174
5 Thermal Control Technology of Lunar Lander
moving toward the adiabatic section. Then the effective length of the condensation
section decreased with the heat dissipation decreasing, and the heat pipe operating
temperature would no longer reduce further. When the input heat was reduced to a
certain extent, the vapor-control gas interface entered the adiabatic section or even the
evaporating section, and the heat pipe no longer transferred heat to the condensation
section by phase change.
According to rationale of VCHP, the position of the vapor-control gas interface
was also affected by the average temperature of the control gas, i.e., the temperature
change of the gas storage chamber also affected the working temperature of heat
pipe. The relationship between the control gas pressure and temperature could be
treated according to the ideal gas state equation, while the relationship between the
vapor pressure and the temperature of working fluid was exponential, so the position
of the vapor-control gas interface was more sensitive to vapor temperature.
Actually, there was no obvious vapor-control interface in VCHP, but there was a
transition section in the condensation section where the concentrations of two gases in
the transition section gradually change. The length of the vapor-gas transition section
could be calculated based on the gas mass diffusion theory. The actual application
could be verified based on experimental data. The existence of the transition section
resulted in the maximum heat transfer capacity of VCHP smaller than the theoretical
value, and the minimum heat transfer capacity larger than the theoretical value. In
order to minimize the length of transition section and the heat leakage during lunar
night, measures should be taken to reduce heat conduction of heat adiabatic section
and condenser section of VCHP along the length direction.
VCHP was used as heat transfer between instruments and heat dissipation surface
in the Chang’E-3 lunar lander to achieve heat transfer during equipment operation and
block during lunar night. Eight and six variable conductance heat pipes were settled
on +Y and −Y modules respectively, where the evaporation section was connected
with instruments in modules and the condensation section was embedded in the heat
dissipation surface. The configuration of VCHP shall consider gravity assistance
under various landing attitude. The volume of gas tank and control gas should satisfy
heat transfer requirement during instruments operation and block during lunar night.
The shape of a VCHP is show in Fig. 5.12.
When instruments of the Chang’E-3 lunar lander were working in LTO, circumlunar and operation on lunar surface in lunar daytime, the heat of instruments was
transferred to heat dissipation surface and radiated to space to ensure temperature
requirement of instruments. During lunar night, the control gas of VCHP would
“choke” the condensation section and heat in module would no longer be transferred
to heat dissipation surface through the condensation section by phase change, so
the temperature of instruments in modules would meet storage requirement in lunar
night.
The moon-based observatory of the Chang’E-3 lunar lander used heat pipe with
special fluid to achieve heat transfer during operation and insulation during lunar
night. The freezing point of the fluid was −40.19 °C. The temperature in lunar
daytime was higher than the freezing point, and the fluid was in the two-phase state.
The heat pipe transferred the heat from instruments to heat dissipation surface when
5 Thermal Control Technology of Lunar Lander
moving toward the adiabatic section. Then the effective length of the condensation
section decreased with the heat dissipation decreasing, and the heat pipe operating
temperature would no longer reduce further. When the input heat was reduced to a
certain extent, the vapor-control gas interface entered the adiabatic section or even the
evaporating section, and the heat pipe no longer transferred heat to the condensation
section by phase change.
According to rationale of VCHP, the position of the vapor-control gas interface
was also affected by the average temperature of the control gas, i.e., the temperature
change of the gas storage chamber also affected the working temperature of heat
pipe. The relationship between the control gas pressure and temperature could be
treated according to the ideal gas state equation, while the relationship between the
vapor pressure and the temperature of working fluid was exponential, so the position
of the vapor-control gas interface was more sensitive to vapor temperature.
Actually, there was no obvious vapor-control interface in VCHP, but there was a
transition section in the condensation section where the concentrations of two gases in
the transition section gradually change. The length of the vapor-gas transition section
could be calculated based on the gas mass diffusion theory. The actual application
could be verified based on experimental data. The existence of the transition section
resulted in the maximum heat transfer capacity of VCHP smaller than the theoretical
value, and the minimum heat transfer capacity larger than the theoretical value. In
order to minimize the length of transition section and the heat leakage during lunar
night, measures should be taken to reduce heat conduction of heat adiabatic section
and condenser section of VCHP along the length direction.
VCHP was used as heat transfer between instruments and heat dissipation surface
in the Chang’E-3 lunar lander to achieve heat transfer during equipment operation and
block during lunar night. Eight and six variable conductance heat pipes were settled
on +Y and −Y modules respectively, where the evaporation section was connected
with instruments in modules and the condensation section was embedded in the heat
dissipation surface. The configuration of VCHP shall consider gravity assistance
under various landing attitude. The volume of gas tank and control gas should satisfy
heat transfer requirement during instruments operation and block during lunar night.
The shape of a VCHP is show in Fig. 5.12.
When instruments of the Chang’E-3 lunar lander were working in LTO, circumlunar and operation on lunar surface in lunar daytime, the heat of instruments was
transferred to heat dissipation surface and radiated to space to ensure temperature
requirement of instruments. During lunar night, the control gas of VCHP would
“choke” the condensation section and heat in module would no longer be transferred
to heat dissipation surface through the condensation section by phase change, so
the temperature of instruments in modules would meet storage requirement in lunar
night.
The moon-based observatory of the Chang’E-3 lunar lander used heat pipe with
special fluid to achieve heat transfer during operation and insulation during lunar
night. The freezing point of the fluid was −40.19 °C. The temperature in lunar
daytime was higher than the freezing point, and the fluid was in the two-phase state.
The heat pipe transferred the heat from instruments to heat dissipation surface when