scholarly journals A Numerical Analysis of the Influence of Nozzle Geometric Structure on Spontaneous Steam Condensation and Irreversibility in the Steam Ejector Nozzle

2021 ◽  
Vol 11 (24) ◽  
pp. 11954
Author(s):  
He Li ◽  
Xiaodong Wang ◽  
Hailong Huang ◽  
Jiuxin Ning ◽  
Jiyuan Tu
Keyword(s):  
Entropy Generation ◽  
Wet Steam ◽  
Steam Condensation ◽  
Throat Radius ◽  
Spontaneous Condensation ◽  
Steam Ejector ◽  
Expansion Angle ◽  
Ejector Nozzle ◽  
Throat Diameter ◽  
Simulation Results

The spontaneous condensation of wet steam often occurs in the steam ejector nozzle, this deteriorates the performance of the steam ejector. In this paper, we take changing the geometric parameters of the nozzle as the focus of our research and construct an internal connection between steam’s condensation behavior and the nozzle’s throat radius, the nozzle’s divergent section expansion angle, and the nozzle’s divergent section length. Our numerical simulation results indicate that an increase in the throat diameter and reduction of the divergent section’s expansion angle can inhibit steam condensation behavior, to a certain extent. In particular, the steam condensation behavior will disappear at a 0° expansion angle, but it is not affected by the change in the divergent section’s length. In addition, the irreversibility that is seen under different changes to the nozzle’s structure parameters was investigated and the results show that the entropy generation that is caused by a phase change accounts for a much higher proportion of the total entropy generation than heat transport and viscous dissipation do. This indicates that steam’s condensation behavior makes a large amount of irreversible energy, resulting in energy waste and reducing the performance of the nozzle. Therefore, this study can provide a theoretical reference for suppressing the spontaneous condensation behavior of steam by changing the nozzle’s geometry.

scholarly journals Simulasi Numerik Aliran Melewati Nozzle Pada Ejector Converging – Diverging Dengan Variasi Diameter Exit Nozzle

2017 ◽  
Vol 2 (1) ◽  
pp. 19
Author(s):  
Novi Indah Riani ◽  
Syamsuri Syamsuri ◽  
Rungky Rianata Pratama
Keyword(s):  
Operating Conditions ◽  
Vapor Compression ◽  
Cooling Process ◽  
Entrainment Ratio ◽  
Steam Ejector ◽  
Mixing Chamber ◽  
Exit Nozzle ◽  
Flow Phenomena ◽  
Ejector Nozzle ◽  
Simulation Results

In the process of cooling or refrigeration, are required components where capable to flow the fluid to create a cycle of the cooling process. Among some of the vapor compression systems, the usage of ejector is the simplest system. Ejector has three main parts: primary nozzle, mixing chamber and diffuser. Various experiments of steam ejectors developed to increase the value of the COP. Entrainment ratio directly affects to the COP value generated by the system, where the geometric shapes and operating conditions in the steam ejector will affect to the value entrainment ratio. This research was carried out numerical simulations using CFD commercial software with k-epsilon to predict flow phenomena which passes through the ejector nozzle in the ejector converging-diverging which varying exit diameters 3.5 mm; 4mm; 5 mm; and 5.5 mm. Respectively the simulation results showed exit nozzle steam ejector that the smallest diameter of 3.5 mm give the optimum performance because it provide the highest speed of fluidity. While the state of vacuum in mixing chamber increase, it cause the secondary mass flow higher as well as the value of the entrainment ratio.

Numerical Investigation of the Effects of Steam Nucleation on the Steam Ejectors Performance

2012 ◽  
Author(s):  
Navid Sharifi ◽  
Masoud Boroomand ◽  
Majid Sharifi
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Numerical Approach ◽  
Nucleation Theory ◽  
Normal Operation ◽  
Computational Domain ◽  
Wet Steam ◽  
Steam Condensation ◽  
Steam Ejector ◽  
Commercial Code

Steam ejectors are widely used in different applications such as propulsion, refrigeration, evacuation and aerospace. The fundamental numerical approach in evaluating the characteristic parameters of steam ejectors was through considering steam as a single-phase gas. But, at some regions in steam ejectors, nucleation of steam is occurred. It is very important to evaluate the amount of wet steam at the first step. At the second step, it is vital to estimate the effect of steam condensation on the aerodynamics and thermodynamic performance of steam ejectors. In the present study, numerical simulation of a steam ejector at normal operation is undertaken. In the mathematical modeling of compressible flow within such equipments, wet-steam nucleation theory is employed to investigate the effects of wetness condition inside the ejectors. In order to verify the numerical simulation, wet steam results have been compared with a set of experimental data reported in previous literatures. By comparison of the numerical results with experimental data, it was concluded that steam condensation in the nozzle declines the maximum Mach number of supersonic flow which has a closer agreement with experimental reports. The numerical calculations were performed with a commercial code with a supplementary user-defined code and applied to a multi-block computational domain with structured elements. Some important items such as shock location, shock strength and pressure distribution along the centerline of the ejector were compared in the cases of wet and ideal steam simulations. Furthermore, the average compression ratio and entraining capability of the ejector were compared for both simulation methods. Moreover, the results show a strengthened shock wave under the assumption of wet steam which leads to an intensified pressure recovery inside the ejector.

Numerical Simulation of Performance of Steam Ejector Influenced by the Distance between Nozzle Outlet and Mixing Chamber Inlet

2011 ◽  
Vol 299-300 ◽  
pp. 970-973
Author(s):  
Xiao Chun Dai ◽  
Guo Jin Liao
Keyword(s):  
Numerical Simulation ◽  
Geometric Parameters ◽  
Experimental Results ◽  
Nozzle Outlet ◽  
Entrainment Ratio ◽  
Optimum Range ◽  
Steam Ejector ◽  
Mixing Chamber ◽  
Throat Diameter

The performance of a steam ejector was simulated using FLUENT. The performance of steam ejector was studied by changing the distance between primary nozzle outlet and mixing chamber inlet (DPM) while operating pressures and other geometric parameters were not varied. The entrainment ratios of the steam ejector with different values of DPM were calculated. The optimum range of DPM was given, which is changed from 1.8 to 2 times of the throat diameter of hybrid diffuser pipe. The errors of the CFD results to the experimental results of the entrainment ratio are not more than 15%.

Study on Effects of Spontaneous Condensation on Performance of Low Pressure Stages in a Steam Turbine

2006 ◽  
Author(s):  
Liang Li ◽  
Zhenping Feng ◽  
Guojun Li
Keyword(s):  
Steam Turbine ◽  
Stokes Equations ◽  
Low Pressure ◽  
Steam Flow ◽  
Vapor Flow ◽  
Wet Steam ◽  
Water Droplets ◽  
Flow Angle ◽  
Spontaneous Condensation ◽  
Wet Steam Flow

The formation of water droplets in low-pressure steam turbine seriously degrades the performance of the turbine. In order to simulate the wet steam flow with spontaneous condensation, an Eulerian/Eulerian model was developed, in which the Navier-Stokes equations for water vapor flow are coupled with two additional equations describing the formation and the distributions of water droplets. The classical condensation theory was used to model the condensation process. With this model, the three dimensional (3D) steady wet steam flow with spontaneous condensation in three low pressure (LP) stages of an industrial steam turbine was numerically investigated and the results were compared with those in superheated flow. The distribution of pressure, the enthalpy drop, the reaction degree, the outflow velocity and flow angle in each wet steam turbine stage obviously change due to the spontaneous condensation in wet steam flow, compare to those in the superheated flow. The re-distribution of flow parameters in condensing flow leads to that the turbine stages run at ‘off-design’ condition actually, which leads to additional efficiency losses besides the well-known non-equilibrium losses.

scholarly journals The thermochemical non-equilibrium expansion effects of the high enthalpy nozzle

2020 ◽  
Author(s):  
Junmou Shen ◽  
Xing Chen ◽  
Hongbo Lu ◽  
Zongjie Shao ◽  
Dapeng Yao ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Flow Region ◽  
Free Flow ◽  
Equilibrium Flow ◽  
Throat Radius ◽  
Maximum Expansion ◽  
High Enthalpy ◽  
Expansion Angle ◽  
Equilibrium Region ◽  
Non Equilibrium

Abstract The high enthalpy shock tunnel can simulate the free-flow speed above 3km/s. The characteristic of the flow is that the kinetic energy of the high enthalpy stagnation gas is high enough to effectuate high-temperature effects such as dissociation even ionization of fluid molecules. The stagnation gas is converted into the hypervelocity free flow through the high enthalpy nozzle. The flow of high enthalpy flow in the high enthalpy nozzle can be divided into three regions: an equilibrium region, a non-equilibrium region and a frozen region. The equilibrium flow region is upstream of the throat, the non-equilibrium flow region is near the throat, and the frozen flow region is not far downstream of the throat. The study focuses on the conical nozzle, testing thermochemical non-equilibrium expansion effects under the different expansion angle of the expansion section, the curvature radius of the throat, the throat radius, and the convergence angle of the convergent section. A multi-block solver for axisymmetric compressible Navier-Stokes equations is applied to simulate the thermochemical non-equilibrium flow in several high enthalpy conical nozzles. The significant conclusions of this study contain tripartite. Firstly, the thermochemical non-equilibrium effects are sensitive to the maximum expansion angle and throat radius, but not to the radius of throat curvature and the contraction angle. Secondly, as the maximum expansion angle decreases and the throat radius increases, the flow approaches equilibrium. Finally, the maximum expansion angle and the throat radius not only affect the position of the freezing point but also impacts the flow field parameters, such as temperature, Mach number, and species mass concentration.

scholarly journals The thermochemical non-equilibrium expansion effects of the high enthalpy nozzle

2020 ◽  
Author(s):  
Junmou Shen ◽  
Xing Chen ◽  
Hongbo Lu ◽  
Zongjie Shao ◽  
Dapeng Yao ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Freezing Point ◽  
Free Flow ◽  
Curvature Radius ◽  
Throat Radius ◽  
Maximum Expansion ◽  
High Enthalpy ◽  
Expansion Angle ◽  
Equilibrium Region ◽  
Non Equilibrium

Abstract The high enthalpy shock tunnel can simulate the free-flow speed above 3km/s. The characteristic of the flow is that the kinetic energy of the high enthalpy stagnation gas is high enough to effectuate high-temperature effects such as dissociation even ionization of fluid molecules. The high enthalpy nozzle converts the high enthalpy stagnation gas into hypervelocity free flow. The flow of the high enthalpy nozzle consists of three distinct flow regions: an equilibrium region upstream of the throat, a non-equilibrium region near the throat, and a frozen region downstream of the throat. The study focuses on the conical nozzle, testing thermochemical non-equilibrium expansion effects under the different expansion angle of the expansion section, the curvature radius of the throat, the throat radius, and the convergence angle of the convergent section. A multi-block solver for axisymmetric compressible Navier-Stokes equations is applied to simulate the thermochemical non-equilibrium flow in several high enthalpy conical nozzles. The significant conclusions of this study contain tripartite. Firstly, the thermochemical non-equilibrium effects are sensitive to the maximum expansion angle and throat radius, but not to the radius of throat curvature and the contraction angle. Secondly, as the maximum expansion angle decreases and the throat radius increases, the flow approaches equilibrium. Finally, the maximum expansion angle and the throat radius not only affect the position of the freezing point but also impacts the flow field parameters, such as temperature, Mach number, and species mass concentration.

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