Question

a heat exchanger consists of a bank of 1200 tubes with thin walls with air in crossflow over the tubes. the tubes are arranged in-line, with 40 longitudinal rows (along the direction of airflow) and 30 transverse rows. the tubes are 0.06 m in diameter and 2 m long, with transverse and longitudinal pitches of 0.14 m. the hot fluid flowing through the tubes consists of saturated steam condensing at 400 k. (a) for calculating the overall heat transfer coefficient u, which modes of heat transfer have negligible resistances, and which dominate?

Answer 1

The dominant modes of heat transfer in this heat exchanger are conduction and convection, while radiation can be neglected.

Step-by-step explanation:

The modes of heat transfer in a heat exchanger can be classified into three categories: conduction, convection, and radiation. In this case, the dominant modes of heat transfer are convection and conduction, while radiation can be neglected due to the thin walls of the tubes.

Conduction heat transfer occurs through the walls of the tubes, where heat is conducted from the hot fluid (saturated steam) to the cold fluid (air). The thin walls of the tubes ensure efficient heat transfer between the two fluids.

Convection heat transfer occurs due to the motion of the air over the tubes. As the air flows over the tubes, it picks up heat from the hot fluid through convection. This mode of heat transfer dominates in this heat exchanger since the air is in crossflow over the tubes.

Overall, conduction and convection are the main modes of heat transfer in this heat exchanger, while radiation can be ignored.