The characteristics of heat transfer in a simulated channel for a large superconducting coil have been investigated. Subcooled He I layer on the heated surface exposed to the pressurized superfluid helium (He II
p) expands the non-boiling region beyond the Kapitza region up to
qn, above which nucleate boiling sets in. As the bath temperature decreases, the orientation-independent
qn is increased more rapidly than
qλ, at which the superfluidity is broken at the center of the heated surface. A decrease in the temperature of the coolant in contact with the heated surface has been detected in He II
p as well as in the saturated He II. Enhanced stabilization can be established for superconducting coils by taking
qn into account; the temperature rise at the hot spot on the superconductor may be restrained below 4.5K without bubbling.
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