Vacuum Housing Cryogenic Pumps
Barber-Nichols Inc. (BNI) was a pioneer in the development of cryogenic pumps for use with vacuum insulated cold boxes. These cryogenic pumps are uniquely suitable for use with extremely cold cryogens such as liquid helium (LHe) and liquid hydrogen. BNI has been designing and manufacturing cryogenic pumps since 1974, and is acutely aware that the preservation of extremely cold cryogenic fluids is a top priority for our customers. Because these fluids are expensive to liquefy, BNI has packed its Vacuum Housing Cryogenic Pumps with features that minimize heat leak.
- Anti-convection/radiation heat shields minimize motor heat leaking into the cryogenic fluid by disrupting natural convection currents and by creating barriers to radiated heat.
- Thin-walled pump shafts and outer vacuum housings minimize conductive motor heat leaking into the cryogenic fluid.
- High-speed operation and the use of variable frequency drives increases hydraulic efficiency and minimizes heat addition.
- Vacuum housings allow pumps to be removed from a system for regular maintenance without breaking the cold box vacuum. This cuts maintenance time and preserves the system integrity during maintenance procedures.
BNI is currently pioneering the next big leap in cryogenic pump technology. Composite materials with extremely low heat transfer coefficients are being used in place of stainless steel, thereby further reducing conductive heat leak and pump shaft length. Pumps with shorter shafts have greater rotordynamic stability and can therefore operate at higher speeds. As a result, hydraulic efficiency is increased and the heating of the cryogenic fluid is minimized. Finally, as composite material usage increases, evidence suggests that the manufacturing cost benefits will bypass that of stainless steel.
Liquid Helium Pump for the Centre Européen de Recherche Nucléaire (CERN):
BNI recently designed and built some of the world's largest LHe pumps. Several of these pumps cool the superconducting toroid magnet system in CERN's ATLAS Detector. Each pump circulates approximately 1.2 kg (2.6 lbs) of LHe per second at 4.5 K. Additionally, the differential pressure is 400 mbar and the hydraulic efficiency is 60%. The ATLAS Detector came to fruition through the collaboration of 1,800 people from 34 different countries and it will help physicists more accurately understand the nature of matter and the forces that shape the universe.
BNI's approach to pump design was uniquely applicable to this project for four primary reasons. First, it is impossible to prevent helium leakage with mechanical seals; therefore, BNI's hermetically designed pumps were the best choice. Next, the thin walled pump shaft, thin walled outer vacuum housing, and anti-convection/radiation heat shields all work together to minimize conductive motor heat leaking into the cryogenic fluid. Third, in order for the pumps to meet the system's high head/flow and efficiency requirements, the pumps were designed to operate at 4,300 rpm. BNI's extensive experience made it possible to select bearings and lubricants that allow these pumps to operate for long periods of time between scheduled maintenance. Finally, the ability to remove the pump from the outer vacuum housing without breaking the cold box seal simplifies scheduled maintenance. The pumps have been successfully tested by CERN and await start-up of the system.
Click Here to read more about CERN's test facility, methodology, and results.