Performance analysis of turbulent convection heat transfer of Al 2 O 3 water-nanofluid in circular tubes at constant wall temperature

Energy ◽  
2014 ◽  
Vol 77 ◽  
pp. 403-413 ◽  
Author(s):  
Vincenzo Bianco ◽  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Heat Transfer ◽  
Performance Analysis ◽  
Wall Temperature ◽  
Convection Heat Transfer ◽  
Turbulent Convection ◽  
Convection Heat ◽  
Constant Wall Temperature ◽  
Circular Tubes

Pseudo-Steady-State Natural Convection Heat Transfer Inside a Vertical Cylinder

1986 ◽  
Vol 108 (2) ◽  
pp. 310-316 ◽  
Author(s):  
Y. S. Lin ◽  
R. G. Akins
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Wall Temperature ◽  
Convection Heat Transfer ◽  
Vertical Cylinder ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Constant Wall Temperature ◽  
Stream Functions

The SIMPLER numerical method was used to calculate the pseudo-steady-state natural convection heat transfer to a fluid inside a closed vertical cylinder for which the boundary temperature was spatially uniform and the temperatures throughout the entire system were increasing at the same rate. (Pseudo-steady state is comparable to the steady-state problem for a fluid with uniform heat generation and constant wall temperature.) Stream functions, temperature contours, axial velocities, and temperature profiles are presented. The range of calculation was 0.25 < H/D < 2, Ra < 107, and Pr = 7. This range includes conduction to weak turbulence. A characteristic length defined as 6 × (volume)/(surface area) was used since it seemed to produce good regression results. The overall heat transfer for the convection-dominated range was found to be correlated by Nu = 0.519 Ra0.255, where the temperature difference for both the Nusselt and Rayleigh numbers was the center temperature minus the wall temperature. Correlations using other temperature differences are also presented for estimating the volumetric mean and minimum temperatures.

Convection Heat Transfer of CO2 at Supercritical Pressures in a Vertical Mini Tube

2009 ◽  
Author(s):  
Pei-Xue Jiang ◽  
Zhi-Hui Li ◽  
Chen-Ru Zhao
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Convection Heat Transfer ◽  
High Heat ◽  
Vertical Tube ◽  
Density Variation ◽  
Heat Fluxes ◽  
Convection Heat ◽  
Downward Flow ◽  
Flow Acceleration

This paper presents the experimental and numerical investigation results of the convection heat transfer of CO2 at supercritical pressures in a 0.0992 mm diameter vertical tube at various inlet Reynolds numbers, heat fluxes and flow directions. The effects of buoyancy and flow acceleration resulted from the dramatic properties variation were investigated. Results showed that the local wall temperature varied non-linearly for both upward and downward flow when the heat flux was high. The difference of the local wall temperature between upward flow and downward flow was very small when other test conditions were held the same, which indicates that for supercritical CO2 flowing in a mini tube as employed in this study, the buoyancy effect on the convection heat transfer was quite insignificant, and the flow acceleration induced by the axial density variation with temperature was the main factor that lead to the abnormal local wall temperature distribution at high heat fluxes. The predicted values using the LB low Reynolds number turbulence model correspond well with the measured data. Velocity profiles and turbulence kinetic energy near the wall varying along the tube generated by the numerical simulations were presented to develop a better understanding.

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