Lorenzo A.

Hey Everyone, newbie here. I'm aiming way over my head here, but was wondering about something has been bugging me all day. At 70000 feet ( 21km) passed the Armstrong Line fluids start to boil, due to the atmospheric pressure, producing steam and therefore energy. Now, its like -56C° at that altitude and possibly colder in the Mesosphere. Does Liquid Hydrogen create enough energy once it has reached the Boiling point of -252C°? Even though liquid hydrogen has low energy density, and has high specific energy. Could a plane with a fully pressurised cabin, something larger than a U2 jet, be powered by a Liquid Hydrogen steam powered engine/jet propulsion? Without any combustion to boil the Liquid?