Demonstration of heat switch function of loop heat pipe controlled by electrohydrodynamic conduction pump

Loop heat pipes (LHPs) are attractive devices to cool electronic devices in spacecraft. The LHP operation must be shut down in some cases to avoid considerable reductions in the temperature of such electric devices. A new active technology capable of heat switching is developed for LHPs using an electrohydrodynamic (EHD) conduction pump that operates to facilitate liquid flow in the reverse direction against the normal LHP flow. To demonstrate our proposed approach, an EHD conduction pump with rod - ring electrodes was developed and evaluated to obtain generated pressure with varying applied voltages. The LHP with R134a as a working fluid was shut down successfully when a sufficiently high voltage was applied. The LHP shutdown continued until the EHD conduction pump was turned off. A comparison with a test in which a manually controlled mechanical valve caused the capillary limit showed that the EHD pump worked differently from the valve: the shutdown by the EHD pump involved a reverse flow. The consumed electric power for the EHD pump was 10 - 30 mW for 6 - 8 kV of applied voltage during the LHP shutdown. Furthermore, pressure loss through the EHD pump during normal LHP operation was approximately 0.5 % of the capillary pressure.