Steam Wetness Research Articles

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%.

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 simulation of ultrasonic velocity in wet steam

Wet steam widely exists in thermal power plants, nuclear power plants and other power engineering. The accurate measurement of steam wetness is very important for the safety and economy of power engineering. Ultrasonic method is feasible to measure the concentration of two-phase flow in particle system. In order to obtain a theoretical model of ultrasonic velocity which can be applied to high flow velocity conditions (Reynolds number > 4000), the numerical results of several ultrasonic propagation characteristics theoretical models are compared with the experimental results. The calculated results of U-A coupled phase model show good agreement with the experimental results (the max error is 3.8%), and the model is more suitable for the numerical calculation of ultrasonic sound velocity in droplet two- phase flow with high flow velocity. The ultrasonic sound velocity of steam system in nuclear power plant is calculated numerically. When the droplet size is less than 8 μm, the sound velocity is sensitive to the variation of the droplet size, and when the droplet size is larger than 8 μm, the sound velocity is almost unaffected (velocity variation <0.5%) by the fluctuation of the droplet size. When the effect of the droplet size change on sound velocity can be ignored, the ultrasonic sound velocity method combined with U-A coupled phase model can be used to measure the steam wetness online.

Study on ultrasonic attenuation characteristics in air-droplet two-phase flow

The wetness of exhaust steam in nuclear power plant steam turbine is an important index to evaluate the safety and economy of nuclear power plant and the ultrasonic attenuation method has the advantages of quick response and non-contact in the steam wetness measurement of nuclear power plant steam turbine. The saturated steam-droplet medium and the air-droplet medium have many similar thermal fluid characteristics, in order to simplify the experiment, the air-droplet two-phase flow is used to simulate the wet steam discharged from steam turbine of nuclear power plant, and the ultrasonic attenuation coefficient in the air-droplet two-phase flow is measured. The correlation between wetness and ultrasonic attenuation coefficient was studied by calibrating the wetness of the air-droplet two-phase flow and measuring the ultrasonic attenuation coefficient under different wetness conditions. Meanwhile, the static characteristics of ultrasonic transducer and the influence of flow velocity on attenuation coefficient are studied experimentally. According to the results of experiment and numerical calculation, the ultrasonic attenuation coefficient is very sensitive to the change of wetness. The ultrasonic attenuation coefficient and wetness has a good linear relationship in the wetness range (0–16%), the ultrasonic attenuation method is appropriate for the wetness measurement of turbine steam exhaust and has high precision when the droplet size is stable.

Effect of cut-off and compression ratio on the isentropic efficiency during off-design and part-load operations of a Wankel rotary steam expander used for small scale cogeneration

• A new Wankel rotary expander has been developed for use with saturated steam. • Peak isentropic efficiency is 88% and in the range 60 to 88% for off-design. • Analysis reveals clear impact of cut-off on isentropic efficiency. • Any cut-off and pressure ratio combination can provide peak isentropic efficiency. • Dynamic admission-volume control can maintain high efficiency for all mass flow. Expanding steam from boiler pressure to process pressure using an expansion device instead of a pressure reducing valve is recommended for improving energy efficiency and reducing operational costs. However, there are challenges in realizing this potential with existing technologies (such as turbines) due to wetness of process steam and mass flow rate variations caused by load changes. Positive displacement expanders, such as screw and reciprocating engines, can handle wet steam but, they are designed to handle variable mass flow only by throttling leading to exergy destruction and poor economic performance. In this paper we present an improved Wankel steam expander by analysing the impact of mass flow variations and translating it into key design elements: cut-off and compression ratio of the expander. Theoretical analysis in this study resolves conflicting definitions found in literature on compression ratio and cut-off used for designing a positive displacement expander (such as Wankel) and its impact on isentropic efficiency prediction. Experimental analysis of the Wankel expander reveals that a peak isentropic efficiency of over 85% can be achieved for high cut-off. The range of measured isentropic efficiencies were from 60 to 88% for different pressure ratios and at 40% and 62% cut-off. As the pressure ratio increased, the peak efficiency shifted to a lower cut-off condition. When compared to the Wankel, the peak efficiency of a reciprocating expander was only in the range of 50–55% . Thus, the Wankel expander developed in this study presents an opportunity to improve the exergetic efficiency of process steam.

A visual mass transfer study in the ejector considering phase change for multi-effect distillation with thermal vapour compression (MED-TVC) desalination system

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.

Measurement of steam flow rates using a clamp-on ultrasonic flowmeter with various wetness fractions

Most of the heat in industrial plants is supplied by steam. To minimize energy waste, measuring the steam flow rates in existing pipes is important. Clamp-on ultrasonic flowmeters are used for this purpose, for which the sensors are attached to the pipe wall. However, flow conditions that can be used are limited because the signal-to-noise ratio of the ultrasonic signal in a steam flow is low. Furthermore, the steam wetness increases with heat losses, which may affect measurement results. Therefore, flow rate measurements in wet steam flows using clamp-on ultrasonic flowmeters have not been fully established. In this study, steam flow rates with various wetness fractions and system pressures were measured using a laboratory-made clamp-on ultrasonic flowmeter. The results show that flow rates in wet steam could be determined within a 10% error under general conditions in a steam piping system, although the conversion factor from line-average to area-average velocities was calibrated in superheated conditions, and the speed of sound in saturated conditions at each pressure was used. However, the error of the flow rates tended to increase with the wetness fraction and was biased toward positive values. The speed of sound and liquid volume fraction were evaluated at different wetness fractions. The flow rate error due to the change in sound speed was less than 1%, and 1.2% of the flow rates were overestimated owing to the liquid volume fraction. The velocity distribution in wet steam was considered different from that in the superheated steam owing to the existence of the liquid phase, and the change in velocity profile may lead to an overestimation of the steam flow rates in the wet steam condition.

Application of Hydrogen–Oxygen Steam Generators for Secondary Flash Steam Superheating at Geothermal Power Plants

One of the promising areas of applying hydrogen technologies in power engineering is to increase the capacity utilization factor and efficiency of turbine units by means of hydrogen–oxygen steam generators for superheating the working medium under the conditions in which the surplus electricity generated at power plants during the periods of daily and seasonal reduction in electric power consumption can be used for generating hydrogen. The use of steam superheating systems on the basis of hydrogen–oxygen steam generators at geothermal power plants is especially important in view of a low energy potential of geothermal heat carrier serving as the initial heat source. The article presents the results from computational studies of the technical advisability and technical-economic efficiency of implementing systems for increasing the secondary flash steam energy potential by using a hydrogen–oxygen steam generator and a binary power unit at a direct-cycle geothermal power plant operating on steam hydrotherms. The results from computational studies into the power characteristics of a combined binary cycle geothermal power plant with secondary flash steam superheating depending on the expansion pressure variations and the hydrogen–oxygen steam generator capacity are considered. It has been determined that the use of a 12-MW hydrogen–oxygen steam generator for superheating secondary flash steam results in that the steam wetness downstream of the steam turbine last stage decreases from 14 to 7%. Calculation results have shown that the topping of a direct-cycle geothermal power plant with a system for increasing the energy potential of secondary flash steam on the basis of a hydrogen–oxygen steam generator and a binary power plant makes it possible to increase the geothermal power plant capacity by almost 25% and its efficiency by 3.0–3.5%. Based on the feasibility study results, investors can select the optimal composition and characteristics of equipment in implementing a system for increasing the energy potential of secondary flash steam using a hydrogen–oxygen steam generator and a binary power unit at a direct-cycle geothermal power plant.

An experimental study of the integral characteristics of the intrachannel liquid film suction in a turbine stator blades cascade

This paper presents the results of an experimental study of the integral characteristics of the intrachannel liquid film suction in a flat cascade of turbine stator blades. Two slots for removing the liquid film from the interblade channel were arranged on the pressure surface of the stator blade. The experiments were carried out with initial steam wetness y 0 = 3 ÷ 9.5 % and theoretical Mach number downstream the cascade M lt = 0.6 ÷ 0.78. The operation mode of the moisture removal system was determined by the relative pressure drop on the moisture-removing slots and varied over a wide range. The investigations were carried out for both the operation of the moisture-removing slots one at a time and the combined suction of the liquid film simultaneously through both slots. The measurement system used in the experiments allowed separately determining the mass flow rates of steam and liquid removed from the interblade channel. The obtained integral characteristics served to evaluate the influence of various factors on the efficiency of the intrachannel moisture removal system. Based on the analysis of the research results, recommendations on the design and operation of intrachannel moisture removal systems have been formulated.

Experimental Investigation for Influence of Static Pressure and Steam Wetness on Pressure Fluctuation of Acoustic Resonance in Coaxial Side-Branch under Wet Steam Flow

Experimental Investigation for Influence of Static Pressure and Steam Wetness on Pressure Fluctuation of Acoustic Resonance in Coaxial Side-Branch under Wet Steam Flow

Combined Effects of Steam Wetness and Pressure on Characteristics of Acoustic Resonance Amplitude in Closed Side Branch

AbstractSteam piping and components in many industrial applications such as power plants sometimes experience structural vibration and fatigue damage caused by flow-induced acoustic resonance in piping with closed side branches. The state of steam in the steam piping can be not only dry (superheated) steam but also wet steam (i.e., a two-phase flow comprising a mixture of saturated steam and saturated water). From our prior research on the general characteristics of acoustic resonance under wet steam flows, the maximum pressure amplitudes under low-pressure wet steam were significantly lower than those under dry steam, which is considered to be caused by the presence of a liquid phase. Here, we investigate how the steam wetness and steam pressure affect the maximum pressure amplitude since practical steam piping may be exposed to various conditions. Experiments on acoustic resonance in a single side branch were conducted under high-quality wet steam flows with a steam pressure of up to 0.8 MPa and a steam quality of 0.9 &amp;lt; x &amp;lt; 1.0 as parameters. For our experimental conditions, it was confirmed that the steam pressure and steam state had little impact on the critical Strouhal number, whereas the maximum amplitudes under wet steam were markedly lower than those under dry steam. Different dependences of the maximum amplitude on the Reynolds number were confirmed for dry steam and wet steam. Moreover, the reduction of the maximum pressure amplitude under wet steam was affected by both the void fraction and the density ratio.

Numerical investigation of the wet steam condensation flow characteristics in stator cascade with blade surface heating

The scientific and effective control of steam wetness in steam turbines is of great significance for improving power generation efficiency. Based on the research status of wet steam, the influence of different surface heating intensity in a stator cascade was studied. The distribution of condensation flow parameters in White cascade under 0–700 kW/m2 surface heating intensity is calculated. On this basis, the positive heating intensity region was determined and refined to obtain the best heating condition with higher accuracy. The results show that the condensation is restrained and the outlet wetness is decreased as the blade surface heating intensity increases. The steam wetness and droplet diameter in the flow field can be controlled by adding heating intensity. Additionally, at the initial stage of applying heat to the blade, an increasing enthalpy drop occurs, and the entropy increase experiences a decline, while negative effects rapidly emerge if the heating intensity is too high. The optimum heating intensity is 120 kW/m2. Compared with the 0 kW/m2, the average outlet wetness, total pressure loss coefficient and entropy increase of 120 kW/m2 surface heating intensity can be reduced by 1.1266%, 15.5% and 1.7%, respectively, and the enthalpy drop can be increased by 1.7%.

Evaluation method of transit time difference for clamp-on ultrasonic flowmeters in two-phase flows

To achieve efficient energy management in industrial plants, it is crucial to measure the steam flow rates at the various points of consumption. Clamp-on time-of-flight ultrasonic flowmeters are useful devices to measure the steam flow rates in existing pipes. However, it is difficult to accurately measure the steam flow rates because of the large acoustic impedance difference between the pipe material and fluid, strong signal attenuation in the fluid, and high temperature. In addition, the steam wetness increases with heat losses and the presence of liquid film and droplets that creates noise in the detected ultrasonic signals, making it difficult to distinguish the target signals from the noisy ones. Hence, a new signal processing method is proposed to determine the transit time difference, particularly at lower signal-to-noise ratios. Two ultrasonic transducers were used to measure the ultrasonic time-of-flight, which varies depending on the flow rate. The transmitted ultrasonic signals were time-dependent due to the generation of guided waves in the pipe wall. The standard deviations of the target signals increased when the flow regime transitioned from stratified to annular mist flow. The guided waves significantly influence the success ratio of determining the transit time difference between the ultrasonic signals transmitted from the upstream and downstream transducers. Based on the results, the use of the standard deviation of the target signals is proposed for estimating the transit time difference. Further, as the standard deviation varied significantly depending on the flow regime, it can be used to identify the flow regime as well.

Investigation of the influence of intra-channel liquid film suction on the structure of the droplet flow downstream a stator blades cascade of a steam turbine

The work is devoted to the study of the effect of intra-channel liquid film suction on the characteristics of the wet steam flow downstream a stator blades cascade of a steam turbine. The moisture removal system consisted of two slots on the pressure side of the blade. Each slot was connected to an individual suction chamber. The investigations were carried out with a theoretical Mach number downstream the cascade M1t = 0.78 and an initial steam wetness y0 = 3%. The main feature of the research was the use of a “PIV-IT” flow laser diagnostics system in which the PTV method was realized. This allowed conducting a detailed study of the structure of a polydisperse wet steam flow. During the investigation an idea of the complex structure of droplets flows downstream the turbine cascade was generated. The analysis of the obtained data allowed us to reveal the main features of the influence of intra-channel liquid film suction on the flows of the liquid particles. It is established that moisture removal does not have a significant effect on the velocity characteristics of the liquid phase. At the same time, the results of studies have shown that intra-channel liquid film suction systems reduce the number of coarse erosion-hazardous droplets downstream a stator blades cascade.

A Combined Binary-Cycle Geothermal Power Plant with a Secondary Flash Steam Superheating System: Choice of Optimal Working Fluids

The article presents the results from numerically modeling the process circuit of a combined binary-cycle double-flash geothermal power plant (GeoPPs) with the use of secondary flash steam superheating by means of a hydrogen–oxygen steam generator. Geothermal heat carrier from substandard wells of the Mutnovsk geothermal field, as well as separated steam and waste brine from the Mutnovsk GeoPP, were taken as the primary heat source. Numerical investigation results have shown that the application of secondary flash steam superheating by means of a hydrogen–oxygen steam generator makes it possible to increase the steam turbine’s power output and its flow path efficiency owing to the steam wetness reduced by more than a factor of two. In addition, reduced steam wetness helps prevent erosion damage to the last-stage turbine rotor blades. Data on the effect that the use of different organic substances has on the efficiency and power output of the binary installation and of the GeoPP as a whole are given. Optimization investigations have shown that the highest power output and efficiency values of the binary installation used as part of a combined binary-cycle GeoPP at the lowest specific brine flowrate are achieved in using organic substances from the groups of nontoxic fire- and flame-proof (R-31-10 and RC-318) and low-toxic fire- and flame-proof ones (R-227ea, R-236fa, R1318, and R-134a) as working fluids. It has been established that the highest power output values of a combined binary-cycle double-flash GeoPP with secondary flash steam superheating by means of a hydrogen–oxygen steam generator are achieved in using the organic working fluids R-31-10, R‑227ea, and RC-318. In so doing, the optimum design pressure in the expander-separator at which the highest efficiency and power output of the studied GeoPP are obtained makes 0.47 MPa. In solving optimization problems on selecting the working fluids for binary combined-cycle GeoPP installations, it is proposed to use multiaxial composite diagrams of the relative values of geothermal power plant parameters and characteristics. An example of drawing a multiaxial composite diagram for the relative values of parameters and characteristics for a combined binary-cycle GeoPP for the R-290, R-31-10, R-32, and RC-318 working fluids is given. The numerical investigation results can be used in designing new and modernizing the operating GeoPPs that use steam geothermal sources.

Sensor for measuring the liquid film thickness on the inner wall of a cylindrical cavity

To measure the steam wetness in a steam turbine accurately, the measurement error caused by the deposited water film on the inner wall of the wetness sensor should be deducted. A hyperbolic slot-shaped resonant cavity sensor for measuring the thickness of the liquid film on the inner wall of a cylindrical cavity is designed in this paper. We establish the relationship between the liquid film thickness and resonant frequency theoretically by the medium perturbation method and verify the feasibility of measuring the liquid film thickness in the TE111 mode. The mathematical model of the current density distribution line at the end of the cavity in the TE111 mode is deduced by the method of the vector field equation. Based on the mathematical model, the sensor is designed by Full-wave simulation software. The simulation results show that the electromagnetic leakage rate of the sensor is basically 0% and the sampling error is no more than -1.3%. The liquid film thickness has a linear relationship with the frequency offsets. The experimental results show that it is feasible to accurately measure the liquid film thickness on the inner wall of a cylindrical cavity by measuring the resonant frequency of the resonator. When the thicknesses of the liquid film are within 100 um, the measuring error does not exceed 0.245, which is about 50% lower than the conductivity method.

Numerical investigation of the condensation flow characteristics and modification optimization of a condensing steam turbine cascade

Purpose The purpose of this study is to improved the efficiency of condensing steam turbines by legitimately reforming the flow structure. It is of great significance to study the condensation flow characteristics of wet steam for optimizing the operation of condensing steam turbines. Design/methodology/approach A two-fluid model was used to study the wet steam flow in a stator cascade. The effects of the inlet temperature and pressure drop on the cascade performance were analyzed. On this basis, endwall protrusion models were set up at varied axial position on the pressure surface to evaluate the wetness control and loss under different design conditions for cascade optimization. Findings The analysis indicates that increasing the inlet temperature or decreasing the pressure drop can effectively control the steam wetness but increase the droplet radius. The increasing inlet temperature can delay the condensation and alleviate the deterioration of the aerodynamic performance of cascades. The non-axisymmetric endwall can significantly affect the distribution of steam parameters below its height and slightly reduce the droplet radius. Compared with the original stator cascade, the optimum design conditions reduce the steam wetness by 8.07 per cent and the total pressure loss by 6.91 per cent below a 20 per cent blade height. Originality/value These research results can serve as a reference for condensing steam turbine wetness losses evaluation and flow passage optimization design.

Dielectric properties of wet steam based on a double relaxation time model.

The last stages of most steam turbines operate in wet steam, resulting in water erosion of the rotor blades and the reduction of turbine efficiency. Accurate measurement of steam wetness is the key to ensure an efficient and stable operation of steam turbines. The equivalent complex permittivity model of wet steam was established by Maxwell-Wagner non-homogeneous dielectric theory, and the complex permittivity distribution of frequency and temperature changes of saturated water, dry saturated steam, and wet steam was derived. The measurement experiments verified the above properties of dry saturated steam and wet steam. The complex permittivity of the wet steam is similar to that for the dry saturated steam. The real part increases with increasing frequency and temperature. When the frequency is large or the temperature is low, the real part approaches 1. The imaginary part increases first and then decreases with the increase of frequency. In addition, with the increase of temperature, the imaginary part becomes larger. When the temperature is low, the imaginary part is close to 0, which is independent of the frequency.

Experimental Investigation for Influence of Static Pressure and Steam Wetness on Pressure Fluctuation of Acoustic Resonance under Wet Steam Flow

Experimental Investigation for Influence of Static Pressure and Steam Wetness on Pressure Fluctuation of Acoustic Resonance under Wet Steam Flow

CFD analysis of probe interaction with expanding wet steam

Research on the impact of the interaction between an optical probe and the expanding steam flow field in a steam turbine on the measured parameters of the liquid phase of the wet steam has been ongoing at Czech Technical University in Prague (CTU) for several years. Previous CFD analyses were newly supplemented by the effect of changing the diameter and number of fine droplets as well as changing of steam wetness in the probe measuring space. The knowledge obtained was used to improve corrections of the extinction measurements at CTU and for conceptual design of a new extinction probe for phase transition investigation in high pressure steam. This paper briefly introduces these results.