Study into nucleation of steam during expansion through a nozzle

1978

An experimental study was undertaken to determine the droplet size distribution, the droplet spatial distribution and the mean droplet

EPJ Web of Conferences, 2012

This paper describes a model of compressible flow including homogenous nucleation and consequent growth and evaporation of droplets. Considered fluid is water vapor with relatively small mass fraction of dispersed water droplets. Main issues of numerical simulation based on this model are discussed. Results of numerical simulation are compared with experimental data.

2007

The effects of chemistry on the flowing steam nucleation are in particular unexplained. An approach is used in the paper which is based on binary nucleation of main impurity NaCl and water. Physical and mathematical models are described and are applied on the steam flow with condensation in convergent divergent nozzle. Bi nary nucleation numerical model is applied for the calculation of the flow with condensation in nozzle with ex pansion rate in divergent nozzle part P & = 4 500 s 1. The flow in the nozzle is smooth and it is possible to observe only a small delay of the pressure and a small shock of the temperature downstream of the nozzle throat.

International Journal of Heat and Mass Transfer, 2003

Near saturation steam undergoing rapid expansion, with homogeneous nucleation of water droplets, is numerically studied in a series of converging/diverging nozzles with and without shocks. To understand loss mechanisms in such flows a numerical model is presented to calculate thermodynamic losses, which is further used to quantify associated total aerodynamic losses. For the converging/diverging nozzle configuration, the model shows that the overall thermodynamic loss is only mildly influenced by increasing shock strength, while the aerodynamic losses follow that of the single phase flow, and are of the same magnitude as the thermodynamic loss only in the case of very weak shocks. The thermodynamic losses can be attributed to two influences, the homogeneous nucleation event, and the post-shock thermal oscillations in the two-phase system. The calculations rely on a new two-phase CFD model, previously reported, for non-equilibrium phase change with droplet nucleation applicable to general 3D flow configurations.

Scientia Iranica, 2010

In this paper, a compressible, one-dimensional and two-phase ow is analytically modeled by using a homogeneous classical nucleation rate equation in a Laval nozzle. For droplet growth calculations, the heat transfer between the droplets and the surrounding steam is modeled by a free molecular ow model and a semi-empirical two-layer model which is deemed to be valid over a wide range of Knudsen numbers. In order to reduce the condensation shock strength, the water droplets are injected at the inlet, and just after the throat of the Laval nozzle. According to the results, the nucleation rate is considerably suppressed due to the small droplet injection, and, therefore, the condensation shock nearly disappears, particularly for the inlet injection of water droplets.

International Journal of Heat and Mass Transfer, 2012

The paper presents the computational results of the wet steam flow through the Laval nozzles for low and high inlet pressures. The results of the numerical modelling are compared with experimental data. The comparisons constitute validation tests of the condensation model implemented into an in-house CFD code solving the RANS equations for the real gas equation of state. The steam condensing flow is modelled by means of the single-fluid model, which means that the conservation equations are formulated for the vapour/liquid mixture. The water vapour properties are described by means of the local equation of state. An effective method of determination of water vapour properties are presented in the cases of expansion in the nozzle at high pressures. The presented results are compared with published experimental values. The validation of the in-house CFD code proves its usefulness for modelling the steam condensing flow for both low and high inlet pressures.

International Journal of Thermal Sciences, 2022

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 10 15 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.

Energy, 2016

The process of energy conversion in the low pressure part of steam turbines may be improved using new and more accurate numerical models. The paper presents a description of a model intended for the condensing steam flow modelling. The model uses a standard condensation model. A physical and a numerical model of the mono-and polydispersed wet-steam flow are presented. The proposed two-fluid model solves separate flow governing equations for the compressible, inviscid vapour and liquid phase. The method of moments with a prescribed function is used for the reconstruction of the water droplet size distribution. The described model is presented for the liquid phase evolution in the flow through the de Laval nozzle.

2000

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Majlesi Journal of Mechanical Engineering

In the course of expansion in turbines steam nucleates to become a twophase mixture, the liquid consisting of a very large number of extremely small droplets carried by the vapor. Formation and subsequent behaviour of the liquid lowers the performance of turbine wet stages. The calculations were carried out assuming that the flow is two dimensional, compressible, turbulent and viscous. A classical homogenous nucleation model applied for the mass transfer in the transonic conditions. The aim of the present study is investigation of outlet pressure effect on second phase generation in a steam turbine. The maximum and minimum of droplet numbers have been achieved and nucleation zone has been specified in blade passage. Pressure profiles around the blades are compared with the experimental data and good agreement is observed. Results show that the most condensation is on the suction surface of blade and it grows by decreasing the downstream pressure.

International Journal of Heat and Mass Transfer, 2018

Steam jet condensation through multi-hole nozzles in a pressure relief pool is important for the design and safe operation of a nuclear reactor system. In this study, stable steam jet condensation through a double-hole nozzle was investigated at different water temperatures and steam pressures by CFD method. Simulation results indicated that the shape of steam cavity changed from conical to ellipsoidal with an increase in water temperature and steam pressure, and steam jet length gradually increased. Meanwhile, the interaction between two steam cavities was enhanced and they even merged under certain conditions. Expansion and compression waves were found by analyzing the thermal hydraulic parameters along the hole centerline. Water temperature and steam pressure exerted different effects on the intensity of expansion/compression waves and the positions of maximum expansion/compression. Finally, thermal hydraulic parameters along the nozzle centerline were analyzed. Steam volume fraction, temperature, and velocity initially increased and then decreased as axial distance increased, which appeared as evident peaks under the present conditions. When water temperature and steam pressure increased, the peak values of steam volume fraction, temperature, and velocity gradually increased and their positions moved downstream.

AIAA AVIATION 2021 FORUM, 2021

This paper presents an extensive understanding of the behavior of steam as a compressible gas through a thrust optimized parabolic nozzle designed for small spacecraft In-Situ Resource Utilization missions. Assuming isentropic steam, the flow was treated as single-phase due to the allotted volume super-heated water was given to expand into prior to entering the nozzle. ANSYS Fluent was used to conduct computational fluid dynamic analysis on the steam as it traveled through the nozzle and after it existed. The change in phase inside the chamber and reduction in the back pressure was not considered in order to study extended firing of the propulsion system. Significant attention was paid to turbulence in the fluid flow and flow detachment in the nozzle to accurately model the behavior of steam in the nozzle due to its small size. The overall nozzle efficiency was calculated to be 94.25%, falling within the optimal efficiency range of 92-98%.

Scientia Iranica, 2014

Under the in uence of intense expansion and supersonic acceleration of the steam ow in a divergent channel, the instability of the ow intensi es. In the lack of external surfaces, this non-equilibrium state causes nucleation and consequent growth of formed nuclei. Due to the release of latent heat from condensation to the supersonic ow at the location of nucleation, an increase in pressure is developed in this small region, which is known as condensation shock. In this research, the e ects of this shock on boundary layer parameters are investigated. First, the water vapor ow that has the capability of nucleation is modeled analytically, as adiabatic, inviscid and one dimensional, and then, using the mathematical equations of laminar and turbulent boundary layer parameters and the inviscid-viscous Interaction method. The results of this analytical modeling show that although the in uence of the boundary layer on the expansion ow is limited, it still causes approximately 3% increase in the diameter of the water droplets. However, the e ects of two-phase ow on the boundary layer parameters at the location of the condensation shock are considerable. The major novelty of this research is determining the quanti cation and quali cation of these e ects.

Nuclear Engineering and Design, 2011

Deposition rate of droplets in steam-water annular two-phase flow was measured using a 5 mm diameter vertical round tube as a test section. In the experimental conditions tested in this work, the droplet mass transfer coefficient decreased with an increase in the droplet concentration in the gas core flow and with an increase in the length of a deposition section. The dependence on these two parameters agreed fairly well with predictions by available correlations. Placing a small cylindrical tube concentrically in the test section round tube, the effect of a flow obstacle on the deposition rate of droplets was also experimentally investigated. It was found that the obstacle effect was significant and the deposition rate of droplets increased approximately three times in average. The obstacle effect measured in this work was compared with an empirical correlation and a simple mechanistic model that were developed using experimental results of air-water annular flows. Fairly good agreement was achieved in both cases, which would indicate that the mechanism of deposition enhancement induced by the flow obstacle is similar between air-water and steam-water flows.

Due to steam condensation passing through the nozzle, simulation of steam flow in nozzle by an ideal gas model is far from the reality. In this study, a mathematical model based on a wet steam model is proposed to investigate the flow behavior of steam fluid in a nozzle of steam ejector. In the wet steam model two transport equations are added to the basic governing equations terms. These equations present mass fraction of the condensed liquid phase and number density of the droplets. The control-volume-based computational fluid dynamics (CFD) code is used to simulate. Since Reynolds stress model (RSM) exactly predicts the turbulent characteristics of flow, this model is chosen. Although there is not agreement between the results of the ideal gas and the experimental data, but the results based on the wet steam model, show good consistency with the experimental data. The numerical outputs also show the condensation of steam as it flows through the nozzle. The values of static pressu...