The effect of temperature on the intensity and the dynamics of cavitation is investigated. Experiments of cavitating flows are conducted at various cavitation numbers and temperatures, leading to ...different cavity intensities and dynamic behaviors. The thermodynamic effects significantly influence the cavitation extent at elevated temperatures (over 58 °C) in water. Three regimes of instability, i.e. the sheet cavitation, the periodic single-cloud cavitation, and the aperiodic multi-clouds cavitation are distinguished based on their temporal-spatial evolutions. Application of DMD and POD decompositions on the velocity fields and gray level snapshots to determine the coherent structures and the various mechanics causing different shedding behaviors are discussed. The coherent structures obtained in cloud cavitation consist of the re-entrant jet and counter-rotating vortex structures, which are more aggressive dynamic behavior and are absent in the sheet cavitation. To inhibit the effects of hydrodynamic cavitation, it is recommended that a temperature range (55 °C–60 °C) of water be avoided in practical applications. Since working under this temperature range has larger potentials of transforming the steady sheet cavitation to unsteady cloud cavitation with the larger cavitation extent and the vigorous vapor cloud shedding.
•Efficiency of machinery with cavitation can be improved by adjusting temperature.•HC phenomenon is highly affected by thermal delays, σ number and Re number. .•Cavitation intensity peaks and shedding regimes transition happens at 58 °C.•Data analysis predicts larger dynamical structures in cloud cavitation process.
•A compressible two-phase model synchronous considering phase change and thermodynamic effect is implemented.•The first two cycles of the cavitation bubble's essential physical features are well ...reproduced.•The quantitative analyses of the effects of γ on the pressure peaks are performed and four distinct stages are identified.
The final collapse of the rebound cavitation bubble may be more violent than its initial, resulting in more severe damage to the nearby structures. To better understand the dynamical behaviors of the rebound cavitation bubble, the multi-period evolution of the cavitation bubble near the solid wall is investigated experimentally and numerically. Due to multiple factors affecting the rebound cavitation bubble behaviors, a compressible two-phase solver considering phase change and thermodynamic effect simultaneously is developed in OpenFOAM in this study. Validations are conducted by comparing the numerical results with corresponding experimental data. The essential and comprehensive dynamics of the rebound cavitation bubble is well reproduced and analyzed, which helps reveal the underlying physical mechanisms. The potential damage is numerically quantified by the pressure peak at the wall center. The quantitative effect of the dimensionless standoff distance γ on the pressure peaks is analyzed with four distinct stages identified. Moreover, the maximum rebound radius, corresponding to the amount of the initial energy during the rebound stage, and maximum temperature within the bubble at different γ are also discussed. The results show that the maximum rebound bubble radius increases first and then decreases with the increase of γ. In addition, the effect of the γ on the maximum temperature is given with three distinct stages identified.
•Cavitation model with thermodynamic effect in multiple regimes was proposed.•Vapour bubble growth rate and vapour bubble number density were formulated.•Model was validated with test data on R114, ...liquid nitrogen, hydrogen and water.•Model underestimates temperature depression by (18.6–43)%.•Model leads to reasonable flow rate-net positive suction head curve for pump.
Mechanical feed pumps in organic Rankine cycle (ORC) power plants can suffer from cavitation to lose their normal feeding performance or even damage. Cavitation models for organic fluids in ORC systems are lacking presently. Hence, a new cavitation model with thermodynamic effect was proposed. Surface tension-controlled, inertia-controlled, intermediate and heat transfer-controlled cavitation regimes, and two key elements: vapour bubble growth rate and vapour bubble number density are included in the model. A known air or non-condensable gas concentration in the liquid was employed to determine cavitation nuclei number density. The model was coded in ANSYS CFX as user defined model and validated with cavitating flows of organic fluid R114 in a venturi, liquid nitrogen and liquid hydrogen on a tapered hydrofoil and warm water around a hydrofoil NACA 0015 in cavitation tunnels based on visualised cavity length. Two model constants, temperature depression, and minimal cavitation number were correlated to bulk liquid temperature, Reynolds number, and Jakob number. The temperature and pressure profiles of liquid nitrogen and hydrogen on hydrofoil surface were examined against the experimental data. The model was applied to simulate unsteady cavitating flows of organic fluid R245fa in a diaphragm pump. It was shown that the temperature depression and minimal cavitation number cannot be correlated to bulk liquid temperature, Reynolds number and Jakob number. Two model constants can be correlated fairly to Reynolds number. The model underestimates the thermodynamic effect by 43% for R114, 18.6% for liquid nitrogen and 32.6% for liquid hydrogen based on temperature depression. The predicted temperature and pressure profiles on hydrofoil surface agree with the experimental data for liquid nitrogen. The model can produce an expected curve of mean pump flow rate against net positive suction head available.
•A novel model for miscible CO2-oil mixtures flow in nanopores is proposed.•Activation free energy for miscible molecules motion in nanopores is determined.•CO2-enhanced confined oil flow and its ...deviation from bulk results are identified.•The effects of microscopic interactions, CO2 content and pore size are analyzed.
Dynamic behavior of miscible CO2-oil mixtures is the heart of CO2 enhanced oil recovery (EOR) and CO2 storage in shale reservoirs. However, the omnipresent nanopores not only raise the difference in CO2-reduced oil viscosity through thermodynamic effect from that of bulk condition but also add additional kinetic resistance resulting from a pore surface. In this work, a novel thermo-kinetic model is proposed to characterize the miscible mixtures flow in nanopores with involving changes in activation free energy induced by thermodynamic effect and kinetic effect, where the former is correlated with Helmholtz free energy by a modified Soave-Redlich-Kwong equation of state, while the latter is determined by a solid–fluid potential model with assuming a miscible mixture as a single pseudo-fluid. Subsequently, CO2-enhanced oil flow in nanopores and its deviation from bulk results are demonstrated. Moreover, the roles of different microscopic interactions are clarified, and the effects of a pore size, CO2 content as well as the strength of fluid-wall interactions are discussed. It is found that CO2 can simultaneously weaken the fluid–fluid interactions and fluid-wall interactions, jointly leading to a reduction in local fluid viscosity and an enhancement in oil flow. The increase in wall-oil affinity and CO2 content can strengthen the enhancement effect. Moreover, our results indicate that the relationship between enhancement effect and pore size strongly depends on the strength of interfacial interactions. For a nanopore with low wall energy (εs/kb < 10 K), a reduction in the enhancement factor is obtained with a decrease in pore size, while the opposite phenomenon is observed for a pore wall with a strong affinity to the oil. Our study lay a theoretical foundation for the reservoir simulation of CO2-EOR and CO2 storage in shale reservoirs.
Butterfly valve is widely used to transport cryogenic medium such as liquid natural gas (LNG), liquid nitrogen and so on. When the pressure of cryogenic fluid is lower than the saturated vapor ...pressure corresponding to the local temperature, the cryogenic fluid will produce the phase transformation from liquid to gas, which is called as cryogenic cavitation. Cavitation phenomenon is the main cause of cavitation erosion, vibration and noise, which seriously affects the stable operation of the system and the lifetime of the valves. Cryogenic medium is more easily cavitated in the process of transportation and regulation due to its unique thermal sensitivity. In order to explore the evolution mechanism of cryogenic cavitation through butterfly valves, numerical simulations were carried out to study the dynamic evolution of cryogenic cavitation through a butterfly valve model at different valve opening degrees. By considering the thermal effect of cryogenic medium, the traditional cavitation model is modified and verified by experimental results. The evolution including generation, development and collapse of cryogenic cavitation is observed and discussed in details at each valve opening degree. The relationship of cryogenic cavitation and vortex structure is revealed and entropy production is obtained to indicate the intensity of dynamic evolution of cryogenic cavitation through butterfly valve.
•A modified cavitation model was proposed and verified by experimental results.•The periodic evolution of cryogenic cavitation was observed and discussed in details.•The spatial and temporal relationship between cryogenic cavitation and vortex was revealed.•The irreversible energy loss induced by cryogenic cavitation was investigated.
Cryogenic pumps are widely used in the fields of liquid rocket engines, liquefied natural gas (LNG) transportation, and International Thermonuclear Experimental Reactor (ITER) systems. An inducer is ...usually installed in front of the cryogenic pump to prevent the pump performance deterioration and flow instabilities caused by cavitation. The objectives of this paper are to investigate the influence of flow conditions on the thermal cavitation in a cryogenic inducer and purpose the theoretical models to predict the inducer performance and flow instabilities. In the present study, inducer working at different inlet temperature and rotating speed with liquid nitrogen was numerically investigated. The results show that the temperature drop around cavity regions increases and the cavity volume decreases with the increasing temperature, which leads to the delay of the drop of head coefficient. The increase of rotating speed leads to the increase of cavity volume and earlier deterioration of cavitation performance. The sub-synchronous rotating cavitation is observed in the inducer. It is characterized by the FFT analysis of cavity area fluctuation. The increase of temperature suppresses both the size and unevenness of the cavitation on each blade. Further analysis indicates that the temperature drop resulting from the cooling effect of evaporation around the cavitation area is significant due to the smaller liquid-vapor density ratio. A theoretical prediction model and a one-dimensional analysis model were developed to investigate the cavitation performance and instability. The theoretical models can accurately predict the influence of thermodynamic effect on the inducer cavitation and the pressure fluctuation inside the blade channel. These theoretical models can be applied to the design and testing of cryogenic pumps in practical applications.
High-temperature water exhibits evident thermodynamic effects during cavitation, which influences the cavitation flow and generates complex flow characteristics. To reveal the mechanism of ...thermodynamic effects on the cavitation flow in high-temperature water, a flow around NACA 0015 hydrofoil was simulated. Based on the existing isothermal cavitation model, the thermodynamic effects were considered by correcting evaporation and condensation source terms and coupling physical parameters with temperature. Numerical results obtained from the thermodynamic effect cavitation model agree well with the available experiments. A comparative analysis of performance characteristics, cavitation shape, and interphase mass transfer rate was performed. The thermodynamic effects on the cavitation flow of hydrofoil under different temperature were presented. The existence of the thermodynamic effects lowers the local temperature of the cavitation, reduces the vapor phase volume fraction of the cavitation area, and inhibits the development of cavitation. Moreover, a novel entropy production analysis was conducted to reveal the thermodynamic effects on the energy loss. The difference of local entropy production rate in the cavitation flow with and without thermodynamic effects was revealed. The analyses show that the existence of the thermodynamic effects reduces the energy loss owing to the reduction of the dissipation loss caused by the velocity gradient. When the thermodynamic effects are considered, the energy loss caused by the temperature gradient shows an increase; however, the proportion of this loss is still small.
•The cavitation flow around a hydrofoil considering the thermodynamic effect was studied.•Cavitation model considering the thermodynamic effect was validated.•The thermodynamic effect on the cavitation flow under different temperature was revealed.•A novel entropy production analysis one the thermodynamic effect was conducted.
•A new cavitation model is proposed by adopting physical bubble growth rates.•Empiricism inherent in the bubble number density is substantially reduced.•Smooth temperature recovery in cryogenic ...cavitation is well captured.•Existing characteristics under isothermal conditions are kept.
Cavitation in thermosensitive fluids is accompanied by a noticeable temperature drop inside a cavity. Motivated by the fact that most popular cavitation models have been developed without considering thermodynamic effects, the present study proposes physics-based corrections to existing cavitation models. Two primary corrections are adopting the physical bubble growth rate and separating bubble number density in the vaporization and condensation terms. The bubble growth rate in the cavitation model is chosen as the limiting factor between the inertia-controlled rate and heat diffusion-controlled rate from the bubble growth theories. To implement the theoretical growth rate of the thermal regime into the computational framework based on the homogeneous mixture model, the bubble time and liquid temperature are newly modeled. Furthermore, the bubble number density, which is often set uniformly throughout the whole computational domain, is separated for the vaporization and condensation processes. The vaporization bubble number density is further modeled by experimental data to reduce the empiricism inherent in the user-defined coefficients. The relation between the remaining model coefficients and characteristic temperature drop (ΔT*) is developed and it is verified to be effective in various types of fluids and working conditions. The newly proposed model is validated by cryogenic cavitating tests and applied to the computations of the 3-D cryogenic cavitating flows around a turbopump inducer. Unlike the sudden temperature recovery by the previous inertial rate-based models, the proposed model predicts a gradual temperature recovery inside a non-isothermal cavity, which is consistent with the experimental observations. It is also confirmed that the new model chooses the physical inertial rate under isothermal conditions, and thus, the model can be used regardless of the flow conditions.
The objective of this paper is to numerically investigate the thermodynamic effect during bubble collapse near a rigid boundary. A compressible fluid model is introduced to accurately capture the ...transient process of bubble shapes and temperature, as well as corresponding pressure, and velocity. The accuracy of the numerical model is verified by the experimental data of bubble shapes, and Keller-Kolodner equation as well as its thermodynamic equation. The results show that a bubble near the rigid boundary presents high-speed jet in collapse stage and counter jet in rebound stage, respectively. In the collapse stage, the bubble margin will shrink rapidly and do the positive work on the compressible vapor inside the bubble, then a significant amount of heat will be generated, and finally the generation of high-speed jet drives the low-temperature liquid outside the bubble to occupy the position of high-temperature vapor inside the bubble. In the rebound stage, the counter jet moving away from the rigid boundary takes part of heat away from the sub-bubble, which avoids the external work of the expansion of the sub-bubble and the temperature reduction caused by the dissipation effect of the vortex structure. In addition, the initial standoff has a significant effect on the thermodynamics of bubble oscillation. The temperature keeps increasing with the increase of the initial standoff in the collapse stage, while it shows a downward trend with the increase of the initial standoff in the rebound stage. That’s because the high-speed jet and counter jet of bubble gradually disappear when the initial standoff increases, which is the important reason for the opposite evolution trend of temperature in collapse and rebound stage.
This paper aims to numerically investigate the thermodynamic effect on attached cavitation and cavitation-vortex interaction around a NACA0015 hydrofoil. Based on the isothermal cavitation model, the ...compressibility and thermodynamic effect are considered by adding the state equation and modifying the evaporation and condensation source term in the mass transport equation. The thermodynamic effect on the hydrodynamic performance and the cavity volume fluctuations, the temporal evolution of the unsteady cavitation, the temporal evolution of vortex structures in the hydrofoil wake, and the cavitation-vortex interaction are presented. The main features of the unsteady quasi-periodic cavitation behavior are illustrated for the isothermal and non-isothermal conditions. The new omega vortex identification method depicts the influence of the thermodynamic effect on the shedding structure around the wake of a hydrofoil. Furthermore, the cavitation-vortex interaction is examined to show the relationship.
•The predicted lift coefficients and the cavity volume change quasi-periodically in both isothermal and non-isothermal conditions in the typical cycles.•The coupling mechanism of thermal effect, vorticity, and cavitation is examined.•The evolution of cavitation is closely related to the vortex structure.•The vortex stretching term, the dilatation term and the baroclinic torque term play a major role in the cavitation-vortex interactions.
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