Simultaneous heat and mass transfer on oscillatory free convection boundary layer flow

The problem of simultaneous heat and mass transfer in two-dimensional free convection from a semi-infinite vertical flat plate is investigated. An integral method is used to find a solution for zero wall velocity and for a mass transfer velocity at the wall with small-amplitude oscillatory wall temperature. Low- and high-frequency solutions are developed separately and are discussed graphically with the effects of the parameters Gr (the Grashof number for heat transfer), Gc (the Grashof number for mass transfer) and Sc (the Schmidt number) for Pr = 0–71 representing aid at 20°C.     

Flow and mass transfer characteristics in wavy channels for oscillatory flow

A study of fluid flow and mass transfer for oscillatory flow has been carried out in wavy channels, which consist of two sinusoidal wavy plates. The experiments were carried out under the following conditions: 5 × 10² < Re_p < 10⁴, 2.1 × 10⁻² < St_p < 8.6 × 10⁻². The flow was neither dominated by viscous forces nor quasi-steady in this experiment. The recirculation vortex is formed within the furrow during the acceleration phase and is ejected from the wall just after flow reversal. The mass transfer rate strongly depends on Re_p but the effect of St_p is insignificant. The wavy channels yield a large mass transfer enhancement as compared with the corresponding straight channel. This enhancement is attributed to the vortex ejection observed.     

Heat transfer for Marangoni‐driven boundary layer flow

Marangoni convection induced by variation of the surface tension with temperature along a surface influences crystal growth melts and other processes with liquid–vapor interfaces, such as boiling in both microgravity and normal gravity in some cases. This paper presents the Nusselt number for Marangoni flow over a flat surface calculated using a similarity solution for both the momentum equations and the energy equation assuming developing boundary layer flow along a surface. Solutions are presented for the surface velocity, the total flow rate, and the Nusselt number for various temperature profiles, Marangoni numbers, and Prandtl numbers. For large bubbles, the predicted boundary layer thickness would be less than the bubble diameter, so the curvature effects could be neglected and this analysis could be used as a first estimate of the effect of Marangoni flow around a vapor bubble. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 105–116, 2002; DOI 10.1002/htj.10019     

Heat and mass transfer boundary layers in radial creeping flow

Heat and mass transfer in radial flow between two parallel disks are analysed. This kind of problem is sometimes encountered in chemical engineering and we faced this situation in membrane separation processes in which the fluid is fed into the center of the cell and flows towards zones at higher radii. In the examined case heat and/or mass are exchanged across one of the two surfaces which confine the flow region. An analysis of the transport phenomena of such a geometry is performed by resorting to two different mathematical models. As a result the concentration and/or temperature profiles, the transport coefficients and the influence of the relevant dimensionless groups are obtained. The capability of the models to predict the experimental behavior of the vacuum membrane distillation process is demonstrated.     

Heat transfer enhancement in oscillatory cavity flow

The unsteady fluid motion driven in a square cavity by the combined effects of a vibrating wall and natural convection is examined. The mean heat transfer characteristics of the oscillatory cavity flow are derived and discussed.     

Fluid mixing and local mass transfer characteristics in a grooved channel for self-sustained oscillatory flow

Flow patterns and mass transfer rates in a periodically grooved channel were studied in the transitional flow regime. Self-sustained flow oscillations occur at a low Reynolds number. Primary flow instability arises from Tollmien–Schlichting waves triggered by a shear layer above the groove, and thus there is a fluid exchange between channel and groove parts through the shear layer. It is found that a further increase of the Reynolds number produces secondary instability causing a three-dimensional flow at the bottom of the groove. Mass transfer was performed by the electrochemical method. The transport rate at the rib increases significantly after the primary instability, but the increment of mass transfer at the bottom of the groove is small. The secondary instability leads to marked transport enhancement at the bottom of the groove. ©1998 Scripta Technica, Heat Trans Jpn Res, 27(7): 522–534, 1998     

Enhanced heat transfer during oscillatory flow in annular channels

Heat transfer during oscillatory flow in a circular straight tube with a solid‐core tube inserted in its center was numerically simulated. The purpose of the solid‐core tube is to enhance axial heat transfer by increasing the lateral heat transfer effect for high frequency of the oscillatory flow. Simulation results showed that (a) axial heat transfer increases with the increasing diameter of the solid‐core tube, (b) the material of the solid‐core tube does not significantly affect axial heat transfer, and (c) efficiency based on the ratio of heat transfer to the work done is higher than that in a bundle of circular capillary tubes. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(1): 61–74, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20094     

A comparison of mass transfer between a plate and submerged conventional and multichannel impinging jets

This study presents a work on the comparison of mass transfer distribution on a plate subjected to impingement by a conventional impinging jet (CIJ) and multichannel conventional impinging jet (MCIJ). The local mass transfer coefficients were measured by the electrochemical limiting diffusion current technique (ELDCT). The jet Reynolds number varied in the range of 10,950–50,800 and jet-to-plate distance 2d–10d, where d is the nozzle diameter. The local mass transfer values were recorded beginning from the impingement point to a radial distance of approximately 15d. The distribution of the local mass transfer coefficients (LMTC) was compared for both jet systems.     

Fully developed hydrodynamic and thermal transport in combined pressure and electrokinetically driven flow in a microchannel with asymmetric boundary conditions

Thermally and hydrodynamically fully developed combined pressure-driven and electroosmotic flow through a channel has been simulated for isoflux wall boundary conditions. Effects of asymmetries in wall zeta potential and heat flux have been considered and closed form expressions have been obtained for transverse distribution of electric potential, velocity and temperature. The results indicate that both flow and heat transfer characteristics are significantly affected by the asymmetries in wall boundary conditions for both purely electroosmotic and combined pressure-driven and electroosmotic flow. These findings have important implications for flow and heat transfer control in microfluidics through alteration of surface conditions.     

A note on heat transfer to MHD oscillatory flow in an asymmetric wavy channel

This note deals with the MHD oscillatory flow of an optically thin fluid in an asymmetric wavy channel filled with porous medium. Based on some simplifying assumptions, the governing momentum and energy equations are solved and analytical solutions for fluid velocity, temperature distribution, Nusselt number and skin friction are constructed. The effects of radiation parameter, Peclet number, Hartmann number, porous medium shape factor and geometric parameters on flow and heat transfer characteristics have been examined in detail.     

MHD oscillatory flow with heat transfer in a flat plate channel

An analysis of the oscillatory MHD channel flow of an electrically conducting, viscous, incompressible fluid under a transverse magnetic field is presented. The transient velocity and the transient temperature are exhibited graphically, whereas the numerical values of the amplitude, phase of the skin-friction and the first and second harmonics of the rate of heat transfer are displayed in tabular form. Also discussed are the effects of M (the Hartmann number), e (the loading parameter), ω* (the frequency), and E (the Eckert number).     

Hydrodynamics and heat transfer in bubbly flow in the turbulent boundary layer

In the work presented is a new approach to modelling the bubbly flow in the boundary layer. The approach is based on summation of dissipation energy coming from the shearing turbulent flow in the absence of bubbles and the dissipation contribution from the presence of bubbles. As a result we obtain the dissipation of equivalent single phase turbulent flow. The model has been solved using the method of asymptotic correction to provide an explicit differential equation describing the velocity profile. That can be solved with the assumption of constant void fraction distribution to yield the analytical velocity profile. Alternatively, author has developed his own model of lateral void migration, which is distinct from other models by virtue of presence of another rotational velocity. Velocity distributions calculated using the new model have been compared against the experimental data of turbulent bubble flows with small void fraction. A good consistency between calculations performed using a new model and available experimental data has been obtained. Additionally, a solution of the temperature field is also given. In the case of a constant void fraction distribution analytical distribution of the Nusselt number is given or the set of differential equations needs to be solved.     

A critical comparison between local heat and mass transfer coefficients of horizontal cylinders immersed in bubbling fluidised beds

Heat and mass transfer coefficients between bubbling fluidised beds and immersed surfaces are analysed in light of recent findings that clarify the properties of the emulsion phase in proximity of immersed surfaces. The correlation between heat and mass transfer in fluidised beds is not straightforward since the two phenomena obey to different transport mechanisms, so that the classical Chilton–Colburn analogy is not valid any longer. Therefore, the link between the two phenomena can be achieved only through a deeper understanding of the fluid dynamic and morphological characteristics of the granular flow in proximity of the exchange surface. In this paper, results available in the pertinent literature are critically compared and used to provide a simple methodology to correlate the average and local heat and mass transfer coefficient with the fluid dynamic field for the case of a horizontal cylinder immersed in a bubbling fluidised bed.     

Analytical and numerical solutions of heat and mass transfer of boundary layer flow in the presence of a transverse magnetic field

The present investigation aims to study the effect of a transverse magnetic field with the presence of an adverse pressure gradient on the two‐dimensional laminar incompressible boundary layer flow over a flat plate. Using appropriated similarity transformations, the partial differential equations governing the studied problems are transformed into the ordinary nonlinear differential equations. Thereafter, these equations are solved numerically and analytically using the fourth‐order Runge‐Kutta method featuring shooting technique and the Adomian decomposition method, respectively. Obtained results reveal an excellent agreement between analytical and numerical data for temperature and concentration profiles.     

Heat transfer in the boundary layer with asymptotic favorable pressure gradient

Numerical modeling of Prandtl equations was undertaken in order to investigate into the effect of mainstream acceleration on characteristics of dynamic and thermal boundary layers. Unlike in dynamic boundary layer, nondimensional characteristics of thermal boundary layer proved to be rather conservative to the action of the favorable pressure gradient. It was found that, unlike the skin-friction coefficient and the momentum-thickness Reynolds number, the Stanton number and the energy-thickness Reynolds number both exhibit no saturation with increasing the Kays acceleration parameter. Also, an analysis of the violation of Reynolds analogy by the stream acceleration is given.     

Fluid flow and mass transfer modelling in lysozyme ultrafiltration

This work addresses the mass transfer modelling of ternary solutions, water/lysozyme/sodium chloride, in the slit feed channel of a ultrafiltration (UF) cell. Permeation experiments are performed using a laboratory-made UF cellulose acetate membrane, characterised by an hydraulic permeability of 2.05 × 10⁻¹¹ m/s/Pa and a molecular weight cut-off of 30 kDa. The simulation of the UF operating conditions with recourse to computer fluid dynamics allows the prediction of the selective permeation performance in terms of permeation fluxes and concentration polarization. The predictions of the permeation fluxes based on different mass transport assumptions are compared with experimental ones and a good agreement is obtained.     

Hydrodynamics and mass transfer in decaying annular swirl flow

This paper reports an electrochemical study of local mass transfer behaviour in decaying annular swirl flow. Initially, flow visualisation experiments were conducted to observe the general behaviour of the flow. It was found that the swirl angle decays exponentially along the tube. Measurements of pressure drop across the vaned swirl generators were correlated in terms of the inverse of the square of the tangent of the vane angle and approximately the square of the mean fluid velocity for vane angles of 30° and over. Measurements of the axial distribution of local mass transfer coefficient for the inner rod were carried out using the electrochemical limiting diffusion current technique and results were correlated for each swirl generator, in the Reynolds number range 3300–50000. It was found that the relative enhancement of mass transfer in swirl flow increases as the vane angle increases and Reynolds number decreases.