Colmac Coil Manufacturing, Colville, Wash., has introduced a Shell and Helix heat exchanger designed for ammonia/CO2 cascade refrigeration systems.

The patent-pending heat exchanger offers all-stainless steel construction “for corrosion resistance and long life” as well as a compact design for “large heat transfer surface in small volume,” the company said in a statement, adding that it is cost effective compared to other heat exchangers in the market.

In addition, the heat exchanger’s “multiple helix design” allows expansion and contraction of tubes during large changes in temperature and pressure, “with very low resulting strain and stress, reducing the risk of failure and leaks,” Comac said. This addresses a major concern about ammonia/CO2 heat exhangers — that the ammonia and CO2 would come in contact with each other, forming system-clogging ammonium carbamate.

Other features include:

  • High tubeside (CO2) pressure capability, up to 1,700 psig (119 bar).
  • Nesting of the multiple helically formed tubes in both radial and axial directions, which results in equal spacing of the tubing and uniform flow distribution on the shell side.
  • Multiple shell-side connections, which allow reversing the flow of the ammonia and CO2 for reverse-cycle hot-gas defrosting.

Colmac also markets a low-charge-ammonia ADX (advanced direct expansion) system, which has been installed in multiple U.S. locations.

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