According to pump affinity laws, how does capacity vary with impeller diameter?

The correct understanding of the pump affinity laws indicates that the capacity of a pump is indeed proportional to the diameter of the impeller. This means that if the diameter of the impeller increases, the flow capacity also increases at a linear rate. Essentially, this relationship arises because a larger impeller can displace more fluid with each rotation, leading to an increase in the flow rate.

To illustrate this concept in practical terms, when an impeller diameter is doubled, the pump will theoretically have the capacity to move twice as much fluid, provided that all other factors remain constant. This direct proportionality helps in pump design and selection, allowing engineers to predict how changes in impeller size will affect the flow capacity of the system.

While other options mention relationships such as inverse proportionality or varying with the square or cube of the diameter, these do not accurately describe the relationship between capacity and impeller diameter as defined by the affinity laws. The laws specifically highlight that capacity directly scales with the diameter, making it a fundamental principle in pump design to understand how adjusting the impeller size can influence performance.