Consider a gas-fired boiler in which five coiled thin-walled, copper tubes of 25-mm diameter and 8-m length are submerged in pressurized water at 4.37 bars. The walls of the tubes are polished and may be assumed to be isothermal. Combustion gases enter each of the tubes at a temperature of Tm,i = 700°C and a flow rate of m = 0.08 kg/s, respectively
