Using the data of Example 9.1, calculate the surface area required to effect the given duty using a multipass heat exchanger in which the cold water makes two passes through the tubes and the hot water makes a single pass through the shell.
As in Example 9.1, the heat load = 1672 kW
With reference to Figure 9.71: T_{1} = 360 K, T_{2} = 340 K
and hence: X={\frac{\theta_{2}-\theta_{1}}{T_{1}-\theta_{1}}}={\frac{316-300}{360-300}}=0.267
and: Y={\frac{T_{1}-T_{2}}{\theta_{2}-\theta_{1}}}={\frac{360-340}{316-300}}=1.25
from Figure 9.58: F = 0.97
and hence: F\theta _{m} = (41.9 x 0.97) = 40.6 K
The heat transfer area is then: A={\frac{1672}{2\times40.6}} = \underline{\underline{20.6\ m^{2}}}