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The Two Phase Flow (TPF) Thermal Control Flight Experiment is an integrated two-phase thermal control system designed to address capillary pumped loop (CPL) component and system performance issues in the microgravity environment of space. The TPF experiment was flown aboard the Space Shuttle Discovery (STS-85) in August 1997 as part of the Technology Applications and Science-01 (TAS-01) mission. Ground and flight tests were performed to demonstrate reliable system start-up from the flooded state and sustained operation under various heat loads and conditions. Use of any of the large evaporator elements as a sacrificial starter pump in conjunction with the capillary vapor flow valve (CVFV) resulted in successful system start-up subsequent to which normal operation was demonstrated for an extended period of time. As expected, start-up from the flooded state with smaller evaporator elements was consistently unsuccessful.

The Two Phase Flow (TPF) Experiment is an integrated two-phase thermal control system designed to address capillary pumped loop component and system performance issues. The Two Phase Flow Experiment was flown aboard the Space Shuttle Discovery (STS-85) from August 7 - 19, 1997 as part of the Technology Applications and Science-01 (TAS-01) mission. The experiment was contained in a Hitchhiker canister and consisted of a capillary pumped loop (CPL), electronics, and associated instrumentation and wiring. The CPL contained four capillary evaporators (two large diameter and two small diameter), two parallel condensers, a two-phase temperature controlled reservoir, liquid and vapor tubing, individual capillary isolators, and a capillary vapor flow valve. The system working fluid was anhydrous ammonia. The system was operated for a total of 176 hours during the mission with 61 test cycles performed.