Consider Example 7.7. Determine the heat rate using the \(\varepsilon\)-NTU method. Assume the air flows in a duct of height \(N_{T} S_{T}\) where \(N_{T}=8\) tubes per row and \(S_{T}\) is the transverse tube pitch. The tube length and the duct width are both \(1 \mathrm{~m}\).

The tubes in Example 7.7 were assumed to be isothermal. Now, consider a water mass flow rate of \(10 \mathrm{~kg} / \mathrm{s}\) through the tube bundle. Using the air-side average convection coefficient of the example, determine the overall heat transfer coefficient for the heat exchanger. Evaluate water properties at \(70^{\circ} \mathrm{C}\). Was the assumption of isothermal tubes valid?

Data From Example 7.7:-

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Pressurized water is often available at elevated temperatures and may be used for space heating or industrial process applications. In such cases it is customary to use a tube bundle in which the water is passed through the tubes, while air is passed in cross flow over the tubes. Consider a staggered arrangement for which the tube outside diameter is 16.4 mm