling is required to improve steam ejector performance. In a steam ejector, non-equilibrium condensation creates a two-phase flow situation. The wet steam model, used in this study, characterizes this two-phase flow. The study’s objective was to compare this wet steam model with the dry gas model. In the wet steam model, the liquid mass fraction is 0.25, and its calculated entrainment ratio is lower than the dry gas model, closely matching experimental observations. The dry gas model reaches a maximum Mach number of about 5, while the wet steam model approximates 4. A significant temperature difference exists between the two models, with the dry gas model indicating lower temperatures compared to the wet steam model. Diagonal shocks and expansion waves are evident in the mixing chamber, fixed cross-section, and diffuser. These phenomena occur with greater intensity and a slight delay in the wet steam model compared to the dry gas model.

Exergy Audit of Thermodynamic Parameters and Performance Analysis of OgorodeThermal Power Plant in Delta State, Nigeria.

The exergy analysis of the Ogorode steam plant is presented. The aim was to determine and identify the magnitudes and locations of real exergy losses in order to improve plant efficiency. The exergy losses occurred in the various components of the steam plant, such as the boiler, economizer, turbine, super heater, condenser, pump, feed water heater, reheater, and air pre-heater, and these have been calculated using the concepts of availability or available exergy and irreversibility. The temperature and pressure of the plant's running conditions were combined to determine the process irreversibility (exergy losses) and the exergy efficiency of the plant. The exergy losses of the individual components of the plant show that the maximum exergy losses are in steam turbine operation one (STO ) and steam turbine operation two (STO ). STO and STO are 813 kJ/kg, 1 2 1 2 820 kJ/kg, 822 kJ/kg, and 815 kJ/kg that occurred in the turbine between 2019 and 2021, while the minimum exergy losses in STO and STO are 68 kJ/kg, 150 kJ/kg, 1 2 280 kJ/kg, and 276 kJ/kg that occurred in the boiler system between 2019 and 2021. There was a high energy efficiency of 82% and 80% in the superheater between 2019 and 2021, while 89% in the feed water heater and 73% in the superheater had the same duration. The efficiency of 15% and 21% were the minimum in the pump system between 2019 and 2021, while the turbine had a minimum of 20% and 27% from 2019 to 2021. The highest losses of exergy occurred in the turbine as a result of the irreversibility inherent in the turbine process, corroded turbine blades as a result of wet steam, and low energy delivered to the superheater tubes. It was concluded that the turbine inlet temperature should be increased, more energy delivered to the superheater should be increased, boiler pressure should be increased, and weak feed water heaters should be replaced for better performance of the thermal plant.

THERMAL STATE OF THE LOW-PRESSURE CYLINDER WORKING BLADES OF THE COGENERATION TURBINE T-250/300-240

The important problem of researching the temperature state of the low-pressure cylinder of a powerful cogeneration turbine, which works, unlike condensing turbines, in conditions of significant changes in electrical and thermal load, is considered. This is since the low-pressure cylinder of the cogeneration turbines in the heating season operates at the low-flow rate modes due to the large selection of steam for heating. Such operating conditions are accompanied by the nucleation of vortex structures in the flow path, which leads to a significant increase in mechanical energy losses and, consequently, to an increase in the temperature of the elements of the flow path. The aim of the study is to determine the thermal state of the steam in a wide range of changes in the operation modes of the cogeneration turbine. The analysis of the results of experimental studies obtained on full-scale low-pressure cylinders of a powerful T-250/300-240 steam turbine by various authors in conditions of wide changes in operating parameters (the pressure in the condenser, the steam consumption in the flow path, the temperature of the lower heating selection) was performed. This made it possible to determine the temperature distribution along the height of the working blade of the last stage, which is of the greatest interest in the conditions of operation at the low-flow rate modes. The location of the minimum temperature is established, and a dependence is proposed for its determination at the exit from the working wheel of the stage, considering that the main generator of heat during steam heating is a rotating vortex in the rim clearance. It is shown that the limiting value of steam consumption through the last stage, which corresponds to the transition of the flow from the area of wet steam to the area of superheated steam, at a given temperature level in the lower heating selection, depends on the pressure in the condenser and can be determined as a function of these parameters. At the same time, with a decrease in the temperature in the lower heating selection and the pressure in the condenser, it will lead to the fact that the transition from the west steam to the superheated steam is observed at lower consumption. The increase of process moisture at the outlet of the working wheel occurs when the steam flow is greater than its limiting value.