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Question

The hot gases enters a parallel flow heat exchanger at 425oC and leaves at 260oC, heating 25kg/s of water from 32oC to 82oC. For a surface area of 370m2, what is the overall heat transfer coefficient in (W/m2K)

A
521.4
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B
13.03
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C
52.14
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D
26.07
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Solution

The correct option is C 52.14

Heat transfered by the heat exchanger = Heat gained by the cold water

UA(LMTD)=˙mcCpc(ΔT)e

U=˙mCp(ΔT)A(LMTD)

LMTD=(ΔT)i(ΔT)eln((ΔT)i(ΔT)e)

From equation (1)

U=25×4200(8232)370×(393178)ln(393178)

U=52.27W/m2K

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