Abstract
The natural convection heat transfer response of discrete heaters flush mounted on a vertical test surface immersed in water to periodic input power has been investigated. The test surface consisted of a plexiglass substrate containing a single column of fifteen heat sources. Identical periodic input power patterns are generated within selected heaters using a computer controlled DC power supply. The mean power levels were varied in the range 0.2–3.0 W, the amplitude to mean ratios of power pulsations in the range 0.17–1.0 and the pulsation frequencies from 0.025–0.1 Hz. The resulting heater temperatures over several cycles were measured and compared with corresponding responses for steady input power equal to the mean of the periodic variation. For a single heater powered case a triangular wave input power pattern was examined. Two types of periodic input power variations were examined with a column of heat sources powered: a triangular wave and an approximate square wave. The responses clearly indicated heat transfer enhancement due to the power pulsation for certain conditions. With the triangular wave pattern, enhancement was most pronounced when the ratio of amplitude to mean power input was the the largest and for the highest pulsation frequency. For the square wave power input the maximum temperature during the cycle was never below the response to steady input power, in contrast to the triangular input power pattern.
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