A hot stream is cooled from 200°C to 60°C in a counterflow exchanger using water that enters at 20°C and leaves at 55°C. The overall coefficient at the warm end of the exchanger is 800 W/m² · °C and at the cold end it is 600 W/m² · °C. The heat flow rate is 1.2 x 10⁶ W. Compare the area required found using Eq. (11.17) with that based on the logarithmic mean temperature difference, Δ̅T̅_L.

Eq. 11.17

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gr = Αγ U, ΔT – U In(U, ΔT/U ΔΥ AT) (11.17)