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Le 3

The document discusses the Steady Flow Energy Equation (SFEE) and outlines the assumptions made in steady flow system analysis, including constant mass flow and uniform fluid composition. It explains the energy balance in a control volume during fluid flow, incorporating various forms of energy such as internal, kinetic, potential, and flow work. The general SFEE is applicable to both compressible and incompressible fluids, and the document provides a symbolic representation of the energy balance according to the first law of thermodynamics.

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31 views2 pages

Le 3

The document discusses the Steady Flow Energy Equation (SFEE) and outlines the assumptions made in steady flow system analysis, including constant mass flow and uniform fluid composition. It explains the energy balance in a control volume during fluid flow, incorporating various forms of energy such as internal, kinetic, potential, and flow work. The general SFEE is applicable to both compressible and incompressible fluids, and the document provides a symbolic representation of the energy balance according to the first law of thermodynamics.

Uploaded by

saritprava sahoo
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Chapter-2

Steady Flow Energy Equation (SFEE): Lect-3

Assumptions
The following assumptions are made in the steady flow system analysis:
a) The mass flow through the system remains constant.
b) Fluid is uniform in composition.
c) The only interaction between the system and surroundings are work and heat.
d) The state of fluid at any point remains constant with time.
e) In the analysis only potential, kinetic and flow energies are considered.

Fig. Schematic flow process for an open system


 Consider a flow of fluid through an open system as shown in above Fig.
 During a small time interval 𝑑𝑡 there occurs a flow of mass and energy into the fixed
control volume; entry is at section 1 and exit occurs at section 2.
 The fluid enters the control volume at section 1 with average velocity V1, Pressure 𝑃1,
Specific volume 𝑣1, and Specific internal energy 𝑢1.
 The corresponding values at the exit section 2 are V2, 𝑃2, 𝑣2 𝑎𝑛𝑑 𝑢2.
 Further during, the fluid flow between the two selected sections, heat (𝑄) and mechanical
or shaft work (𝑊𝑠) may also cross the control surface.
 The following species of energy are taken into account while drawing up the energy
balance:
A. Internal energy stored by the fluid = 𝑈
1
B. Kinetic energy = mV 2
2
C. Potential energy = 𝑚𝑔𝑍
D. Flow work = 𝑃1𝑉1
E. Heat interaction = 𝑄
F. Work interaction i.e. shaft work = 𝑊𝑠
According to 1st law of thermodynamics, energy balance in the symbolic form may be written as,
(Mass flow rate)in=(Mass flow rate)out
Ʃ Energyin = Ʃ Energyout
V12 V2 2
u1  Pv
1 1 m1  m1 gZ1  Q  u2  P2 v2  m2  m2 gZ 2  Ws
2 2
 V12   V2 2 
m1  u1  Pv
1 1   gZ1  Q  m u
2 2  P v
2 2   gZ 2   Ws
 2   2 
Above Equation is the general steady flow energy equation (SFEE) and is equally applicable to
compressible and incompressible; ideal and real fluids, liquids and gases.
 But according to assumption (1),

Also enthalpy

So
 V12   V2 2 
m  h1   gZ1   Q  m  h2   gZ 2   Ws
 2   2 

 V12   V2 2 
m  u1  Pv
1 1   gZ1  Q  m u  P
 2 2 2 v   gZ 2   Ws  m  m1  m2
 2   2 
 V2   V2 
m  h1  1  gZ1   Q  m  h2  2  gZ 2   Ws  h  u  pv
 2   2 
 V12   V2 
 h1   gZ1   Q   h2  2  gZ 2   Ws
 2   2 
SFEE on unit mass basis
V12 V2
h1   gZ1  q  h2  2  gZ 2  Ws
2 2
Here, all the terms represents energy flow per unit mass of the fluid (J/kg).

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