scholarly journals Experimental Correlations Nu vs Gr.Pr at Varying Widths for Convective Heat Flow Through a Large Aperture in a Full Scale Enclosed Space

2021 ◽  
Vol 39 (5) ◽  
pp. 1643-1648
Author(s):  
Sebbar Yazid Youcef ◽  
Belaidi Abdelkader
Keyword(s):  
Heat Flow ◽  
Convective Heat ◽  
Air Flow ◽  
Simulation Models ◽  
Full Scale ◽  
Neutral Axis ◽  
Large Aperture ◽  
Scale Models ◽  
Flow Through ◽  
Enclosed Space

Convective heat transfer through a large aperture has been studied theoretically and experimentally using reduced scale models for many years. This paper describes the effect of the width of a large opening on the convective heat flow in an enclosure for 5.6×108< Rayleigh number (Ra)<2.8×1010. In our case a full scale realistic calorimetric chamber (5.5m x 2.5m x 2.5m) was used in this study. This chamber contains two zones connected by a large aperture of height H. A hot and cold wall on each side of the aperture will create a temperature difference between the two zones. Empirical equations are expressed in terms of varying door aspect ratio ADS, i.e.: NuPr=(α+βWH)∗Grb, at various temperature differences between the two zones. It was clearly found that as the width decreases the convective flux increases substantially. The instability of the air flow due to the apparition of a small turbulence increased when the opening width gets larger. It was also noticed that the neutral axis (air velocity = 0) goes up when the width of the opening decreases resulting in an acceleration of the air flow above the neutral axis. The liability of these experimental results could be useful for the validation of simulation models.

Theoretical research of heat exchange between air flow and shaft lining subject to convective heat transfer

2020 ◽  
pp. 151-167
Author(s):  
M. A. Semin ◽  
L. Yu. Levin
Keyword(s):  
Heat Transfer ◽  
Heat Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Transfer Factor ◽  
Air Flow ◽  
Air Interface ◽  
Heat Transfer Factor ◽  
Shaft Lining ◽  
Ventilation Duct

The heat and mass transfer in a mine shaft under construction is researched theoretically under temperature conditions in the shaft lining lower than the temperature of air flow fed in the shaft via a ventilation duct. The research was aimed to ensure stable airing of mine shafts in the period of construction before cutting a shaft-to-shaft connection with artificial freezing of surrounding rock mass. The multi-parametric numerical modeling of nonstationary aeroand thermo-dynamic parameters in a mine shafts was performed using 3D convective heat transfer model in ANSYS. It is found that convective heat can exert considerable influence on the heat and mass exchange in the air space of the shaft when the shaft lining temperature is lower than the temperature of air flow from the ventilation duct at the shaft bottom. Inside the shaft, the back convective flows appear and air circulates in convective cells, which increases air flow rate in the shaft. As a consequence, the heat transfer factor at the shaft lining-air interface is much higher than the calculated factor without regard to the convective heat. The influence of the temperature difference at the air and shaft lining interface and the shaft lining roughness on the average values of the heat transfer factor and heat flow at the shaft lining and air interface is investigated. The empirical formulas are proposed for calculating the heat transfer factor and specific heat flow at the shaft lining and air interface depending on the temperature difference, shaft diameter and roughness of walls of underground openings.

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