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|  ACT maintains an ongoing life test program of aluminum/ammonia constant conductance heat pipes (CCHPs). The purpose of this life test program is to demonstrate that ACT's manufacturing processes result in heat pipe products meeting even the most stringent reliability requirements. The figure below shows a CCHP on a life test stand. The evaporator is heated with an aluminum heater block that has internal cartridge heaters. The adiabatic and condenser sections are not insulated to reject heat to the room by natural convection. The heat pipe is operated at an elevated temperature, 24 hours a day and 365 days a year. Periodically, the life test heat pipe is placed back into a performance test fixture, fully insulated, and operated at very low temperatures to look for signs of non-condensable gas (NCG). At these low temperatures, the vapor pressure of ammonia is extremely low, and any significant NCG would expand and block part of the condenser section. This would show up as a temperature gradient in the condenser section thermocouples. 
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| The figure below shows the thermocouple readings along the condenser section of one of the life test heat pipes during a NCG test at the milestone of 11,000 hours of operation. The heat pipe showed no sign of NCG at -40°C, -50°C, -60°C or -65°C.
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(click graph to enlarge)
Most NCG phenomena occur early in the life of a heat pipe. ACT continues to operate the life test heat pipes at elevated temperatures and periodically perform the NCG test to demonstrate real-time, long life performance. Additional information on ACT's other heat pipe life tests: |
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  Constant Conductance Heat Pipes Variable Conductance Heat Pipes Temperature Calibration and Control Products Contact and Visit ACT Information ISO 9001:2000 and AS 9100-B Certification ACT Brochures and Product Datasheets
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