Originally Posted by
CX500T
Liquid Hydrogen is kept liquid by keeping it COLD, How cold? Keeping it cold is easier/lighter than keeping it compressed to a pressure where it will have similar energy density. It is practically impossible to compress hydrogen to the density of liquid hydrogen in large quantities in anything light enough to fly. Hence why LH2 is the preffered way to fuel rockets.
Liquid Hydrogen boils at sea level pressure at 20K.
Liquid Hydrogen or Gaseous Hydrogen still has the same size H2. They leak through exactly the same size holes.
Liquid Hydrogen boil off is like LNG boil off. Liquified Natural Gas (LNG) is dropped to -260F in its liquifaction process plants, on shore. It is then moved by ship, long distances. The ships use LNG as boiler fuel. Nothing keeps it cold, other than insulation, once it is in the storage vessels of the ship. As it boils off, the gaseous natural gas is used or is vented. There is nothing to reliquify it, once on board. When more is needed for boiler fuel, they have heat exchangers to use sea water to vaporize the LNG.