Open-cycle OTEC In Ocean Thermodynamics

What Is Open-cycle OTEC?

Open-cycle OTEC is an ocean thermal energy conversion process that uses seawater itself as the working fluid. Warm surface water enters a low-pressure chamber, where part of it evaporates into steam, and cold deep water condenses that steam after it passes through a turbine. The heat-engine limit is eta_max = 1 – T_cold/T_hot.

In real systems, the steam pressure is very low, so turbines, condensers, and ducts must handle large vapor volumes. The condensed vapor is fresh water because salts remain in the source seawater. Used in devices include offshore power platforms, vacuum desalination units, and island microgrid water-energy plants.

The concept matters because it links renewable power production with desalination in one thermodynamic cycle. In marine heat-engine design, open-cycle OTEC trades compact machinery for direct fresh-water output. Its performance depends on temperature difference, vacuum integrity, pumping load, heat exchanger cleanliness, and control of noncondensable gases.

Operators monitor chamber pressure, vapor quality, condenser temperature, and fresh-water conductivity. Those measurements show whether the vacuum system, demister, turbine inlet, and condenser are maintaining clean separation between seawater, vapor, and distilled output.

Example:
An island facility can use warm seawater and cold deep water to generate electricity while producing distilled water from condensed vapor.

Related Terms:

• Flash Evaporation
• Latent Heat Of Condensation
• Carnot Efficiency