Liquid Film Flow Characteristics Research Articles

Numerical simulation on the condensation heat transfer and flow characteristics outside smooth and enhanced tubes

Most of the current studies only conducts two-dimensional simulations of condensation heat transfer and flow outside enhanced tubes, which cannot accurately reflect the flow and heat transfer characteristics of liquid film outside enhanced tubes. In order to provide theoretical support for the design optimization of enhanced tubes, this study adopts the VOF multiphase model and Lee condensation model to simulate the condensation heat transfer(HTC) of refrigerants outside smooth and enhanced tubes. The instantaneous film flow characteristics of the liquid film outside the horizontal smooth and enhanced tubes are analyzed, and the thickness of the liquid film and the relationship with the condensation heat transfer coefficient of the smooth and enhanced tubes under different working conditions are calculated. The refrigerants are compared under the same working conditions, and the results are shown: The simulation results are in good agreement with the experimental data and the Nusselt analytical solution, and the error is all within 15%; the distribution of liquid film is highly sensitive to the magnitude of local condensation heat transfer coefficients, and the condensation HTC outside the enhanced tube is approximately six times of that of smooth tube. Combining the distribution of the liquid film and the thermophysical properties of the refrigerants, it was determined that R410A has the highest HTC, while R1234yf has the lowest HTC.

Experimental investigation on cooling characteristic of transpiration-film combined cooling structure using liquid coolant

Transpiration cooling has gained significant attention as a promising strategy for thermal protection in scramjet engines. However, this approach faces limitations due to its susceptible block in fuel gas environment and significant fluctuation when using liquid coolants. To address these challenges, this work proposes a novel transpiration-film combined cooling structure (CCS), where the lower porous layer could ensure sufficient heat transfer and the upper film-hole layer could keep impurities from blocking porous layer and enhance the mechanical strength. Experimental and theoretical investigation on the combined cooling structure with liquid coolant phase change are carried out, and the cooling efficiency, temperature uniformity and cooling chamber pressure of the combined structure are compared with those of the transpiration cooling structure (TCS). Remarkably, the combined structure effectively suppresses temperature fluctuations, reducing the amplitude of temperature variation to just 1/5 of that observed in the transpiration cooling system. Although the combined structure shows a modest 0.026 drop in time-averaged cooling efficiency, it significantly improves temperature uniformity and reduces pressure peaks within the cooling chamber. Furthermore, the flow characteristics of liquid film and vapor film are analyzed and the coolant utilization rate for vapor film is 6.4 times higher than that for liquid film. Consequently, the design of combined structures using liquid coolant holds great promise for achieving highly efficient thermal protection in scramjet engines.

Analytical investigation of convective phenomena with nonlinearity characteristics in nanostratified liquid film above an inclined extended sheet

Abstract This work focuses on the time-variant convective thin-film nanoliquid fluid flow and heat transfer over a stretching, inclined surface under the effect of magnetism for different energy technologies for sustainability. It is crucial to understand how solid materials can be treated with thin films while focusing on the actual ability to improve the body surface features for infiltration, shock resistance, rigidness, brightness, dispersal, absorption, or electrical efficiency. All of these improvements are invaluable, especially in the field of nanotechnology. As with any mass and thermal transport phenomena, the study breaks down important factors such as thermophoresis and Brownian movement, in an attempt to improve the energetic balance and lessen fuel consumption. Utilizing the mathematical model of the temporal evolution on the liquid film flow characteristics over an inclined surface, we obtain a system of nonlinear partial differential equations and convert it to a system of coupled ordinary differential equations appropriately. Finally, the results of the model problem computational analysis are produced using the Laplace Adomian decomposition method (LADM) and are shown both quantitatively and visually. During the flow analysis, the impact of specific flow parameters such as the magnetic, Brownian, and thermophoresis parameters are examined and found to be highly significant. Furthermore, it is found that the effects of ( M M ) and (Nt) factors on ( F F ), ( Φ \Phi ), and ( ϕ \phi ) lead to decreased conduction. Conversely, the thermal gradient within the liquid films rises in proportion to the (Nb) factor. This research is distinguished from similar attempts made in the past in terms of thin-film nanoliquid flow from inclined planes and application of LADM approach toward modeling. The findings have provided tangible use in coming up with new methods of cooling electronics gadgets, energy harvesting for solar energy, and eco-friendly industrial processes.

Dynamics and heat-transfer characteristics of the liquid film flow in upward- and vertical-facing spray cooling

In this study, an experimental investigation was conducted on the dynamics and heat-transfer characteristics of liquid film flow for upward- and vertical-facing spray cooling. The heat-transfer performances at different inlet pressures, nozzle-to-surface distances, and heat flux inputs between the two orientations were compared, and the morphologies, wetted areas, and velocities of the isolated liquid films were quantitatively captured. The morphologies of the HFE-7100 liquid films and their distributions on the vertical and upward surfaces exhibited no significant differences. In most cases, the heat-transfer performance of the upward surface was slightly better than that of the vertical surface. Gravity affected the velocity of the isolated liquid films on a smooth vertical surface, whereas its effect was significantly suppressed on an unpolished surface. The Bond number of the isolated liquid film flow on the upward surface was verified to be naturally smaller than that on the vertical surface. Dimensionless groups, including the Bo, We, and Re numbers of the liquid film flow in spray cooling, were obtained to further account for the effect of gravity. The reason why the dimensionless groups presented such small orders was explained. The data map of liquid film flow (dimensionless groups) during spray cooling was further enriched.

Study on the effect of wall roughness on the flow characteristics of liquid film in airflow

During the flight, water flows under the action of shear force to form the overflow liquid film and freezes to form overflow ice. Overflow ice will change the aerodynamic shape of the aircraft and affect the safety and stability. In this paper, the three-dimensional structure of the liquid film in airflow was measured transiently with the digital image projection technology. The effects of different flat wall roughnesses, airflow velocities, and liquid film flow rates on the flow characteristics of the liquid film were analyzed. The experimental results show that the lower the wall roughness, the more pronounced the liquid film contraction toward the central axis. When the liquid flow rate drops to 0.228 l/min, the continuous liquid film transforms into rivulets on the surface of a large contact angle or low roughness. The average thickness of the liquid film on the flat is greater than that on the rough flat at low airflow velocity and low liquid flow rate, but smaller than that on the rough flat at high airflow velocity and high liquid flow rate. The wave near the inlet has an obvious acceleration process, and after reaching the peak speed, it gradually decreases and stabilizes near a certain value. The smoother the surface, the faster the acceleration of the wave at the inlet, and the greater the final stable wave speed.

Modeling and Analysis of Metal Liquid Film Flow Characteristics during Centrifugal Spray Forming

Liquid films are an important part of liquid metal granulation in the process of centrifugal spray forming. The size of the granulated particles has an important influence on the density, grain size and microstructure uniformity of the deposited blanks. The particle size is closely related to the flow characteristics of liquid films. Therefore, enhancing our understanding of the flow characteristics of liquid films can provide guidance for forming blanks. In this study, force analysis of a liquid film on the surface of a high-speed rotating centrifugal disc used in centrifugal spray-forming technology was carried out using D’Alembert’s principle and Newton’s law of viscosity. Then, combined with the principle of mass conservation, a theoretical model of the smooth flow of the liquid metal film was established. The experimental values obtained by Leshev were compared with our values to verify the correctness and accuracy of the model. Through the model, the influencing factors of the liquid film flow were obtained, such as the centrifugal disc speed, centrifugal disc radius, inlet volume flow rate and kinematic viscosity. Taking A390 aluminum alloy as the research object, the influence of the process parameters on the thickness, velocity and trajectory of the liquid film was revealed theoretically, and the relationship between the process parameters and the trajectory length and liquid film thickness was clarified. Modeling and analysis can not only help us to understand the flow of a liquid film, but also help us to predict the relevant parameters, which is convenient for the accurate and rapid regulation of the process to obtain the desired flow parameters. Therefore, the research content of this paper is of great significance for the preparation of billets with a uniform microstructure and excellent mechanical properties.

Numerical Investigation of the Water-Drop Impact on Low-Drag Airfoil Using the Euler–Euler Approach and Eulerian Wall Film Model

The Eulerian Wall Film (EWF) model is a mathematical model employed to analyze the behavior of fluid films on a surface. The model has been widely adopted in various engineering applications due to its accuracy and efficiency. However, it is rarely applied in the aerospace field. The solution of the water-drop impact constitutes an indispensable prerequisite for the computation of ice accretion on the exterior of aircraft wings. In this study, we propose a novel approach for the estimation of water-drop impact on wing surfaces by integrating the Euler–Euler approach and EWF model. This approach is capable of furnishing a point of reference and a theoretical foundation for prospective water-drop impact experiments. Through comparison with pertinent experimental findings, the precision of the numerical simulation approach utilized in this paper is substantiated. Specifically, the research object is the NACA653-218 airfoil of the C-919 transport aircraft, for which the aerodynamic properties, water-drop collision, and liquid film flow characteristics during steady flight were simulated.

Experimental investigation of oil film flow and droplets behavior in the annular channel of a cyclone separator

The separation of the gas and liquid in the gas-liquid cyclone separator is achieved through the swirling flow. The liquid film flow characteristics and the dynamics of droplets impacting the liquid film are very important for the separation performance, but these phenomena have not been well understood in the swirling flow. In this work, an experiment was conducted to investigate the liquid film flow and droplet impingement in the annular channel of the gas-liquid cyclone separator. Three regions of the annular channel could be divided based on the film flow patterns, which were the inlet region, the annular region, and the outlet region; and four typical droplet impact outcomes could be observed, which were splashing, coalescence, bouncing, and jet breakup. According to the characteristics of the liquid film and the outcome of droplet liquid film impingement, if the droplet splashing in the inlet region could be weakened and the length of the annular region was lengthened, it would be beneficial for gas-liquid separation. The impact outcomes were shown to undergo a transition from bouncing to coalescence as the droplet Weber number increased. Droplet coalescence was affected by the disturbance of gas flow and the evenness of the liquid film, so when the superficial velocity of the gas flow was fixed, the transition boundary was constant whatever the liquid volume fraction in the channel, and when the Reynolds number of the gas flow increased, the transition boundary of droplet Weber number increased first and then decreased. This work may provide a basis for a comprehensive understanding of the liquid film flow pattern and droplet behavior in the cyclone separator, and the results have the potential to be applied in other multiphase studies.

Experimental Study of Flow Boiling and Condensation in Tubes with Pin-Fin and Metallic Foam Structures

Appropriate arrangement of the fin structures in the evaporator and condenser not only enhances the heat transfer coefficient but also suppresses the increase of pressure drop. Due to this reason, a new method of using large-scale pin fins is explored to increase the heat transfer area and to modify the liquid film flow characteristics in the enhanced tubes. In the present study, four enhanced tubes and one plain tube were manufactured by selective laser melting. The working fluid is R407C and the enhanced tubes are eight short pin fins tube, five long pin fins tube, twisted pin fins tube and a tube filled with metallic foam. The results show that the shorter fin tube has the largest heat transfer coefficient for condensation at 3967 W/m2⋅K and the metallic foam tube demonstrates the largest heat transfer coefficient for boiling at 10606 W/m2⋅K. However, the shorter fins have the highest efficiency indices based on the heat transfer coefficient-pressure drop evaluation criterion and the heat transfer coefficient-area evaluation criterion. For condensation, the indices are 1.28 and 1.35, respectively. For boiling, the indices are 2.55 and 1.62, respectively.

Analysis of the Flow Characteristics of the Liquid Film on the Wall Surface of the Corrugated Plate Dryer Based on PSD Method: A Short Communication

Corrugated plate dryer is an important steam-water separation equipment in steam generator of secondary loop of nuclear power plant. Its steam-water separation efficiency has a certain influence on economic index of nuclear power plants. It is meaningful to understand flow characteristics of liquid film on corrugated plate wall. Besides, the fluctuation of the liquid film may cause the occurrence of liquid film rupture, thus the research on the fluctuation of the liquid film on the wall of the corrugated plate is very important. This paper uses PLIF (Plane laser induced fluorescence) method to measure liquid film thickness. Curve of film thickness with time is obtained. Calculation formula of average value of liquid film thickness is given. Based on power spectral density (PSD) method, nonlinear characteristics of liquid film thickness are studied. Results show that the relationship between film thickness and Reynolds number conforms to Nusselt theory. Nevertheless, the results show deviation from Nusselt as well as Karapantsios estimation. When Reynolds number is in the range of 600 to 3000 and surface roughness is 0.03, the fluctuation of the power spectrum of the liquid film thickness caused by gravity can be ignored, which provides a reference for study on steam-water separation.

Three‐dimensional large eddy simulation of wave characteristics of liquid film flow in a spinning disk reactor

AbstractThe waves of liquid film flow play an important role on the process intensification in spinning disk reactors (SDRs). However, the mechanism of wave formation was still unclear. In this work, a three‐dimensional large eddy simulation was developed to investigate the mechanism, as well as the characteristics of waves in the SDR. Agreed with the imaging results, different wave patterns were identified as: smooth film, concentric, and spiral waves in spreading direction; sine‐like and pulse‐like waves in fluctuating direction. The radial and tangential relative movements among the layers of liquid film were found to dominate the formation of different wave patterns. Local average film thickness (havg) and local wave amplitude (Δh) ranged from 0 to 500 μm and 0 to 200 μm, respectively. The waves can improve the turbulent intensity and enlarge the specific surface area, resulting in the intensification of transfer processes.

Experimental investigation of liquid film cooling in hypersonic flow

Film cooling is generally considered as a promising active cooling technology for developing thermal protection systems of hypersonic vehicles; however, most of experimental and numerical studies of film cooling mainly concentrated on gaseous film cooling. Since the phase change of liquid coolants can absorb a large amount of latent heat, liquid film cooling should have more potential advantages, especially for severe environments accompanied by hypersonic flight. To address this issue, the film cooling using water as a coolant was experimentally investigated in hypersonic flow. Experiments were carried out in a detonation tunnel, at a hypersonic Mach number of 6 using a 25° apex-angle wedge. Characteristic physical quantities, such as surface temperature rise, shock wave structure, film thickness, and cover area, are measured by thermocouples, schlieren, and a specially devised liquid film measurement system. The experimental results verify that the liquid film cooling is feasible in hypersonic flow and also indicate that it is featured with maintaining aerodynamic performances due to the weak effect on the main flow caused by coolant injection. Inspired by these results, liquid film flow characteristics and its influencing factors including mass flow rate, dynamic pressure, coolant injection direction, and surface tension are investigated to guide the design of a thermal protection system.

Enhanced heat transfer in unsteady magnetohydrodynamic nanofluid flow embedded with aluminum alloy nanoparticles

Extrinsic magnetic fields are capable to set the thermal and physical properties of magnetic-nanofluids and regulate the flow and heat transfer characteristics. Applied magnetic field affects the thermal conductivity of magnetic-nanofluids and makes it aeolotropic. With this incentive, we investigate the flow and heat transfer characteristics of liquid film flow of magnetic-nanofluids over the vicinity of a thin elastic sheet by considering the transverse magnetic field with variable heat source/sink. We consider water as a base fluid embedded with the two different types of aluminum alloy nano/particles namely AA 7072 and AA 7075. AA 7072 is a special type of heat treatable aluminum alloy with 98% Al and 1% of Zn with the additives such as Si, Fe and Cu etc. Similarly, AA 7075 contains 90% Al, 5–6% Zn, 2–3% Mg, 1–2% Cu with the additives as Si, Fe and Mn etc. The transformed governing partial differential equations are solved numerically using R-K based shooting technique. The diagrammatic and tabular results depict the effect of pertinent parameters on common profiles of interest. It is found that the heat transfer rate of water-AA 7075 is significantly high when compared with the heat transfer rate of water-AA 7072. It is also found that the increasing percentage of Cu leads to enhance the heat transfer rate.

気液環状二相流における液膜流動特性と物質移動に関する研究

In this study, characteristics of liquid film flow and mass transfer were experimentally investigated in a downward annular flow system with two-phase flow of air and water. The liquid film thickness was evaluated by laser induced fluorescence, and the mass transfer was measured by the plaster dissolution method. The experiments were carried out in the vertical straight pipe flow with and without orifice at Reynolds numbers for liquid-film of 230, 470, 710 and 950, which were evaluated based on liquid film thickness and bulk velocity. The experimental results revealed that the mass transfer coefficient in the two-phase flow was higher than that in the single-phase flow at the same Reynolds number due to the influence thinner liquid film and boundary layer. The non-dimensional mass transfer coefficient behind the orifice in the two-phase flow showed a decrease in the peak value with decreasing liquid film Reynolds number, thought the distribution was similar to that of the single-phase flow.

New models of droplet deposition and entrainment for prediction of liquid film flow in vertical annuli

Droplet deposition and entrainment significantly affect dryout occurrences in annular two-phase flow. Currently, most of the correlations for droplet deposition and entrainment are derived from flows in tubes. However, the main challenge in thermal-hydraulic analyses of BWRs is the prediction of dryout occurrence in the rod bundle geometry of fuel assemblies. In the work reported here, the applicability of several tube-based droplet deposition and entrainment correlations to the annular geometry (effectively a “one-rod” bundle) is checked. It is found that the prediction values from all those correlations deviate from the experimental measurements. Therefore, a set of simple and easy-to-implement models for deposition and entrainment rates in annuli is developed based on the tube-based Hewitt-Govan correlations (Hewitt and Govan, 1990), with considering the liquid film flow characteristics in annuli and the geometry effect of the annulus. The present models are verified by comparison with experimental data for developing liquid films in adiabatic annuli. By using these models to predict dryout in heated annuli, we find that these new relationships have good capability in predicting dryout occurrence in annuli with uniform as well as non-uniform axial power distribution.

Numerical Investigation of the Flow Characteristics of Liquid Film in the Process of Falling Film Evaporation

In order to study the flow characteristics of fluid falling film evaporation in a vertical pipe and obtain the dynamic parameters of steam-water two-phase flow, a three dimensional numerical simulation on flow behavior of falling film evaporation was carried out to capture the free surface of falling liquid film with the volume of fluid (VOF) model. The steam-water two-phase flow dynamic characteristics including liquid film flow pattern, liquid film thickness, wall shear stress and velocity distribution of flow field were analyzed through changing feed flow velocities. The results show that under different inlet flow velocities, the average thickness of liquid film from simulation agrees with empirical value well. The film thickness decreases sharply in the entry section which is less than 100mm. The change of wall shear stress is similar to that of film thickness along flow direction, but the change of film thickness has hysteresis quality. Under the influence of gravity and wall shear stress, the accelerated motion and decelerated motion of liquid film alternate, and the flow velocity inside liquid film increases with the distance from liquid film to wall surface, and reaches the maximum at the steam-water interface.

Oxygen transfer and power consumption in an aeration system using mist and circulation flow generated by a rotating cone

We have experimentally found the liquid film flow characteristics rising along the outer surface of a rotating cone. When the film flow goes up fully upward, the liquid film cannot keep the filmwise condition and is eventually atomized into a mist flow. In this research, we apply the mechanism to atomize the liquid and to transport oxygen from the air to the water through the atomized water droplets. It is recognized that the mixing is effective in oxygen mass transfer. It is found that a dual effect of the mixing and mist flow by using a rotating cone increases the oxygen mas7s transfer because the mist flow has a small diameter and large surface area between liquid and gas. In addition, the flow pattern is changed from steady flow to unsteady one if the rotation rate increases further, where the oxygen mass transfer is slightly enhanced. Furthermore, a correlation between the unit volume power consumption and the oxygen mass transfer is examined and shows that the oxygen transfer increases in power law relationship with the unit volume power consumption in the case with the mist flow.

Numerical Simulation of the Effect of the Uneven Wall on the Liquid Film Flow

Two-dimensional models of inclined flat and corrugated walls are established based on VOF method to numerically simulate the flow characteristics of liquid film. The impact of wall structures on the wave profile of the film is studied. The results indicate that the wall structure plays an important role on the liquid film, there are vortexes generated on the trough of wavy wall, the vortex has the "rolling" effect in machinery, which reduces the viscous resistance. and continuous film is easier to form on the wall whose corrugated size is smaller.

Enhancement of Oxygen Dissolution Using Mist Flow Generated by a Rotating Cone

We have experimentally found the liquid film flow characteristics rising along the outer surface of a rotating cone, where the surface tension, Coriolis force, pressure gradient etc. work to maintain the liquid film on the surface of the cone. When the film flow goes up fully upward, the liquid film can not keep the filmwise condition and is eventually atomized into a mist flow. The mechanism can be used in a new device to atomize liquid and to generate the mist flow. In this research, we apply the new atomization mechanism to an oxygen mass transfer from the air to the water through the atomized water droplets. A dissolved oxygen concentration is measured for variations of rotation rates of the cone, and a volumetric mass transfer coefficient is calculated from the measured data. It is found that the mist flow is effective for the oxygen mass transfer judging from the obatained quite large oxygen transfer coefficient.

Liquid film flow rising along the outer surface of the rotating cone

AbstractWe have investigated fluid flow characteristics of liquid film flow rising along the outer surface of a rotating cone. The fluid is given a centrifugal force due to the rotation of the cone, while strong surface tension maintains the centrifugal force at the outer surface of the liquid film flow. Therefore, the fluid does not spread outward from the cone, but goes up along it. We have visualized the interesting flow phenomena with a high‐speed video camera. In addition, we have measured the correlation between the wetted radius, rotation rate of the cone, and flow rate of the rising film flow. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; 39(7): 492–496, 2010; Published online 2 June 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/htj.20307