Experimental Investigation on Cavity Pressure Inside Sheet Cavitation

2021 ◽  
Author(s):  
Keisuke Kobayashi ◽  
Yusuke Katayama ◽  
Satoshi Watanabe ◽  
Shin-ichi Tsuda
Keyword(s):  
Mass Transfer ◽  
Partial Pressure ◽  
Flow Velocity ◽  
Saturated Vapor Pressure ◽  
Saturated Vapor ◽  
Gas Content ◽  
Cavity Pressure ◽  
Dissolved Gas ◽  
Sheet Cavitation ◽  
Diffusive Mass Transfer

Abstract The gas content is one of the important factors in cavitation, which may increase the pressure inside the cavity through the diffusive mass transfer of the dissolved gas into the cavity. In the present study, we try to directly measure the cavity pressure inside the sheet cavity at the throat of a converging-diverging nozzle. Then the influences of the flow velocity and the gas content (amount of dissolved oxygen) on the gas partial pressure are investigated. It is found that, even in low gas content level, the cavity pressure is slightly but apparently higher than the saturated vapor pressure, indicating the presence of gas partial pressure. It is observed that the gas partial pressure in significantly developed cavitation is almost constant regardless of the flow velocity but slightly increases against the increase of the saturation level of dissolved gas. It is also found that the gas partial pressure inside cavity depends on the degree of cavitation development; the gas partial pressure decreases with the development of cavitation.

Scaling of Gas Diffusion Into Limited Partial Cavities

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
In-ho Lee ◽  
Simo A. Mäkiharju ◽  
Harish Ganesh ◽  
Steven L. Ceccio
Keyword(s):  
Reynolds Number ◽  
Cavity Length ◽  
Diffusion Rate ◽  
Gas Diffusion ◽  
Gas Content ◽  
Cavity Pressure ◽  
Dissolved Gas ◽  
Noncondensable Gas ◽  
Scaling Relationships ◽  
Dissolved Air

Bubbles populations in the wake of a partial cavity resulting from gas diffusion were measured to determine the noncondensable gas flux into the cavity. The diffusion rate is related to the dissolved gas content, the local cavity pressure, and the flow within and around the cavity. The measurements are used to revisit various scaling relationships for the gas diffusion, and it is found that traditional scaling that assumes the presence of a gas pocket overpredicts the gas diffusion. A new scaling based on diffusion into the low void fraction bubbly mixture within the partial cavity is proposed, and it is shown to adequately scale the observed production of gas bubbles for dissolved air saturation from 30% to 70% at 1 atm, limited cavities on the order of 0.3–3 cm in length at a freestream speed of 8 m/s (σ = 2.3–3.3 and Reynolds number based on the cavity length of order 105).

In-Situ Measurement of Liberation of a Dissolved Gas in Unsteady Cavitating Flow in Water

2019 ◽  
Author(s):  
Daiki Makii ◽  
Hirotoshi Sasaki ◽  
Yuka Iga
Keyword(s):  
Vapor Pressure ◽  
Dissolved Oxygen ◽  
Phase Change ◽  
Saturated Vapor Pressure ◽  
Saturated Vapor ◽  
Cavitating Flow ◽  
In Situ Measurement ◽  
Cfd Model ◽  
Dissolved Gas

Abstract Cavitation is a phenomenon in which phase change occurs in a liquid by pressure decrease due to flow acceleration. The phase change is caused by mainly evaporation of the liquid but sometimes by liberation of dissolved non-condensable gas in the liquid. In particular, unsteady cavitation causes vibration, noise, erosion and performance deterioration, which has been a serious problem in the development of fluid machinery. Therefore, it is important to research the characteristics of cavitation generation and develop methods to suppress or control it. In the current CFD (computational fluid dynamics) model of cavitating flow, the saturated vapor pressure has been used as a criterion for determining the cavitation generation or disappearance based on the idea of phase equilibrium, however it is well known that these calculation results don’t agree well with experimental results. For example, it is reported that the cavitation inception pressure is higher than its saturated vapor pressure in water. This is predicted to be resulting from the generation of gaseous cavitation which is caused by liberation of dissolved air, however this has not been taken into consideration in the current CFD model. Here, liberation of non-condensable gas is supposed to be treated by MD (molecular dynamics) then it is not suitable for CFD. Thus, in order to develop a more accurate CFD model for cavitating flow, it is necessary to develop a macroscopic and coarse-grained model of liberation should be developed, which may be related to flow dynamic-stimulation of the unsteady flow field with cavitation. In the present study, we focus attention on relationship between liberation of dissolved gas and unsteadiness of cavitation. Experiment is conducted in high-temperature water cavitation tunnel in which in-situ measurement of the amount of dissolved oxygen can be performed during the operation with cavitation. The variation of dissolved oxygen is used as one of the indexes of liberation of dissolved non-condensable gas during the experiment. The degree of cavitation unsteadiness is judged by calculation based on the FFT (Fast Fourier Transform) of the downstream fluctuation pressure and the RMS (root mean square) of brightness value using images taken with a high-speed camera. In addition, in order to eliminate the factors of dissolved gas liberation other than cavitation unsteadiness, the mainstream pressure, the mainstream temperature and volume of the cavity are made to be equal, respectively. Under the above preconditions, the time evolution of dissolved oxygen amount is measured in several kinds of cavitating flow fields around NACA0015 and NACA16012 hydrofoils.

Study of Characteristics of Cloud Cavity Around Axisymmetric Projectile by Large Eddy Simulation

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Xianxian Yu ◽  
Chenguang Huang ◽  
Tezhuan Du ◽  
Lijuan Liao ◽  
Xiaocui Wu ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Large Eddy Simulation ◽  
Vapor Pressure ◽  
Saturated Vapor Pressure ◽  
Saturated Vapor ◽  
Cavitation Number ◽  
Clear Understanding ◽  
Computation Model ◽  
Eddy Simulation ◽  
Large Eddy

Cavitation generally occurs where the pressure is lower than the saturated vapor pressure. Based on large eddy simulation (LES) methodology, an approach is developed to simulate dynamic behaviors of cavitation, using k-μ transport equation for subgrid terms combined with volume of fluid (VOF) description of cavitation and the Kunz model for mass transfer. The computation model is applied in a 3D field with an axisymmetric projectile at cavitation number σ = 0.58. Evolution of cavitation in simulation is consistent with the experiment. Clear understanding about cavitation can be obtained from the simulation in which many details and mechanisms are present. The phenomenon of boundary separation and re-entry jet are observed. Re-entry jet plays an important role in the bubble shedding.

Diffusive mass transfer in island films

1978 ◽  
Vol 125 (7) ◽  
pp. 489-525 ◽  
Author(s):  
Ya.E. Geguzin ◽  
Yu.S. Kaganovskii
Keyword(s):  
Mass Transfer ◽  
Diffusive Mass Transfer ◽  
Island Films

scholarly journals Study on a Quaternary Working Pair of CaCl2-LiNO3-KNO3/H2O for an Absorption Refrigeration Cycle

Entropy ◽  
2019 ◽  
Vol 21 (6) ◽  
pp. 546 ◽  
Author(s):  
Yiqun Li ◽  
Na Li ◽  
Chunhuan Luo ◽  
Qingquan Su
Keyword(s):  
Heat Capacity ◽  
Crystallization Temperature ◽  
Saturated Vapor Pressure ◽  
Saturated Vapor ◽  
Specific Enthalpy ◽  
Refrigeration Cycle ◽  
Absorption Refrigeration ◽  
Evaporation Temperature ◽  
Corrosion Rates ◽  
Specific Entropy

When compared with LiBr/H2O, an absorption refrigeration cycle using CaCl2/H2O as the working pair needs a lower driving heat source temperature, that is, CaCl2/H2O has a better refrigeration characteristic. However, the crystallization temperature of CaCl2/H2O solution is too high and its absorption ability is not high enough to achieve an evaporation temperature of 5 °C or lower. CaCl2-LiNO3-KNO3(15.5:5:1)/H2O was proposed and its crystallization temperature, saturated vapor pressure, density, viscosity, specific heat capacity, specific entropy, and specific enthalpy were measured to retain the refrigeration characteristic of CaCl2/H2O and solve its problems. Under the same conditions, the generation temperature for an absorption refrigeration cycle with CaCl2-LiNO3-KNO3(15.5:5:1)/H2O was 7.0 °C lower than that with LiBr/H2O. Moreover, the cycle’s COP and exergy efficiency with CaCl2-LiNO3-KNO3(15.5:5:1)/H2O were approximately 0.04 and 0.06 higher than those with LiBr/H2O, respectively. The corrosion rates of carbon steel and copper for the proposed working pair were 14.31 μm∙y−1 and 2.04 μm∙y−1 at 80 °C and pH 9.7, respectively, which were low enough for engineering applications.

scholarly journals Effects of nanoparticles on hydraulic cavitation

2018 ◽  
Vol 240 ◽  
pp. 03004
Author(s):  
Min-rui Chen ◽  
Jin-yuan Qian ◽  
Zan Wu ◽  
Chen Yang ◽  
Zhi-jiang Jin ◽  
...  
Keyword(s):  
Vapor Pressure ◽  
Saturated Vapor Pressure ◽  
Saturated Vapor ◽  
Geometric Model ◽  
Pressure Ratio ◽  
Perforated Plate ◽  
Significant Parameter ◽  
Operation Conditions ◽  
Small Bubbles ◽  
Crucial Condition

When liquids flowing through a throttling element, such as a perforated plate, the velocity increases and the pressure decreases. If the pressure is below the saturated vapor pressure, the liquid will vaporize into small bubbles, which is called hydraulic cavitation. In fact, vaporization nucleus is another crucial condition for vaporizing. The nanoparticles contained in the nanofluids play a significant role in vaporization of liquids. In this paper, the effects of the nanoparticles on hydraulic cavitation are investigated. Firstly, a geometric model of a pipe channel equipped with a perforated plate is established. Then with different nanoparticle volume fractions and diameters, the nanofluids flowing through the channel is numerically simulated based on a validated numerical method. The operation conditions, such as the temperature and the pressure ratio of inlet to outlet, are the considered variables. As a significant parameter, cavitation numbers under different operation conditions are achieved to investigate the effects of nanoparticles on hydraulic cavitation. Meanwhile, the contours are extracted to research the distribution of bubbles for further investigation. This study is of interests for researchers working on hydraulic cavitation or nanofluids.

The Effect of Shear Flow and Dissolved Gas Diffusion on the Cavitation in a Submerged Journal Bearing

2000 ◽  
Vol 123 (3) ◽  
pp. 494-500 ◽  
Author(s):  
M. Groper ◽  
I. Etsion
Keyword(s):  
Mass Transfer ◽  
Shear Flow ◽  
Mass Transport ◽  
Transport Mechanism ◽  
Journal Bearing ◽  
Gas Diffusion ◽  
Gas Bubble ◽  
Dissolved Gas ◽  
Rotating Shaft ◽  
Mass Transfer Mechanism

Two possible, long standing speculated mechanisms are theoretically investigated in an attempt to understand previous experimental observations of pressure build up in the cavitation zone of a submerged journal bearing. These mechanisms are (1) the shear of the cavity gas bubble by a thin lubricant film dragged through the cavitation zone by the rotating shaft and (2) the mass transfer mechanism which dictates the rate of diffusion of dissolved gas out of and back into the lubricant. A comparison with available experimental results reveals that while the cavitation shape is fairly well predicted by the “shear” mechanism, this mechanism is incapable of generating the level of the experimentally measured pressures, particularly towards the end of the cavitation zone. The “mass transport” mechanism is found inadequate to explain the experimental observations. The effect of this mechanism on the pressure build up in the cavitation zone can be completely ignored.

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