Liquid Hydrogen Pumps

It is critical that liquid hydrogen pumps are hermetically sealed and leak only very small trace amounts hydrogen to the outside environment. And because liquid hydrogen (LH2) temperatures are typically close to 20 K, it is also critical that heat input is minimized. Barber-Nichols’ LH2 pumps meet both of these critical requirements and more by incorporating the following features:

• No dynamic seals are used and the pump is hermetically sealed to meet the most stringent helium leak rate requirements.
• Anti-convection/radiation heat shields minimize heat input to the cryogenic fluid by disrupting natural convection currents and creating barriers to radiated heat.
• A long, thin-walled pump shaft and an outer vacuum housing minimize heat conduction into the cryogen.
• High-speed operation and the use of variable frequency drives increase hydraulic efficiency and minimizes generated heat.
• Vacuum housings allow pumps to be removed from a system for regular maintenance without breaking the cold box vacuum. This reduces time and preserves the system integrity during routine maintenance.

Cryogenic Fluid Management demands components and systems which are compact, reliable, and introduce minimal heat to the cryogen. Barber-Nichols designed and manufactured the BNHP-08-000 in-line liquid hydrogen pump to support NASA’s Zero Boil Off Program. In-line cryogenic pumps are used to circulate fluid within and between tanks as well as through cryocoolers. Barber-Nichols in-line mounted cryogenic pumps are fully seal welded to ensure no leakage and utilizes a mixed flow impeller and diffuser for increased weight savings and compactness.

Slush hydrogen, a mixture of frozen and liquid hydrogen similar to a “slushie,” is denser than the purely liquid phase and allows more hydrogen mass to be stored in the same space. Barber-Nichols designed and manufactured a slush hydrogen pump to transfer densified liquid hydrogen propellant.

The pump shown at left was used for cryogenic supercritical hydrogen service at Oak Ridge National Laboratory’s Spallation Neutron Source. This pump rotates at speeds up to 60,000 rpm with no contacting parts as the magnetic bearings levitate the shaft. It is made for service at 20 K and pressures up to 20 bar (g).

As part of innovative development on a NASA SBIR, BN designed, produced, and tested a liquid hydrogen pump utilizing composite materials. Composite materials that have extremely low heat transfer coefficients are being used in place of stainless steel on select components, further reducing conductive heat leak. Because the conducted heat transfer is negligible, the pump shaft can be shortened and a shorter pump shaft has greater rotor dynamic stability and can, therefore, operate at higher speeds. As a result, hydraulic efficiency is increased and the heating of the cryogenic fluid is further minimized. Finally, as composite material usage increases, evidence suggests the manufacturing cost benefits will bypass that of stainless steel.