Turbulent Film Flow Research Articles

Interfacial characterization of spinning water film along a concave wall

Abstract Thin liquid film flowing down the inner concave surface of a vertical cylindrical vessel is examined. At the top of the vessel, the water is injected horizontally at high speed circumferentially along the vessel wall and flows downwards due to the action of gravity. This turbulent film flow is modeled using the large eddy simulation (LES) and Reynolds averaged Navier–Stokes (RANS) approaches combined with the volume-of-fluid method. The results of both methods are validated with direct numerical simulation. The Favre-filtered two-phase LES, which is implemented and studied in this paper, can reasonably predict the film thickness similarly to that of the RANS approach using the elliptic blending Reynolds stress model, although it requires fine resolution in the wall region. The effect of volume flow rate on the film structure and thickness is investigated. The film thickness is shown to be nearly constant when the wall is partially wetted and changes as the cubic root of the volume flow rate when the spinning film encloses the entire circumference of the vessel.

Heat Transfer at Film Cooling of an Array of Horizontal Tubes with an Enhanced Surface

The paper presents investigation results about the influence of various methods of surface treatment on heat transfer enhancement in falling films of R21 Freon on an array of horizontal tubes. The experiments were carried out on the aluminum alloy tubes with a ceramic coating obtained by micro-arc oxidation and on copper tubes with a structured surface, treated by deformational cutting. The experiments were carried out in a regime of turbulent film flow at Reynolds numbers from 400 to 1500. The results of measuring the heat transfer coefficients on the surface of samples with a developed surface and on the standard smooth tube are compared. The highest values of heat transfer coefficients in falling films during nucleate boiling were obtained on a structured surface with semi-closed cavities. Heat transfer enhancement on the surface of a tube made of alloy D16T with the MAO coating of 30 μm thick, obtained in a silicate-alkaline electrolyte, is comparable to heat transfer enhancement on the surface of copper tubes with a microstructure applied by the deformational cutting method.

Development of an analytical model for pure vapor downflow condensation in a vertical tube

In-tube condensation of pure vapor are widely adopted by passive safety systems of advanced nuclear reactors to remove the decay heat. Accurate calculation of the in-tube condensation heat transfer coefficient is important for evaluating the heat removal ability. A better understanding of the mechanism of pure vapor condensation heat transfer and its modelling are essential for the design and assessment of those passive safety systems. An analytical model for pure vapor condensation in a vertical tube is developed based on mass, momentum and energy conservation equations. The total axial pressure drop is calculated through the momentum equation of the vapor core assuming a uniform radial pressure distribution. An optimized transition area between the laminar and turbulent film flow is defined to avoid discontinuity of heat transfer coefficients. Based on the sensitivity analyses, Kay’s turbulent eddy diffusivity model and his turbulent Prandtl number model were recommended for the newly proposed model. The predicted results were compared with results of Shah (2016a,b), Chen et al. (1987) and Cavallini et al. (2002) correlations as well as Kuhn’s and KAIST experimental data. It was found that the proposed model predicts the heat transfer coefficient well with a mean absolute deviation of 11.99% for Kuhn’s data and 8.08% for KAIST’s data.

The evolutionary design of condensers

Condensers are flow architectures needed to provide high rates of condensation (or cooling) per unit volume, in enclosures with fixed volume. Their design has not changed from configurations consisting of the banks of horizontal tubes. In this paper, we outline a free path to evolving the design by exploring new features of flow configuration: flattened tubes, multiple tube sizes, arrays of flattened tubes, vertical tubes with turbulent film flow, forced convection condensation instead of gravity driven condensation, and the optimal length of a horizontal tube, i.e., the number of tubes in a column aligned with vapor cross flow. We show that the condensation density can be increased sizably by varying freely and without bias the morphology of the flow system: the shapes and arrangement of the cooled surfaces on which condensation occurs. The evolution of technology is described in terms of the special time direction of the useful (purposeful) changes in the configuration (shapes, arrangements) of surfaces on which flow/condensation occurs. This explains what “evolution” means. It is an important step for physics, not just technology.

Experimental Study on Heat Transfer of Heated Falling Film Under Gas–Liquid Cross-Flow Condition

With the influence of the different gas Reynolds numbers and liquid Reynolds numbers on heated falling film heat transfer, an experiment was performed by noncontact thermal infrared imaging technology under the gas–liquid cross-flow condition. The results indicated that during the increase of liquid Reynolds number the thickness and thermal resistance of liquid film increased in the determined temperature of the heating water, which weakened the heat transfer of the liquid film. However, the increase of liquid Reynolds number strengthened liquid film turbulence and therefore enhanced heat transfer. Under the synergistic effect of these two factors, there should be an optimal liquid Reynolds number that minimizes thermal resistance and maximizes the heat transfer coefficient of the liquid film. Temperature plays an important role in heat transfer of laminar liquid film flow. However, the heat transfer of turbulent liquid film flow is not sensitive to liquid film inlet temperature.

Ascending cocurrent flows in an inclined flat channel

A conjugate solution has been obtained for ascending cocurrent turbulent gas flow and laminar liquid wavy film flow in an inclined flat channel without drop entrainment. The waves have been represented as surface roughness features. Experimental studies have been conducted for air-water, air-diethylene glycol, and air-aqueous sucrose systems, and the results have been compared with the calculated data.

Theoretical and Experimental Analysis of Turbulent Liquid Film Flowing down a Vertical Surface

The purpose of the present study is to obtain a comprehension for the momentum and heat transfer developments in gravitational liquid film flow. Analytical study of stabilized heat transfer for turbulent film was performed. A calculation method of the local heat transfer coefficient for a turbulent film falling down a vertical convex surface was proposed. The dependence of heat flux variation upon the distance from the wetted surface has been established analytically. Experimental study of velocity profiles for turbulent liquid film flow in the entrance region is performed as well. Analysis of profiles allowed estimating the length of stabilization for turbulent film flow under different initial velocities.

Shear-Driven Liquid Film in a Duct

Two-dimensional flow simulations of shear-driven thin liquid film by turbulent air flow in a duct is performed using the Reynolds Averaged Navier Stokes and continuity equations along with the Volume of Fluid (VOF) model that is part of the FLUENT-CFD code. The purpose of this study is to determine the suitability of using this code/model for predicting reported measurements of shear driven liquid film in a duct. Both a laminar and a turbulent flow models were examined for the liquid film flow region to assess their impact on film thickness and velocity. The Low Reynolds number k-ε turbulence model is utilized for simulating the turbulent air and film flow. Simulated results for the distributions of the air velocity, liquid film velocities along with the liquid film thickness as a function of inlet air and liquid film flow rates are presented. Simulated results show that the film thickness decreases but surface film velocity increases with increasing air flow rate; film thickness and surface film velocity increase with increasing film flow rate; the imposed laminar film flow model produces linear velocity distribution inside the film but the turbulence film flow model produces a nonlinear velocity distribution; the developing thin film influences significantly the air velocity distribution; and these results compare favorably with measured behavior.

Simultaneous heat and mass transfer inside a vertical tube in evaporating a heated falling alcohols liquid film into a stream of dry air

A numerical study of the evaporation in mixed convection of a pure alcohol liquid film: ethanol and methanol was investigated. It is a turbulent liquid film falling on the internal face of a vertical tube. A laminar flow of dry air enters the vertical tube at constant temperature in the downward direction. The wall of the tube is subjected to a constant and uniform heat flux. The model solves the coupled parabolic governing equations in both phases including turbulent liquid film together with the boundary and interfacial conditions. The systems of equations obtained by using an implicit finite difference method are solved by TDMA method. A Van Driest model is adopted to simulate the turbulent liquid film flow. The influence of the inlet liquid flow, Reynolds number in the gas flow and the wall heat flux on the intensity of heat and mass transfers are examined. A comparison between the results obtained for studied alcohols and water in the same conditions is made.

Stabilization Of Heat Transfer InA Turbulent Film Flow

The aim of the present study is to clarify the tendencies of the heat transfer developments in gravitational liquid film flow. Heat transfer in a turbulent film flow on a vertical tube has been investigated in this paper. The analytical study of stabilized heat transfer of turbulent film has been performed. The calculation method for the local heat transfer coefficient of turbulent film falling down a vertical convex surface is proposed. The analytical approach is used to establish the dependence of heat flux variation on the distance from the wetted surface. An experimental investigation of heat transfer in the entrance region of the turbulent film has also been carried out. The methodology involves determining the local heat transfer coefficient and establishing the transfer stabilization length. The description of the experimental set-up and procedure is presented in this study. The experiments have been performed in water film flowing down a surface of vertical tube for Reynolds number ranged from 5850–6700. The results of experiments are discussed with respect to the local heat transfer dependence on the Reynolds number and initial velocity of the film in liquid distributor.

Exploratory studies of flowing liquid metal divertor options for fusion-relevant magnetic fields in the MTOR facility

Abstract This paper reports on experimental findings on liquid metal (LM) free surface flows crossing complex magnetic fields. The experiments involve jet and film flows using GaInSn and are conducted at the UCLA MTOR facility. The goal of this study is to understand the magnetohydrodynamics (MHD) features associated with such a free surface flow in a fusion-relevant magnetic field environment, and determine what LM free surface flow option is most suitable for lithium divertor particle pumping and surface heat removal applications in a near-term experimental plasma device, such as NSTX. Experimental findings indicate that a steady transverse magnetic field, even with gradients typical of NSTX outer divertor conditions, stabilizes a LM jet flow—reducing turbulent disturbances and delaying jet breakup. Important insights into the MHD behavior of liquid metal films under NSTX-like environments are also presented. It is possible to establish an uphill liquid metal film flow on a conducting substrate, although the MHD drag experienced by the flow could be strong and cause the flow to pile-up under simulated NSTX magnetic field conditions. The magnetic field changes the turbulent film flow so that wave structures range from 2D column-type surface disturbances at regions of high magnetic field, to ordinary hydrodynamic turbulence wave structures at regions of low field strength at the outboard. Plans for future work are also presented.

Heat Transfer in Condensation of Vapor Moving inside Vertical Tubes

A review of works devoted to the study of heat transfer in condensation of moving vapor in cocurrent flow of vapor and film is presented. Generalization of a wide range of experimental data obtained by different authors showed that in wave regimes of film flow conditions take place under which an increase in vapor velocity does not lead to enhancement of heat transfer, as compared to heat transfer in condensation of motionless vapor. In turbulent film flow, an intense entrainment of the film from the crests of waves into the vapor core begins when W > Wecr, thus leading to considerable enhancement of heat transfer.

Modelling of the transfer processes in turbulent film flows considering the influence of the vapour phase

Modelling of the transfer processes in turbulent film flows considering the influence of the vapour phase

Modelling of the transfer processes in turbulent film flows considering the influence of the vapour phase

The ideas of Prigogine and Naue are the basis of theoretical modelling. The momentum and energy transfer processes at the distance of the thermodynamic equilibrium are associated with the formation of dissipative motion structures. The existence of rotation movements is defined for describing turbulent fluid flow in addition to translation motion quantities. The calculation of the velocity fields follows from these balance equations for translation and rotation movements. The interaction is expressed by the use of special source terms. The balance equations of energy are determined in the same way. The heat flux which is caused by angular momentum is formulated by a balance of its own. This model is applied to the situation of a vertical film flow with parallel gas flow. Particular boundary conditions are used. The calculated velocity and temperature profile in the film show a physically understandable interpretation. The convective heat transfer inside the film can be described by this spin modelling. A comparison of the calculated local heat transfer coefficients shows a satisfactory correspondence with the experimental data of different authors.

Transport model of buoyant metamorphic fluid by hydrofracturing in leaky rock

Abstract Aqueous fluid released in metamorphism is transported upwards from depth to the Earth's surface. I propose a hydrofracturing model for the fluid transport. In the model, fluid is transported by the upward propagation of a two‐dimensional vertical fluid‐filled crack from a fluid reservoir (e.g. overpressured compartment under a seal) at depth to the Earth's surface; fluid is injected consecutively from the reservoir into the crack at a given (but not necessarily constant) injection rate; some of the injected fluid is lost by infiltration from the crack walls into the surrounding permeable rock. An approximate solution of the crack propagation is obtained using fluid dynamics for turbulent film flow and linear elastic fracture mechanics. The solution shows the transition from a regime in which the excess pressure of the fluid in the reservoir drives the propagation to a regime in which the buoyancy of the fluid in the crack drives the propagation. For example, if the net injection rate of H2O is 1 m2/s, the regime transition occurs when the vertical crack length becomes 280 m; after the transition, the propagation velocity and average aperture are constant: 21 m/s and 4.8 cm. If the injection rate is lower than a critical value, hydrofracturing cannot be an effective mode for the fluid transport because of the significant fluid loss by infiltration from the crack walls into the surrounding permeable rock. Assuming a fluid‐saturated crust with hydrostatic pore fluid pressure, a lower limit can be estimated for the injection rate required to transport H2O by hydrofracturing without significant fluid loss. For example, the lower limit for transport from a depth of 15 km to the Earth's surface is estimated at 0.2 m2/s if the crustal permeability is 10‐17 m2. The lower limit decreases with decreasing crustal permeability.

Heat transfer in turbulent falling films

AbstractIn condensers with high condensation rates or in falling film evaporators the falling film at the vertical tube wall shows a turbulent flow pattern. For optimal dimensioning of these apparatuses the knowledge and the description of the heat transfer in this turbulent falling film is necessary. Especially in fluids with a low thermal conductivity in liquid phase (i.e. hydrocarbons) the main heat transfer resistance is in the falling film, also if there are several components in gas phase. For calculating the heat transfer usually dimensionless Nusselt equations were used. These equations mainly base on experimental results which were found with water vapour as test fluid. It is shown that these equations fail for fluids with low thermal conductivity resp. high Prandtl numbers. Based on a Nusselt equation for turbulent tube flow a new equation for turbulent film flow is derived. A comparison between calculated and measured data for Prandtl numbers up to 50 shows good agreement.

Initial liquid metal magnetohydrodynamic thin film flow experiments in the McGA-loop facility at UCLA

Abstract Free surface, thin film flows of liquid metal were investigated experimentally in the presence of a coplanar magnetic field. This investigation was performed in a new magnetohydrodynamic (MHD) flow facility, the McGA-loop, utilizing a low melting temperature lead-bismuth alloy as the working metal. Owing to the relatively low magnetic field produced by the present field coil system, the ordinary hydrodynamic and low MHD interaction regimes only were investigated. At the high flow speeds necessary for self cooling, the importance of a well designed and constructed channel becomes obvious. MHD drag, increasing the film height, is observed as Haβ2 becomes greater than unity. Partial MHD laminarization of the turbulent film flows is observed when Haβ/Re > 0.002, but fully laminar flow was not reached. Suggestions for facility upgrades to achieve greater MHD interaction are presented in the context of these initial results.

Liquid-side mass transfer coefficient for gas slugs rising in liquids

The present work reports a series of experimental measurements of liquid-side mass transfer coefficient for slugs rising in liquids with viscosities in the range 0.9 × 10 −3−0.14 Pa s. Three column diameters were used (19, 32 and 52 mm) and slugs with values of L/D up to 38 were studied. The data obtained compare well with the theoretical predictions of van Heuven and Beek and they show the limited range of applicability of the empirical equations of Filla and Niranjan. The data reported for slugs rising in water in the 52 mm i.d. column clearly suggest that transition to turbulent film flow occurs at a value of z/D of about 11, the mass transfer in the turbulent portion being well predicted by correlations developed for wetted wall columns. A simple asymptotic expression for the evaluation of mass transfer coefficients in long slugs (i.e. slugs alongside which fully developed film flow is observed over a large portion of the total length) in viscous liquids was also developed and it is seen to compare very well with the experimental data.

Heat transfer and film thickness during condensation of steam flowing at high velocity in a vertical pipe

In the present study the heat transfer of pure steam flowing downward in a vertical condenser pipe is determined and the thickness of the wavy film is measured using a laser absorption method. The measured data are compared to numerical predictions based on the solution of the conservation equations for mass, momentum and energy for the vapor and liquid phases. The k- ε turbulence model of Jones and Launder is used for both phases. It will be shown that the transition from laminar to turbulent film flow can be predicted reasonably well if the turbulent kinetic energy in the film is conserved to a minimum value.

Microporosity of powders produced by centrifugal sputtering

The nature of the liquid-metal film flow about the end of the pulverized billet is defined by its rotational velocity. In the case of a turbulent film flow regime gas is captured and pores are formed in individual powder particles.