Convective heat and mass transfer from a falling film to a laminar gas stream

A numerical study has been made of convective heat and mass transfer from a falling film to a laminar gas stream between vertical parallel plates. The effects of gas-liquid phase coupling, variable thermophysical properties, and film vaporization have been considered. Simultaneous mass, momentum and heat transfer between liquid film and gas stream is numerically studied by solving the respective governing equations for the liquid film and gas stream together. The influences of the inlet liquid temperature and liquid flowrate on the cooling of liquid film are examined for air-water and air-ethanol systems. Results show that the heat transfer from the gas-liquid interface to the gas stream is predominantly determined by the latent heat transfer connected with film evaporation. Additionally, better liquid film cooling is noticed for the system having a higher inlet liquid temperature or a lower liquid flowrate.     

Mass transfer with gas desorption from the surface of a liquid film in the presence of a cocurrent flow

Results of a thcoretical and experimental study of dynamics and mass transfer during desorption of a gas from a liquid film in the presence of a cocurrent air flow are presented. The calculation model is based on solving integral momentum and diffusion relations for the gaseous and liquid phascs. Both laminar and turbulent regimes of the film flow are analyzed. The experimental study of mass transfer was conducted for carbon dioxide desorption from a water film. Criterial relations for mass transfer in the gaseous and liquid phases are obtained. The experiments showed that the heat-transfer coefficients for the case under study are one order of magnitude grcater than those for the flow of a smooth film. Possible mechanisms of such an appreciable intensification of the liquid-film mass transfer in a cocurrent gas flow are discussed. Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 4, pp. 131–138, July–August, 2000.     

Studying disturbance waves in vertical annular flow with high-speed video

In many annular two-phase gas–liquid flows, large disturbance waves propagate liquid mass. These waves are important for modeling of gas-to-liquid momentum transfer and liquid film behavior. High-speed videos of vertical upflow have been analyzed to extract individual and average wave data. Two types of structures, coherent waves and piece waves, have been identified in these flows. Velocities, lengths, and temporal spacings of individual waves and average velocities, lengths, frequencies, and intermittencies have been studied as functions of both gas and liquid flow rates. Velocity and frequency increase with liquid and gas flow rates, length decreases with increasing gas flow and increases with increasing liquid flow, and intermittency is predominantly an increasing function of liquid flow.     

“Ion wind”, a gas-dynamic flow in the corona discharge,and its interaction with the external flow

The “ion wind”, a gas-dynamic flow in the corona discharge that arises owing to transfer of the ion component momentum to the neutral particles of an initially stationary gas, and its interaction with the external flow perpendicular to it are studied. A physico-mathematical model of the flows considered is proposed and the corresponding equations are analyzed numerically. The boundary conditions used for the electric quantities approximately model the conditions in the negative corona discharge between a thin corona-forming electrode and a plane grid electrode transparent to the gas.     

Experimental study on hydrodynamic characteristics of upward gas–liquid slug flow

To clarify the impacts of the hydrodynamic boundary layer and the diffusion boundary layer in the near wall zone on gas–liquid two-phase flow induced corrosion in pipelines, the hydrodynamic characteristics of fully developed gas–liquid slug flow in an upward tube are investigated with limiting diffusion current probes, conductivity probes and digital high-speed video system. The Taylor bubble and the falling liquid film characteristics are studied, the effects of various factors are examined, and the experimental results are compared with the data and models available in literature. The length of Taylor bubble, the local void fraction of the slug unit and the liquid slug, the shear stress and mass transfer coefficient in the near wall zone, are all increased with the increase of superficial gas velocity and decreased with the increase of superficial liquid velocity, whereas the length of liquid slug and the liquid slug frequency are changed contrarily. The alternate wall shear stress due to upward gas–liquid slug flow is considered to be one of the major causes for the corrosion production film fatigue cracking. A normalized formula for mass transfer coefficient is obtained based on the experimental data.     

Heat transfer and interfacial drag in countercurrent steam-water stratified flow

Local condensation heat transfer coefficients and interfacial shear stresses have been measured for countercurrent stratified flow of steam and subcooled water in rectangular channels over a wide range of inclination angles (4–87°) at two aspect ratios. Dimensionless correlations for the interfacial friction factor have been developed that show that it is a function of the liquid Reynolds number only. Empirical correlations of the heat transfer coefficient, based upon the bulk flow properties, have also been set up for the whole body of data encompassing the different inclination angles and aspect ratios. These indicate that the Froude number as a dimensionless gas velocity is a better correlating parameter than the gas Reynolds number. As an alternative approach, a simple dimensionless relationship for the beat transfer coefficient was obtained by analogy between heat and momentum transfer through the interface. Finally, a turbulence-centered model has been modified by using measured interfacial parameters for the turbulent velocity and length scales, resulting in good agreement with the data.     

A Kinetic Approach to the Plane Poiseuille Flow Over a Porous Matrix

The Poiseuille–Couette gas flow in a channel and the gas flow through an adjacent porous medium are considered when the governing equations are obtained via a molecular kinetic approach based on the Boltzmann equation. The mass continuity, momentum balance and energy conservation are written for the gas in the contiguous regions, whereas the behavior of the solid matrix obeys to the heat diffusion equation. Two different space scalings lead to different forms of the equations for the steady flow through the fully saturated matrix. The boundary conditions at the interface between the two domains are investigated via a matching procedure.     

Momentum transfer in a vertical down flow liquid jet ejector: case of self gas aspiration and emulsion flow

Momentum transfer in a vertical liquid jet contactor consisting of an ejector supported in a vertical column has been studied, using three different liquids as motive fluids, and air as the entrained gas.On the basis of macroscopic momentum and energy balance, an overall loss factor is derived. Moreover, an empirical correlation is proposed to predict the mass flow rate of entrainment by the liquid jet system. Finally, an expression to predict the volumetric flow rate of the carried fluid available at a pressure higher than atmospheric, is given.     

Nonstationary Gas Filtration Caused by an Intense Thermal Action on a Damp Porous Medium

A mathematical model and an algorithm are proposed for evaluating nonstationary heat and mass transfer in a porous medium that contains a mechanically absorbed liquid and a two–component gas (vapor—inert gas mixture). The case of an intense thermal action on a damp porous mixture caused by an external heat flux and convective heat transfer is considered. Typical flow regions and typical regions of the interaction between the phases are described.     

横向气流穿过垂直下落液滴场的二维流动数值计算

对Cl2/He混合气体横向穿过垂直下落的BHP(按重量25%的KOH,25%的H2O2及50%的H2O)液滴场的化学反应流动作了数值计算.模拟的流场是气体/液滴两相流场,在气相方程中,考虑了液滴与Cl2反应产生及释放O2(1Δ)的质量源项及表示液滴对气流阻碍作用的动量源项.由于气相动量小,液滴在下落过程横向偏移小,下落...     

Model of gas absorption in gas-liquid plug flow with first-order and zero-order chemical reaction

A model of mass transfer during gas absorption in gas-liquid plug flow accompanied by irreversible chemical reaction of the first order and zero order is suggested. The expressions for coefficients of mass transfer during chemical absorption from a single Taylor bubble are derived in the approximation of the thin concentration boundary layer in a liquid phase. Under the assumptions of a perfect liquid mixing in liquid plugs recurrent relations for the dissolved gas concentrations in the n-th liquid plug and mass fluxes from the n-th Taylor bubble are derived. The total mass fluxes in gas-liquid plug flow during chemical absorption are determined. In the limiting case of absorption without chemical reaction the derived formulas recover the expressions for mass transfer during physical absorption in gas-liquid plug flow. Theoretical results are compared with available experimental data.     

Experimental study on near wall transport characteristics of slug flow in a vertical pipe

In this work, the wall shear stress and the mass transfer coefficient of the gas–liquid two-phase upward slug flow in a vertical pipe are investigated experimentally, using limiting diffusion current probes and digital high-speed video system. In experiments, the instantaneous and averaged characteristics of wall shear stress and mass transfer coefficient are concerned. The experimental results are compared with the numerical results in previous paper of the authors. Both experiment and numerical simulation show that the superficial gas and liquid velocities have an obvious influence on the instantaneous characteristics of the two profiles. The mass transfer coefficient has characteristics similar to the wall shear stress. The instantaneous wall shear stress and mass transfer coefficient profiles have the periodicity of slug flow. The averaged wall shear stress and mass transfer coefficient increase with increased superficial gas velocity. However, there is inconsistency in the variation trends of the averaged wall shear stress and mass transfer coefficient with superficial liquid velocity between experimental result and numerical simulation result, which can be attributed to the difference in flow condition. Moreover, the Taylor bubble length is also another impacting factor. The experimental and numerical results all shows that the product scale can not be damaged directly by the flow movement of slug flow. In fact, the alternative forces and fluctuations with high frequency acting on the pipe wall due to slug flow is the main cause for the slug flow enhanced CO₂ corrosion process.     

Gas–liquid mass transfer in the gas–liquid–solid mini fluidized beds

The gas–liquid–solid mini fluidized bed (GLSMFB) combines the advantages of fluidized bed and micro-reactor, and meets the requirements for safety and efficiency of green development of process industry. However, there are few studies on its flow performance and no studies on its mass and heat transfer performance. In this paper, the characteristics of gas–liquid mass transfer in a GLSMFB were studied in order to provide basic guidance for the study of GLSMFB reaction performance and application. Using CO₂ absorption by NaOH as the model process, the gas–liquid mass transfer performance of GLSMFB was investigated. The results show that the liquid volumetric mass transfer coefficient and the gas–liquid interfacial area both increase with the increase of the superficial gas velocity within the experimental parameter range under the same given superficial liquid velocity. At the same ratio of superficial gas to liquid velocity, the liquid volumetric mass transfer coefficient increases with the increase of the superficial liquid velocity. Fluidized solid particles strengthen the liquid mass transfer process, and the liquid volumetric mass transfer coefficient is about 13% higher than that of gas–liquid mini bubble column.     

DSMC (direct simulation Monte Carlo) analysis of microchannel flow with gas–liquid boundary

High heat capacity and constant operation temperature make a 2-phase heat remover tool promising for solving high heat dissipation problems in MEMS devices. However, microscale analysis of the flow with the conventional Navier–Stokes equation is inadequate, because the non-continuum effect is important when the characteristic dimension is comparable to the local mean free path. DSMC is a direct, particle-based numerical simulation method that uses no continuum assumption. In this paper, the gas–liquid boundary effects in microchannel flow are studied using this method. Modified DSMC code is used to simulate low-speed flow—under which viscous heating produces no significant temperature change—and MD results are incorporated into the DSMC boundary condition. Steady Couette flow simulation results show that the gas–liquid boundary affects the density distribution and the temperature dependence of the slip velocity. Unsteady simulation results show that mass transfer by diffusion is faster than momentum transfer by collision.     

Planar dynamics of inclined curved flexible riser carrying slug liquid–gas flows

Flexible risers transporting hydrocarbon liquid–gas flows may be subject to internal dynamic fluctuations of multiphase densities, velocities and pressure changes. Previous studies have mostly focused on single-phase flows in oscillating pipes or multiphase flows in static pipes whereas understanding of multiphase flow effects on oscillating pipes with variable curvatures is still lacking. The present study aims to numerically investigate fundamental planar dynamics of a long flexible catenary riser carrying slug liquid–gas flows and to analyse the mechanical effects of slug flow characteristics including the slug unit length, translational velocity and fluctuation frequencies leading to resonances. A two-dimensional continuum model, describing the coupled horizontal and vertical motions of an inclined flexible/extensible curved riser subject to the space–time varying fluid weights, flow centrifugal momenta and Coriolis effects, is presented. Steady slug flows are considered and modelled by accounting for the mass–momentum balances of liquid–gas phases within an idealized slug unit cell comprising the slug liquid (containing small gas bubbles) and elongated gas bubble (interfacing with the liquid film) parts. A nonlinear hydrodynamic film profile is described, depending on the pipe diameter, inclination, liquid–gas phase properties, superficial velocities and empirical correlations. These enable the approximation of phase fractions, local velocities and pressure variations which are employed as the time-varying, distributed parameters leading to the slug flow-induced vibration (SIV) of catenary riser. Several key SIV features are numerically investigated, highlighting the slug flow-induced transient drifts due to the travelling masses, amplified mean displacements due to the combined slug weights and flow momenta, extensibility or tension changes due to a reconfiguration of pipe equilibrium, oscillation amplitudes and resonant frequencies. Single- and multi-modal patterns of riser dynamic profiles are determined, enabling the evaluation of associated bending/axial stresses. Parametric studies reveal the individual effect of the slug unit length and the translational velocity on SIV response regardless of the slug characteristic frequency being a function of these two parameters. This key observation is practically useful for the identification of critical maximum response.     

Simulation of gas absorption into string-of-beads liquid flow with chemical reaction

This study is an attempt to investigate the chemical absorption of CO₂ in aqueous monoethanolamine (MEA) solution in a wetted-wire column consisting of one wire. Computational fluid dynamics method along with volume of fluid model was employed for modeling of two-phase flow, mass transfer and chemical reaction inside the column. The modeling results were compared with available experimental data and very good agreement was achieved. The simulation results showed that the diameter and intervals of liquid beads increases by increasing the gas and liquid flow rates. The beads velocity increases by increasing the liquid flow rate and decreasing mass fraction of MEA in the liquid phase. Also, mass transfer resistance in the liquid phase reduces by formation of the beads. It was concluded that the developed model is capable to predict the effect of operating and physical parameters on the investigated chemical absorption process.     

Combined heat and mass transfer in natural convection between vertical parallel plates

This study purposes to examine the effects of latent heat transfer associated with the liquid films vaporization on the heat transfer in the natural convection flows driven by the simultaneous presence of combined buoyancy forces of thermal and mass diffusion. Results are especially presented for an air-water system under various conditions. The influence of channel length and system temperatures on the momentum, heat and mass transfer in the flow are investigated in great detail. The important role of transport of latent heat of vaporization under the situations of buoyancy-aiding and opposing flows is clearly demonstrated.     

Breakup of gas bubbles in a liquid by shock waves

The nature of the propagation of shock waves in various media is related to the characteristics of the latter, including their compressibility, thermophysical properties, the presence of multiple phases, etc. The structure of a shock wave varies appreciably as a function of the properties of the medium. The most significant property of a liquid mixture with gas bubbles is the compressibility of the latter under the influence of an externally applied pressure, for example, in a shock wave propagating in the liquid—gas medium. The transfer of momentum and energy between phases and the pressure variation behind the wave depends on the behavior of the gas bubbles behind the shock front.