Concurrent studies of enhanced heat transfer and materials for ocean thermal exchangers. Progress report

Abstract

Aluminum alloys 1100, 3003, 5052, and 6063 were examined for their compatibility with the proposed working fluids for Ocean Thermal Energy Conversion (OTEC), anhydrous ammonia, Freon 22 and propane, and mixtures of these with sea water. Such mixtures would occur if leaks develop in evaporator or condenser heat exchangers. These aluminum alloys are compatible with the anhydrous working fluids. In ammonia-sea water solutions only limited general corrosion is found in 0-30% ammonia, no corrosion in 30-90% ammonia, and "self limiting" pits in 90-100% ammonia so rapid deterioration of the exchangers would not occur. No corrosion was observed in sea water saturated with Freon 22 or propane. No differences in alloy performance were evident in any of these tests so selection can be made on the basis of compatibility with sea water. A review of the available literature indicates that 5052 shows the best performance in surface sea water followed by 1100, 3003 and then 6063 alloy. In deep sea water only 5052 and 1100 alloys appear suitable although more data is required. In both surface and deep sea waters, alcladding offers the best protection against tube perforation; few instances of penetration into the core alloy have been observed for the alclad alloys examined in this stud.y.

The Hydrogen Economy of 2050: OTEC Driven?

“…Corrosion and bio-fouling considerations are influential to the selection process. Studies indicate there are several possible heat exchanger materials and configurations suitable for seawater applications [14][15][16]. Makai has worked many years with major heat exchanger manufacturers to quantify component costs and understand the implications of using heat exchangers in seawater applications.…”