An energy storage system is proposed to absorb ther- mal energy collected during the day with a solar col- lector and release thermal energy at night to heat a building. The key component of the system is a shell-and-tube heat exchanger with the shell side filled with n-octadecane (see Problem 8.47).

(a) Warm water from the solar collector is delivered to the heat exchanger at Th,i 40°C and m 2 kg/s through the tube bundle consisting of  50 tubes, two tube passes,  and  a  tube  length  per  pass of Lt 2 m. The thin-walled, metal tubes are of diam- eter D 25 mm. Free convection exists within the molten n-octadecane, providing an average heat transfer coefficient of ho 25 W/m2 · K on the out- side of each tube. Determine the volume of n- octadecane that is melted over a 12-h period. If the heat exchanger, increasing the water temperature and solidifying the n-octadecane. Do you expect the heat transfer rate to be the same, greater than, or less than the heat transfer rate in part (a)? Explain your reasoning.