Compare the osmotic power available from freshwater flowing at a rate of $1000 \mathrm {~m} ^ { 3 } / \mathrm { s }$ into the ocean (assuming an efficiency of $40 \%$ ) and the thermal power available from water flowing at $1000 \mathrm {~m} ^ { 3 } / \mathrm { s }$ through a heat exchanger and cooling by $5 ^ { \circ } \mathrm { C }$ (assuming an efficiency of $3 \%$ ).

Question

Quizplus · Accepted Answer

The Answer is For a total osmotic power of 1

ext { MW per } \mathrm { m } ^ { 3 } / \mathrm { s } ext { of flow (at an assumed efficiency of }

40 \%

) the total power is

\left( 10 ^ { 6 } \mathrm { Ws } / \mathrm { m } ^ { 3 } ight) imes \left( 1000 \mathrm {~m} ^ { 3 } / \mathrm { s } ight) = 1.0 imes 10 ^ { 9 } \mathrm {~W}

The thermal power available at an efficiency of

3 \%

(typical of an OTEC facility) is

P = \eta ( d m / d t ) C \Delta T

So

P = ( 0.03 ) imes \left( 1000 \mathrm {~m} ^ { 3 } / \mathrm { s } ight) imes \left( 1000 \mathrm {~kg} / \mathrm { m } ^ { 3 } ight) imes \left( 4180 \mathrm {~J} / \left( \mathrm { kg } \cdot { } ^ { \circ } \mathrm { C } ight) ight) imes \left( 5 ^ { \circ } \mathrm { C } ight) = 0.627 imes 10 ^ { 9 } \mathrm {~W}

Only slightly less than the osmotic power.

Compare the Osmotic Power Available from Freshwater Flowing at a Rate