Boiling Heat Transfer from a Small Heating Element

Boiling heat transfer from a small-scale heating element on a glass plate has been investigated using various sizes of elements (0.02 mm sq. to 5 mm sq.) in R 113 and FX 3250. It was shown that, with the decrease of the element size, the heat flux increases, with only one nucleation site for smaller sized elements, in which case significant temperature fluctuations occurred due to bubble growth and departure. Heat conduction in the substrate was analyzed numerically. The increasing effect of the heat conduction for smaller heating elements, and the effective surface heat-transfer coefficient and heat flux were estimated. The surface heat-transfer coefficient deviates from a conventional correlation when the size of the element is smaller than the bubble diameter.