Question

consider a across flow heat exchanger has an area of 54 m2 The heat capacity of both cold and hot fluid flow is 900 W/K and the overall heat transfer coefficient is 100 W/m2-K find the number of transferred units
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Answer 1

Answer:

The heat transfer coefficient decreases by ˜10% with a threefold increase in the mass flow rate under these conditions, based on the commonly used Dittus-Boelter correlation for estimation of the heat transfer coefficient. ... Doubling the mass flow rate will result in a 92% increase in the heat transfer coefficient.

Explanation:

ΔTm =

1 ΔTm = ...

2 = 94.9 °F. 0.10536.

3 The preliminary area estimate of the heat exchanger can now be calculated as: A = Q / (U x ΔTm) =

4 A = 2, 035, 000 Btu/hr.

5 = 178.7 ft² (120 Btu/h.ft².°F).(94.9°F)

6 The required mass flow rate of water can be calculated from Q = m.Cp. ΔTm: Rearranging:

7 m = Q…… = Cp x ΔTm.

8 m = (2,035,000 Btu/hr)

Answer 2

Answer:

6

Explanation:

NTU= AU/Cmin

=54*100/900= 6