Being a homogeneous diatomic molecule, hydrogen hydrogen (in its ground
electronic state) has no electric dipole moment. Therefore,
ro-vibrational transitions (ie, those likely to be in the IR), will be
of high order (e.g., electric quadrupole), and therefore weak. Hence, I
would guess that most of the IR would pass straight through the hydrogen
ullage and would be absorbed by the tank walls or by the liquid hydrogen.
On 12/12/2015 12:02 AM, William Claybaugh wrote:
Brian:
As you may know, blowdown systems using self-pressurized Lox have been
used by amateurs for more than half a century (Jim Nudding of the PRS
for hybrids, in the 1950's, as an example). Environmental heat is
sufficient if you size the tank L/D correctly. The Lox will be warm
and you will get lower density in consequence.
Local heating to the surface can provide makeup pressure if you want
constant pressure through the burn.
Hydrogen is tougher using traditional assumptions but I would not do
that: a "cold" radiant heat source at the top of the tank (i.e., IR
LED's) can provide lots of gas while keeping the overall liquid cold;
the obvious trick is in keeping control of the system, for which
modern control systems appear to be more than sufficient: if a four
rotor helicopter is stable enough to be sold as a toy, keeping control
of the local heating and pressurization of a cryogen ought to be in
family.