The Behavior and Characteristics of the InterfacialWaves in Gas-Liquid Two-Phase Separated FlowThrough Downward Inclined Rectangular Channel

INTaoDUCTIONInhorizontalandslightlyinclinedgas-liquidtwo-phaseflow,thestratifiedflowmnyoccurinthecaseofthelowgasandliquidflowratecombinations.Inthiskindofflowwhenthegasvelocityisincreasedwithintheregimeofthestratifledfiow,wavesappearonthegasandliquldinterfacel1'2].Forthesestrati-fiedwavyflowpatterns,thestructureanddynamicsoftheinterfacegreatlyinfiuencetheratesofmasslmo~umandheattransferaswellasthestabilityofthesysteml3'4l,thereforeanaccurateknowledgeofint~ialwavformationandwavparameterssuc…     

Numerical analysis on heat transfer enhancement by waves on falling liquid film

IntroductionLiquid films flowing on a vertical or inclined wall bythe gravitational force are encountered in the wideindustrial and engineering fields['1, such as condensatefilm, evaporating falling film, gas absorb by liquid film,etc. In the case of Indnar film flow with smooth surface,heat transfer through the liquid film is mainly carried outby conduction, and it is sufficiently explained by theNusselt's theory. On the other hand, the heat transfer isfairly enhanced for films generating su…     

Study on transport phenomena for flow film condensation in vertical mini-tube with interfacial waves

The Kelvin-Helmholtz instability of phase-change interface during flow film condensation in vertical mini-diameter tube was studied here by means of energy analysis. According to the interfacial boundary conditions, the film thinning effect and the phase-change area enlarging effect by interfacial waves on heat transfer enhancement were analyzed for flow condensation in tubes with different diameter. It is indicated that, in mini-diameter tube, more obvious heat transfer enhancement due to interfacial waves can be expected than that in normal-sized tube, and the interfacial waves enhance the heat transfer mainly by film thinning effect.     

Numerical simulation of wavy liquid film flowing down on a vertical wall and an inclined wall

Interfacial wave behavior and flow characteristics of falling liquid films on a vertical wall and an inclined wall have been studied by means of a numerical simulation, in which the algorithm is based on MAC method. Basic equations are discretized on a staggered grid fixed on a physical space. Interfacial boundary conditions are treated with a newly proposed method and the wave behavior can be calculated accurately. Simulation results agree well with experimental observations. For both the simulation and the experiment of the vertical wall, a low-frequency disturbance develops to a solitary wave, which is a big-amplitude wave accompanied by small-amplitude short capillary waves. In the big wave, a circulation flow generates and grows downstream, in which the scale of the circulation flow is comparable to the wave amplitude, while there is no circulation in the capillary waves. Although waves on the slightly inclined wall develop to the solitary wave, no circulation flow appears in the big wave because of the gravitational effect. Increasing the frequency, the wave amplitude becomes small and accompanied capillary waves disappear. In a certain frequency, the circulation flow repeats generation and collapse due to the wave interaction.     

Effects of liquid viscosity on inception of disturbance waves and droplets in gas–liquid annular two‐phase flow

The structure of gas–liquid two‐phase flow is investigated in order to establish a reliable criterion for the development of disturbance waves and droplets considering the effects of liquid viscosity. The structure of the gas–liquid interface and the flow rate of droplets entrained in gas are measured simultaneously at five kinematic viscosities (1.0, 3.2, 9.9, 30, 70 mm²/s). The time‐series traces of liquid film thickness measured by five holdup probes reveal that the inception of disturbance waves occurs at a liquid Reynolds number of 200 or a non‐dimensional liquid film thickness of 6.5. It is also shown that droplets are generated before the inception of disturbance waves with increasing liquid kinematic viscosity at a liquid velocity of 0.02 to 0.03 m/s. As previously published criteria for the inception of droplets are found to be unsatisfactory, a new critical condition for droplet generation balancing the interfacial shear stress $τi$ with the wave height h and surface tension σ is proposed: $τih/σ=0.025$. This relation describes the action of shear force and surface tension on wave crests, and is notably independent of liquid viscosity. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(8): 529–541, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20176     

Buoyancy and wall conduction effects on forced convection of micropolar fluid flow along a vertical slender hollow circular cylinder

This paper presents a numerical analysis of the flow and heat transfer characteristics of forced convection in a micropolar fluid flowing along a vertical slender hollow circular cylinder with wall conduction and buoyancy effects. The non-linear formulation governing equations and their associated boundary conditions are solved using the cubic spline collocation method and the finite difference scheme with a local non-similar transformation. This study investigates the effects of the conjugate heat transfer parameter, the Richardson number, the micropolar parameter, and the Prandtl number on the flow and the thermal fields. The effect of wall conduction on the thermal and the flow fields are found to be more pronounced in a system with a greater buoyancy effect or Prandtl number but is less sensitive with a greater micropolar material parameter. Compared to the case of pure forced convection, buoyancy effect is found to result in a lower interfacial temperature but higher the local heat transfer rate and the skin friction factor. Finally, compared to Newtonian fluid, an increase in the interfacial temperature, a reduction in the skin friction factor, and a reduction in the local heat transfer rate are identified in the current micropolar fluid case.     

Numerical oscillatory on the simulation of thermoacoustic waves

The SIMPLE algorithm for compressible flows is introduced to predict the thermoacoustic wave in a one‐dimensional closed region. The thermoacoustic waves are generated by an impulsive rise of the temperature on the left wall, while the other walls are kept at the initial temperature. Four different schemes are employed to deal with the convection‐diffusion terms, i.e., CD, FUD, QUICK, and MUSCL. The calculations and analysis show that numerical oscillation occurs under all four schemes, affected by the intensity of the waves, type of schemes, and other factors. The results are beneficial for the further investigation of the thermoacoustic waves and high efficiency scheme development. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(5): 265– 275, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20162     

Effect of interfacial heat transfer on the onset of oscillatory convection in liquid bridge

In present study, effect of interfacial heat transfer with ambient gas on the onset of oscillatory convection in a liquid bridge of large Prandtl number on the ground is systematically investigated by the method of linear stability analyses. With both the constant and linear ambient air temperature distributions, the numerical results show that the interfacial heat transfer modifies the free-surface temperature distribution directly and then induces a steeper temperature gradient on the middle part of the free surface, which may destabilize the convection. On the other hand, the interfacial heat transfer restrains the temperature disturbances on the free surface, which may stabilize the convection. The two coupling effects result in a complex dependence of the stability property on the Biot number. Effects of melt free-surface deformation on the critical conditions of the oscillatory convection were also investigated. Moreover, to better understand the mechanism of the instabilities, rates of kinetic energy change and “thermal” energy change of the critical disturbances were investigated     

Study on behavior of ephemeral wave in gas‐liquid two‐phase flow: Part 2. Characteristics in flow parameter of ephemeral waves

In order to clarify the behavior of ephemeral waves, flow parameters of ephemeral waves, such as the number and residence zone lengths per unit axial length, mean values and standard deviations of wave velocity, width, and maximum holdup, were determined using a wave‐vein analysis in upward huge wave flow and annular flow. The mean values of wave velocities, widths, and maximum holdups of ephemeral waves are compared with those of liquid lumps having main wave‐veins, and the differences in the parameters between those liquid lumps are discussed. Furthermore, the parameters of both active ephemeral waves and inactive ephemeral waves are determined, and the characteristics in the flow parameters of two types of ephemeral waves are presented. © 1999 Scripta Technica, Heat Trans Asian Res, 29(1): 1–14, 2000     

The role of interfacial mobility in determining the interfacial shear factor in two-phase wavy film flow

A new approach towards the prediction of the interfacial friction factor in two-phase wavy film flow is presented. It is shown that the associated interfacial shear and pressure drop are directly related to the waviness characteristics and to the mobility of the interface. Comparison of the predicted interfacial shear factor with experiment for concurrent downwards annular flow is satisfactory. The proposed approach appears to offer a possibility for closed form modelling of the interfacial shear and wave characteristics.     

Forced convection condensation in the presence of noncondensables and interfacial resistance

The effect of a noncondensable gas on condensation in a forced convection laminar boundary-layer flow is explored analytically. The analysis is first carried out in general for any arbitrary flow consisting of a vapor and a noncondensable gas, and certain universal results are obtained. Solutions of the similarity differential equations are found both numerically and by an integral method. The general formulation is applied to the steam-air system, and the heat transfer with and without the noncondensable is compared for a wide range of operating conditions. The reductions in heat transfer due to the non-condensable are accentuated at low operating pressures. In general, condensation in the forced convection flow is much less sensitive than that in a gravity flow. The effect of an interfacial resistance (i.e. a temperature jump at the liquid-vapor interface) is also examined. The computed results reveal a negligible effect on the heat transfer.     

Effect of nonequilibrium condensation of moist air on transonic flow fields

luttoductionMany studies on condensation occwhng in the caseof the rapid expansion of moist air mr steam in asupersonic nozzle have been performed experimentallyand numerically, and the characteristics of condensationhave been nearly clchfiedll4]. Schnerr et al.[5] and lriya atal.le] investigated the effect of condensation on thestrength of shock wave on suiface of wing, drag and liftnumerically. However, the. effect of condensation on theshock wave on s~e of wing and talulences behindshock wa…     

A linear and non-linear analysis on interfacial instability of gas-liquid two-phase flow through a circular pipe

A linear instability analysis was conducted firstly on the interface of a stratified gas-liquid two-phase flow in a circular piper employing a two-fluid model. The constitutive equations simulation technique was discussed, and the dispersive equation of interfacial waves was derived. The effects of flow rates of gas and liquid, liquid viscosity, surface tension and tube inclination on the stability of interface were investigated. A set of non-linear hyperbolic governing equations was deduced from the complete two-fluid model equation by omitting the effect of the surface tension and assuming a quasi-steady-state for the gas phase. Using characteristic line and finite difference, the propagation and growth of the interfacial disturbances were investigated in terms of gas and liquid superficial velocities. Then the results of the non-linear stability analysis were compared with those obtained by the linear stability analysis and experimental data. The non-linear stability analysis not only confirms the conclusions reached by the linear instability analysis, but also gives an insight into the growth and propagation of the interfacial disturbances on the interface of a gas-liquid two-phase flow.     

Interfacial instabilities of air-driven liquid films

Experiments were conducted to develop a better understanding of stress distribution at the interface of air-driven liquid films using solid waves similar in shape to the interfacial disturbances. Pressure and velocity measurements around the contour of each wave indicate that the air flow separates from the downstream side of the wave. These results suggest that the mass and momentum transport of liquid films in parallel two-phase flow may be dominated by form drag forces exerted on the interfacial waves rather than shear forces.     

Configuration of Shock Waves in Two-Dimensional Overexpanded Jets

An experimental and analytical study has been carried out to obtain the clear understanding of a shock wave transition associated with a steady two-dimensional overexpanded flow. Two-dimensional inviscid theory with respect to a shock wave reflection is used in the present study on the characteristic of shock waves. The results obtained from the flow analysis are compared with those obtained from flow visualizations. It is shown that in the region of regular reflection, the angle of an incident shock wave becomes lower than that calculated by two shock theory with an increment in the ratio pe/pb of the nozzle exit pressure pe to the back pressure pb. It is indicated that the configuration of shock waves in overexpanded jets is influenced by the divergent angle at the nozzle exit. Also it is shown from the flow visualization that a series of shock waves move into the nozzle inside with a decrease in pressure ratio pe/pb, even if the pe/pb is under overexpanded conditions.     

Numerical simulation of developing natural convection in an enclosure due to rapid heating

Effects of thermoacoustic wave motion on the developing natural convection process in a compressible gas-filled square enclosure were investigated numerically. In the cases considered, the left wall temperature is raised rapidly (impulsively or gradually) while the right wall is held at a specified temperature. The top and the bottom walls of the enclosure considered are thermally insulated. The numerical solutions of the full Navier-Stokes equations were obtained by employing a highly accurate flux-corrected transport algorithm for the convection terms and by a central differencing scheme for the viscous and diffusive terms. The strength of the pressure waves associated with the thermoacoustic effect and resulting flow patterns are found to be strongly correlated to the rapidity of the wall heating process. Fluid thermal diffusivity was found to affect the strength of the thermoacoustic waves and the resulting interaction with the buoyancy-induced flow.     

Effect of the body position on natural convection within the anterior chamber of the human eye during exposure to electromagnetic fields

ABSTRACT

Heating is the main biological effect of the electromagnetic (EM) fields to human eye. This study intends to focus attention on the differences in the heat transfer characteristics of the human eye induced by EM fields in different body positions. The effect of three different body positions – sitting, supine, and prone – on natural convection of aqueous humor (AH) in the anterior chamber of the eye is systematically investigated. The specific absorption rate (SAR) value, fluid flow, and the temperature distribution in the eye during exposure to EM fields are obtained by numerical simulation of EM wave propagation. In this study, the frequencies of 900 and 1,800 MHz are chosen for the investigations. The heat transfer model used in this study is developed based on natural convection and porous media theories. The results show that the AH temperature inside the anterior chamber is the highest in the supine position at both frequencies. It is found that during exposure to EM fields, body position plays an important role on AH natural convection and the heat transfer process within the anterior chamber and its periphery in the front part of the eye. However, the body position has no significant effect on temperature distribution for the middle part of the eye. The obtained results provide information on the body position and thermal effects from EM fields exposure.     

Passive Control of Transonic Flow Fields with Shock Wave Using Non—equilibrium Condensation and Porous wall

When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.