An Ocean Thermal Energy Conversion (OTEC) system is proposed to generate 10 MW o

Question

An Ocean Thermal Energy Conversion (OTEC) system is proposed to generate 10 MW of electricity. The proposed location of the plant has an ocean surface temperature of 25 C and the cold water for the plant comes from 1000 m at a temperature of 5 C. If the actual efficiency of the plant is estimated to be 50% of the Carnot efficiency, determine the rate of thermal energy supplied to the plant by the ocean surface water. If the thermal energy supplied to the plant is obtained by pumping the surface ocean water through a heat exchanger where the temperature of the surface water drop by 5 C, determine the flow rate of surface water through the heat exchanger. If the heat exchanger has an overall heat transfer coefficient of 6000 W/m^2 K, estimate the heat transfer area of the heat exchanger. Assume that the ocean water has the same density and specific heat as those of typical water.

Explanation / Answer

Carnot eff = (Th-Tc)/Th = (25-5)/(273+25) = 0.067 or 6.7 %

Actual eff = 0.5*0.067 = 0.033 or 3.3 %

Actual Eff = Power/heat input

Heat input = 10/0.033 = 298 MW

mCp(dT) = 298*10^6

m*4184*(5) = 298*10^6

m = 14244.7 kg/s

Q = hA(dT)

298*10^6 = 6000*A*5

Area A = 9933.33 m^2

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