Study of transition to helium film boiling during step-by-step heat load increasing

Transition to helium film boiling during step-by-step heat load increadse has been studied experimentally. The experiments are conducted with the test section of brass foils with the dimensions 65x4x0.05 mm, heated by electric current and heat-insulated from one side, in the range of helium saturation pressure 40-200 kPa at four different orientations of heat- liberating surface in the field of .o.ravitational forces. Experimental results have shown, that with the increase in thermal flow q the value of time tausub(kp) from the moment of thermal loading increase to the moment of film boiling decreases sharply. At that, orientation of heat-liberatin.g surface considerably affects the value tausub(kp). For horizontally oriented sample element its heating side turned upward, the values of tausub(kp) are the highest. With further increase in q the effect of orien-- tation is not observed, and relation of q to tausub(kp) can be described by a simple degree function q=Ctausub(kp)sup(-n), where degree index n for different pressures varies inconsiderably from 0.43 to 0.48. The value of proportionality coefficient C for any pressures of helium saturation can be calculated according to the known value C for atmospheric pressure, using the formula presented