What is the maximum percentage of heat at 900 degree C that could be converted i

Question

What is the maximum percentage of heat at 900 degree C that could be converted into electricity if the waste heat was produced as steam at 100 degree C? Electricity could be obtained by exploiting the thermal gradient between the surface and the deep waters of the ocean. The maximum gradient, about 20 degrees, is achieved in tropical waters. What is the maximum percentage of the energy associated with this gradient that could be converted to electricity if the surface (cooling) water temperature is 25 degree C? In order to reach a conversion efficiency of 50%, to what minimum Celsius temperature must a heat source be raised if the3 waste heat has a temperature of 57 degree C?

Explanation / Answer

8-3. Max. percentage converted to electrivity = Heat converted/initial heat = [(273+900)K - (273+100)K]/(273+900)K * 100%= 68.2%

8-4. Cooling temp. = 25 degree C = 298 K, max gradient = 20 degree C, i.e. higher temp. = 45 degree C = 318 K

Hence, max percentage of energy associated with this gradient = Heat converted/initial heat = 318-298/318 * 100
% = 6.29%

8-5. Conversion efficiency = Th-Tc/Th = 50%, Tc = 57 degree C = 330 K

So, heat source need to raised to the temp. of Th i.e. 660 K

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