Browsing by Author "CHANG, J"

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TRANSIENT NATURAL-CONVECTION HEAT AND MASS-TRANSFER OVER A VERTICAL PLATE OF FINITE HEIGHT
(1992-03-01)
CHANG, J
;
LIN, TF
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
A detailed numerical analysis has been carried out to study transient natural convection in a binary mixture adjacent to a vertical plate of finite height with the simultaneous presence of temperature and concentration gradients. The full elliptic Navier-Stokes equations and the energy and species diffusion equations were solved together by the projection method with the convective terms treated by the QUICK scheme. Computations were performed for a mixture with Pr = 0.7, Sc = 3.5, and thermal Grashof number fixed at 10(6). Both the augmenting and opposing flows were investigated with the buoyancy ratio varied from - 5 to 5 and the concentration ratio, an interface velocity parameter, from 10 to 1000. Results are presented to illustrate, in particular, the effects of combined thermal and solutal buoyancy forces on the temporal evolution of the flow pattern and the associated heat and mass transfer. Representative transient velocity, temperature, and concentration profiles are presented, along with the transient local and average Nusselt and Sherwood numbers. In the initial transient, the interface velocity at the plate induced by the concentration gradient dominates the flow patterns. After the initial period, the recirculating flows generated by the two buoyancy forces in the fluid are prevalent. In opposing flows, countercurrent flows may result at a high buoyancy ratio.
UNSTEADY THERMOSOLUTAL OPPOSING CONVECTION OF A LIQUID WATER MIXTURE IN A SQUARE CAVITY .1. FLOW FORMATION AND HEAT AND MASS-TRANSFER CHARACTERISTICS
(1993-03-01)
CHANG, J
;
LIN, TF
;
CHIEN, CH
;
交大名義發表
;
機械工程學系
Transient thermosolutal opposing convection of a liquid- water mixture in a square cavity subject to horizontal temperature and concentration gradients is numerically investigated by a third-order upwind finite-difference scheme. Results are particularly presented to illustrate the effects of the Lewis and Grashof numbers on the evolution of flow patterns and the associated heat and mass transfer characteristics for solutally dominant situations. Results for Le = 100 clearly show the double-diffusive nature of the convection. In the initial stage the flow is dominated by the interface velocities at the vertical side walls driven by the concentration gradients there. Later, the flow is governed by the thermal buoyancy. At a much later time, the solutal buoyancy set in inducing new recirculating cells along the side walls. These cells gradually grow and squeeze the thermally driven cell in the core region. Multilayer flow structure is finally formed. The counterrotating cells resulting from the opposing thermal and solutal buoyancies cause significant velocity, temperature and concentration oscillations with time at high Grashof numbers.
UNSTEADY THERMOSOLUTAL OPPOSING CONVECTION OF LIQUID WATER MIXTURE IN A SQUARE CAVITY .2. FLOW STRUCTURE AND FLUCTUATION ANALYSIS
(1993-03-01)
CHANG, J
;
LIN, TF
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
Effects of buoyancy ratio on the flow structure and fluctuating characteristics of the velocity, temperature and concentration fields are numerically investigated for a liquid-water mixture cavity subject to opposing horizontal thermal and solutal buoyancies at high thermal and solutal Rayleigh numbers. Three different flow structures, namely, the multilayer, mixed and secondary cell flows, were predicted. Time histories and power spectra for flow variables probed at several locations indicate that the flow is highly unstable. The collision of the thermally and solutally driven cells causes the secondary cell flow to be chaotic. Moreover, flow bifurcation is noted.