An experimental investigation of natural convection wakes above a line heat source

Abstract The natural convection wake arising from a heated horizontal line source in liquids and in air is investigated in detail. The three-dimensional effects for a wire with a length to diameter ratio of 250 is observed in air and water with a schlieren system. The temperature field in the plume above wires with length-diameter ratios of 250 and 1200 in liquid silicone ( Pr = 6·7) is determined using a 20 cm Mach—Zehnder interferometer. Various wire heating rates are used yielding Grashof numbers, based on the vertical distance in the plume, in the range from 4 × 10 3 to 1·7 × 10 6 . Excellent agreement of the temperature distributions with theory are found for the larger length-diameter ratio wire at a Grashof number around 10 5 . A regular natural swaying motion of the plume, observed at a high Grashof number, caused temperature fluctuations across the entire plume width. The applicability of the idea of a virtual line and point source is considered in detail. Discrepancies in the level of the plume centerline temperature distribution in this and in previous experimental work are attributed to three-dimensional effects of the finite diameter, non-infinite length line sources.