Why are superheater tubes typically of small diameter?

Superheater tubes are typically of small diameter primarily because it enhances gas flow and heat transfer. A smaller diameter helps maintain a higher velocity of the flue gases flowing through the tubes, which improves the overall heat transfer efficiency. When the gas velocity is increased, there is a greater turbulence effect, which promotes better heat exchange between the gases and the tube walls.

Additionally, smaller diameter tubes can also increase the surface area to volume ratio, which bolsters the effectiveness of heat transfer by allowing more contact area for heat conduction. This is critical in superheating applications where the goal is to efficiently raise the temperature of steam to improve the thermodynamic efficiency of steam cycles.

This focus on enhancing gas flow and heat transfer is fundamental in optimizing the performance of steam-generating systems, particularly in applications where efficiency and output are paramount.