Date post: | 02-Jun-2018 |
Category: |
Documents |
Upload: | kiron-bule |
View: | 217 times |
Download: | 1 times |
of 22
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
1/22
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
2/22
Menu
Slow Speed considerations
Viscosity Chart
Moody Diagram
Relative Roughness Reynolds Number
Kinematic Viscosity
Units of Viscosity Unit conversion
Examples
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
3/22
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
4/22
Slow Speed FO System
For heavy fuel oil consider the system a ClosedLoop system:
The viscosity near the main FO pump is a little
lower than when the fuel is injected As the fuel comes from the Service Tank to the
engine its increased in temperature
We should therefore calculate the pipe losses at
a viscosity averaged from Service Tanktemperature at say 55C to 120C at the transferpump up to the main FO pump
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
5/22
15 cts
9 cts
9cts at Main Fuel Pump Pressure 15cts at Main Fuel Pump Pressure
1000Redwood N
From 4 to 3 the
temperature increasesand the viscosity drops
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
6/22
Consider two plates
Absolute Viscosity =Shear Rate
dydv
A
P
Stress
dv
dy
Load
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
7/22
Units of Viscosity
Absolute Viscosity =Shear Rate
Stress
Absolute Viscosity (units) = poise
Stress
Shear Rate
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
8/22
Stress
Shear Rate
Absolute Viscosity
Kinematic Viscosity = Absolute Viscosity / density
Units of Viscosity
Units are called centipoise
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
9/22
Kinematic Viscosity
Units of Viscosity
We could find the pressure exerted by a fluid by using these formulas and
hence the Pressure drop per metre length
Although the normal units of Kinematic Viscosity are centistokes they are
sometimes in mm/s
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
10/22
Conversion factors
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
11/22
Moody Diagram
We use this diagram to find the Friction Factor (f)and f is used in finding the pressure losses in a
pipe
(metres)
(Pa)
(The tables previously handed out are directly
related to Moody Chart values)
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
12/22
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
13/22
Relative Roughness
4105.2
x
Material Roughness () in metres
Glass or Plastic Smooth
Copper, Brass, lead (tubing)
Cast Iron (uncoated)
Commercial mild steel or welded steel
4105.1
x
Pipes can are of different roughness internally and this affects the
pressure losses. As pipes age roughness factors will increase
this is particularly true for water carrying pipes
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
14/22
For constant Reynolds Number
If is increased as the Friction Factor (f) decreases
If increases as the value of in the turbulent zone increases
Also:
Relative Roughness
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
15/22
Reynolds Number
Absolute and Kinematic Viscosity is used to
define the Reynolds Number
V= velocity
v = kinematic viscosityD = pipe internal diameter
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
16/22
Examples
Oil of density 800kg/m has a kinematic
viscosity of 40cts. Calculate the critical velocity
when flowing in a pipe of 50mm diameter
A Reynolds Number of 2000 is normallyselected for find the critical velocity
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
17/22
Surface Roughness Coefficient
We use more accurate charts when working out
pipe Friction Factors
Mean surface roughness coefficient (k)
Diameter (D)
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
18/22
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
19/22
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
20/22
Moody Chart
We use a slightly different method
Mean surface roughness coefficient (k)
It gives more accurate results
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
21/22
More accurate Moody Chart
8/11/2019 Calculating Pressure Losses in Fuel Pipes for Emailing 21373 9 18
22/22
Finding the Friction Factor
Friction Factor (f)