Transient helium heat transfer. Phase I - Static coolant

Transient heat-transfer data have been obtained for flat heating surfaces in static liquid and supercritical helium. Measurements start 0.00002 sec after step power inputs and cover a heat flux range of 0.05-20 W/sq cm, pressures from 0.09-0.3 MPa, and four different heater orientations. Initial heat-transfer coefficients, being limited primarily by the Kapitza resistance, are 10-100 times greater than steady state, and the time to reach steady state varies from 0.00001 to 1 sec. For heat flux below the steady state peak nucleate boiling limit, the temperature follows calculations based on pure conduction to the steady state nucleate boiling level. Above that limit, the transient conduction period leads to an apparent metastable nucleation period followed by a transition to film boiling.