Recent advances in the field of boiling heat transfer under natural convection (pool boiling and boiling in confined channels) for helium-I are reviewed. The published experimental data are compared with some of the proposed correlations. It would appear that the data of nucleate boiling are widely scattered, whereas the film boiling regime can be predicted successfully. The works on channel boiling mostly deal with critical heat flux to establish its empirical correlation.
Heat analysis of a wide aperture liquid helium dewar is described. Radiant heat input from the top surface has been calculated accurately as far as possible. Absorption and reflection at the inner wall are treated by introducing a new concept of “effective solid angle”. Heat exchange between the cold evaporating gas and the dewar wall has been calculated as “apparent solid conduction” to the liquid surface. This factor is determined from the balance of the heat inputs to the liquid column and to the vapor column. In order to estimate the radiant heat input from the top surface, evaporating rates of two dewars were analyzed. The inner wall of the first one was polished by #400 emery. The second dewar was painted with aquadag. Furthermore, in order to estimate “apparent solid conduction”, various heater powers have been supplied in the liquid helium. The results suggest: 1) In the wide aperture liquid helium dewar, the radiant heat input from the top surface is the largest factor and can be calculated using “effective solid angle” which is function of dewar dimensions, liquid level and reflectivity of inner wall. 2) “Apparent solid conduction” is zero when the radiant heat input from the top surface is the largest one. 3) If the inner wall of the dewar is painted with aquadag, the radiant heat input from the top surface is reduced and “apparent solid conduction” becomes the largest factor.