2.3. The available “cold” in the vapour, i.e. the enthalpy increase between boiling point and ambient temperature
at the boil-off pressure, is much larger than the latent heat of evaporation of the liquid, for helium (x 75), and
hydrogen (x 7.9 ); and the same magnitude for oxygen (x 0.9), nitrogen (x 1.2), and methane (x 0.8). Heat inflows
into the stored liquid can be divided into ‘A’ heat inflows, absorbed only by the latent heat of the evaporation loss,
and ‘B’ heat inflows which can be absorbed by the available cold in the boil-off vapour. Thus, to design for
minimum boil-off, all the various A heat inflows into the liquid need to be identified and reduced to zero as far as
possible, or converted into B heat inflows.