Characteristics Of Liquid Film Research Articles

Numerical Investigation on the Thermodynamic Characteristics of a Liquid Film upon Spray Cooling Using an Air-Blast Atomization Nozzle.

This paper developed a three-dimensional model to simulate the process of atomization and liquid film formation during the air-blast spray cooling technological process. The model was solved using the discrete phase model method. Several factors including the thermodynamic characteristics of the liquid film as well as the spray quality with different spray mass flow rates under different spray heights were numerically investigated and discussed. The results show that the varied spray height has little effect on the Sauter Mean Diameter (d32) of the spray droplet, while the thermodynamic characteristics of liquid film including the liquid film height, the liquid film velocity, and the liquid film generation rate are sensitive to the change of the spray height. With the growth of spray mass flow rates, d32, the liquid film generation rate and liquid film height become larger, while the liquid film velocity with different spray mass flow rates has a similar velocity distribution, indicating that the spray mass flow rate has little effect on the liquid film velocity. The average d32 of droplet size shows a sharp drop when sprayed from the nozzle in a short period of time (<1.5 ms), then approaching smoothness, below a value of 40 , the spray status tends to be stable.

Theoretical and experimental analysis of a water-lubricated rubber journal bearing with a large aspect ratio

Purpose The hydrodynamic characteristics of liquid film for bearings, especially water-lubricated bearings with a large length-to-diameter ratio, affect the dynamics behavior of rotor bearing systems. The purpose of this study is to carry out theoretical analysis and experiments to determine the hydrodynamic characteristics of water-lubricated journal bearings. Design/methodology/approach The finite difference method is adopted for the simulation of the characteristics of water-lubricated bearings. The comparison results between water-lubricated bearings with and without grooves, as well as with and without the consideration of the effects of rubber deformation, are presented. The test bearings, test bench, and monitoring system, especially the force exciter for the bearing experiment, are presented. Dynamic coefficient identification verification experiments were performed in different working situations. The obtained results include the calibration of magnetic force, two kinds of excitation, vibration data of the rotor system and dynamic coefficients. Findings The theoretical results demonstrate that the hydrodynamic effect was obvious when the speed was increased and that the water film had improved capability at a working speed of 1800 rpm. The identification results reveal the lubrication situation of the test bearing under low-speed and high-load conditions. Moreover, it was found that the liquid film was not continuous at low speeds. Originality/value The theoretical results can lead to the enhancement of the design level of water-lubricated rubber journal bearings with a large aspect ratio. The experimental results can lead to the improvement of the dynamic behavior design of rotor systems supported using water-lubricated bearings with a large length-to-diameter ratio.

Experimental study on the oscillation characteristics of thin liquid film in a microchannel

Characterization of thin liquid film is important for comprehensive understanding the phase-change heat transfer mechanisms in an oscillating slug flow. In this study, the thin film thickness of oscillating slug flow in a square tube was experimentally investigated using a nano-particle tracking velocimetry technique. Square tubes with inner dimension of 3.0 × 3.0, 1.6 × 1.6, 0.5 × 0.5, and 0.3 × 0.3 mm2 were used for test tubes, water was used as test fluids. The results show asymmetric velocity distribution in the thin liquid film. An obvious decrease of response time was observed for the thin liquid film when the oscillation frequency increases. The measured thin film thickness fits well with Taylor’s law when the capillary number is small. Deviation from Taylor’s law was found for larger capillary number, due to the prominent effect of bubble deceleration on the thin film thickness when the oscillation frequency increases. The relationship between acceleration process and deceleration process in different oscillation frequency is also studied.

Absorption and desorption of liquid film flowing over a porous layer

A hybrid multiphase model is used to facilitate modeling mass transfer of liquid film flowing over porous medium. The improved method relies on the combination of the VOF and Eulerian-Eulerian models. However, the coupled model cannot be directly applied to a two-domain situation because the Eulerian-Eulerian framework is found not compatible with computational mesh consisting of multi domains. To increase robustness of the coupled model for flow field of non-uniform spatial properties, several field functions relative to the position and properties of the porous zone are implanted, which keeps fluid domain single in mesh. The resulting model is then used to investigate the mass transfer characteristics of liquid film flowing over a thin compressed SiC foam layer. The gas side and liquid side mass transfer characteristics are investigated respectively by absorption of ammonia from air into water, and desorption of oxygen from water into nitrogen. By comparison with the results of liquid film flowing over a rigid surface, it is found that mass transfer performance degrades when liquid film flows over a porous layer. Besides, for liquid side mass transfer, desorption rate is greatly affected by the properties of the porous layer, and a non-linear relationship between desorption rate and liquid flow rate is observed.

Analysis of fluctuation and breakdown characteristics of liquid film on corrugated plate wall

Corrugated plate dryer is a very vital separation equipment for nuclear engineering and it is meaningful to study the flow, fluctuation and breakdown characteristics of the liquid film on corrugated plate wall. Liquid film thickness of steady flow is measured based on plane laser induced fluorescence (PLIF) technique and time series of liquid film thickness are obtained. Besides, amplitude and frequency domain information of liquid film fluctuations are analyzed by probability density function (PDF), power spectral density (PSD) and wavelet method. A two-dimensional liquid film breakdown model is established. Critical airflow velocity when the water film breakdown is measured experimentally. Based on theoretical results, equations for calculating critical airflow velocity of the corrugated plate under different liquid film thicknesses are fitted in the form of nike function. Fitting equations for calculating critical airflow velocity in the form of nike function agree well with experimental results.

Distortion correction and characteristics measurement of circumferential liquid film based on PLIF

AbstractFor its advantages of noninvasion and high temporal–spatial resolution, planar laser‐induced fluorescence (PLIF) is increasingly applied to measure the liquid film near axial flow. However, the circumferential distribution characteristics of liquid film, which are significant for heat and mass transfer process, cannot be measured briefly by the axial imaging. Because of the refractive index difference of the gas and liquid as well as the circular pipe, circumferential observation suffers distortion inevitably. In this paper, PLIF is developed to measure the circumferential film with a virtual dual‐view vision sensor, besides, the distortion model is established and a new distortion correction method is proposed. The effective view of circumferential liquid film is extended to 260°. Characteristics of vertical falling film are measured under different Reynolds numbers. Compared with the classical prediction models, the experimental results show the proposed method is capable for measuring circumferential film and the distribution characteristics conveniently and reliably.

Hydraulic Characteristics of Liquid Film Generated by Slit Injector

Liquid film generated by a jet slit injector on a wall was analyzed experimentally. Liquid film characteristics were investigated by measuring the liquid film thickness distribution for various experimental conditions. At first, the distributions were qualitatively analyzed using backlight imaging. Furthermore, quantitative measurements were performed using a liquid film thickness sensor based on the electric conductance method, which was applied to the high-speed wire-mesh method. The injection angle (15, 30, 45 °), jet velocity (7, 10.5, 13.5 m/s), and injection distance (45, 55, 65 mm) were varied, and the responses of the liquid film were observed. Having increased the injection angle, the main stream thickness decreased and the position of the maximum film thickness moved upstream. A faster jet velocity corresponded to a wider liquid film area and larger perturbation of the liquid film. The injection distance did not affect the characteristics of the liquid film considerably. A hydraulic jump effect was also observed, and a large hydraulic jump affected the film thickness distribution of the main stream. The results of this study can be applied to the development of liquid rocket engines or thrusters using the film-cooling method.

Laser-based investigation into injection, formation and flow processes of ethanol films on metal surface

Abstract Dynamic liquid films exist widely in various industrial processes, and the investigations into these films with high temporal and spatial resolution are of great significances to understand the formation mechanisms and flow characteristics of liquid films, as well as to optimize relevant processes. Since ethanol is often used as a diluent for the film-forming substance in the coating process, it was chosen as research object here. In the work, the absorption spectrum of ethanol in the near-infrared region (6000 cm−1–8000 cm−1) was firstly analyzed. And liquid films on horizontal metal surface were investigated based on diode laser absorption spectroscopy (DLAS) by manual injection of ethanol with a needle (injection mode 1) and automatic injection of ethanol with a peristaltic pump (injection mode 2), respectively. Meanwhile, ultrasonic pulse-echo method (UPEM) was employed to verify the measurement accuracy of DLAS method. It revealed that the variations of liquid film thicknesses during the injection and formation processes obtained by these two methods were in good agreement. Furthermore, the formation and falling processes of ethanol films on vertical metal surface by injection mode 2 at different outlet flow rates were also investigated by DLAS method. It revealed that if the flow rates increased by 100 ml/min, the time increased by ∼0.14 s on average for dynamic liquid film to get a steady state. And the film kept stable for 7.31/31.20/50.73/52.43 s at flow rates of 100/200/300/400 ml/min, and the corresponding film thickness was 246.3/243.5/202.7/200.1 μm, respectively.

Free-Flowing Shear-Thinning Liquid Film in Inclined μ-Channels

Among the most important variables in the design of falling film microreactors (FFMRs) is the liquid film thickness as well as the gas/liquid interfacial area, which dictate the mass and heat transfer rates. In a previous work conducted in our lab the characteristics of a free-falling Newtonian liquid film have been studied and appropriate correlations have been proposed. In this work the geometrical characteristics of a non-Newtonian shear thinning liquid, flowing in an inclined open microchannel, have been experimentally investigated and design correlations that can predict with reasonable accuracy the features of a FFMR have been proposed. The test section used was an open μ-channel with square cross section (WO = 1200 μm) made of brass which can be set to various inclination angles. The liquid film characteristics were measured by a non-intrusive technique that is based on the features of a micro Particle Image Velocimetry (μ-PIV) system. Relevant computational fluid dynamics (CFD) simulations revealed that the volume average dynamic viscosity over the flow domain is practically the same as the corresponding asymptotic viscosity value, which can thus be used in the proposed design equations. Finally, a generalized algorithm for the design of FFMRs, containing non-Newtonian shear thinning liquids, is suggested.

Flow behaviors and heat transfer characteristics of liquid film during the pyrolysis process of molten plastics using OpenFOAM

Falling film pyrolysis can improve the quality of pyrolysis products of waste plastics. The pyrolysis process of molten plastics is a complex process and the interphase force has an important influence on the flow and heat transfer process of the liquid film. Based on OpenFOAM® and considered the interphase drag force, the flow behaviors and heat transfer characteristics of the liquid film during the falling film pyrolysis of molten plastics were numerically simulated by VOF (Volume of Fluid) method. The results show that the surface of the liquid film is a wavy structure and the liquid film presents a comprehensive flow pattern of film, rivulet and droplet. With the increase of pyrolysis temperature, the length of liquid film and the average apparent heat transfer coefficient decrease, and the average thickness increases slightly. With the increase of the liquid film inlet velocity, the liquid film thickness and the average apparent heat transfer coefficient increase.

Experimental investigation on the surface wave characteristics of conical liquid film

The disintegration of the liquid sheet is due to the growth of the unstable surface wave. Research on the surface wave characteristics mainly uses the linear stability analysis, and the surface wave characteristics, for example the frequency and wave length of the surface wave, have not been analyzed well experimentally. In the present study, the proper orthogonal decomposition is adopted to analyze the instantaneous spray images and the extracted surface waves on the interface of the gas and liquid. The wavelength and frequency of the surface wave are obtained, and the influence of the injector mass flow rate is investigated. The results show that the spray pattern moves from onion stage to tulip stage and fully developed wavy cone stage with the increase of liquid mass flow rate. In the tulip stage, the wave frequency decreases slightly and then increases with the increase of liquid mass flow rate. On the contrary, the wavelength increases gradually with the increase of liquid mass flow rate and then decreases slightly. This variation trend is caused by the competition effect of the film thickness and the axial film velocity. The decrease of film thickness decreases the wave frequency and increases the wavelength, while the increase of the axial film velocity increases the wave frequency and decreases the wavelength. In the fully developed wavy cone stage, the wave frequency increases gradually with the increase of liquid mass flow rate. And the bandwidth of the surface wave frequency increases gradually, which means that the leading role of the dominant surface wave is weakened and the conical film is dominated by surface waves with multiple frequencies. The wavelength decreases with the increase of liquid mass flow rate because of the significant increased axial film velocity.

Liquid film characteristic in fluid hydrodynamic fixed abrasive grinding

Fluid hydrodynamic fixed abrasive grinding (FHFAG) process is a promising finishing method for large optical elements which has been proposed in early research. However, liquid film characteristic remains unqualified given its complex working condition. In this research, the liquid film in the microchannel is used in a novel perspective. A fully coupled flow deformation model for fluid media subject to elasto-plastic rough surfaces is presented. This model predicts the concrete situation including dynamic pressure distribution and basic film thickness of the liquid flow in microchannel. A preliminary experiment has been done to verify the correctness. Our result shows that the liquid film can exist in the microchannel stably; there is a controllable mapping relation between the working parameters and the liquid film characteristics.

Atomistic modelling of thin film argon evaporation over different solid surfaces at different wetting conditions

In the present study, non-equilibrium molecular dynamics (MD) simulations have been performed to reveal the effect of solid–liquid interfacial wettability on the evaporation characteristics of thin liquid argon film placed over the flat solid surface. The atomistic model considered herein comprises of a three-phase simulation domain having a solid wall over which liquid argon and argon vapour co-exist. Initially, the system is thermally equilibrated at 90 K for a while after which rapid increase in the solid wall temperature induces a phase change process, i.e. evaporation. Both hydrophilic and hydrophobic wetting conditions of the solid surface have been considered at an evaporation temperature of 130 K for three different surface materials such as platinum, silver, and aluminium. The simulation results show that both the surface wettability and surface material have a significant role in phase transition phenomena of thin liquid film, particularly the surface wettability for the present system configuration. The thermal transport phenomena between the wall and liquid thin film have been studied thoroughly and discussed in terms of wall heat flux, evaporative mass flux, upper bound of maximum possible heat flux etc. The results obtained in the present MD simulation study are compared with the macroscopic predictions based on classical thermodynamics. Interestingly, a very good agreement has been found indicating that macroscopic thermodynamics approach can predict the characteristic of phase change phenomena of nanoscale thin liquid film.

Characteristics of liquid film on the tip surface of indium field-emission electric propulsion thrusters

The characteristics of the propellant film on the tip surface of the field-emission electric propulsion thruster have a close relationship with the work state of the thruster. In this paper, the distributions of both the liquid film thickness and the fluid velocity along the needle tip have been calculated by building the liquid mechanics equations and a cone coordinate system suitable for the tip. The results show that the film thickness is tens to hundreds of nanometers and the fluid velocity along the needle tip is from tens of µm/s to a few mm/s.

Numerical simulation of wickless gravity-assisted two-phase cooling system used in heavy duty extrusion pelleting line

Efficient cooling system is an essential part of heavy duty extrusion pelleting line which plays an important role in 300kt/a production engineering of polyolefin. In this paper, a wickless gravity-assisted two-phase cooling system (WGATPCS) used in heavy duty extrusion pelleting line was presented. The volume of the fluid (VOF) model in FLUENT was used to simulate the two-phase flow and heat transfer characteristic during the operation of WGATPCS by solving the equations of continuity, momentum and energy. The vapor velocity and temperature distribution of cooling system were obtained. The operating conditions applied in this paper are the followings: the filling ratio is 0.3, cooling water flow rate is 180L/h, and heating power is 11kW. The predicted temperature profile showed a good agreement with experimental data and the maximum relative error was below 0.99%. Therefore, it was concluded that the CFD model successfully reproduced the heat and mass transfer processes in proposed cooling system. The variation of liquid film thickness, the characteristics of liquid film and vapor-liquid interface were also analyzed. The maximum liquid film thickness was 0.017mm at the bottom of condenser pipe, the velocity of vapor and liquid at vapor-liquid interface were 0.00785m/s and 0.09m/s respectively. The average condensation and evaporation heat transfer coefficients were 68083W/(m2K) and 3929W/(m2K), respectively.

Experimental study of heat transfer between thin liquid films flowing down a vertical string in the Rayleigh-Plateau instability regime and a counterflowing gas stream

Direct contact heat exchangers based on wetted string columns offer an intriguing alternative to packed beds and spray columns. We experimentally examine the flow and heat transfer characteristics of thin liquid films flowing down strings of a diameter approximately 1mm against a counterflowing air stream. Numerical simulations are also performed to help interpret and validate our experimental results. The Rayleigh-Plateau instability caused by interplay among surface tension, gravity, and viscous forces leads to the formation of uniformly spaced drop-like liquid beads traveling down a string. The liquid mass flow rate and also the nozzle radius influence the radius and spatial/temporal frequency of liquid beads. Aerodynamic drag exerted by the counterflowing air stream deforms liquid beads. The relationship between flow characteristics and heat transfer effectiveness are examined experimentally for different combinations of the air velocities, liquid mass flow rates, and nozzle radii. We show that the liquid mass flow rate and the air velocity are two primary factors influencing heat transfer effectiveness whereas details of the liquid flow instability affect local bead-to-air heat transfer coefficients. We also compare the heat transfer effectiveness and the pressure drop between a wetted string column that consists of an array of vertical strings and a well-established structured packing that consists of vertical plates. The wetted string column is shown to deliver comparable heat transfer performance but at a lower air pressure drop than the structured packing. The present work helps improve our understanding of the flow and heat transfer performance of string-based direct-contact heat exchangers and helps build a foundation for their systematic design and optimization.

Experimental Investigation on Characteristics of Liquid Film at Different Angle of Attack

Experimental Investigation on Characteristics of Liquid Film at Different Angle of Attack

Heat transfer characteristics of thin power-law liquid films over horizontal stretching sheet with internal heating and variable thermal coefficient

The effect of internal heating source on the film momentum and thermal transport characteristic of thin finite power-law liquids over an accelerating unsteady horizontal stretched interface is studied. Unlike most classical works in this field, a general surface temperature distribution of the liquid film and the generalized Fourier’s law for varying thermal conductivity are taken into consideration. Appropriate similarity transformations are used to convert the strongly nonlinear governing partial differential equations (PDEs) into a boundary value problem with a group of two-point ordinary differential equations (ODEs). The correspondence between the liquid film thickness and the unsteadiness parameter is derived with the BVP4C program in MATLAB. Numerical solutions to the self-similarity ODEs are obtained using the shooting technique combined with a Runge-Kutta iteration program and Newton’s scheme. The effects of the involved physical parameters on the fluid’s horizontal velocity and temperature distribution are presented and discussed.

Investigating the liquid film characteristics of gas–liquid swirling flow using ultrasound doppler velocimetry

A novel gas–liquid two‐phase flow metering method was proposed. A spiral vane mounted in the inner pipe was used to transform inlet flow patterns into gas–liquid swirling annular flow. The thickness and velocity profile of liquid film were measured by ultrasound Doppler velocimetry. The liquid flow rates were obtained by integrating of velocity profile during the liquid film zone. Experiments were carried out in an air–water two‐phase flow loop and an ultrasonic transducer was installed under the bottom of the test section with the Doppler angle of 70°. The flow patterns included stratified wavy, annular, and slug flows. Compared with non‐swirling flow, the liquid film thickness at the bottom reduces greatly. The measurement accuracy of liquid flow rate was independent of inlet flow patterns, gas and liquid velocities. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2348–2357, 2017

A Study on the Mixing Characteristics of Thin Liquid Film Flows over Horizontal Spinning Disk Surface

A reactor based on spinning disk technology offered an intensified mass transfer and rapid mixing in the liquid film with short liquid residence time. This paper reports the outcome of the experimental study of mixing visualization by dye tracer that carried out in a spinning disk test rig to compare with computational fluid dynamics (CFD) simulation of mixing by particle injection. The qualitative comparison used to visualize the influence of disk rotational speed on the mixing characteristics showed the identical pattern of dye particle distribution over the spinning disk surface. Further, the mechanistic model of the mixing characteristics of thin liquid films based on convective-diffusion equation is compared with the mathematical model by Tsibranska et al. (2009). The comparison shows the identical trend of the increment of the average of mass transfer coefficient as the disk rotational speed increases.