Experimental Study of Natural Convection Heat Transfer Between a Cylindrical Envelope and an Internal Concentric Heated Octagonal Cylinder With or Without Slots

1991 ◽  
Vol 113 (1) ◽  
pp. 116-121 ◽  
Author(s):  
H. L. Zhang ◽  
Q. J. Wu ◽  
W. Q. Tao
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Convection Heat Transfer ◽  
Flow Patterns ◽  
Working Fluid ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Enhancement

In this paper, the results of an experimental study of laminar natural convection heat transfer and fluid flow in horizontal annuli between a cylindrical envelope and its inner concentric octagonal heated cylinder are presented. Two octagonal cylinders are investigated: one with a complete surface and the other with two horizontal slots on the top and bottom surfaces. The ratio of the slot width W to H is 0.072. Air is used as the working fluid. The range of Rayleigh number is 2.1×102–1.58×106 for the unslotted case and 1.2×102–1.5×106 for the slotted case. The average heat transfer correlations for the two cases are provided. The results show that the heat transfer intensity of the unslotted octagon is slightly weaker than that in a cylindrical annulus, while for the slotted case, the overall heat transfer enhancement may be as high as 74 percent. The smoke technique is used to visualize the flow patterns. A series of photographs of the flow patterns are provided, which enhances our understanding of the mechanism of heat transfer enhancement for the slotted octagonal case.

Convective heat transfer enhancement: effect of multi-frequency heating

2019 ◽  
Vol 29 (10) ◽  
pp. 3822-3856 ◽  
Author(s):  
Nirmal Kumar Manna ◽  
Nirmalendu Biswas ◽  
Pallab Sinha Mahapatra
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Convection Heat Transfer ◽  
Enhancement Effect ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Enhancement ◽  
Content Type ◽  
Frequency Heating

Purpose This study aims to enhance natural convection heat transfer for a porous thermal cavity. Multi-frequency sinusoidal heating is applied at the bottom of a porous square cavity, considering top wall adiabatic and cooling through the sidewalls. The different frequencies, amplitudes and phase angles of sinusoidal heating are investigated to understand their major impacts on the heat transfer characteristics. Design/methodology/approach The finite volume method is used to solve the governing equations in a two-dimensional cavity, considering incompressible laminar flow, Boussinesq approximation and Brinkman–Forchheimer–Darcy model. The mean-temperature constraint is applied for enhancement analysis. Findings The multi-frequency heating can markedly enhance natural convection heat transfer even in the presence of porous medium (enhancement up to ∼74 per cent). Only the positive phase angle offers heat transfer enhancement consistently in all frequencies (studied). Research limitations/implications The present research idea can usefully be extended to other multi-physical areas (nanofluids, magneto-hydrodynamics, etc.). Practical implications The findings are useful for devices working on natural convection. Originality/value The enhancement using multi-frequency heating is estimated under different parametric conditions. The effect of different frequencies of sinusoidal heating, along with the uniform heating, is collectively discussed from the fundamental point of view using the average and local Nusselt number, thermal and hydrodynamic boundary layers and heatlines.

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