Film boiling of liquid nitrogen from porous surfaces with vapor suction: Experimental extensions



Previous work on film boiling of liquid nitrogen on flat horizontal porous surfaces with porous ceramic flow control elements is extended to tubular geometries and to very thin (asbestos paper) flow control members. At no loss in stability it is demonstrated that heat transfer coefficients more than five times greater than those in conventional film boiling can be obtained. An approximate model for a single liquid tongue breaking through the heating section at the critical flow rate is also presented. The upper (complete breakthrough) and lower (local breakthrough) limits on critical flow rate can be obtained theoretically. The experimental points lie between these two limits and, in general, are fairly close to the upper limit.