Water Film Model Research Articles

Experimental and numerical research on flow characteristics of inlet particle separator for aero-engine under the influence of water film

An aero-engine must be able to operate in all-weather conditions, which requires the aircraft to be safe throughout the flight even in bad weather. Excessive intake of rainwater can induce stall and surge of compressor and flameout of combustion chamber, which will lead to the loss of power of the engine. In rainy weather, water come into the engine inlet protection device, which directly determines the compressor inlet conditions and will further affect the compressor working condition and the matching features. In this paper, special attention was paid to the experimental characteristics of aero turbo-shaft engine inlet particle separator (IPS) and the numerical study employing ANSYS-CFX under water spraying condition. Based on the phenomenon of water film forming on the wall surface of the IPS and the experimental data under different water spraying conditions, combined with the predictions from CFD study, an empirical model of water film flow on the wall surface has been developed. The results indicate that in the case of high water ingestion, droplets will inevitably form water film on the wall after entering the IPS. Due to the viscous resistance of wall water film and its influence on the airflow boundary layer, the flow state inside the IPS will change. By establishing a wet wall water film model, the flow characteristics near the wall are closer to the experimental state. The total pressure loss prediction error was reduced from 24.8% to 5.2% and 26.4% to 5.7% under the uniform water spraying rate of 2.93% and 4.84%, respectively.

Numerical calculation method of steam-liquid separation efficiency of the corrugated plate dryer based on the discrete phase model and the Euler water film model: A short communication

The corrugated plate dryer (CPD) is a sort of steam-liquid separation (SLS) equipment widely employed in energy and chemical industries, etc. Moreover, the steam-liquid separation efficiency of CPD, a crucial secondary SLS device of the nuclear power plant’s second loop, has a significant impact on the quality of the steam, which will indirectly affect the efficiency of energy conversion in the process that nuclear energy is converted into electronic energy. In practical engineering applications, it is necessary to give the steam-liquid separation efficiency (SLSE) value of CPD with different structural parameters according to different working conditions for the design and selection of CPD. At present, the SLSE of CPD is mainly measured based on some indirect measurement method such as conductivity measurement. However, this method generally requires the production of large amounts of CPDs. Meanwhile, successful structural design of CPD is based on extensive trials, which will consume a lot of time and research and development (R&D) expenses. Therefore, finding a solution to the problem of precise calculation of SLSE of CPD at present is urgent. The use of numerical simulations to realize this calculation has important engineering applications. In this paper, based on the coupling of Discrete Phase Model (DPM) and Euler Water Film (EWF) model, the precise calculation of the SLSE of CPD is realized. This is the first time that the academic community has obtained a precise calculation method for the Re-entrainment phenomenon (Maximum value of separation efficiency) of CPD, which can provide a very important technical support for CPD structure design.

Simultaneous measurement of near-water-film air temperature and humidity fields based on dual-wavelength digital holographic interferometry.

We present a method to reconstruct the near-water-film air temperature and humidity distributions synchronously by measuring the phase delays based on dual-wavelength digital holographic interferometry. A falling water film device was used to create a water film evaporation environment and generate axially uniform temperature and humidity fields. The relationship between air temperature, humidity and phase delay is derived from the Edlen equations. With such relationship, the temperature and humidity distributions can be solved directly according to phase delays of two different wavelengths. An edge phase enhancement method and an error elimination method with PSO are presented to improve the measurement accuracy. The temperature and humidity fields in the falling water film model were experimentally reconstructed with temperature deviation of 0.06% and relative humidity deviation of 2.61%.

Prediction of acid rock drainage in waste rock piles part 2: Water flow patterns and leaching process

In waste rock piles, the leaching process involved in acid rock drainage is mainly controlled by water flow. This paper (Part 2) investigates the effects of heterogeneities on the water flow patterns by applying probability density functions to hydrogeological properties. In this study, a piecewise constant distribution is proposed to describe the permeability inside waste rock piles, which reflects the effect of both finer and coarser pores. Compared with uniform water flow obtained from traditional homogeneous modeling, various water flow patterns and their pathways inside waste rock piles can be simulated by the proposed model. In addition, the leaching process is also investigated by coupling the calculated water flow with the geochemical reaction based on the water film model proposed in part 1. For demonstration, these models are integrated and applied to the full-scale waste rock pile at Equity Silver mine in British Columbia, Canada. Because the iron loading is highly correlated to the acidity at this site, it is found that the fluctuation of annual lime consumption for neutralization at this site can be well predicted by the integrated model. In addition, the results indicate that waste rock piles with different spatial patterns of permeability distribution, but with the same probability density function, may have different water flow patterns and spatial distributions of iron concentrations inside the pile. However, the total water flow discharge rate and iron loading profiles from the pile are almost the same on the temporal scale.

A Full-Scale Case Study on the Leaching Process of Acid Rock Drainage in Waste Rock Piles and the Net Infiltration Through Cover Systems

The leaching process and drainage chemistry of acid rock drainage is mainly controlled by geochemical reactions and how water carries soluble reaction products in waste rock piles. This paper studied how water flows through a full-scale waste rock pile at the Equity Silver mine site in British Columbia, Canada and elaborated on their effects on the leaching process and drainage chemistry. A revised dual-permeability model coupled with mass transport was adopted to investigate preferential flow and matrix flow in the pile simultaneously while considering water and geochemical products leaching/exchange between them. Furthermore, a particle-level water film model and also the effects of air flow, oxygen transport, and heat transfer in pile scale were integrated to account for geochemical reactions. Simulation results of full-scale iron discharge showed that aqueous concentrations in drainage water did not vary significantly relative to variations in drainage flow rate, which was confirmed by 12 years of field monitoring data. In addition, the comparison of pre- and post-cover simulations with measured lime consumption during ARD treatment, and mass-balance/dilution calculations for the entire pile, indicates that roughly 15–20% of total precipitation passes through the cover.

Prediction of acid rock drainage in waste rock piles Part 1: Water film model for geochemical reactions and application to a full-scale case study

Geochemical reactions taking place at the rock surface and pore water interface, and rapid preferential water flow through waste rock piles are identified as two primary steps for acid rock drainage (ARD) and metal leaching (ML) processes. This paper (Part I) develops a water film model to describe the interactions among sulphide minerals, pore water and oxygen, which considers the reactive surface areas as the primary sites to capture geochemical reactions including sulphide oxidation and neutralization reactions, and also considers acid and metal ion storage in pore water. In addition, the proposed water film model is further coupled with a pile-scale mass transport model to investigate a specific case of the main waste rock pile at the Equity Silver mine, Canada. Overall, the simulated profile of oxygen concentration matches the historical monitoring data. The modeling results revealed potential controlling mechanisms for ARD generation inside the waste rock pile and provided insights into the impact of an engineered cover on the waste rock pile.

Status of dynamic water film model development in 3-D CFD code GASFLOW-MPI for analysis of passive containment cooling system

The advanced passive PWR AP-1000 and AP-1400 are pressurized water reactors (PWR) with advanced passive safety systems. Most recognize the passive containment cooling system (PCCS) as being one of the most important concepts for advanced passive safety systems. Following a postulated design-base-accident (DBA), an outside cold liquid-water spray is injected on the apex of the spheroidal dome. The resulting water film drains under gravitational body forces over the outside dome surface and down the cylinder surface. This PCCS removes heat from the containment interior to reduce potentially damaging pressure and temperature loads. A numerical model for simulating the falling water film transport in PCCS has been developed in 3-D CFD code GASFLOW-MPI. The water film model is governed by mass, momentum and energy transport equations with essential source terms for inter-phase exchange. The conjugate heat and mass transfer between the gas mixtures inside the containment, water film, and the gas in the annular space outside of the steel containment can be simulated. The heat conduction in the solid steel containment is calculated as well. In order to facilitate model validation in GASFLOW-MPI, we have developed an exact numerical solution (ENS) for the one-dimensional steady-state liquid film flow over an ellipsoidal-domed cylinder. Although the ENS assumes constant containment wall temperature and outside ambient air temperature, it can incorporates any generalized heat transfer correlation between the containment surface and water film as well as any generalized heat and mass (evaporation) transfer correlations between the film and outside ambient air. ENS results for draining liquid water films clearly present the coupling effects of heat and mass transfer. Excellent comparisons between the ENS and CFD calculation results support the reliability and accuracy of the dynamic water film model in GASFLOW-MPI code which provides an efficient way to analyze PCCS in 3-D full scale advanced light water reactors.

Evaluation of Passive Containment Cooling with an Advanced Water Film Model in a Lumped-Parameter Code

Falling water films have been employed for passive containment cooling in several Generation III pressurized water reactor designs. In this paper, the lumped-parameter (L-P) containment code system COCOSYS with an advanced water film model is applied to evaluate the performance of a passive containment cooling system (PCCS) during accidents. Based on the recent work and with further modification, an integrated water film model is developed. The new model considers different flow regimes of a liquid film as it flows downward and is being evaporated. The integrated model has been adapted to the L-P code and then implemented into COCOSYS. The new model enables the containment code to capture previously neglected phenomena, including the behavior of film breakup due to the reduction in mass; the formation of rivulets; the change in coverage rate and the development of rivulets; the change of velocity distribution as well as film thickness by considering the interfacial shear stress created by countercurrent air on the film surface; the hysteresis of rivulets, i.e., the process of advancing or retreating, involving changes in contact angles; and the influence of waves on the film surface.The new model is validated against existing test results and experimental observations in the authors' recent work and is further modified in this paper taking into account the influence of waves and the processes of rivulet hysteresis. The model is then assessed based on test nodalization, and the expected phenomena are observed. Afterward, the new model is applied to evaluate the performance of PCCS film cooling employed in the AP1000 containment.It is concluded that the original film model tends to underestimate the pressure loads due to the absence of film breakup, rivulet behavior, and shear stress models. The coverage rate, as a new factor captured in the new model, limits the evaporation rate and thus restricts the cooling efficiency of the falling film. The sensitivity analysis reveals that the contact angle and hysteresis phenomenon, which were not previously considered in the code, play significant roles in PCCS film cooling. The advancing contact angle of the rivulets is a decisive factor for the peak pressure, while the retreating contact angle is influential in the later phase of cooling. It can be inferred from the study that the ideal situation for PCCS cooling is that in which the water film is approaching complete dryout at the bottom of the containment. The newly developed liquid film model helps improve the accuracy and reliability of the simulation results.

Large-eddy simulation of thin film evaporation and condensation from a hot plate in enclosure: First order statistics

Numerical investigation of water evaporation and condensation in buoyancy driven flow, along with the thermal coupling between fluid and surrounding solids, is interesting for many industrial applications. The physical complexity of the evaporation and condensation processes, the mutual thermal influence of water change of phase and solid–fluid heat transfer, the anisotropy of turbulence quantities are challenging problems from numerical and theoretical side. The archetypal case of a vertical hot plate inside a cold square enclosure, filled with humid air, is studied. The solid surfaces are wetted by a thin water film. The plate cooling process due to film evaporation is analysed. Numerical simulation adopts the large-eddy methodology along with the dynamic Lagrangian sub-grid scale model. The conjugate heat transfer technique accounts for the solid–fluid thermal coupling, while the water phase is modelled under the thin film assumption. First, a preliminary case with isothermal solid boundaries and fixed film thickness is reproduced at Ra=5×108. The absence of surface heat transfer leads to analogous distribution of temperature and humidity. The cavity is characterised by strong stratification that confines the motion in the upper part. The same setting is used to simulate the case of dry air. It is found that the presence of vapour increases the velocity by a maximum of 20%. Also, the heat transfer generated by the water change of phase, in case of humid air, overcomes the other heat transfer modes. Successively, conjugate heat transfer and water film model are activated, and three cases are studied changing the plate material. The specific heat ρCp of materials is the parameter controlling the plate cooling process, that is mainly due to evaporation and the evolution of the thermodynamic field within the enclosure. An analysis of the dew-point temperature suggests that recondensation onto the plate surface cannot occur, even for materials that are rapidly cooled.

Influence of Stern Shaft Inclination on the Cooling Performance of Water-Lubricated Bearing

The water film model of the marine water-lubricated stern bearing was established by FLUENT. The influence law of water flow rate on the cooling performance of water-lubricated bearing was studied in consideration of the stern shaft inclination. It will be helpful to improve the performance of marine water-lubricated stern bearing and both security and reliability of propulsion system. The simulation results show that the increase of cooling water flow rate in a certain range can effectively reduce bearing temperature. The bearing temperature rises sharply with thinning of water film thickness which is caused by the increase of inclination angle. Larger inclination angle can deteriorate the operating reliability of bearing.

3차원 착빙 형상 예측을 위한 2세대 시뮬레이션 코드 개발

The 2 nd generation ice accretion analysis program has been developed and validated for various icing conditions. The essential feature of the 2 nd generation code lies in its capability of handling general 3-D geometry and improved accuracy. The entire velocity fields are obtained based on Navier-Stokes equations in order to take the massively separated flow field into account. Unlike 1 st generation code, the droplet trajectories are calculated using Eulerian approach, which is adopted to yield appropriate collection efficiency even in the shadow region. For improved thermodynamic analysis on the surfaces, water film model and modified Messinger model are newly included in the present analysis. The ice shape for a given time step is obtained by considering the exact amount of ice accreted on the surface. Each module of the icing analysis code has been seamlessly integrated on the OpenFOAM platform. The developed code was validated against available experimental data for 2D airfoils and 3D DLR-F4. Due to the lack of experimental data, the computed results of DLR-F4 were compared with those obtained from FENSAP-ICE, which is state-of-the-art 3D icing analysis code. It was clearly shown that the present code produces comparable results to those of FENSAP-ICE, in terms of prediction accuracy and the capability of handling general 3-D geometries.

Computational studies of atmospherically-relevant chemical reactions in water clusters and on liquid water and ice surfaces.

CONSPECTUS: Reactions on water and ice surfaces and in other aqueous media are ubiquitous in the atmosphere, but the microscopic mechanisms of most of these processes are as yet unknown. This Account examines recent progress in atomistic simulations of such reactions and the insights provided into mechanisms and interpretation of experiments. Illustrative examples are discussed. The main computational approaches employed are classical trajectory simulations using interaction potentials derived from quantum chemical methods. This comprises both ab initio molecular dynamics (AIMD) and semiempirical molecular dynamics (SEMD), the latter referring to semiempirical quantum chemical methods. Presented examples are as follows: (i) Reaction of the (NO(+))(NO3(-)) ion pair with a water cluster to produce the atmospherically important HONO and HNO3. The simulations show that a cluster with four water molecules describes the reaction. This provides a hydrogen-bonding network supporting the transition state. The reaction is triggered by thermal structural fluctuations, and ultrafast changes in atomic partial charges play a key role. This is an example where a reaction in a small cluster can provide a model for a corresponding bulk process. The results support the proposed mechanism for production of HONO by hydrolysis of NO2 (N2O4). (ii) The reactions of gaseous HCl with N2O4 and N2O5 on liquid water surfaces. Ionization of HCl at the water/air interface is followed by nucleophilic attack of Cl(-) on N2O4 or N2O5. Both reactions proceed by an SN2 mechanism. The products are ClNO and ClNO2, precursors of atmospheric atomic chlorine. Because this mechanism cannot result from a cluster too small for HCl ionization, an extended water film model was simulated. The results explain ClNO formation experiments. Predicted ClNO2 formation is less efficient. (iii) Ionization of acids at ice surfaces. No ionization is found on ideal crystalline surfaces, but the process is efficient on isolated defects where it involves formation of H3O(+)-acid anion contact ion pairs. This behavior is found in simulations of a model of the ice quasi-liquid layer corresponding to large defect concentrations in crystalline ice. The results are in accord with experiments. (iv) Ionization of acids on wet quartz. A monolayer of water on hydroxylated silica is ordered even at room temperature, but the surface lattice constant differs significantly from that of crystalline ice. The ionization processes of HCl and H2SO4 are of high yield and occur in a few picoseconds. The results are in accord with experimental spectroscopy. (v) Photochemical reactions on water and ice. These simulations require excited state quantum chemical methods. The electronic absorption spectrum of methyl hydroperoxide adsorbed on a large ice cluster is strongly blue-shifted relative to the isolated molecule. The measured and calculated adsorption band low-frequency tails are in agreement. A simple model of photodynamics assumes prompt electronic relaxation of the excited peroxide due to the ice surface. SEMD simulations support this, with the important finding that the photochemistry takes place mainly on the ground state. In conclusion, dynamics simulations using quantum chemical potentials are a useful tool in atmospheric chemistry of water media, capable of comparison with experiment.

Modification and application of water film model in COCOSYS for PWR's passive containment cooling

In this paper the physical model describing water film behaviors in German containment code system COCOSYS has been modified by taking into consideration the film breakup and subsequent phenomena as well as the effect of film interfacial shear stress created by countercurrent air flow. The modified model has extended its capability to predict particular water film behaviors including breakup at a critical film thickness based on minimum total energy criterion, the formation of rivulets according to total energy equilibrium as well as subsequent performance of rivulets according to several assumptions and observations from experiments. Furthermore, the modification considers also the change of velocity distribution on the cross section of film/rivulets due to shear stress. Based on the geometry of AP1000 and Generic Containment, simulations predicting containment pressure variation during accidents with operation of passive containment cooling system have been carried out. With the new model, considerably larger peak pressures are observed by comparing with those predicted with original water film model within a certain range of water film flow rate. Sensitivity analyses also point out that contact angle between water rivulets and steel substrate plays a significant role in the film cooling.