Void Fraction Measurements During Saturated Pool Boiling of Water on Partially Wetted Vertical Surfaces

Void fraction profiles adjacent to a vertical wall 6.3 cm wide and 10.3 cm high were measured during nucleate boiling. The experiments were conducted in saturated water at 1 atm pressure. In the experiments, the wettability of the surface was varied by controlling the degree of oxidation of the surface. Static contact angle was used as an indicator of the surface wettability. The void fraction was measured with a gamma densitometer. The experimental results show that the maximum void fraction occurs about 1–1.5 mm away from the heater surface. The wall void fraction, the maximum void fraction, and the thickness of the void layer increase with wall heat flux. It is found that for a given heat flux, the wall void fraction increases as the surface becomes less wettable, whereas the maximum heat flux decreases with increase in contact angle.