Experimental Studies of Burnout under Boiling : 2nd Report, On the Effects of Subcooling, Tube Diameter and Air Content

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Continued from the 1st Report, this paper deals with the effects of subcooling, tube diameter and air content under the transient boiling caused by step heat input. The experiments were carried out under the condition of a natural circulation of the water under atmospheric pressure. The results obtained are as follows : 1) Until a burnout occurs, the surface temperature of heat generator (nichrome wire) is independent of subcooling, the tube diameter or the air content, and the characteristics of heat transfer are similar to those under steady boiling. 2) The time lag to the burnout caused, which increases with the decreasing of the power input, is proportional to the subcooling or the tube diameter, but it has no relation to the air content. 3) When the value of subcooling, the tube diameter or the power input is large, a burnout is caused by the partial film boiling, while it is caused by the bubble blocking when that value is small. In the case of the subcooling of 0℃, especially, a burnout occurs owing to the film boiling without being affected by the tube diameter. 4) The critical heat flux, which does not cause a burnout, depends on the subcooling or the tube diameter, but it is independent of the air content.
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