Energy balances on mechanical systems, just as open system energy balances, are derived from the closed system energy balance. It is used for systems in which kinetic energy, potential energy, or shaft work are of prime importance.
closed system balance, splitting up the work terms:
Doing some rearranging, substituting the definitions of Wflow, Ek, and Ep, and then dividing by the mass flow rate, we get the desired equation.
Mechanical System Energy Balance Equation:
A modified form of this equation, used for a frictionless (F=0) process with no moving parts (Ws=0), is called the Bernoulli equation.
ΔP = 0 if the inlet pressure is equal to the outlet pressure
Δu2 = 0 if the system doesn't change velocity
Δz = 0 if the system doesn't move vertically
© 2007 Arizona Board of Regents for The University of Arizona