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31.
A numerical study of a buoyancy driven convection flow in presence of thermocapillarity has been developed. The fluid is a silicone oil (Prandtl number equal to 105) contained in a three-dimensional box bounded by rigid and impermeable walls with top free surface exposed to a gaseous phase. At the lateral box walls a different non-uniform temperature distribution is assumed so to induce horizontal convection and to keep separated thermocapillary and buoyancy effects. The vorticity-velocity formulation of the time-dependent Navier–Stokes equations for a non-isothermal incompressible fluid is used. A procedure based on a linearized fully implicit finite difference second order scheme has been adopted. We obtained very complex steady configurations for several values of the temperature difference at the lateral walls, T=30, 40 and 50°C. Along the direction perpendicular to the lateral walls, for T increasing, we observe a physically meaningful growth of heat transfer. Confidence in these results is supported by a comparison with recent experimental and numerical observations. 相似文献
32.
The objectives of this study are to investigate theoretically the effect of additive on the onset of Marangoni convection and to find the meaningful relationships between the important parameters. The propagation theory in which the penetration depth is chosen as the length scale and the scaling analysis are adapted in the present study. It is found that the combined absorbate Marangoni number MB is linearly related to the modified Biot number Bi* and there is a critical Biot number Bi to cause the most unstable state of liquid layer. It is concluded that it is not always advantageous to increase the mass transfer coefficient in the gas phase in order to enhance the absorption rate. It is interesting that the additive Marangoni number MaA and the relative surface diffusivity of additive RA which represent the additive properties act as the stabilizer and the destabilizer respectively for the onset of Marangoni convection. 相似文献
33.
34.
The effect of natural convection on forced convection in a horizontal flow was investigated during zinc electrodeposition on a horizontal electrode facing upward in a channel. The previous findings of Tobias and Hickman [1] are confirmed. A secondary flow in the form of roll cells whose axes are parallel to the flow direction is formed at some distance from the leading edge. This distance depends linearly on the flow velocity through the critical Rayleigh number for the onset of natural convection across the diffusion boundary layer. Striated zinc deposits reveal the imprint of the secondary flow on the planar cathode facing upward. 相似文献
35.
《Drying Technology》2013,31(3):413-438
Abstract Although a detailed mathematical model incorporating all physical mechanisms of moisture and heat transfer in the material would yield valuable design information, it is not feasible to do this on a routine basis for the design of dryers. A simple liquid diffusion model was developed in the present study to quantitatively assess the influence of various operating parameters of engineering interest in drying of heat-sensitive materials. Heat of wetting, temperature, and moisture dependent effective diffusivity and thermal conductivity, changes in product density and drying-induced ideal shrinkage of the product are considered in this model. The effects of combining convection with conduction, radiation, and volumetric heating using a microwave field are simulated in view of the increasing interest in multimode heat input drying processes. Numerical results are reported on drying of potato slices to demonstrate how the moisture and temperature profiles as well as drying performance are affected by multi-mode heat input. Effects of key parameters e.g., drying air velocity, temperature, relative humidity, and product thickness are computed and discussed. 相似文献
36.
Chang Kyun Choi Kyoung Hoon Kang Min Chan Kim In Gook Hwang 《Korean Journal of Chemical Engineering》1998,15(2):192-198
This paper concerns the analysis of convective instabilities and fully developed transport properties in Bénard convection.
The onset of convective instabilities driven by surface-tension variations and buoyancy forces is analyzed theoretically by
using the propagation theory we have developed. Based on these stability criteria, the subsequent transport correlations of
fully developed buoyancy-driven convection in horizontal fluid layers are suggested. It is found that the present predictions
are compared favorably with existing experimental results. 相似文献
37.
Young Gyu Park 《Korean Journal of Chemical Engineering》1999,16(1):128-138
A theoretical model has been derived in an electrophoretic packed column where an electric potential is applied to a column
in the axial direction. The effect of electrophoretic convection in gel particles packed in the column significantly contributes
to the separation of large polyelectrolytes because the conformation of polyelectrolyte quickly orients in the field direction.
The dependence of the transport in the gel particle upon field intensity and molecular size aids in understanding the transport
of polyelectrolyte in the packed column, since the convective velocity of polyelectrolyte is accelerated inside a porous gel
particle. There are few convection studies of large poly-electrolyte in a column packed with porous gel particles under an
electric field for the separation. Convective-diffusive transport of a large polyelectrolyte is analyzed using Peclet number
described by electrophoretic mobility and diffusion coefficient measured experimentally. The separation of two different polyelectrolytes
in the packed column is performed using a value ofPe
f/Peg of individual polyelectrolyte by molecular size and an electric field. The purpose of this paper is to study the separation
of solute from a mixture in the column using the physicochemical properties in the gel particle which are measured experimentally. 相似文献
38.
汪琦 《石油化工设备技术》1997,18(1):28-31
介绍了积灰、结渣形成的机理,讨论了积灰、结渣对热载体加热炉辐射受热面、对流受热面传热的影响 相似文献
39.
A passive chilled beam is a source of natural convection, creating a flow of cold air directly into the occupied zone. Experiments were conducted in a mock-up of an office room to study the air velocities in the occupied spaces. In addition, velocity profiles are registered when underneath heat loads exist and the cool and warm air flows interact. Experimental laboratory study revealed that in the case of the underneath heat gains, even no upward plume was generated and the dummy only acted as a flow obstacle, having a significant effect on the velocity profile. Furthermore, in an actual occupied office environment, the thermal plumes and the supply air diffuser mixed effectively the whole air volume. The maximum air velocity measured was still below 0.25 m/s with the extremely high heat gain of 164 W/m2. The results demonstrate that analysis methods were the interaction of convection flow and jet are not taken into account could not accurately describe air movement and draught risk in the occupied room space. 相似文献
40.
Turbulence and mixing across gravitationally unstable interface were studied in the laboratory by overturning a tank of two-layer fluids initially of stable stratification. As the dense fluid fell under gravity to mix with the lighter fluid from below, highly unsteady exchange of fluids across the unstable interface was produced by the buoyancy force. The exchange was captured in the experiment by a video camera using dye in the dense fluid as tracer. Absorption of light by the dye determined the excess mass at every pixel of the digitized images. The position of the excess-mass center and the speed of the center were computed from the excess-mass profiles as parameters to characterize the mixing across the unstable interface. With positive feedback by the buoyancy force, mixing across the interface rapidly intensified. It increased linearly from zero to a maximum in an acceleration regime and then asymptotically toward a terminal state, as the total buoyancy in the layer stayed constant. In the terminal state, the excess-mass center advanced at a terminal speed in proportion to the square root of the layer's total buoyancy. 相似文献