Improved designs have been conceived for lightweight tubes that can withstand the large (as much as 8 or 9 volume percent) freeze/thaw expansions and contractions of typical heat-transfer fluids like water and ammonia. Intended originally for radiators for rejecting waste heat from spacecraft, these designs may also be suitable for such terrestrial applications as freeze-tolerant water pipes in houses and sprinkler systems. Typical prior freeze-tolerant-tube designs are characterized by short operating lives because they rely on compressible polymeric inserts that are degraded by permeability and by embrittlement at low temperatures. The improved designs call for thin tube walls with noncircular (typically oval) cross sections and solid or hollow metal inserts of various shapes, all selected together to obtain specific combinations of limited volume expansion and mechanical advantage such that the stresses in the tube walls remain sufficiently low under all anticipated freeze/thaw conditions.
This work was done by Robert J. Copeland and Mark M. Weislogel of TDA Research for Johnson Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Mechanics category.