Technical Standards and Safety Authority (TSSA) G3 Practice Exam

How is air heated when passing over a heat exchanger?

1. Conduction

2. Convection

3. Radiation

4. Infrared

The correct answer is: Convection

When air passes over a heat exchanger, it is primarily heated through convection. Convection is the process of heat transfer that occurs between a solid surface and a fluid (in this case, air) that flows over it. As the air moves through the heat exchanger, it comes into contact with surfaces that have been heated, such as pipes or fins containing hot fluid. The heat from the hotter surfaces of the heat exchanger transfers to the cooler air by the movement of the air itself. The warmer air then rises, and cooler air takes its place, creating a continual flow of air that gets heated as it travels over the heat exchanger. This continuous cycle enhances the efficiency of heat transfer, allowing for effective heating of the air. While conduction also plays a role in heat transfer when the air touches the heated surfaces of the heat exchanger, the dominant method in this scenario is convection due to the movement of air. Radiation and infrared heating are not the primary means by which air is heated in this context, as they concern heat transfer through electromagnetic radiation rather than through the direct movement of air or contact with a solid surface.