There are 2 primary methods we use for measuring efficiency in prototype machines:
(a) The thermodynamic method is used in high head machines (greater than 100m heads) where temperature sensors are used to measure machine energy loss.
(b) The current meters method (measurement of discharge) can be used in all types of hydraulic machines to directly measure flow in the intake/penstock.
Efficiency is obtained by directly measuring the water temperature increase between the intake (high pressure measuring section, pictured left) and the exit (draft tube, pictured right) of the hydraulic machine. Using the principle of conservation of energy (1st Law of Thermodynamics), the mechanical energy can be directly measured by the heat produced. Using this method, it is not necessary to measure the discharge.
Current Meters Method
This method involves the measurement of discharge by measuring over a velocity-area using propeller-type current meters attached to a support frame placed in an up or downstream open channel or closed conduit/penstock.
The support frame can be placed at an intake gate, such as pictured above. By placing the frame on the moving gate, velocity measurements can be made at various levels in the conduit, allowing for a more complete area flow analysis.