2.10. The enhanced heat transfer capability by natural convection in a vapour column in a neck tube cannot be
improved by inserting vertical tubes or high conductivity metals into the vapour to change the convective
recirculation. This has been tried many times and results in an increase in boil-off on every occasion. For example,
trying to force the vapour into closer contact with the neck wall, or with a superconducting current lead, via annular
inserts will only result in a significant increase in boil-off.