A barge-mounted, ocean thermal energy conversion (OTEC) power station is being t

Question

A barge-mounted, ocean thermal energy conversion (OTEC) power station is being tested off the island of Hawaii. The 50 kWturbogenerator runs on a closed ammonia cycle. This uses the temperature difference between warm surface water (27?C), which is cooled just a fraction of a degree in the exchanger, and cold bottom water, which is heated from 6?C to 7?C on the exchanger surface. If the operation is only 10% as effective as a Carnot cycle between these temperatures (that is, between 6-7?C and 27?C), find the needed pumping rate of cold water up from the ocean bottom.

Explanation / Answer

efficiency of the carnot cycle = 1- T2/T1

= 1 - (6 + 273)/(27+273) = 0.07

so efficewincy of ammonia cycle = 0.1 x0.07 = 0.007

Now efficeincy = Wnet/Q

so, 0.007 = 50/Q

so, heat taken up = 50/0.007 = 7142.85 KW

so heat rejected = Q2 = Q - W = 7142.85 - 50 = 7092.85 KW

so, m.Cp.dT = 7092.85

so, m x 4.18 x (7 - 6) = 7092.85

so, mass flow rate = m = 1696.855 kg/s

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