The energy equation modified to deal with power
The energy equation as it is most often used is expressed in energy per
unit weight and each term has units of Joules/Newton or just metres if one
thinks in terms of energy head. When the pipe system involves pumps, motors or
turbines it is more convenient to work in terms of power. All that is required
to change the several terms of the energy equation to power terms is to
multiply by the weight flow which is, of course, the mass flow multiplied by g.
The equation applied to two sections 1 and 2 of a pipe system then becomes :-
+ input power from a pump =
+ power output to a motor or turbine + loss
of power to friction.
See worked examples at the end
of this chapter for the use of this equation.