Budati Anil Kumar, Peter Ho Chiung Ching, Pachara Venkateswara Rao and Shuichi Torii
Shuichi Torii and WenâJei Yang
A numerical study is performed to investigate turbulent flowcharacteristics in a pipe rotating around the axis. Emphasis is placed on theeffect of pipe rotation on the frictionâŠ
Abstract
A numerical study is performed to investigate turbulent flow characteristics in a pipe rotating around the axis. Emphasis is placed on the effect of pipe rotation on the friction coefficient and velocity distribution in the hydrodynamically, fullyâdeveloped flow region. The kâΔ turbulence model is modified by taking the swirling effect into account, in which the model function including the Richardson number is introduced to the Δ equation. The governing boundaryâlayer equations are discretized by means of a control volume finiteâdifference technique for numerical computation. Results obtained from the modified model agree well with experiment data in the existing literature. It is found from the study that (i) an axial rotation of the pipe induces an attenuation in the turbulent kinetic energy, resulting in a reduction in the friction coefficient, the turbulent and (ii) an increase in the velocity ratio causes substantial decreases in the friction coefficient, the turbulent kinetic energy and the streamwise velocity gradient near the wall.
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Shuichi Torii and WenâJei Yang
A theoretical study is performed to investigate transport phenomena in channel flows under uniform heating from either both side walls or a single side. The anisotropic t2ÂŻâ ΔtâŠ
Abstract
A theoretical study is performed to investigate transport phenomena in channel flows under uniform heating from either both side walls or a single side. The anisotropic t2ÂŻâ Δt heatâtransfer model is employed to determine thermal eddy diffusivity. The governing boundaryâlayer equations are discretized by means of a control volume finiteâdifference technique and numerically solved using a marching procedure. It is found that under strong heating from both walls, laminarization occurs as in the circular tube flow case; during the laminarization process, both the velocity and temperature gradients in the vicinity of the heated walls decrease along the flow, resulting in a substantial attenuation in both the turbulent kinetic energy and the temperature variance over the entire channel cross section; both decrease causes a deterioration in heat transfer performance; and in contrast, laminarization is suppressed in the presence of oneâsideâheating, because turbulent kinetic energy is produced in the vicinity of the other insulated wall.
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Shuichi Torii and WenâJei Yang
A numerical study is performed to investigate turbulent Couette flow and heat transfer characteristics in concentric annuli with a slightly heated inner cylinder moving in theâŠ
Abstract
A numerical study is performed to investigate turbulent Couette flow and heat transfer characteristics in concentric annuli with a slightly heated inner cylinder moving in the flow direction. A twoâequation kâΔ 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 given as functions of the temperature variance t2â and the dissipation rate of temperature fluctuations Δt, together with k and Δ. The governing boundaryâlayer equations are discretized by means of control volume finiteâdifference technique and numerically solved using a marching procedure. It is disclosed from the study that the streamwise movement of the inner core causes substantial reductions in the turbulent kinetic energy and the temperature variance, particularly near the inner wall region, resulting in the deterioration of the Nusselt number, and that an attenuation in heat transfer performance is induced by the velocity ratio of the moving inner cylinder to the fluid flow.
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Shuichi Torii, WenâJei Yang and Shinzaburo Umeda
A theoretical and experimental study is performed to investigate unsteady, twoâdimensional, incompressible fluid flow over both sides of a slotâperforated flat surface, which isâŠ
Abstract
A theoretical and experimental study is performed to investigate unsteady, twoâdimensional, incompressible fluid flow over both sides of a slotâperforated flat surface, which is placed in a twoâdimensional channel. The governing boundaryâlayer equations are discretized by means of a finiteâdifference technique to determine streamwise and transverse velocity components. The roles of both the Reynolds number and the ratio of the slot width, d, to the plate thickness, ÎŽ, on the velocity field are disclosed. It is found from the study that: (i) the flow pattern between two plates can be classified into four categories depending on a combination of Re and d/ÎŽ, (ii) at a small value of Re and/or d/ÎŽ, flow over the slot exhibits no timewise variation, (iii) when Re and d/ÎŽ exceed certain values, an alternate crossing of flow from one side of the plate to the other occurs across the slot, and (iv) a further increase in Re results in a complex flow both inside the slot and on the plate downstream of the slot. These results are confirmed by the flow visualization using ionâexchange resins.
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The aim of this article is to present the results of a parametric analysis of the entropy generation due to mixed convection in the entryâdeveloping region between twoâŠ
Abstract
Purpose
The aim of this article is to present the results of a parametric analysis of the entropy generation due to mixed convection in the entryâdeveloping region between two differentially heated isothermal vertical plates.
Design/methodology/approach
The entropy generation was estimated via a numerical solution of the mass, momentum and energy conservation equations governing the flow and heat transfer in the vertical channel between the two parallel plates. The resultant temperature and velocity profiles were used to estimate the entropy generation and other heat transfer parameters over a wide range of the operating parameters. The investigated parameters include the buoyancy parameter (Gr/Re), Eckert number (Ec), Reynolds number (Re), Prandtl number (Pr) and the ratio of the dimensionless temperature of the two plates (ΞT).
Findings
The optimum values of the buoyancy parameter (Gr/Re) optimum at which the entropy generation assumes its minimum for the problem under consideration have been obtained numerically and presented over a wide range of the other operating parameters. The effect of the other operating parameters on the entropy generation is presented and discussed as well.
Research limitations/implications
The results of this investigation are limited to the geometry of vertical channel parallel plates under isothermal boundary conditions. However, the concept of minimization of entropy generation via controlling the buoyancy parameter is applicable for any other geometry under any other thermal boundary conditions.
Practical implications
The results presented in this paper can be used for optimum designs of heat transfer equipment based on the principle of entropy generation minimization with particular focus on the optimum design of plate and frame heat exchanger and the optimization of electronic packages and stacked packaging of laminarâconvectionâcooled printed circuits.
Originality/value
This paper introduces the entropy generation minimization via controlling the operating parameters and clearly identifies the optimum buoyancy parameter (Gr/Re) at which entropy generation assumes its minimum under different operating conditions.