WE-NET Home Page/Summary of Annual Reports 1998

5.4 Development of devices for common use

5.4.1 R & D Goals

Goals of studies in the Phase I are that to make a conceptual design of devices and equipment necessary for constructing large-scale liquid hydrogen transportation-storage system, and to select technical items to be developed.

A large liquid hydrogen pump is required to supply liquid hydrogen stably for a long time. Liquid hydrogen, which is working fluid, is cryogenic fluid with the temperature of 20K and density of 71kg/m³ and ultra-low viscosity of less than 1.3e-5kg/m^.s. Therefore, shaft bearing for liquid hydrogen pump is exposed to severe lubricating environment. As one of shaft bearing options there is magnetic bearing. In FY1997, prototype magnetic bearing was fabricated and tested. In FY1998, the improved magnetic bearing, in which a inducer is installed to prototype pump in order to improve pump suction characteristics was tested in series. Also a feedthrough for sensors was developed and tested in liquid hydrogen.

5.4.2 Results in FY 1998

5.4.2.1 Modified Points

Specifications and configuration of a new inducer are shown in Fig. 5-4-1. The inducer was installed at the inlet of the pump in order to improve pump suction characteristics.

In addition, the feedthrough was developed for sensor cables, which is shown in Fig. 5-4-2.

A new controller was also fabricated with modification based on the results of the previous year.

5.4.2.2 Tests

The LN₂ and LH₂ tests were carried out by using the modified prototype pump in FY1998. Fig. 5-4-3 shows the test device with the prototype pump.

(1) Magnetic Bearing Test

[Ambient Temperature Test]
A test to obtain characteristic data of magnetic bearing at ambient temperature was conducted and followed by a rotation test.

[LN₂ Test]
Tests to obtain characteristic data of displacement sensor and electromagnet at LN₂ temperature were conduct followed by a rotation test at the same temperature.

[LH₂ Test]
Tests to obtain characteristic data of displacement sensor and electromagnet at LH₂ temperature were conducted and followed by a rotation test at the same temperature.

(2) Feedthrough Test

Fig. 5-4-4 shows the test device for the feedthrough. The transfer function and leakage data were obtained at LH₂ temperature

(3) Test Results

Characteristics of sensor and electromagnet were verified at ambient temperature, LN₂ temperature and LH₂ temperature. It was confirmed that magnet bearing was operative in different temperatures from 20K to ambient temperature. After confirming characteristics of the sensor and the electromagnet, rotation test was planned in order to confirm the bearing performance at the rotation speed up to 36,000rpm.

In LN₂ test (77K), the rotation speed reached 18,000rpm at the highest. At critical speed of round 10,000prm, shaft vibration was less than 30mmp-p. Over critical speed, it was decreased less than 20mmp-p.

In LH₂ test (20K), the rotation speed reached 26,000rpm at the highest. The shaft vibration over critical speed is shown in Fig. 5-4-5. It is less than 20mmp-p at critical speed. Changes of discharge pressure in LH₂ test is shown in Fig. 5-4-6. Discharge pressure of pump increased according to rated speed until it reached around 24,000rpm. At around 26,000rpm, discharge pressure dropped temporarily due to gas suction, but it recovered soon. The inducer could improve suction characteristics.

Over 26,000rpm, the shaft touched the outer case. Test data indicates that coil current also increases with the increment of shaft vibration. The cause of shaft vibration increase is under investigation now.

The pump head - flow rate characteristics was obtained as shown in Fig. 5-4-7. It was found that pump head was about 950m, or 84% of designed head(1,320m).

As for feedthrough, transfer function up to 5kHz were obtained through test at ambient temperature and LH₂ temperature. The transfer functions were good with gain=1 and phase=0°. At He leakage test with 60kgf/cm², the result was less than 1e^-9 atm^.cc/s, which meets requirements.

5.4.2.3 Conclusions

Test results can be summarized as follows:

Installing inducer enabled stable rotation up to 24,000rpm at LH₂ temperature.
Pump performance data were obtained.
Critical speed for the shaft was around 10,000rpm. Over critical speed, vibration value decreased less than 30mmp-p.
The cause of the unstable phenomenon of the shaft at the rotation speed of 26,000rpm is under investigation.
A feedthrough, which was prepared experimentally, was confirmed to meet functional requirements at LH₂ temperature.

5.4.3 Research Plan for Fiscal Year of 1999

Elemental development of liquid hydrogen pumps will be continued in FY 1999. The magnetic bearing device will be modified in order to prevent the shaft vibration and evaluated its performance up to 36,000rpm with liquid hydrogen.