Heat Convection Within an Eccentric Annulus Heated at Either Constant Wall Temperature or Constant Heat Flux

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
F. M. Mahfouz
Keyword(s):  
Heat Flux ◽  
Numerical Solution ◽  
Wall Temperature ◽  
Outer Wall ◽  
Constant Heat Flux ◽  
Heat Convection ◽  
Radius Ratio ◽  
Constant Heat ◽  
Constant Wall Temperature ◽  
Eccentric Annulus

Natural heat convection within an annular annulus bounded by two horizontal vertically eccentric long cylinders has been investigated. The annulus inner wall has been heated and maintained at either constant wall temperature CWT or constant heat flux CHF while the outer wall is cooled and maintained at constant temperature. The induced buoyancy driven flow and the associated heat convection are predicted through solving numerically the full conservation equations for mass, momentum, and energy using Fourier spectral method. Beside Rayleigh and Prandtl numbers, the heat convection process in the annulus depends on the annulus radius ratio and eccentricity (normalized by the radius difference). The study considered a moderate range of Rayleigh numbers up to 105 while Prandtl number is fixed at 0.7. The radius ratio is considered up to 3.2 while the eccentricity is varied between − 0.65 and + 0.65. The study has revealed that at certain radius ratio for a given Rayleigh number and eccentricity, the heat transfer is minimum in case of CWT and the mean inner wall temperature is maximum in case of CHF. The study has also shown, in the range considered for controlling parameters, that multiple convection cells only exist in case of CWT and only for positive eccentricity. Moreover, the study has shown that the present numerical solution of the pure conduction problem is almost identical with the newly presented analytical solution which confirms the high accuracy of the numerical solution.

Natural Convection in a Vertical Slit Microchannel With Superhydrophobic Slip and Temperature Jump

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
C. Y. Wang ◽  
Chiu-On Ng
Keyword(s):  
Heat Flux ◽  
Flow Rate ◽  
Wall Temperature ◽  
Temperature Jump ◽  
Slip Surface ◽  
Critical Value ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Constant Wall Temperature ◽  
Temperature Jump Coefficient

Recent developments in microscale heat exchangers have heightened the need for the understanding of fluid flow and heat transfer in a microchannel. In this study, we look into fully-developed buoyancy-driven flow in a vertical parallel-plate microchannel, which has one wall exhibiting superhydrophobic slip and temperature jump, and another wall being a normal no-slip surface. Analytical solutions are derived for free convection in the channel, where the heating is applied to either one of the two walls, and by either constant wall temperature or constant heat flux. We examine how the superhydrophobic slip and temperature jump may affect the volume flow rate and the Nusselt number under various heating conditions. There exists a critical value of the temperature jump coefficient, above which the flow rate will be larger by heating the no-slip surface than by heating the superhydrophobic surface, whether by constant wall temperature or by constant heat flux. The opposite is true when the temperature jump coefficient is below the critical value. Also, the temperature jump can have a negative effect on the flow rate when the heating is by constant temperature on the superhydrophobic side of the channel, but will have a positive effect when the heating is on the no-slip side of the channel.

Heat-Transfer Effects on the Developing Laminar Flow Inside Vertical Tubes

1966 ◽  
Vol 88 (2) ◽  
pp. 214-222 ◽  
Author(s):  
W. T. Lawrence ◽  
J. C. Chato
Keyword(s):  
Heat Flux ◽  
Transition Process ◽  
Constant Heat Flux ◽  
Wall Heat Flux ◽  
Axial Position ◽  
Fluid Viscosity ◽  
Constant Heat ◽  
Constant Wall Temperature ◽  
Constant Wall Heat Flux ◽  
Vertical Tubes

A numerical method was developed for the calculation of entrance flows in vertical tubes for the cases of upflow or downflow and constant wall heat flux or constant wall temperature. The solutions were in excellent agreement with experimental data obtained with water flowing upward in a vertical heated tube. The results show that both the density and the viscosity have to be treated as nonlinear functions of temperature. Consequently, for the constant heat flux condition, the velocity and temperature profiles constantly change and never reach “fully developed” states. The transition to turbulent flow was also studied. The experimental measurements demonstrated that the transition process depends on the developing velocity profiles. For the constant heat flux case, transition will always occur at some axial position. For a given entrance condition, the distance to transition is fixed by the fluid flow rate and the wall heat flux. For the experimental results, a tentative transition criterion was obtained, which depends only on the velocity profile shape, fluid viscosity, and the entrance Reynolds number.

Infrared experiment on the wall temperature distribution for a particle packed channel with constant heat flux

2001 ◽  
Vol 46 (18) ◽  
pp. 1566-1568 ◽  
Author(s):  
Jianhua Du ◽  
Xuejiao Hu ◽  
Bin Ma ◽  
Wei Wu ◽  
Buxuan Wang
Keyword(s):  
Heat Flux ◽  
Temperature Distribution ◽  
Wall Temperature ◽  
Constant Heat Flux ◽  
Constant Heat

Laminar Combined Convection in a Horizontal Annulus Subject to Constant Heat Flux Inner Wall and Adiabatic Outer Wall

1986 ◽  
Vol 108 (2) ◽  
pp. 392-397 ◽  
Author(s):  
M. Kaviany
Keyword(s):  
Heat Flux ◽  
Rayleigh Number ◽  
Outer Wall ◽  
Constant Heat Flux ◽  
Lateral Flow ◽  
Temperature Fields ◽  
Constant Heat ◽  
Average Temperature ◽  
Finite Difference Approximations ◽  
Structure Changes

Steady-state, fully developed velocity and temperature fields in mixed convection through a horizontal annulus (ratio of outside to inside radii of 1.25), with a prescribed constant heat flux on the inner cylinder and an adiabatic outside cylinder are analyzed using finite difference approximations. The effects of the buoyancy-driven lateral flow on the temperature of the inner surface are studied in detail. The results show that, as the buoyancy potential (Rayleigh number) increases, the lateral flow structure changes from one cell (on each side) to two cells. The consequence of these flow regimes is that as Rayleigh number increases the temperature of the upper portion of the inner cylinder first increases significantly above its value for pure forced convection and then decreases significantly as the number of cells increases. The average temperature of the inner cylinder decreases monotonically as the Rayleigh number increases.

Effects of Nanoparticle Migration on Water/Alumina Nanofluid Flow Inside a Horizontal Annulus with a Moving Core

2014 ◽  
Vol 31 (3) ◽  
pp. 291-305 ◽  
Author(s):  
A. Malvandi ◽  
D. D. Ganji
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Outer Wall ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Thermal Boundary Conditions ◽  
Alumina Nanofluid

AbstractThe present study is a theoretical investigation of the laminar flow and convective heat transfer of water/alumina nanofluid inside a horizontal annulus with a streamwise moving inner cylinder. A modified, two-component, four-equation, nonhomogeneous equilibrium model is employed for the alumina/water nanofluid, which fully accounts for the effect of the nanoparticle volume fraction distribution. To determine the effects of thermal boundary conditions on the migration of the nanoparticles, two cases are considered: constant heat flux at the outer wall with an adiabatic inner wall (Case A) and constant heat flux at the inner wall with an adiabatic outer wall (Case B). The numerical results indicate that the thermal boundary conditions at the pipe walls significantly affect the nanoparticle distribution, particularly in cases where the ratio of Brownian motion to thermophoretic diffusivities is small. Moreover, increasing the velocity of the moving inner cylinder reduces the heat transfer rate for Case A. Conversely, in Case B, the movement of the inner cylinder enhances the heat transfer rate, and anomalous heat transfer enhancement occurs when the thermophoretic force is dominant (in larger nanoparticles).

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