9.3 Application of HTSB Ë 341Fig. 9.10:Experimental testing device for a liquid nitrogen pump with a RSB. (a) Photograph of
testing device. (b) Schematic view of liquid nitrogen pump in testing. (1) DC motor. (2) PM coupling.
(3) RSB. (4) Output tube. (5) Electronic scale and liquid nitrogen vessel. (6) Main body of pump.
(7) Dewar. (8) Liquid nitrogen.
If the flow rate of the pump isQ(L/s), the speed of the liquid nitrogen in the output
tube,v(m/s), is
v=Q
1000
2 휋×^0.^012
2
2 =^8.^84 Q. (9.18)
The head of the pump,Hpump, and the speed of the liquid nitrogen in the output tube
have the following relation:
Hpumpag=^1
2v^2 + 0. 04 ag, (9.19)whereag(=9.8 m/s^2 ) is acceleration of gravity and 0.04 (m) is height difference between
the center line of outlet and surface of liquid nitrogen in the Dewar. The head of the
pump can be calculated as
Hpump=^1
19. 6v^2 + 0. 04 = 3. 987 Q^2 + 0. 04. (9.20)Figure 9.11 and Tab. 9.2 show the flow rate and the head of the liquid nitrogen
pump with the RSB operation at a rotational speed range between 756 rpm and
2245 rpm. It was observed that operation of the pump was stable and that the flow
rate and the head increased with the increasing rotational speeds. During more tests
at 2061 rpm, the pump worked very well for 1200 s without any abnormal vibration or
noise.
There are still some problems that must be solved before commercial application
of the RSB to a cryogenic pump. First, the total efficiency of the pump is not high. At