Question: A parallel flow heat exchanger has its tubes of 5 cm internal and 6 cm external diameter. The air flows inside the tubes and receives heat from hot gases circulated in the annular space of the tube at the rate of 100 kW. Inside and outside heat transfer coefficients are 250 W/ m2K and 400 W/ m2K respectively. Inlet temperature of hot gases is 500 °C; outlet temperature of hot gases is 300 °C, inlet temperature of air 50°C, Exit temperature of air 140 °C. Calculate: i) Overall heat transfer coefficient based on outer surface area ii) Length of the tube required to affect the heat transfer rates. Neglect the thermal resistance of the tube. iii) If each tube is 3 m length find the number of tubes required. – Free Chegg Question Answer

Transcribed text From Image: A parallel flow heat exchanger has its tubes of 5 cm internal and 6 cm external diameter. The air flows inside the tubes and receives heat from hot gases circulated in the annular space of the tube at the rate of 100 kW. Inside and outside heat transfer coefficients are 250 W/ m2K and 400 W/ m2K respectively. Inlet temperature of hot gases is 500 °C; outlet temperature of hot gases is 300 °C, inlet temperature of air 50°C, Exit temperature of air 140 °C. Calculate: i) Overall heat transfer coefficient based on outer surface area ii) Length of the tube required to affect the heat transfer rates. Neglect the thermal resistance of the tube. iii) If each tube is 3 m length find the number of tubes required.