Study of Thermodynamic Effect On the Mechanism of Flashing Flow Under Pressurized Hot Water by a Homogeneous Model

2021 ◽  
Author(s):  
Anh Dinh Le
Keyword(s):  
Numerical Method ◽  
Saturated Vapor ◽  
Homogeneous Model ◽  
Temperature Drop ◽  
Numerical Data ◽  
Hot Water ◽  
Two Phase ◽  
Suppression Effect ◽  
Flow Parameters ◽  
Thermodynamic Effect

Abstract The flashing flow in a Moby_Dick converging-diverging nozzle under pressurized hot water from 460.5 K to 483.5 K is simulated using a homogeneous compressible water-vapor two-phase flow model. The kinematic and thermodynamic mass transfer are accessed using the cavitation model based on the Hertz-Knudsen-Langmuir equation. Our simplified thermodynamic model is coupled with the governing equations to capture the phase-change heat transfer. This numerical method proved its reliability through a comparison with available experimental data of flow parameters inside the nozzle. Consequently, the present numerical method shows good potential for simulating the flashing flow under pressurized hot water conditions. The satisfying prediction of averaged flow parameters with a slight improvement compared to reference numerical data is reproduced. The results confirm a noticeable impact of the thermodynamic effect on the mechanism of flashing flow, resulting in a considerable decrease in the flow temperature and the saturated vapor pressure. The flashing non-equilibrium is significantly decreased, forcing the flashing flow to be classified as the usual cavitation behavior and better suited to homogeneous model. While the temperature drop is highly dependent on evaporation, the thermodynamic suppression is influenced by the condensation. The suppression effect, unobserved in water at a lower temperature in previous studies, is noticeable for the pressurized hot water flow characterized by the cavitation mechanism. The vapor void fraction decreased considerably in the radial and axial directions as the water temperature rose to 483.5 K in this study.

Modification of Energy Equation for Homogeneous Cavitation Simulation With Thermodynamic Effect

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Anh Dinh Le ◽  
Junosuke Okajima ◽  
Yuka Iga
Keyword(s):  
Thermodynamic Model ◽  
Saturated Vapor ◽  
Homogeneous Model ◽  
Industrial Applications ◽  
Working Fluid ◽  
Suppression Effect ◽  
Evaporation And Condensation ◽  
Thermodynamic Effect ◽  
Cavitation Region ◽  
Cryogenic Liquids

In industrial applications, cryogenic liquids are sometimes used as the working fluid of fluid machineries. In those fluids, the thermodynamic suppression effect of cavitation, which is normally ignored in water at room temperature, becomes obvious. When evaporation occurs in the cavitation region, the heat is supplied from the surrounding liquid. Hence, the liquid temperature is decreased, and cavitation is suppressed due to the decrease in saturated vapor pressure. Therefore, the performance of the fluid machinery can be improved. Computational fluid dynamics, which involves the use of a homogeneous model coupled with a thermal transport equation, is a powerful tool for the prediction of cavitation under thermodynamic effects. In this study, a thermodynamic model for a homogeneous model is introduced. In this model, the source term related to the latent heat of phase change appears explicitly, and the degree of heat transfer rate for evaporation and condensation can be adjusted separately to suit the homogeneous model. Our simplified thermodynamic model coupled with the Merkle cavitation model was validated for cryogenic cavitation on a two-dimensional (2D) quarter hydrofoil. The results obtained during the validation showed good agreement (in both pressure and temperature profiles) with the experimental data and were better than existing numerical results obtained by other researchers.

Numerical Analysis of Cavitation Instabilities Arising in the Three-Blade Cascade

2004 ◽  
Vol 126 (3) ◽  
pp. 419-429 ◽  
Author(s):  
Yuka Iga ◽  
Motohiko Nohml ◽  
Akira Goto ◽  
Toshiaki Ikohagi
Keyword(s):  
Numerical Method ◽  
High Speed ◽  
Homogeneous Model ◽  
Rotating Stall ◽  
Two Phase ◽  
Wide Range ◽  
Phase Medium ◽  
Long Time ◽  
Entire Flow ◽  
Locally Homogeneous

Three types of cavitation instabilities through flat plate cascades, which are similar to “forward rotating cavitation,” “rotating-stall cavitation” and “cavitation surge” occurring in high-speed rotating fluid machinery, are represented numerically under the three-blade cyclic condition. A numerical method employing a locally homogeneous model of compressible gas-liquid two-phase medium is applied to solve the above flow fields, because this permits the entire flow field inside and outside the cavity to be treated through only one system of governing equations. In addition, the numerical method suites to analyze unsteady cavitating flow with a long time evolution. From the calculated results of the present numerical simulation with wide range of cavitation number and flow rate, we obtain a cavitation performance curve of the present three-blade cyclic cascade, analyze the aspects of unsteady cavitation, and discuss the characteristics and mechanisms of cavitation.

Penetration Jet Impingement Calculation in Engineering Application

2017 ◽  
Author(s):  
Tong Wu ◽  
Ying Zhou ◽  
Tao Qi
Keyword(s):  
Pressure Field ◽  
Two Phase Flow ◽  
Saturated Vapor ◽  
Jet Impingement ◽  
Hot Water ◽  
Saturated Steam ◽  
Phase Flow ◽  
Plant Design ◽  
Wet Steam ◽  
Two Phase

In the process of nuclear power plant design, Pipe Rupture Hazards Analysis (PRHA) was obliged, including postulated rupture location and configurations, jet impingement effects, compartment pressurization effects, environmental influences, flooding effects, leak-before-break and influence on SSC, etc. The analysis of jet impingement is of great importance; aims at obtaining the jet impingement configuration and the impingement force acting on the target. Jet impingement configuration and force depended on the jet flow properties. A jet discharging from a saturated steam line will accelerate and expand due to the pressure differential, and it will partially condense to a low-moisture wet steam with liquid phase in the form of dispersed, entrained water droplets. A jet discharging from a sub-cooled or saturated hot water line (greater than 100°C) would flash to a low quality wet steam and the flashing would cause the jet diameter to expand very rapidly. These jet flows have a phase change and two-phase flow process; the recommended two-phase flow model that should be used was presented in ANSI/ANS 58.2-1988. However, penetration jet impingement which is often encountered in the PRHA was not introduced. In normal cases, the saturated steam, sub-cooled or saturated hot water (greater than 100°C) expands directly to the surroundings. But for penetration jet impingement, the fluid is first discharged to the narrow annular section formed by the pipe and the penetration, then flows through this area, and finally expands to the surroundings at the open side of the penetration. The penetration expanding jet analysis is much more complicated. A method of determining penetration jet impingement in engineering applications was derived based on the fundamental method presented in ANSI/ANS 58.2-1988, Henry and Fauske model recommended. The simplified method took advantage of the two-phase flow models and equations given by ANSI/ANS 58.2-1988; the jet configuration could be calculated effectively and the target impingement force could be derived using the result presented by these equations simultaneously. The impingement pressure field was defined using the program for different initial states of the postulated pipe rupture — namely sub-cooled and saturated. The pressure distribution along the jet centerline obtained has shown clearly the three regions in ANSI/ANS 58.2-1988. The pressure field has shown that sub-cooled water has a larger zone of influence and saturated vapor has a higher mean impingement pressure as Sub-cooled water was under expanded while saturated vapor has higher enthalpy as it contains more energy.

Experimental Study On Temperature Change by Cavitation Accompanying Self-Pressurization of Propellant for Small Rocket Engines

2021 ◽  
Author(s):  
Kazuki Yasuda ◽  
Daisuke Nakata ◽  
Masaharu Uchiumi
Keyword(s):  
Saturated Vapor ◽  
Temperature Drop ◽  
Flow Characteristics ◽  
Rocket Engines ◽  
Discharge Process ◽  
Fluid Temperature ◽  
Hybrid Rocket ◽  
Two Phase ◽  
Liquid Rocket ◽  
Pressurized Fluids

Abstract As a propellant for hybrid rocket engines using liquid oxidizer and solid fuel and for liquid rocket engines, the use of self-pressurized fluids such as nitrous oxide has become widespread. Since these fluids can be self-pressurized by their high saturated vapor pressure, the propulsion system becomes smaller and simpler. However, this self-pressurization generally forms a gas-liquid two-phase flow by flashing or cavitation. This flow is considered highly unsteady because the temperature and pressure greatly change with the discharge process. In this study, unsteady flow characteristics due to self-pressurization were experimentally obtained by conducting many cold flow tests with carbon dioxide as self-pressurizing fluids. As a result, it was clarified that the fluid temperature dropped about 10-15 K with the pressure drop due to feed line pressure loss during the discharge process. From these experimental results, we estimated the bubble growth and void fraction change that would satisfy the temperature drop. In this paper, the obtained test results and estimated temperature drop are reported.

scholarly journals Experimental and numerical evaluation of thermodynamic effect on NACA0015 hydrofoil cavitation in hot water

2021 ◽  
Author(s):  
Anh Dinh Le
Keyword(s):  
Flow Behavior ◽  
Temperature Drop ◽  
Hot Water ◽  
Maximum Temperature ◽  
Flow Conditions ◽  
Thermodynamic Effect ◽  
Pressure Water ◽  
Phase Change Phenomena ◽  
Temperature Depression ◽  
Effect Phase

In this study, the cavitation in hot water, which implies tight interaction of thermodynamic effect, phase change phenomena, and flow behavior, was studied by a combination of experiment and numerical simulation. The experiment in water up to 90°C was performed in the high temperature and high-pressure water tunnel with NACA0015 as a cavitator. The temperature inside the cavity was measured using the high-accuracy thermistor probe. According to the result, the temperature depression in the cavity was increased proportionally with the increase of freestream temperature. The inverse thermodynamic effect was observed with the increase of cavity length when temperature increased. The maximum temperature depression of about 0.41°C was measured in the water at around 90°C. The temperature drop was reasonably captured in simulation by coupling our simplified thermodynamic model with our cavitation model and governing equations. The tendency of temperature depression in the cavity agreed well with experimental data under different flow conditions.

A Numerical Method for Two-Phase Flow Consisting of Separate Compressible and Incompressible Regions

2001 ◽  
Vol 166 (1) ◽  
pp. 1-27 ◽  
Author(s):  
Rachel Caiden ◽  
Ronald P. Fedkiw ◽  
Chris Anderson
Keyword(s):  
Numerical Method ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase

Experimental investigation of degassing properties of geothermal fluids

2021 ◽  
Author(s):  
Chris Boeije ◽  
Pacelli Zitha ◽  
Anne Pluymakers
Keyword(s):  
High Pressure ◽  
Temperature Drop ◽  
Hot Water ◽  
Visual Cell ◽  
Dissolved Gas ◽  
Bubble Point ◽  
Free Gas ◽  
Bubble Point Pressure ◽  
Geothermal Fluids ◽  
Point Pressure

<p>Geothermal energy, the extraction of hot water from the subsurface (500 m to 5 km deep), is generally considered one of the key technologies to achieve the demands of the energy transition.  One of the main problems during production of geothermal waters is degassing. Many subsurface waters contain substantial amounts of dissolved gasses. As the hot water travels up the production well, the pressure and/or temperature drop will cause dissolved gas to come out of the solution. This causes several problems, such as corrosion of the facilities (due to pH changes and/or degassing-related precipitation) and in some cases even to blocking of the reservoir as the free gas limits the water flow.  To better understand under which conditions free gas nucleates, we need confirmation of theoretical bubble point pressure and temperature, and understand what controls the evolution of the bubble front:  i.e. what are the conditions under which free gas emerges from the solution and at what rate are bubbles created?</p><p>An experimental setup was designed in which the degassing process can be observed visually. The setup consists of a high-pressure visual cell which contains water saturated with dissolved gas at high-pressure. The pressure within the cell can be reduced in a reproducible manner using a back-pressure regulator at the outlet of the system. A high-speed camera paired with a uniform LED light source is used to record the degassing process. The pressure in the cell is monitored using a pressure transducer which is synchronized with the camera. The resulting images are then analysed using a MATLAB routine, which allows for determination of the bubble point pressure and rate of bubble formation.</p><p>The first two sets of experiments at ambient temperatures (~20 <sup>o</sup>C) were carried out using two different gases, N<sub>2</sub> and CO<sub>2</sub>. Initial pressure was 70 and 30 bar for the N<sub>2</sub> and CO<sub>2</sub> experiments respectively. In these first experiments we determined the influence of the initial fluid used to pressurize the system. Using gas as the initial fluid causes a large amount of bubbles, whereas only a single bubble was observed for a system where degassed water is used as the initial fluid. An intermediate system where degassed water is pumped into a system full of air at ambient conditions and is subsequently pressurized yields a number of bubbles in between the two systems described previously. All three methods give reproducible bubble point pressures within 2 bar (i.e. pressure where the first free bubble is formed). There are clear differences in bubble point between N<sub>2</sub> and CO<sub>2</sub>.</p><p>A series of follow-up experiments is planned that will investigate specific properties at more extreme conditions: at higher pressures (up to 500 bar) and temperatures (500 <sup>o</sup>C) and using high-salinity brines (2.5 M).</p>

Vapour explosion under hot water depressurization

2016 ◽  
Vol 812 ◽  
pp. 65-128
Author(s):  
Oleg E. Ivashnyov ◽  
Marina N. Ivashneva
Keyword(s):  
Compression Wave ◽  
High Speed ◽  
Saturation Pressure ◽  
Pressure Rise ◽  
Hot Water ◽  
Hyperbolic Model ◽  
Two Phase ◽  
Saturation State ◽  
Break Up ◽  
Bubble Fragmentation

This paper continues a series of works developing a model for a high-speed boiling flow capable of describing different fluxes with no change in the model coefficients. Refining the interfacial area transport equation in partial derivatives, we test the ability of the model to describe phenomena that cannot be simulated by models that average the interfacial interaction. In the previous version, the possibility for bubble fragmentation was considered, which permitted us to reproduce an explosive boiling in rarefaction shocks moving at a speed of ${\sim}10~\text{m}~\text{s}^{-1}$ fixed in experiments on hot water decompression. The shocks were shown to be caused by a chain bubble fragmentation leading to a sharp increase in the interphase area (Ivashnyov et al., J. Fluid Mech., vol. 413, 2000, pp. 149–180). With no change in the free parameters (the initial number of boiling centres in the flow bulk and the critical Weber number) chosen for a tube decompression, the model gave close predictions for critical flows in long nozzles, $L/D\sim 100$. The formation of a boiling shock in the nozzle was shown to be the reason for the onset of autovibrated regimes (Ivashnyov & Ivashneva, J. Fluid Mech., vol. 710, 2012, pp. 72–101). However, the previous model does not simulate the phenomenon of a vapour explosion at a primary stage of a hot water decompression, when the first rarefaction wave is followed by an extended, 1 m width, several MPa amplitude compression wave in which the pressure reaches a plateau below a saturation value. The model proposed assumes initial boiling centre origination at the channel walls. Due to overflowing, the wall bubbles break up, with their fragments passing into the flow. On growing up, the flow bubbles can break up in their turn. It is shown that an extended compression wave is caused by the fragmentation of wall bubbles, which leads to the increase in the interphase area, boiling intensification and the pressure rise. The pressure reaches a plateau before a saturation state is reached due to flow momentum loss accelerating the fragments of wall bubbles. The phenomenon of pressure ‘oscillation’ fixed in some experimental oscillograms when the pressure in the compression wave increases up to a saturation pressure and then drops to the plateau value has been explained as well. The ‘illposedness’ defect of the generally accepted model for two-phase two-velocity flow with a compressible carrying phase, which lies in its complex characteristics, has been rectified. The calculations of a stationary countercurrent liquid-particle flow in a diffuser with the improved hyperbolic model predicts a critical regime with a maximal liquid mass flux, while the old non-hyperbolic model simulates the supercritical regimes with ‘numerical instabilities’. Calculations of a transient upward flow of particles have shown the formation of a superslow ‘creeping’ shock wave of particles compacting.

scholarly journals MECHANISMS OF GENERATION AND SOURCES OF NOISE IN SUPERSONIC JETS

Akustika ◽  
2019 ◽  
Vol 32 ◽  
pp. 144-150
Author(s):  
Vladislav Emelyanov ◽  
Aleksey Tsvetkov ◽  
Konstantin Volkov
Keyword(s):  
Pressure Ratio ◽  
Supersonic Jet ◽  
Numerical Data ◽  
Jet Flows ◽  
Noise Generation ◽  
Noise Sources ◽  
Cavity Depth ◽  
Flow Parameters ◽  
Nozzle Pressure ◽  
Physical Pattern

Interest in the development of models and methods focused on the mechanisms of noise generation in jet flows is due to strict noise requirements produced by various industrial devices, as well as the possibilities of using sound in engineering and technological processes. The tools of physical and computational modeling of gas dynamics and aero-acoustics problems are considered, and noise sources and mechanisms of noise generation in supersonic jet flows are discussed. The physical pattern of the flow in free supersonic under-expanded jets is discussed on the basis of experimental and numerical data, as well as the flow structure arising from the interaction of a supersonic under-expanded jet with a cylindrical cavity. The influence of the nozzle pressure ratio and cavity depth on the sound pressure level, amplitude and frequency characteristics of the flow parameters is studied.

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