Question: Fuel oils such as #2 fuel oil may be used in boiler burners to provide energy to the working fluid in the boiler tubes. Due to the high viscosity of the fuel oil, a heater is usually needed in the oil storage tank to warm the oil to facilitate pumping. Heating the oil to at least 150?F will maintain good combustion in the burner. A design engineer wishes to reduce the total power required by the oil storage tank heater. They have devised a system in which hot exhaust gases from the boiler burner will be directed through an 18 in. × 20 in. rectangular ductwork to a heat exchanger for the purposes of providing additional energy to heat the oil. The average flue gas temperature from the burner is on the order of 650?F, and to avoid metal corrosion and proper operation of pollution control equipment, the temperature can never be lower than 480?F. The oil pumping system available to the engineer will fail if the oil temperature is lower than 50?F. Design a heat exchanger that could be used in the engineer's system.
Properties of #2 fuel oil are: Tfreezing = -22?F; Tboiling = 374-689?F; SG = 0.86; ν = 3.66 × 10-5 ft2/s; cp = 0.44 Btu/lb-?F; k = 0.0797 Btu/(h ft ?F).