In July 2011 a new heat exchanger test facility has been opened at the Natural Energy Laboratory of Hawaii (NELHA), on the Big Island of Hawaii. The facility, designed and operated by Makai Ocean Engineering, provides the “OTEC Industry” with a tool for the development and testing of candidate OTEC heat exchangers. Heat Exchangers are the single most expensive component of an OTEC plant and thus their cost, longevity and performance are critical for OTEC’s economic success. Knowledge gained from these tests will inform the final design and development of future commercial-scale offshore OTEC plants.
The heat exchanger test facility is a 40′-tall tower that supports up to three different evaporators, three different condensers, 24″ seawater piping, and an accurately instrumented ammonia working fluid piping system with two pumps and pressure vessels. The test facility will allow Makai to measure the performance of evaporators and condensers, as a function of water velocity, temperature difference, and ammonia flow rate.
Ammonia circulates between the two heat exchangers; liquid ammonia boils in the evaporator, expands in a valve or a power generating turbine, and returns to liquid in the condenser before being pumped through the cycle again. This facility has been designed for expansion; Makai plans to add a turbine and generator, providing electrical power to the grid and allowing operations and controls to be perfected.
In addition to evaluating heat exchanger performance, Makai is testing heat exchanger materials for corrosion resistance. In Makai’s laboratory are thousands of aluminum heat
exchanger samples being exposed for long periods (since 2009) to warm and cold seawater flows. A variety of materials, fabrication methods, and operational procedures are being evaluated.
NAVFAC and ONR sponsored the facility. For more information, please visit: http://www.makai.com/e-otec.htm