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Heat Transfer Research
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Heat Transfer Research

DOI: 10.1615/HeatTransRes.v33.i7-8.10
50 pages

On Laminarization of Gas Flow in Strongly Heated Flow Passages

Shuichi Torii
Kumamoto University, Kumamoto, Japan
Wen-Jei Yang
Department of Mechanical Engineering and Applied Mechanics University of Michigan, Ann Arbor, Michigan 48109-2125, U.S.A.

ABSTRACT

A numerical study is performed to investigate thermal transport phenomena of the laminarizing flows in strongly heated circular tube, channel, and concentric annulus. A k-e turbulence model is employed to determine the turbulent viscosity and the turbulent kinetic energy. The turbulent heat flux is expressed by Boussinesq approximation in which the eddy diffusivity for heat is determined by a t2-et heat-transfer model. The governing boundary-layer equations are discretized by means of a control volume finite-difference technique and numerically solved using a marching procedure. Results are obtained for heat transfer rate, velocity, temperature, turbulent kinetic energy, and temperature variance in the laminarizing flows. Consideration is given to the effects of pipe rotation and channel geometry on the flow and thermal fields.
When the pipe is at rest, it is disclosed that (i) with a substantial reduction in heat transfer at the relatively high Reynolds number, i.e., laminarization takes place, the velocity gradient near the heated wall is attenuated and the turbulent kinetic energy diminishes over the whole cross section along the flow, and (ii) both the temperature variance and the turbulent heat flux also diminish over the whole tube cross section in the flow direction. The presence of pipe rotation induces an attenuation in the turbulent kinetic energy and the turbulent heat flux, resulting in the promotion of laminarization of a gas flow.
If the channel and the concentric annulus are simultaneously heated from both sides with high heat flux, the fluid flow is laminarized as well as in the tube flow case. However, the presence of inner core rotation in the annulus suppresses substantial reductions of the velocity and turbulent kinetic energy in the laminarizing flow. In other words, inner core rotation contributes to the suppression of laminarization of the strongly heated gas flow.
On the contrary, when the two-dimensional channel and the annulus with a stationary inner tube are strongly heated from a one-side wall, the fluid flow cannot be laminarized even for the heat-flux level which courses the laminarizing flow in the tube. The corresponding turbulent kinetic energy and velocity gradient in the vicinity of the heated wall is substantially decreased along the flow, while these levels on the other wall side are induced in the flow direction. Consequently, this amplification suppresses the deterioration of heat transfer performance.


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