Page 123 - DJJ20063- Thermodynamics 1
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DJJ20063- Thermodynamics 1
b ) STEADY FLOW ENERGY EQUATION
This equation is a mathematical statement on the principle of Conservation of Energy as
applied to the flow of a fluid through a thermodynamic system. The
various forms of energy which the fluid can have are as follows:
i) Potential energy
If the fluid is at some height Z above a given datum level, then as a result of its mass it
possesses potential energy with respect to that datum. Thus, for unit mass of fluid, in the
close vicinity of the earth,
Potential energy = g Z
9.81 Z
ii) Kinetic energy
A fluid in motion possesses kinetic energy. If the fluid flows with velocity C, then, for unit
mass of fluid,
C 2
Kinetic energy =
2
iii) Internal energy
All fluids store energy. The store of energy within any fluid can be increased or decreased
as a result of various processes carried out on or by the fluid. The energy stored within a
fluid which results from the internal motion of its atoms and molecules is called its
internal energy and it is usually designated by the letter U. If the internal energy of the
unit mass of fluid is discussed this is then called the specific internal energy and is
designated by u.
iv) Flow or displacement energy
In order to enter or leave the system, any entering or leaving volume of fluid must be
displaced with an equal volume ahead of itself. The displacing mass must do work on the
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