On the low limit of subcooled film boiling.

An experimental study has been conducted to investigate the low limit of film boiling in subcooled water. Test specimens selected for the present experiments were a silver cylinder (20mm in diameter and 70mm long) and a silver sphere (30mm in diameter), whose heat transfer surfaces were coated with a thin refractory paint. The heated specimen was plunged into the subcooled water under atmospheric pressure. The subcooling was varied from 0 to 85 K, and the coating thickness ranges between 0 and 29μm. In the uncoated cylinder the minimum film boiling temperature Tmin and heat effect of subcooling on Tmin while the qmin increased with higher subcooling. The paint coating produced a much greater enhancement in T for the subcooled boiling than that for the saturated boiling.