Question

A proposed Ocean Thermal Energy Conversion (OTEC) plant draws heat from the ocean surface at 22°C and rejects heat to the water near the ocean bed at 4°C. What is the highest thermal efficiency the plant could achieve? [4] (b) Consider a system undergoing an adiabatic process from a fixed state 1 to a fixed state 2. Use the Second Law of Thermodynamics to prove that the maximum work is done by the system if the process is reversible. [6] (c) Steam at 20 MPa and 460°C flows at 12 kg/s into an adiabatic turbine and exits at 20 kPa. What is the maximum possible power output of the turbine? What is the temperature of the steam at the exit in that case? [5] (d) Steam at 20 MPa and 460°C flows at 12 kg/s into an adiabatic turbine and exits at 20 kPa and 85% quality. What is the isentropic efficiency of the turbine?

Answer 1

i). The maximum efficiency of otec cycle is same as carnot efficiency.

ii). During reversible adiabatic process work done is maximum because change in entropy of system is zero.

iii) the maximum work which turbine can be delivered is till the steam can be expanded till it becomes saturated liquid.

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