9.3 Application of HTSB Ë 339pump is employed to speed up the liquid flow rate and enhance the cooling efficiency.
Second, this pump can improve stability of superconducting magnets and increase
the pressure at the inlet to ensure the supercritical helium at the outlet. Moreover,
with this pump the flow rate of liquid helium can be controlled conveniently.
At present, the cryogenic pump usually works with cryogenic mechanical bea-
rings. However, lubricating oil cannot be used in the cryogenic mechanical bearing be-
cause it freezes and would also pollute to the cryogenic liquid. With these limitations,
the cryogenic mechanical bearing has a short service life. In addition, the cryogenic
pump has to be shut down in order to replace the cryogenic mechanical bearing. To
solve this problem, RSB may replace the conventional cryogenic mechanical bearing.
The obvious advantages of this RSB application include no abrasion to affect the
working life and no need for an extra cooling device for the HTS stator of RSB.
9.3.2.1Liquid nitrogen pump with HTSB
Structure of a liquid nitrogen pump with a RSB is shown in Fig. 9.8a. The pump is laid
vertically and contains six components: a motor, a PM coupling, a RSB, a pump body,
a blade wheel, and a radial PM bearing.
The motor is a DC motor with rated voltage of 24 V and rated speed of 1200 rpm.
The PM coupling is made up of upper and lower PMs. Driving torque is transmitted
Fig. 9.8:(a) Schematic diagram of the structure of the liquid nitrogen pump. (b) Photos of PM rotor,
HTS stator and blade wheel. (1) DC motor. (2) PM coupling. (3) Liquid nitrogen. (4) PM rotor. (5) HTS
stator. (6) Blade wheel. (7) Pump body. (8) Outlet of pump. (9) Inlet of pump. (10) Radial PM bearing.