Distributions of Void Fraction above a Horizontal Heating Surface in Pool Boiling

抄録

Local void fractions averaged with time were measured above and adjacent to a horizontal heating surface in saturated pool boiling of water at atmospheric pressure. Measurements were performed by the"Probe Method"previously developed by authors. Main results are as follows : (1) Characteristic changes of void fraction distribution occur below a height of 4 mm. (2) An explanation about relationship of mechanism among three boiling regions can be derived. (3) In nucleate boiling, the distribution curves versus height have a peak near the heating surface. However, there is a liquid-rich layer under the peak, and the layer is considered as the region which governs heat transfer. (4) Void fractions over 90% were measured at a height of 0.3∼1.0 mm near the condition of the burn-out point. (5) In transition boiling, liquid is in contact with the heating surface. (6) In our experiment on film boiling, the minimum film thickness is very little.