The history of ocean thermal energy conversion (OTEC), a process that employs the temperature difference between surface and deep ocean water to alternately evaporate and condense a working fluid, is reviewed. In the open-cycle OTEC configuration, the working fluid is seawater. In the closed-cycle configuration, a working fluid such as propane is used. OTEC is assessed for its practical merits for electric power generation. Because rather large amounts of seawater and working fluid are required, the energy requirements for pumping them may be greater than the energy recovered from the OTEC engine itself. The concept of net power production is discussed. The components of a typical OTEC plant are described with emphasis on the evaporator heat exchanger. Operation of an OTEC electric generating station is discussed, including transient operation. Recent experiments and efforts at the National Energy Laboratory-Hawaii (NELH) are summarized. Remarks are made on bottlenecks and the future of OTEC as an advanced electric generation methodology. >

An assessment of ocean thermal energy conversion as an advanced electric generation methodology

Ocean thermal energy attracted significant attention for its large storage in the ocean. With the increasing exploitation of ocean thermal energy due to the development of technology, several devices were proposed, which can be categorized into the closed cycle, open cycle and hybrid cycle systems. Many researchers have focused on the evaluation of these systems in regard to the economic evaluation, power and efficiency evaluation, function evaluation and environmental impact evaluation. To analyze the performance of such device in the ocean environment, several fluid mechanics problems need to be considered, including steam turbine specific for OTEC system, the wake induced by the long cold water pipe and the turbidity currents on the steep slope. The current work gives a review of these different systems, and presents the power and efficiency calculation formulas. The mechanical applications in the ocean thermal energy conversion (OTEC) system are then discussed.

Review of the applied mechanical problems in ocean thermal energy conversion

Heat transfer - a review of 1975 literature

Ocean thermal energy conversion—A significant solar resource

This paper presents the results of an ongoing analytical study at the Univ. of Mass, for the design of major components and a total power system for Gulf-Stream-based ocean-thermal power of 400 Megawatts electrical net power output. On the basis of these studies, the ultimate power potential of a 15 mile wide by 550 miles long length of the Gulf-Stream extending from south of Miami, Fla. to Charleston, S.C. is estimated to be approximately 2 trillion kilowatt hours per year which could be transmitted to shore by undersea cables. Critical subsystems and components (such as heat exchangers, ocean-based hulls, and cold water inlet pipe) are identified, and the technical basis for their configuration and design is discussed. 90/10 copper-nickel alloy plate-fin heat exchangers, with propane flowing upward (evaporators) or downward (condensers) through small passages in the plates and sea water flowing horizontally between the plates, have been selected. The latest power system (Mark II) is based on a submerged, twin catamaran concrete hull configuration with hulls approximately 80 ft in diameter by 800 ft long. The evaporators are staggered serially in height in 6 tiers placed above the twin hulls which contain the condensers, turbines, pump, and other power cycle components. A cold-water inlet pipe of elliptical cross section (1500 ft long and with a hydraulic diameter of 87 ft) is hinged between the hulls with a gun-buckler type joint. Technical problems facing the deployment of such plants are summarized, and the latest cost estimates predict busbar power costs of approximately 15 mills per kilowatt hour.

J. G. McGowan

Papers

Variations in heat exchanger design for ocean thermal difference power plants