Abstract
The effect of tilt angle on free convection heat transfer is investigated experimentally inside a rectangular parallelepiped cavity filled with water. The cavity had the dimensions S × S × H (m3), where S was the inside length, and H was the inside height of the cavity. The lower surface was subject to constant heat flux, and the upper surface was cooled by a stream of ambient air. The free convection heat transfer data were generated using different uniform heat fluxes. Four tilt angles were considered: 0°, 30°, 60°, and 90°. The surface temperature measurements were collected 10 h after the experimental run to ensure that a steady-state was reached. It was noticeable that the free convection heat transfer strongly depended on the tilt angle and the modified Rayleigh numbers. The 3D results showed that the Nusselt number reached a maximum at 60° at a fixed modified Rayleigh number. An enhancement in the Nusselt number at any tilt angle was observed over that of a zero tilt angle, and the percent of enhancement was 7.92–62.38%, depending on the modified Rayleigh numbers and the tilt angle. It was also observed that as the modified Rayleigh number increased, the temperature uniformity on both the hot and cold surfaces was disturbed. Furthermore, an empirical correlation between the modified Rayleigh numbers and Nusselt numbers was obtained for each angle. Moreover, two overall general correlations are obtained to cover the four tilt angles (i.e., 0°, 30°, 60°, and 90°) and the modified Rayleigh numbers, which should be helpful for engineering applications.
Highlights
The study of free convection in enclosures has extensive application in numerous fields
The results show that the percent of radiation heat transfer to the total input power and to the convection heat rate was 3.89% and 4.3%, re‐ spectively
Temperature contours of the hot and cold stainless‐steel surfaces at a 0° tilt angle for the cavity are shown in Figure 5, which were generated using the steady‐state values measured by the sixteen thermocouples at each surface and for various modified Rayleigh numbers
Summary
The study of free convection in enclosures has extensive application in numerous fields. Natural convection is a heat transfer mode that arises due to the buoyancy‐induced flows occurring from temper‐ ature gradients within fluids. The buoyancy force has both components relative to the walls of the enclosure, which strongly modifies the flow structure and the heat transfer therein [4]. A compre‐ hensive review of the studies on free convection in cavities was carried out by Pandey et al [5]. The effects of internal bodies with different shapes (e.g., square, circular, and an elliptical cylinder) on free convection heat transfer were summarized. A natural dimensionless heat transfer coefficient inside two water‐filled square cavities was investigated experimentally by Ali et al [6].
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