In an attempt to reduce cost, a solar designer has proposed replacing the shell-and-tube heat exchanger in Figure 7.27 with a tube coil immersed in the storage tank. The shelland-tube heat exchanger originally specified had a surface area of 10 m2 and a U value of 2000 W/m2 K to be used with a 100 m2 solar collector. Using Equation 7.66 to estimate the U value of the submerged coil, how much length of 0.5 in. (1.27 cm) diameter copper pipe would be needed to achieve the same value of UA product as the shell-and-tube heat exchanger? What percentage of the storage tank volume would be consumed by this coil if 50 kg of water is used per square meter of collector? Use a storage water temperature of 60°C and a collector water outlet temperature of 70°C for the calculations.
