Chapter 02 - Basic Engineering Aspect of Processing.pdf

engineering

1. BASIC ENGINEERING ASPECT OF
AGRICULTURAL AND FOOD
PROCESSING
by
Engr. Alexis T. Belonio
Department of Agricultural Engineering and
Environmental Management
College of Agriculture
Central Philippine University
Iloilo City
[email protected]

2. INTRODUCTION
Hydrostatic
–Fluid at rest
–A study deals with the fluid at rest such as those fluid
stored in tanks, etc.
Hydrodynamics
–Fluid in motion
–A study deals with the various factor affecting the
relationship between the rate of flow and the various
pressures tending to cause or inhibit the flow

3. Classifications of Fluids
Gases
–They are compressible in nature and when
compressed some gases change their state of
matter.
–Examples of these are air, flue gases, biogas,
etc.
Liquids
–They are not highly compressible. They can
be compressed into a very small degree only.
–Examples of these are oil, milk, water, etc.

4. Analytical Basis of Fluid System
Conservation of Mass
Conservation of Energy
Newton’s Law of Motion
–Everybody continues in a state of rest or of
the uniform motion in a straight line unless
compelled by force to change that state.
–The rate of change of momentum is
proportional to the force applied and takes
place in the direction of the force application.
–To every action there is always an equal and
opposite reaction.

5. Rate of Flow
The rate of flow of fluid is constant at any
point in a system and there is no
accumulation or depletion of fluid within
the system.
Formula
Q = A
1V
1d = A
2V
2d = … = A
nV
nd
where: Q –mass flow rate, kg/s
A –cross-sectional area of pipe, m
2
V –linear velocity of fluid, m/s
d –specific weight of fluid, kg/m
3

7. Given: Inside diameter of pipe -2 in.
Fluid velocity -0.02 m/s
Specific weight of fluid-1500 kg/m
3
Required: Mass flow rate
Solution:
Q = A V d
= 3.14 (2 in.)
2
/4 x 0.025 m/in. x 0.02 m/s
x 1500 kg/m
3
= 2.35 kg/sec
What is the rate of flow of coconut oil in a 2-in. pipe if
the velocity of the fluid is measured at 0.02 m/s? The
specific weight of oil is 1500 kg/m3.

8. Mechanical Energy Balance
Energy available because of elevation
above a reference plane (Potential
Energy)
Energy available because of the internal
pressure (Pressure Energy)
Energy available from the moving fluid
(Kinetic Energy)

9. Potential Energy
When fluid is released and is permitted to fall or
move from an initial position or a given reference
plane, the fluid will have an ability to do an amount
of work equal to the product of weight of fluid and
its distance from reference plane.
Formula
E
h= x h
Where:E
h -potential energy, lb-ft
x -weight of fluid, lb
h -distance above a
reference plane, ft

10. Pressure Energy
Fluid, in addition to the potential energy, is
subjected into an internal static pressure
expressed in lbs per in
2
, kg per m
2
.
Formula
E
p = 144 w p / d
Where:E
p -pressure energy, lb
w -weight of fluid, lb
p -pressure of fluid, psi
d -specific weight of material flowing,
lb/ft3

11. Velocity Energy
A body in motion possesses an amount of
kinetic energy
Formula
E
k= x ( V
2
/ 2g )
Where:E
k-kinetic energy, lb-ft
x -weight of the material, lb
V -velocity of material, ft/sec
g -gravitational acceleration, ft/sec
2

12. Total Hydraulic Energy
It is the sum of the three types of energy
plus the work supplied by a machine
(pump) less friction of fluid in the system
(conduit and fittings, etc)
Formula
xh
1+ 144xp
1/d + x V
1
2
/2g + x W –x F =
xh
2+ 144 xp
2/ d + x V
2
2
/ 2g

13. Bernoulli’s Equation
h
1+ 144p
1/d + V
1
2
/2g
+ W –F =
h
2+ 144 p
2/ d
+ V
2
2
/ 2g

14. Characteristics of Fluid Flow
Factors affecting the flow of fluid
–Characteristics of the fluid
–Size of pipe
–Shape of pipe
–Condition of the inside surface of the pipe
–Fluid velocity

15. Classifications of Flow
Streamlined Flow
–Fluid flows in parallel
elements
–Direction of motion of
each element is parallel
with the other element
Turbulent Flow
–Fluid moves in elemental
swirls or eddies
–Both velocity and direction
of each element changes
with time

16. Velocity Distribution in Pipes
Fluid flowing in a pipe shows that highest
velocity is at the center and decreases towards
the surface of the container.
The velocity gradient for streamlined flow in a
long circular conduit is parabolic in shape.
The average velocity is one-half the maximum
which is at the center of the conduit.
The velocity gradient for turbulent flow flattens
and the relationship between the maximum and
the average velocity changes.

17. Reynolds Number
Reynolds is an English investigator who first demonstrate
the finite existence of the streamlined and turbulent flow.
Equation
Re = D V d / u
where: Re -Reynolds number, dmls
D -inside diameter of pipe, ft
V -average velocity of fluid, ft/sec
d -specific weight of fluid, lb/ft3
u -fluid viscosity, lb/ft-sec

18. Viscosity
It is the internal
resistance of fluid to
shear.
The coefficient may
be considered as the
coefficient of friction
of fluid to fluid.

19. Fluid Classification
Newtonian Fluid
–Characterized by the rate of fluid shear that is
linearly related to shear force.
–Example, oil, water, etc.
Non-Newtonian Fluid
–The characteristics of fluid is not linear with
the shear force.
–Examples, slurries, food purees, paints,
butter, mayonnaise, etc

21. Friction Losses
Darcy’s formula
F = f ( L/D ) ( V
2
/ 2 g )
where:
F -friction loss, ft
f -coefficient, dmls
L -length of pipe, ft
D -pipe diameter, ft
V -linear velocity, fps
g -gravitational acceleration, 32.2 ft/sec
2

22. Friction losses in
agricultural and food
processing operations
are usually found in
pipe lines and fittings,
air duct and
branching, heat
exchanger, perforated
floors, materials being
processed, and others

23. Flow of Granular Materials
Rate of Flow -The flow rate varies with the
cube of the orifice diameter. The exponent
range from 2.50 to 2.96.
Angle of Repose –It is the side of pile in relation
to the horizontal. It varies with the moisture
content, and the amount of foreign matters
present.
Coefficient of Friction –This characteristic
determines the minimum pitch of conduit
intended to move the materials by gravity.

24. Pressure and Velocity
Measurements
Pressure head is expressed in column of fluid
under consideration in ft, inches, meters, etc.
Pressure is usually indicated in psi, in. mercury,
in. of water.
At higher pressure, psi is usually used.
At lower pressure, inches of water is used.
At pressure lower than the atmospheric, inches
mercury is used.

26. Pressure Conversion
psi x 27.648 = inches of water
psi x 2.036 = inches mercury
in. of water x 0.0361= psi
in. of water x 0.0736= in. mercury
in. mercury x 0.491= psi
in. mercury x 13.6= in. water

27. Static and Dynamic Pressures
Static Pressure
–It is a pressure resulting from elevation and
indicates forces perpendicular to the walls of
a container.
–Pressure taken perpendicular from the
direction of fluid.
Dynamic Pressure
–It is a pressure that results from force due to
change in velocity of the fluid.
–Pressure taken from the direction of fluid.

28. Pressure Gauges
Manometer –This is the
simplest and most reliable
pressure gauge wherein
the pressures are
determined by the
difference in height of the
fluid inside a tube.

29. Bourdon Tube –This is
widely used for operation
control wherein accuracies
of approximately 2% are
acceptable.

30. Diaphragm –It
consists of spring
loaded diaphragm or
bellow which actuates
a series of levers
attached to the
indicating hand.

31. Velocity Measurement
Pitot tube
-It is an open tube pointing into
the stream of
fluid
-The impact of moving fluid
creates pressure
head nearly equal to the
velocity (V2/2g)
-The fluid static pressure or head
is added to the pressure head so
that a pressure gage attached to
the tube indicates the sum of
the velocity pressure and
elevation head.

32. Venturi meter
-preferable to the pitot
tube when average
cross-sectional velocity
is desired
-velocity indicated is a
true average
-pressure difference can
be magnified by
increasing the diameter
ratios
-more accurate readings
can be obtained
-an excellent measuring
device for permanent
installation

33. Hot-wire anemometer
-based on the variation in
resistance of an
electrical conductor
-with conduit temperature
-variation of the conductor
temperature
with the velocity of gas past the
wire
-increase in velocity will permit
an increase in
the current flowing
-cooled wire will offer less
resistance to
electrical flow

34. Flow Measurement
Operating conditions
a) characteristics of materials to be
metered
b) operating range
c) line pressure
d) characteristics of flow, steady, or
surging
e) required accuracy

35. Meter characteristics
a) operating range
b) accuracy through operating range and
consistency of calibration with time
c) resistance to corrosion
d) ability to be disassembled for cleaning
if
used for foods

37. Gas and Liquid Meters
Bellow meters
-consists of two bellows
-inner connected by valves used for
measuring gas flow
-as bellows being filled from the supply
line, the other emptying into a service line
-valve shifts the direction of flow at the end of
the stroke
-emptied bellow fills from the supply line
-oscillation of the mechanism activates a volumetric
indicator

38. Piston meter
-a displacement or volumetric meter
-operates on the basis of and indicate the
volume of fluid passing a certain time.

39. Disc and cylinder meters
-recommended for most installations
because:
a) reliable
b) reasonably accurate
c) economical
-are displacement type meters

40. Propeller meter
-operates from the
motion of the fluid
rather than the
volume that is flowing
-activated by the
fluid motion
-examples are vane,
propeller, or cup
rotors

41. Rotameter
-rotor is supported by the upward motion
of the fluid
-its position in the tube indicates the rate
of flow

42. References
Henderson, S. M, and R. L. Perry. 1976.
Agricultural Process Engineering. Third
Edition. The AVI Publishing Company,
Inc. Wesport Connecticut. 442pp.