This paper describes an experimental and theoretical study of the periodic on and off heating of water on a horizontal surface. The heat transfer is effected by natural convection and isolated bubbles. The experiments cover the heat flux range 33–154 kW/m2 and the wall excess temperature range 7–13°C. It is shown experimentally that the cycle-averaged thermal conductance between the surface and the pool can be maximized by properly selecting the time intervals of the on and off heating cycle. The maximum relative augmentation of the thermal conductance is approximately 15 percent. In the second part of the study, an order of magnitude analysis shows that the cycle-averaged thermal conductance can be maximized analytically by considering only the single-phase natural convection effect, and that the optimal time interval when heating is “on” agrees with the experimental results.

Issue Section:
Boiling and Nucleation
Keywords:
Boiling, Natural Convection, Transient & Unsteady Heat Transfer
Topics:
Heat transfer, Heating, Natural convection, Optimization, Pool boiling, Cycles, Thermal conductivity, Boiling, Bubbles, Heat flux, Temperature, Transients (Dynamics), Water
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