This paper presents an experimental study of gas mixing processes and heat transfer augmentation by a forced jet in a large cylindrical enclosure with an isothermal bottom heating/cooling surface. Cold/hot air was injected at several positions with varying pipe diameters and injection orientations, and was removed from the top of the enclosure. Under natural convection, the mean Nusselt number was correlated by the enclosure Rayleigh number RaD1/3, and under strong forced convection, by the jet Reynolds number Rej2/3. A combining rule for mixed convection was found for both the stabilizing (cooled surface) and destabilizing (heated surface) density gradients. Using the ratio of forced and free convection Nusselt numbers, this correlation could be further reduced to predict forced-jet augmentation as a function of the Archimedes number, with a correction factor to account for jet orientation and enclosure aspect ratio.

Issue Section:
Natural and Mixed Convection
Keywords:
natural convection, mixing, jets, pipe flow, flow instability, Enclosure Flows, Fire, Heat Transfer, Impingement, Jets, Mass Transfer, Mixed Convection, Natural Convection
Topics:
Heat transfer, Natural convection, Flow (Dynamics), Forced convection
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