Forced and Mixed Convection Heat Transfer at High Pressure and High Temperature in a Graphite Flow Channel

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Francisco I. Valentín ◽  
Narbeh Artoun ◽  
Masahiro Kawaji ◽  
Donald M. McEligot
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Pressure ◽  
High Temperature ◽  
Mixed Convection ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Lower Wall ◽  
Convection Heat ◽  
Flow Laminarization

High pressure/high temperature forced and mixed convection experiments have been performed with helium and nitrogen at temperatures and pressures up to 893 K and 64 bar, respectively. The test section had a 16.8 mm ID flow channel in a 108 mm OD graphite column. Flow regimes included turbulent, transitional, and laminar flows with the inlet Reynolds numbers ranging from 1500 to 15,000. Due to strong heating, the local Reynolds number decreased by up to 50% over the 2.7 m test section. In addition, heat transfer degradation and flow laminarization caused by intense heating led to Nusselt numbers 20–50% lower than the values given by the modified Dittus–Boelter and modified Gnielinski correlations. Flow laminarization criteria were considered based on a dimensionless acceleration parameter (Kv) and buoyancy parameter (Bo*). Upward turbulent flows displayed higher wall temperatures than downward flows, due to the impact of flow laminarization which is not expected to affect buoyancy-opposed flows. Laminar Reynolds number flows presented an opposite behavior due to the enhancement of heat transfer for buoyancy-aided flows. At low Reynolds numbers, downward flows displayed higher and lower wall temperatures in the upstream and downstream regions, respectively, than the upward flow cases. In the entrance region of downward flows, convection heat transfer was reduced due to buoyancy leading to higher wall temperatures, while in the downstream region, buoyancy-induced mixing caused higher convection heat transfer and lower wall temperatures.

Experimental Study of Forced Convection From Isothermal Circular and Square Cylinders and Toroids

1997 ◽  
Vol 119 (1) ◽  
pp. 70-79 ◽  
Author(s):  
G. Refai Ahmed ◽  
M. M. Yovanovich
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Empirical Models ◽  
Experimental Program ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Wide Range

Experimental studies of forced convection heat transfer from different body shapes were conducted to determine the effects of Reynolds number and different characteristic body lengths on the area-averaged Nusselt number. Although the bodies differed significantly in their shapes, they had approximately the same total surface area, A = 11,304 mm2 ± 5%. This ensured that for a given free stream velocity and total heat transfer rate all bodies had similar trends for the relationship of Nusselt and Reynolds numbers. The experimental program range was conducted in the Reynolds number range 104≤ReA≤105 and Prandtl number 0.71. Finally, the empirical models for forced convection heat transfer were developed. These empirical models were valid for a wide range of Reynolds numbers 0≤ReA≤105. The present experimental correlations were compared with available correlation equations and experimental data. These comparisons show very good agreement.

Investigation of Temperature Uniformity in an Open Cavity of Buoyancy Assisted Mixed Convection Heat Transfer With Multiple Discrete Inlet and Outlet Ports

2014 ◽  
Author(s):  
G. Yang ◽  
J. Y. Wu ◽  
Y. W. He ◽  
L. Yan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Temperature Gradient ◽  
Mixed Convection ◽  
Convection Heat Transfer ◽  
Open Cavity ◽  
Temperature Uniformity ◽  
Convection Heat ◽  
Grashof Number ◽  
Mixed Convection Heat Transfer

Turbulent buoyancy assisted mixed convection heat transfer in an open cavity with multiple discrete inlet and outlet ports is investigated experimentally. The side walls of the rectangular cavity are symmetrically heated with constant and uniform temperature. The temperature distribution in the interior of the cavity is presented and discussed for the Reynolds numbers of 3919 ≤ Re ≤ 35405, the Grashof numbers of 1.56 × 107 ≤ Gr ≤ 3.45 × 107, the Prandtl number of Pr = 0.71 and for various quantities of inlet and outlet ports ranging from 1 × 1 to 5 × 5 with the same total opening area. Increasing Reynolds number and decreasing Grashof number can improve the temperature uniformity in the cavity. As the dispersion of the inlet ports increases, the maximum temperature gradient of the fluids in the cavity is decreased while the average temperature gradient is increased. The effect of inlet/outlet forms, Reynolds number and Grashof number on the Nusselt number is also investigated.

Performance of a variety of low Reynolds number turbulence models applied to mixed convection heat transfer to air flowing upwards in a vertical tube

2004 ◽  
Vol 218 (11) ◽  
pp. 1361-1372 ◽  
Author(s):  
W S Kim ◽  
J D Jackson ◽  
S He ◽  
J Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Vertical Tube ◽  
Convection Heat ◽  
Mixed Convection Heat Transfer ◽  
Low Reynolds

The study reported here is concerned with mixed convection heat transfer to air flowing upwards in a vertical tube. Computational simulations of experiments from a recent investigation have been performed using an ‘in-house’ code which was written specifically for variable-property, developing, buoyancy-influenced flow and heat transfer in a vertical passage. The code incorporates a selection of two-equation, low Reynolds number turbulence models. The objective of the study was to evaluate the models in terms of their capability of reproducing the effects on turbulent heat transfer of non-uniformity of fluid properties and buoyancy. Direct comparisons have been made between results from the experimental investigation and those obtained by computational modelling for a range of conditions. The trends of impairment and enhancement of heat transfer owing to the influence of buoyancy found in the experiments were captured to some extent in the simulations using each of the models. However, none reproduced observed behaviour correctly over the entire range of buoyancy influence.

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