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Journal ArticleDOI

Experimental investigation for fluid flow and heat transfer in an elliptical duct rotating about a parallel axis

01 Apr 1993-Experimental Heat Transfer (Taylor & Francis Group)-Vol. 6, Iss: 2, pp 97-109

AbstractExperimental investigation was carried out for fluid flow and heat transfer in the case of an elliptical duct rotating about a parallel axis using air as the working medium. It was found thai the increase in heat transfer (due to rotation relative to the stationary condition) for an elliptical duct lies between the values for a circular duct and those for a square duct for fully developed laminar and turbulent flows. It was observed that elliptical ducts are more advantageous from the viewpoint of heat transfer augmentation.

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Citations
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Journal ArticleDOI
Abstract: The present study investigates rotation-induced secondary flow and mixed convection heat transfer in the entrance region of rectangular ducts rotating about a parallel axis. Boussinesq approximation is invoked to take into account the centrifugal buoyancy. Mechanisms of the secondary vortex development in ducts of isothermal or iso-flux walls are explored by a vorticity transport analysis. Numerical solutions of the parabolized velocity–vorticity formulation of Navier–Stokes⧹Boussinesq systems are used to corroborate the above theoretical analysis and provide evidence for the relevance of axial variation of transport rates to the evolution of the secondary vortices. The present results also reveal that the rotational effect in an iso-flux duct is more significant than that in an isothermal flux. In a fully developed flow region, the iso-flux case can still retain a secondary vortex effect, while the effect vanishes in isothermal ducts.

21 citations

Journal ArticleDOI
Abstract: The study of combined heat transfer of convection and radiation in rectangular ducts rotating in a parallel mode was investigated numerically in detail. The coupled momentum and energy equations are solved by the DuFort–Frankel numerical scheme to examine the interactions of convection with radiation. The integro-differential radiative transfer equation is solved by the discrete ordinates method. Results are presented over a wide range of the governing parameters. The present results reveal that the rotational effect in a square duct is more significant than that in a rectangular one. The predictions also demonstrate that the radiation presents significant effects on the axial distributions of the total Nusselt number, Nut, and tends to reduce the centrifugal-buoyancy effects. The effect of rotation on the Nut is restricted in the entrance region, however, the radiation affects the heat transfer through out the channel. Additionally, the Nut increases with the decrease in the conduction-to-radiation parameter NC.

21 citations

Journal ArticleDOI
Abstract: In this paper, turbulent airflow and heat transfer are studied numerically in a square sectioned channel which is rotating about a parallel axis. Channel rotation may create secondary flows as a result of centrifugal buoyancy and Coriolis forces which may increase the heat transfer coefficient and wall friction. Under certain conditions that the axial flow is dominant over the rotation, the effects of rotation can simply be ignored which means that friction factor and Nusselt number can be calculated regardless of rotation. This paper explores a novel criterion to demonstrate how the rotation affects the fluid flow and heat transfer. Rotational Grashof number ( Gr Ω ) and Reynolds number ( Re Ω ) are chosen to describe the rotation effects in addition to Reynolds number (Re) taking the axial flow into account. The results show that at a given Gr Ω and, Re Ω a specific Reynolds number ( Re ∗ ) in which the effects of rotation vanishes can be defined. It is revealed that Re ∗ may be presented as a function of Gr Ω only. With this regards, a non- dimensional group as Gr Ω a 1 / R e is obtained which is utilized to judge the rotational effects. It is shown that for Gr Ω a 1 / R e > 0.0167 the rotation starts to become important while for Gr Ω a 1 / R e 0.0167 the Nusselt number is approximately equal to stationary counterpart.

5 citations

Journal ArticleDOI
Wei-Mon Yan1
Abstract: A numerical study was performed to examine the characteristics of laminar mixed convection heat and mass transfer in rectangular ducts rotating about a parallel axis with water film evaporation along the porous duct walls. Particular attention is paid to the investigation of the extent of the energy transport through the mass transfer related to film evaporation. Numerical results are presented for an air–water vapor system under various conditions. For a specific condition, a vorticity–velocity method implemented with a marching technique was employed to solve the resultant three-dimensional system for simultaneously developing flow, temperature and concentration fields. Results reveal that the effects of water film vaporization along the porous duct walls on the mixed convection heat and mass transfer are significant. The heat exchange along the porous wetted wall is dominated by the latent heat transport in association with liquid film vaporization. Additionally, the local friction factors and heat and mass transfer rates can be enhanced by the rotational effects, including Coriolis and centrifugal forces, and liquid film evaporation; and the variations of the local values are closely related to the evolution of the secondary vortices in the duct.

5 citations


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Journal ArticleDOI
Abstract: A finite-difference procedure is employed to predict the turbulent flaw in ducts of rectangular cross-section, rotating about an axis normal to the longitudinal direction. The flows were treated as “parabolic”; and the turbulence model used involved the solution of two differential equations, one for the kinetic energy of the turbulence and the other for its dissipation rate. Agreement with experimental data is good for a constant-area duct at low rotation, but less satisfactory for a divergent duct at larger rotation. It is argued that a “partially-parabolic” procedure will be needed to predict the latter flow correctly.

47 citations