In the case where the flow resistance is due to a flow-measurement device for either pipe flow or open channel flow, the flow resistance causes an unknown pressure drop, Δp in the case of pipe flow...

In the case where the flow resistance is due to a flow-measurement device for either pipe flow or open channel flow, the flow resistance causes an unknown pressure drop, Δp in the case of pipe flow and an unknown Δy in the case of open channel flow, which causes an unknown head loss, hf, where the head loss is due to a conversion of kinetic energy to heat, which is modeled/displayed in the integral form of the energy equation. Explain how (and why) the flow resistance due to a flow-measurement device for either pipe flow or open channel flow is ultimately modeled.