5.6 Testing and Verification
191
was Earth gravitation (average gravitational acceleration 9.81 m/s
2 ) in ground tests.
The lunar gravity was about 1/6 of the Earth. The flow resistance of the two-phase
fluid loop was not only related to flow velocity, but also related to flow pattern
of the fluid during operation of the two-phase fluid loop. Compared to 1 g Earth
gravity, there were differences under 1/6 g lunar gravity in weakened or elimination
of the asymmetrical and stratified flow caused by the density difference in two-phase
flow, mechanism of flow pattern generation and transformation, phase distribution,
pressure drop and heat transfer characteristics. It was difficult to simulate a stable 1/6 g
gravity condition on Earth. The difficulty in ground tests of the two-phase fluid loop
was to equivalently simulate the driving force and resistance under lunar gravity.
There were little flow characteristics and empirical parameters of two-phase flow
under different gravity conditions for reference in China or other countries. When
the two-phase fluid loop was developed, envelop processing methods were generally
used. Ground tests conditions should consider various influencing factors and cover
the worst combination of driving force and flow resistance that might occur on lunar
surface, i.e., the most unfavorable conditions for heat transfer should be covered.
The rationale of ground simulation method for driving force was that the driving
force in all operation conditions of ground tests should not be greater than the actual
driving force on lunar surface so as to ensure that the ground verification was not
under-tested. Nevertheless, the over-conservative simulation of driving force that
might cause failure of ground tests should be avoided. The diagram of driving force
simulation of the two-phase fluid loop with consideration of difference and change
of the liquid level is shown in Fig. 5.20, where the cross-sectional area of fluid tank
was 6 times of actual tank and reference height was 1/6 of actual reference height on
lunar surface [17].
3. Status of Test Article
The actual resistance of the two-phase fluid loop was related to the length of each
part of the pipeline, the number of joints, the bending form, and etc. According to
the ground simulation method of driving force and resistance, the ground test article
was inconsistent with the design status besides adjustment of fluid tank and reference
height with increasing adaptive bend.
The start-up operation characteristics of the two-phase fluid loop were related
to the heat capacity and contact method of the heat source. The heat capacity and
installation method of the heat source in ground tests should be the same as the
actual heat source. There might be obvious temperature oscillation in the two-phase
heat transfer. Therefore, more temperature measurement points with high sampling
frequency should be arranged at the possible interfaces such as the condenser. The
heat transfer capability under different working temperatures should be examined
in tests. The electric heating mode should be adopted to conveniently control the
temperature of condensing plates. A set of test curves for heat transfer capability
of the two-phase fluid loop of the Chang’E-3 lunar lander at −50 °C is shown in
Fig. 5.21 [17].
191
was Earth gravitation (average gravitational acceleration 9.81 m/s
2 ) in ground tests.
The lunar gravity was about 1/6 of the Earth. The flow resistance of the two-phase
fluid loop was not only related to flow velocity, but also related to flow pattern
of the fluid during operation of the two-phase fluid loop. Compared to 1 g Earth
gravity, there were differences under 1/6 g lunar gravity in weakened or elimination
of the asymmetrical and stratified flow caused by the density difference in two-phase
flow, mechanism of flow pattern generation and transformation, phase distribution,
pressure drop and heat transfer characteristics. It was difficult to simulate a stable 1/6 g
gravity condition on Earth. The difficulty in ground tests of the two-phase fluid loop
was to equivalently simulate the driving force and resistance under lunar gravity.
There were little flow characteristics and empirical parameters of two-phase flow
under different gravity conditions for reference in China or other countries. When
the two-phase fluid loop was developed, envelop processing methods were generally
used. Ground tests conditions should consider various influencing factors and cover
the worst combination of driving force and flow resistance that might occur on lunar
surface, i.e., the most unfavorable conditions for heat transfer should be covered.
The rationale of ground simulation method for driving force was that the driving
force in all operation conditions of ground tests should not be greater than the actual
driving force on lunar surface so as to ensure that the ground verification was not
under-tested. Nevertheless, the over-conservative simulation of driving force that
might cause failure of ground tests should be avoided. The diagram of driving force
simulation of the two-phase fluid loop with consideration of difference and change
of the liquid level is shown in Fig. 5.20, where the cross-sectional area of fluid tank
was 6 times of actual tank and reference height was 1/6 of actual reference height on
lunar surface [17].
3. Status of Test Article
The actual resistance of the two-phase fluid loop was related to the length of each
part of the pipeline, the number of joints, the bending form, and etc. According to
the ground simulation method of driving force and resistance, the ground test article
was inconsistent with the design status besides adjustment of fluid tank and reference
height with increasing adaptive bend.
The start-up operation characteristics of the two-phase fluid loop were related
to the heat capacity and contact method of the heat source. The heat capacity and
installation method of the heat source in ground tests should be the same as the
actual heat source. There might be obvious temperature oscillation in the two-phase
heat transfer. Therefore, more temperature measurement points with high sampling
frequency should be arranged at the possible interfaces such as the condenser. The
heat transfer capability under different working temperatures should be examined
in tests. The electric heating mode should be adopted to conveniently control the
temperature of condensing plates. A set of test curves for heat transfer capability
of the two-phase fluid loop of the Chang’E-3 lunar lander at −50 °C is shown in
Fig. 5.21 [17].