The effect of reduced gravity on cryogenic nitrogen boiling and pipe chilldown

It takes longer and more liquid nitrogen to cool down a pipe of cryogenic propellant in reduced gravity conditions. The finding, from a team led by Jacob Chung at the University of Florida, USA, should help in the design of future space explorations that rely on cryogenic propulsion systems like liquid hydrogen or liquid oxygen. Chung and colleagues studied cryogenic chilldown aboard a C9 aircraft flying parabolic trajectories to simulate reduced gravity. They delivered liquid nitrogen through a short, narrow, stainless steel pipe at various flow rates and pressures. The researchers found that heat transfer efficiency was reduced by around 25% in reduced gravity, but could be enhanced by increasing the flow rate. This can be explained by the absence of buoyancy force in reduced gravity, leaving forced convection to propagate the heat transfer process.