Download Government Engineering College Dahod

A Presentation on
Continuity, Momentum and Energy
Submitted By :
Name
Enrolment No.
Gohil Kiran R.
140183119005
Kadam Harshal P.
140183119008
Panchal Parth H.
140183119014
Rane Vaibhav S.
140183119017
Sathwara Vipul P.
140183119019
Savaliya Nitin J.
140183119020
B.E. Sem – 5th Heat Transfer
Year : 2015 - 2016
Mechanical Engineering Department
Government Engineering College
Dahod
Equation
Energy Equation
 In open system fluid flow is may be two types.
1. Steady flow
2. Unsteady flow
 Steady flow means that the rate of flow of mass
and energy across the controlled surface are
constant.
 Unsteady flow means that the rate of flow of
mass and energy across the controlled surface
are does not constant.
The steady flow process is characterized by the
following condition in control volume
1.
2.
3.
4.
5.

The mass flow rate remains constant within the system, i.e.
mass entering the control volume must be equal to the mass
leaving it and do not very with time.
The state of fluid at any fixed point in control volume is same
and do not vary with time.
The state of energy of the fluid at entrance and exit of the
control volume does not vary with time.
Heat and work transfer rate across the control surface does not
vary with time.
Chemical composition of fluid within the control volume is fixed.
When any flow process does not satisfy the above condition of
steady state, the process is known as unsteady flow process.
Derivation energy equation

Consider flow of fluid through generalized open system
as shown in figure. the working fluid enter the system at
section 1 and leave the system at section 2 and passing
at a steady rate.
Let,
Sr No
1
Mass flow rate, Kg/s
2
Specific internal energy, J/Kg
3
At inlet section 1-1
At inlet section 2-2
4
5
6
7
8
Velocity, m/sec
Elevation above an arbitrary datum, m
Potential energy / mass, Kj/kg
Kinetic energy / mass, Kj/Kg
9
Flow work, Kj/Kg
10
Net rate of heat transfer through system J/Kg
Q
11
Work done by system
W
Control Surface
Fluid Out
2
Control Volume (C.V)
System
Fluid In
1
Datum
Open System
C.V. = Control volume
q = Heat entering the control volume per kg of fluid, kJ/kg.
w = Work transferred from the control volume per kg of fluid, kJ/kg.



Application of SFEE


Momentum Equation



Consider a fluid flow through steam tube as shown in figure.

The fluid flow is assumed to be steady, uniform and normal to the
inlet area PQ and outlet area RS.
According to the principle of mass conservation.
Mass flow rate through a control volume PQRS.
P
Q
R
S

Application of the momentum equation

We will consider the following examples :

Impact of jet on a plane surface.
Force due to flow round a curved vane.
Force due to the flow of fluid round a pipe bend.
Reaction of jet.



Continuity equation



The equation base on the principle of conservation of mass called as
continuity equation.
Fluid flowing through the pipe at all the cross section, the quantity of
fluid per second remain constant.
Consider fluid flow through the pipe as shown in figure
1
pipe
2
2
1


References :
I.
II.
III.

I.
II.
Books : Engineering thermodynamics By J.P. Hadiya, H.G. Katariya – Books
India publication
Engineering thermodynamics By C.M. Desai, R.B. Varia – Atul
publication
Fluid mechanics and hydraulic machines By I.D. Patel, N.J. parmar - Atul
publication
Websites :-
http://home.anadolu.edu.tr/~esuvaci/egitim/Fluid%20Dynamics%20Lectu
re%205.pdf
http://www.sfu.ca/~mbahrami/ENSC%20388/Notes/Forced%20Convecti
on.pdf