density is very low, usually below 10 mA=cm
2 . It can be processed by ordinary
solid-state electronic devices. Because the working current is very small (no more
than 2 mA), the input power is very low. The small-signal response of ER fluid is
approximate to the first-order link, and its angular frequency is about 1 kHz. This
value is one order of magnitude higher than the rotation frequency of most electromagnetic devices, including electro-hydraulic servo valves, and avoids the
unique electromagnetic effect of magnetic coils. ER fluid is suitable for pulse width
modulation control, which can reduce energy consumption, simplify design, save
moving parts, reduce wear, and prolong life. However, ER fluids also have some
practical problems. Firstly, the curing strength is not high enough. Usually, the
shear strength is below 5 kPa=mm, so the transfer of moment is limited. Further
improvement of curing strength requires higher electric field strength (e.g., from 2
to 4 kV) or higher free viscosity of fluids. However, high electric field strength
corresponds to large consumption current, and there are some problems both in
terms of safety and economy. If the free viscosity of the fluid is too large, the
surface abrasion of the device will be aggravated, and particle deposition will occur
easily. Therefore, the increase of field strength and free viscosity is limited, and
there is no more room to improve the curing strength of fluids. Secondly, the
temperature stability of ER fluid (especially water-bearing ER fluid) is poor, so the
working temperature is usually limited to a narrow range of 0*80 °C. Although
these defects have limited the application of ER fluid technology, the technology
has made significant progress in the past 20 years, and anhydrous ER fluid is close
to practical use. Electrorheological fluid technology has tremendous application
potential and may represent the future of hydraulic technology.
Today’s hydrodynamic technology is an automation technology including drive,
control, and detection. The process of electro-hydraulic integration that hydraulic
technology combined with microelectronics technology is accelerating. With the
development of electro-hydraulic control technology, it is still possible to make
some evolutionary changes and developments. The most significant progress may
be made in electronic equipment, control strategy, software, and materials.
9.1.2 Elastic O-Ring Sealing Technology
Elastic O-ring has been used for sealing fluid to prevent leakage for more than
70 years. The key technology of this type of sealing ring is discussed, and the
selection, design, protection, and development of sealing technology are emphatically analyzed.
The application of fluid transmission and control mostly needs to solve the
leakage problem. The leakage of fluid system not only wastes energy, reduces
volumetric efficiency and mechanical efficiency, but also affects the static and
dynamic performance of the system. Fluid leakage can cause environmental pollution, which is considered as a public hazard in today’s increasing environmental
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9 High-Temperature and High-Speed Gas Turbine Pump …
2 . It can be processed by ordinary
solid-state electronic devices. Because the working current is very small (no more
than 2 mA), the input power is very low. The small-signal response of ER fluid is
approximate to the first-order link, and its angular frequency is about 1 kHz. This
value is one order of magnitude higher than the rotation frequency of most electromagnetic devices, including electro-hydraulic servo valves, and avoids the
unique electromagnetic effect of magnetic coils. ER fluid is suitable for pulse width
modulation control, which can reduce energy consumption, simplify design, save
moving parts, reduce wear, and prolong life. However, ER fluids also have some
practical problems. Firstly, the curing strength is not high enough. Usually, the
shear strength is below 5 kPa=mm, so the transfer of moment is limited. Further
improvement of curing strength requires higher electric field strength (e.g., from 2
to 4 kV) or higher free viscosity of fluids. However, high electric field strength
corresponds to large consumption current, and there are some problems both in
terms of safety and economy. If the free viscosity of the fluid is too large, the
surface abrasion of the device will be aggravated, and particle deposition will occur
easily. Therefore, the increase of field strength and free viscosity is limited, and
there is no more room to improve the curing strength of fluids. Secondly, the
temperature stability of ER fluid (especially water-bearing ER fluid) is poor, so the
working temperature is usually limited to a narrow range of 0*80 °C. Although
these defects have limited the application of ER fluid technology, the technology
has made significant progress in the past 20 years, and anhydrous ER fluid is close
to practical use. Electrorheological fluid technology has tremendous application
potential and may represent the future of hydraulic technology.
Today’s hydrodynamic technology is an automation technology including drive,
control, and detection. The process of electro-hydraulic integration that hydraulic
technology combined with microelectronics technology is accelerating. With the
development of electro-hydraulic control technology, it is still possible to make
some evolutionary changes and developments. The most significant progress may
be made in electronic equipment, control strategy, software, and materials.
9.1.2 Elastic O-Ring Sealing Technology
Elastic O-ring has been used for sealing fluid to prevent leakage for more than
70 years. The key technology of this type of sealing ring is discussed, and the
selection, design, protection, and development of sealing technology are emphatically analyzed.
The application of fluid transmission and control mostly needs to solve the
leakage problem. The leakage of fluid system not only wastes energy, reduces
volumetric efficiency and mechanical efficiency, but also affects the static and
dynamic performance of the system. Fluid leakage can cause environmental pollution, which is considered as a public hazard in today’s increasing environmental
58
9 High-Temperature and High-Speed Gas Turbine Pump …