Mechanical Technologies reposted this
Why do water coils require a minimum GPM? 🤔 Turbulence is needed to ensure the fluid makes sufficient contact with the inner walls of the water coil. More contact means more heat transfer. If a fluid moves too slow, it becomes uniform and laminar (think straight lines). Due to frictional forces at the walls, the water flows primarily through the center of the tube. This results in less contact with the side walls. The minimum velocity in a tube is 0.5 ft/s for chilled or hot water coils (according to Table 1 of AHRI 410). For a 1/2" nominal diameter tube, this translates to approximately 0.31 GPM. Keep in mind this is per circuit, so multi-row coils, which will likely have multiple circuits, will need a greater GPM. For more information, refer to the AHRI standard or a college fluid dynamics textbook. #mechanicalengineering #hvac #airdistribution