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Measurement of heat transfer coefficient in concentric and eccentric annuli Choudhury, Wasiuddin

Abstract

Heat transfer coefficients were measured at the inner wall of smooth concentric and eccentric annuli. The annuli were formed by an outer plastic tube of 3 in. inside diameter and an inner core cylinder of 1 in outside diameter. Air at room temperature was allowed to flow through the annuli at a Reynolds number range from 15,000 to 65,000. The measurement of heat transfer coefficient was made by a transient heat transfer test technique. The method consisted in establishing an initial temperature gradient between the fluid and a solid body mounted on the core cylinder by heating, then observing and recording the temperature-time history of the body as it returned to equilibrium condition with the fluid stream. The heat transfer coefficient was calculated from this record. The final results were presented in graphical form showing variations of Nusselt number with Reynolds number. The results of the concentric annulus tests agreed favourably with those predicted by Wiegand (2) and Monrad and Pelton (3). The effect of eccentricity was to reduce the heat transfer coefficient although the general trend was identical to that in the concentric annulus case. It was observed that the decrease of heat transfer coefficient was not linearly related to the eccentricity of the core cylinder. The effect of eccentricity was more pronounced in the range 0 ≤ e ≤ 0.5 where the value of heat transfer coefficient decreased considerably.

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