OTEC Heat Transfer Experiments at Keahole Point, Hawaii, 1982-1983

This paper presents results of biofouling, corrosion and heat transfer studies on candidate materials for closed cycle OTEC heat exchangers. The work was performed at the Seacoast Test Facility of the Natural Energy Laboratory of Hawaii. The facility was constructed by DOE and the State of Hawaii for the conduct of OTEC-related research. Warm surface water at 24-
28\deg
C and deep ocean water at
9-10\deg
C from a depth of 2000' are pumped through test loops in the facility. Each loop contains a heat transfer monitor and a number of corrosion coupons. Daily measurements of heat transfer resistance due to fouling have been made since mid-1981 and corrosion data for the same period are available for four different aluminum alloys. The main conclusions from the heat transfer studies are
\bullet
there is no measurable biofouling in the cold water after one year of continuous operation,
\bullet
The warm water loops foul to the heat exchanger design limit in 20-40 days, depending on water temperature, distance of intake from shore,
\bullet
the fouling is readily removed by light brushing,
\bullet
the fouling can be inhibited by light chlorination, 65-70 ppb applied for one hour per day, and
\bullet
established fouling films can be removed by chlorination. The main conclusions from the corrosion studies are
\bullet
the aluminum alloys pit in the cold water, not in the warm,
\bullet
alloys 3004 and 5052 show very low corrosion rates in the warm water,
\bullet
the corrosion behavior of aluminum alloys in warm tropical seawater is different from the behavior in temperate zone seawater, and
\bullet
a thin inorganic film forms on the aluminum alloys and lowers the rate of heat transfer somewhat.