As the diameter of a capillary tube decreases, what happens to the pressure drop?

When the diameter of a capillary tube decreases, the pressure drop increases due to the principles of fluid dynamics, particularly Bernoulli's principle and the concept of flow resistance. In a capillary tube, the fluid experiences friction as it moves through the constraints of the smaller diameter. This friction generates resistance to flow, which leads to a greater pressure drop as the fluid travels through the narrower section.

As the tube's diameter shrinks, it restricts the area available for fluid movement, causing an increase in velocity to maintain the same flow rate. The higher velocity results in increased kinetic energy but also leads to a greater difference in pressure between the inlet and outlet of the capillary tube. This pressure drop is critical in HVAC systems, especially in applications involving refrigerants, where maintaining proper pressure levels is essential for efficient operation and performance of the system.

By understanding how pressure drop is influenced by tube diameter, HVAC professionals can better design and troubleshoot systems for effective thermal management.