Two documents discuss improvements in traps for removing noncondensable gases (e.g., air) from heat-transfer liquids (e.g., water) in spacecraft cooling systems. Noncondensable gases must be removed because they can interfere with operation. A typical trap includes a cylindrical hydrophobic membrane inside a cylindrical hydrophilic membrane, all surrounded by an outer cylindrical impermeable shell. The input mixture of gas bubbles and liquid flows into the annular volume between the membranes. Bubbles pass into the central hollow of the hydrophobic membrane and are vented. The liquid flows outward through the hydrophilic membrane and is recirculated. The proposed improvements include the following:
- The outer membrane would be made of a more hydrophilic, commercially available material so that membrane pores could be made smaller without increasing the pressure drop. Decreasing the pore size would increase the bubble pressure, thereby increasing the degree of retention of bubbles in the trap.
- Multiple hydrophobic membranes would be used to increase venting area at the downstream end, where bubbles tend to collect.
- Upstream of the venting area, the hydrophobic membranes would be coated with a dense polymer to reduce evaporation of the coolant liquid.