Which of the following defines the efficiency of a pump?

The definition of the efficiency of a pump is appropriately captured by the ratio of brake horsepower to liquid horsepower. This measure reflects how effectively the pump converts the input energy (brake horsepower) into useful work for moving the fluid (liquid horsepower). The greater this ratio, the more efficient the pump is at performing work relative to the energy it consumes.

Liquid horsepower specifically accounts for the energy imparted to the fluid, measured by both the flow rate and the total head, which are crucial factors in determining how much energy is effectively transferred to move the fluid. Thus, by comparing these two forms of horsepower, one can assess the operational efficiency of the pump in transferring energy to the liquid it is moving.

The other options do not effectively encapsulate what is meant by pump efficiency. The relationship between flow rate and fluid density, for example, can influence the performance but does not represent efficiency directly. Similarly, the volume of fluid transported per unit time indicates the pump's output but not how well it converts energy. Finally, total head linked to fluid density describes performance characteristics rather than efficiency metrics. Hence, defining efficiency through the horsepower ratio provides a clear, standardized measure for evaluating pump performance.