Enhancement of natural convection fins by high-frequency forced oscillations

This paper conveys a numerical simulation of an active enhancement device for natural convection in the interfin spaces of a fin array. A baseline solution for the non-enhanced situation revealed that the confinement created by the walls of adjacent fins and the base surface gave rise to a drastic reduction of the heat transfer coefficient values compared with those for the standard vertical plate. This outcome demonstrated the necessity for enhancement. The enhancement device investigated here communicated with the interfin space via an opening in the base surface. Enhancement was achieved by alternately introducing and extracting air into and from the space. The frequency of the introduction/extraction cycle was varied over values of 0, 10, 50, and 100 Hz. For each of these cases, spatially local, cycle-averaged heat transfer coefficients were determined on the bounding surfaces of the interfin space and on the outboard surface of a fin that faced a large ambient space. Results were also obtained for the cycle- and spatially averaged coefficients. Even at a low oscillation frequency of 10 Hz, the interfin heat transfer coefficients were significantly enhanced but not sufficiently to overcome the confinement effect. At 100 Hz, the enhancement gave rise to coefficient values that are about 64 times greater than the unenhanced values.