Needs for forced cooling instead of conventional bath cooling are increasing in the field of large superconducting apparatus for power transmission and generation, high energy physics, and fusion reactors. This paper surveys forced convection heat transfer to subcritical (including boiling two-phase flow) and supercritical helium. Comparisons of the data, conclusive results, and future problems to be investigated are described.
A method for making free a multi-layer toroidal field coil from bending moment is studied by appling File's theory to each winding layer. The theory seems to be valid for a line conductor in a toroidal magnetic field or for an ideal one-layer toroidal field coil. According to the present method, the shape of the multi-layer toroidal field coil is satisfactorily decided so that each winding layer is in pure tension or is not subject to any bending moment. The winding thickness of the resultant coil does not become uniform along the winding. The successive layers are no longer in contact leaving some empty space, and the tension on a conductor varies in magnitude from layer to layer. A practical toroidal field coil with a total ampère-turn of 18.8 MAT, a vertical bore of 1.51m, and a horizontal bore of 1.07m has deen designed by this method.
We designed a calorimeter for the liquid helium and constructed it. The calorimeter has a needle valve assembly which operates at the liquid helium temperature. The needle valve assembly enables one to seal the sample cavity and evacuate the filling tube. This excludes next troubles; the large heat leak due to the superfluid film flow, the change of the 3He mole fraction and the amount of the sample during the experiment. When this calorimeter is isolated thermally, it can be kept at extremely constant temperature by controlling the temperature of the surrounding liquid helium bath. The drift rate of temperature was less than 1.7×10-6K/hour. It corresponds to the heat leak of 0.5erg/min. This temperature stability and our temperature resolution. 1×10-7K, enable one to perform heat capacity measurements very near Tλ (superfluid transition temperature), 3×10-6K_??_|T-Tλ|<10-2K. The drift rates of resistivity at Tλ were also examined on a carbon thermometer (Allen-Bradley 1/8W 47Ω) and a germanium thermometer (Scientific Instruments model NI). The indication of a germanium thermometer was found to be constant within experimental errors, but that of a carbon thermometer varied markedly. After cooling a carbon thermometer and keeping it at Tλ±0.1K for 40 hours, the drift rate of its indication was reduced to about 6×10-6K/hour.