Forced Convection Heat Transfer in Superfluid Helium at Pressures up to Supercritical

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Major Results of this study are as follows.Critical Heat Fluxes (CHFs) in He II under subcritical and supercritical pressures are higher for higher flow velocity and lower liquid temperature. Under supercritical pressures, there exists a heat transfer region similar to film boiling for the heat flux higher than the CHF.In He I under supercritical pressures, the heat transfer curve for lower heat flux range has a steeper gradient and the curve for higher heat flux has a lower gradient. The peak heat fluxes of the former curves are treated as the pseudo-critical heat fluxes in this study. The pseudo-CHFs for T_<in>=2.2 K at 2.3 atm and 2.8 atm are nearly the same for each flow velocity and are about 2.2 times of those for the same temperature liquid at 2.0 atm. At the flow velocity of 2.1 m/s, they reach the value for He II under supercritical pressure (2.0 K, 2.8 atm). The pseudo-CHFs become significantly lower with the increase in T_<in>.CHFs in He I under subcritical pressures are significantly dependent on pressure in the low flow velocity range : they are lower for higher pressures. The CHFs increase with the increase in flow velocity in such a way that the pressure dependence becoming smaller. The pressure dependence is almost negligible for the flow velocities higher than 1.2 m/s.