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Title: The experimental investigation of buoyant flows in inclined differentially heated cavities
Author: Esteifi, Khaled
Awarding Body: Manchester
Current Institution: University of Manchester
Date of Award: 2011
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Buoyant flows are present in nature and also in many engineering applications,from domestic heating to the cooling of nuclear power plants. This experimental study focuses on the effects of angle of inclination on buoyancy-driven flows inside tall, rectangular, differentially-heated cavities. The objective is to produce detailed local flow and thermal data, which will advance our understanding of the flow physics and also provide CFD validation data. It considers a 2.18m × 0.52m × 0.0762m cavity, resulting in an aspect ratio of 28.6, with its two opposing long walls maintained at constant but different temperatures, while all the remaining walls are thermally insulated. The Rayleigh number, based on the temperature difference and spacing of the long sides, is 0.86 x 106 for most cases and the working fluid is air (Prandtl number0.71). Experimental data for the flow and the thermal fields, using laser Doppler anemometry and Chromel-Alumel thermocouple traverses respectively, are presented for the cavity inclined at 60° and 15° to the horizontal, for both stable (the hot surface being the upper surface) and unstable (the hot surface the lower one) orientations. The 15° stable case is investigated at a higher Rayleigh number of 1.54 x106 and some additional data for the 15° unstable case are also presented at this high value of Rayleigh number. Comparisons with the measurements of Betts and Bokhari [1], for the same cavity at the vertical position, are also included. For moderate angles of inclination, the flow is two-dimensional and the effects of inclination are primarily confined to the fluctuating fields. For large angles of inclination, the flow becomes three-dimensional. In the unstable 15° angle of inclination case, a set of four longitudinal vortices are formed over the entire length of the cavity, with four counter-rotating re-circulation cells within the cross-section parallel to the thermally active walls. The enhanced mixing at 15° unstable inclination leads to uniform temperature in the cavity core and thus only minor deviations from two dimensionality in the thermal field. A modest rise in Rayleigh number, in the 15° unstable case, does not affect the mean motion, but causes an increase in the normalised turbulence intensities, which in turn leads to a more uniform temperature within the cavity core and a practically two-dimensional thermal field. The stable 15° angle of inclination case, surprisingly, leads to the formation of two longitudinal vortices and two re-circulation cells. The lack of mixing, in the 15° stable case, leads to more noticeable three-dimensional thermal field. The thesis includes a full set of flow and thermal predictions and also spectral analysis of thermal fluctuations, which show a significant effect of the angle of inclination on both the power density level and the ranges of frequencies involved.
Supervisor: Iacovides, Hector ; Cooper, Dennis ; Craft, Timothy Sponsor: Aleppo University - Syrian Arab Republic
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Natural Convection, Heat transfer, Experimental investigation, Inclined Cavity, Turbulent buoyant flow