Alaundry uses a boiler to heat up cold fresh water from 10°c to 65 c at a flow rate of 5kg/sec. the laundry discards used water into the sewer where the water temperature is now 60°c. an engineer decides to install a shell-and-tube heat exchanger to use the discarded water exiting the laundry to preheat the fresh water. the heat exchanger has one shell pass and 6 tube passes. the surface area of the thin walled tubes is 100m2 and the overall heat transfer coefficient for the surface is 1000w/m2.c (a) determine the ntu (number of transfer units) that can be achieved by the new setup. (b) determine what % of the heating is contributed by the heat exchanger and what is contributed by the gas boiler.