Experimental Studies of Burnout under Boiling : 1 st Report, Transient Phenomena to Meltdown

Abstract

This paper deals with the burnout and meltdown caused by step-input to a fine nichrome wire (0.2 mm diameter) which is vertically supported at the center of a glass pipe (annulus) and cooled by natural circulation of water of 80°C subcooling at atmospheric pressure. The results obtained are as follows : (1) For the transient nucleate boiling which exists between the beginning of boiling and the burnout point, the correlation between the heat flux and the superheating of surface temperature shows the same tendency as obtained in the results by Nukiyama or McAdams, even if the heat flux is higher than the burnout critical heat flux. (2) The time interval until the burnout occurs is given by the following equation : τ_B=C (q/10⁶)^-1.7 sec where C is a constant, which is dependent on the pipe diameter, and q is the heat flux (kcal/m²hr). (3) The burnout critical heat flux, namely, maximum heat flux which does not cause the burnout is 5.3×10⁵, 8.2×10⁵, 1.33×10⁶, 2.4×10⁶, and 2.4×10⁶ kcal/m²hr, respectively, in the cases of 2, 3, 4, 6 and 8 mm of pipe diameter. (4) There are four different types of change in the temperature of a nichrome wire, until it is melted down after the burnout point.