Transient and steady-state natural convection heat transfer from a heated horizontal concrete cylinder

Steady-state external natural convection heat transfer from vertically-mounted rectangular interrupted fins is investigated numerically and experimentally. To perform an experimental study, a custom-designed testbed was developed to verify the analytical and numerical results. FLUENT software was used in order to develop a 2-D numerical model for investigation of interruption effects. After regenerating, and validating the existing analytical results for fin spacing, a systematic numerical and experimental study was conducted on effect of fin interruption. Results show that adding interruptions to vertical rectangular fins enhances the thermal performance of fins. In a parametric study optimum interruption length for maximum fin performance was found and correlated.

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Heat Transfer by Natural Convection in a Square Enclosure Containing PCM Suspensions

Energies ◽

10.3390/en14102857 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2857

Author(s):

Ching-Jenq Ho ◽

Chau-Yang Huang ◽

Chi-Ming Lai

Keyword(s):

Heat Transfer ◽

Steady State ◽

Natural Convection ◽

Pure Water ◽

Convection Heat Transfer ◽

Natural Convection Heat Transfer ◽

Convection Heat ◽

Concentration Gradients ◽

Thermal Systems ◽

Square Enclosure

Research on using phase change material (PCM) suspension to improve the heat transfer and energy storage capabilities of thermal systems is booming; however, there are limited studies on the application of PCM suspension in transient natural convection. In this paper, the implicit finite difference method was used to numerically investigate the transient and steady-state natural convection heat transfer in a square enclosure containing a PCM suspension. The following parameters were included in the simulation: aspect ratio of the physical model = 1, ratio of the buoyancies caused by temperature and concentration gradients = 1, Raleigh number (RaT) = 103–105, Stefan number (Ste) = 0.005–0.1, subcooling factor (Sb) = 0–1.0, and initial mass fraction (or concentration) of PCM particles (ci) = 0–0.1. The results showed that the use of a PCM suspension can effectively enhance heat transfer by natural convection. For example, when RaT = 103, Ste = 0.01, ci = 0.1, and Sb = 1, the steady-state natural convection heat transfer rate inside the square enclosure can be improved by 70% compared with that of pure water. With increasing Sb, the Nusselt number can change nonlinearly, resulting in a local optimal value.

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

Journal of Heat Transfer ◽

10.1115/1.3246921 ◽

1986 ◽

Vol 108 (2) ◽

pp. 310-316 ◽

Cited By ~ 10

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.

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