"Heat-switch technology that can switch between daytime heat dissipation and nighttime insulation is essential for long-term lunar exploration," said lead researcher Masahito Nishikawara. "During the day, the lunar rover is active, and the electronic equipment generates heat.
Since there is no air in space, the heat generated by the electronics must be actively cooled and dissipated. On the other hand, during extremely cold nights, electronics must be insulated from the outside environment so that they don"t get too cold."
Current devices often use heaters or passive valves attached to loop heat pipes for nighttime insulation. However, heaters are costly, and passive valves can increase the velocity of fluid flow, leading to a drop in pressure that affects heat transfer efficiency. Nishikawara"s team has developed a technology that offers a middle ground. With a lower pressure drop than passive valves and lower power consumption than heaters, it retains heat at night without compromising daytime cooling performance.
The thermal control device combines a loop heat pipe (LHP) with an electrohydrodynamic (EHD) pump. During the day, the EHD pump is inactive, allowing the LHP to function normally. In lunar rovers, the LHP uses a refrigerant that cycles between vapor and liquid states.
When the device heats up, the liquid refrigerant in the evaporator vaporizes, releasing heat through the rover"s radiator. The vapor then condenses back into liquid, which returns to the evaporator to absorb heat again, driven by capillary forces in the evaporator.
At night, the EHD pump applies pressure opposite to the LHP flow, stopping the movement of the refrigerant. Electronics are insulated from the cold night environment with minimal electricity use. The team's research included selecting the EHD pump"s electrode shape, device design, performance evaluation, and a demonstration test to stop LHP operation with the EHD pump. The results showed almost zero power consumption at night.
"This important approach not only ensures the rover's survival in extreme temperatures but also minimizes energy expenditure, a critical consideration in the resource-constrained lunar environment," Nishikawara said. "It lays the foundation for potential integration into future lunar missions, contributing to the realization of sustained lunar exploration efforts."
The technology has broader applications in spacecraft thermal management. Integrating EHD technology into thermal fluid control systems could improve heat transfer efficiency and mitigate operational challenges, playing a key role in space exploration.
The development of this heat-switch device marks an important milestone in technology for long-term lunar missions and other space exploration endeavors. Future lunar rovers and spacecraft will be better equipped to operate in the extreme environments of space.
Research Report:Demonstration of heat switch function of loop heat pipe controlled by electrohydrodynamic conduction pump
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