340 Ë 9 HTS Maglev bearing and flywheel energy storage system
Fig. 9.9:(a) Blade wheel. (b) Blade wheel inside the pumping chamber of pump body. (1) Shape
of blades inside the blade wheel. (2) Inlet of blade wheel. (3) Outlet of pump. (4) Blade wheel.
(5) Pump body.
from the upper PM to the lower PM by magnetic forces. Due to non-contact between
the upper and lower PMs, heat leakage can be reduced as much as possible. The RSB
shown in Fig. 9.8 is installed in the middle of the pump. The HTS stator includes six
pieces of HTS bulks and each bulk has the dimension of 13× 32 ×64 mm while the PM
rotor has a diameter of 52 mm and a length of 66 mm (Fig. 9.8b). The working gap of
RSB is 1.5 mm. As discussed in Fig. 9.4, the maximum decrease of the axial stiffness
of the RSB at different speeds is less than 8%. This is the minimum requirement for
the application of the RSB to liquid nitrogen pump. The blade wheel with six blades is
made of plastic, with a diameter of 65 mm and a blade discharge angle훼of about 40°
(Fig. 9.9a). This type of blade is called a back curved blade, which can reduce the flow
loss and increase the efficiency of the pump. Fig. 9.9b shows the blade wheel placed
inside the pumping chamber of the pump body. It is clear that the section of channel
between the blade wheel and pumping chamber is variable. The radial PM bearing
enforces the radial stiffness and stability of the rotor during the operation of the pump.
9.3.2.2Operation of liquid nitrogen pump
Figure 9.10 shows the testing device for the liquid nitrogen pump with a RSB, which
is used to test the flow rate and head of the pump at different rotational speeds. The
testing device includes the liquid nitrogen pump with a RSB, a Dewar, a DC power
supply, a non-contact tachometer, an electronic scale, and a liquid nitrogen vessel.
When the DC motor is operated, liquid nitrogen is pumped from the Dewar into the
liquid nitrogen vessel. The speed of the pump is controlled by the DC voltage of
the motor and measured with the tachometer. Flow of the pump is determined by
measuring the mass of liquid nitrogen pumped into the vessel during one minute.
The head of the pump means the increase of potential energy of 1 kg liquid nitrogen
pumped from the output tube. In Fig. 9.10b, the inner diameter of output tube is 12 mm,
and the height difference of center line of outlet and surface of liquid nitrogen in the
Dewar is 40 mm.