Optimization principle for natural convection pulsating heating
This is a theoretical, numerical, and experimental study of natural convection heat transfer from an immersed surface with intermittent uniform heat flux. Scale analysis predicts that the `on' time interval can be optimized such that the overall Nusselt number is maximized. Furthermore, Nu increases monotonically as the `off' time interval decreases. These features are verified and determined more accurately by complete numerical simulations for a vertical flat surface in the range 103 ≤ Ra ≤ 105 and Pr = 7, where Ra is based on heat flux and wall height. They are further verified by means of water experiments in the range 1010 ≤ Ra 1011. The pulsating heater configurations tested experimentally are the vertical cylinder, which approximates boundary layer flow on a plane surface, and the horizontal cylinder. The optimal square-wave heat pulse for a natural convection immersion heater is reported in general (scaling correct) terms.
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