G2 Gas Fitter Practice Exam

How is air heated when it passes over a heat exchanger?

1. By conduction

2. By radiation

3. By convection

4. By induction

The correct answer is: By convection

Air is heated as it passes over a heat exchanger primarily through the process of convection. In a heat exchanger, there is a temperature difference between the heated surface and the air passing over it. The heat from the surface is transferred to the air through the movement of air particles that come into contact with the surface. This process effectively warms the air due to the transfer of thermal energy from the surface to the moving air, which occurs as the air circulates around and absorbs heat. Convection is significant in this context because it combines the effects of conduction (the direct transfer of heat through the material of the heat exchanger) and the movement of the air. However, conduction alone does not account for the overall heating process involving the moving air, and other methods like radiation and induction are not applicable in typical heat exchange scenarios for air heating. In summary, convection is the correct answer as it describes the interaction between the heated surfaces and the air that leads to increased air temperature during the heating process.