muhammad jawhar

1. College of engineering Fourth class
Mechanical department Laboratory of Power
Experiment No.: 4
Investigating of Lagging Efficiency and
Determination of thermal conductivity of lagging materials
3
Object of the test:
1- to investigate and compare the energy losses between lagged and unlagged pipes
2- to determine a value for the coefficient of thermal conductivity of the lagging
material.
Theory:
Pipes transporting fluids shall be lagged for three reasons:
3- To reduce transfer and loss of Energy.
4- To prevent the fluid freezing
5- To safe guard persons
Energy loss depends on:
The difference in temperature between the steam inside and the air outside the pipe.
The pipe thickness.
The velocity of the steam in the pipe.
The state of the air surrounding the pipe, i.e. still or in motion
Condensation of steam, i.e. saturated or superheated.
The loss of energy takes place partly by convection, but mainly by radiation. It is greater
when the steam is flowing through the pipe and not quiescent. If saturated steam is used, a
film of water is deposited on the inside of pipe. This aids the transfer of energy, and more
energy is lost as a result. The fact that the use of superheated stem permits a reduction of
temperature without deposing moisture account. For some of the economy attending its used
in the majority of case of heat transmission that arise in engineering practice.
Heat flows from some mediums through a solid retaining wall into some other medium.
To affect a transfer of heat,a temperature difference or gradient is essential, the thicker the
material, the less energy will be transferred in the same period of time.
It can be said that:
Energy transfer temperature difference
Energy transfer Area
Energy transfer l/thickness
dx
kAdt
Q 

Where: Q = Quantity of energy transferred
A = Area
dt = Element temperature difference
dx= Element thickness
k = coefficient of thermal conductivity
The (–)ve sign shall be introduced since that dt/dx is in itself negative.
Mass flow of condensate:
Since each cm of condensate in the pipe = 18 ml volume,
3
10
18




t
H
m c
c


Where:
ṁc = the mass flow rate of the condensate (Kg/s)
Hc = the difference in level of the condensate (cm)
ρ = the density of water (kg/m³)
t = total time of the experiment (seconds)

2. College of engineering Fourth class
Mechanical department Laboratory of Power
Experiment No.: 4
Investigating of Lagging Efficiency and
Determination of thermal conductivity of lagging materials
3
Enthalpy of Evaporation lost/ seconds :
fg
h
x
m
Q 

 
To determine k( coefficient of thermal conductivity):
Heat transmitted = Enthalpy lost /seconds
fg
h
x
m
r
r
T
T
l
k
Q 






 
)
/
ln(
)
(
2
1
2
2
1

)
(
2
10
)
/
ln(
2
1
3
1
2
T
T
l
r
r
h
x
m
k fg










Percentage Energy saved = ( Energy loss(unlagged) – Energy loss(lagged)) / Energy loss(unlagged)
Having steam in all the pipes at the same properties, P,T and x,
Then we can express the above as follows:
Percentage Energy saved =lagging efficiency
unlagged
lagged
unlagged
lagging
H
H
H 


Apparatus:
A 3phased 30KW capacity Fulton electrical boiler (steam generator) completed with the
accessories and automatic protection system is to be used for this experiment. The steam
boiler is set to produce steam of around 5bars supply pressure.
Tubes bench, in which contains 4 steal tubes of known similar dimensions. The 1st tube is a
plain tube painted but unlagged. The rest are lagged in different ways, 2nd piped is fiber
glassed isolated, 3rd tube is isolated with the asbestos tape while the 4the tube is chrome
coated. Temperature of the surfaces of the metal and the laggings can be determined from
thermocouples installed to the bench. Each tube is installed with a sight glass provided with a
metric ruler indicating the level of condensate in each tube.

3. College of engineering Fourth class
Mechanical department Laboratory of Power
Experiment No.: 4
Investigating of Lagging Efficiency and
Determination of thermal conductivity of lagging materials
3
Test procedure:
1- Prepare the steam in the boiler. allow steam to blow down in order to clean up the system.
2- Let steam enters to the tubes by opening the inlet valves until the steady state have been
attained, as indicated by temperature stability. Hence tubes may be filled with condensate to
different levels, according to the ambient temperature.
3- Adjust the level of water in the tubes to a visible level near to the zero level, by opening the
outlet valves while the inlets are closed. Close the outlets and open the inlet valves.
4- Start stopwatch and record the levels of the condensate water in each tube. Record the
pressure and temperature of the steam and all the other temeratures of the tubes as described
in the data list.
5- Repeat the procedure five times each 4 minuets. At the end, record the final level of the
condensates in each tube.
6- Empty all the tubes to the blow down line, close the main isolating valve, turn off the
boiler.
Details of the Pipes:
Pipe material mild steel
Length 818 mm
Inside diameter 47.7 mm
Metal thickness 6.3 mm
Pipe #1 insulation none
Pipe #2 insulation fiber glass 106.6 mm outer diameter
Pipe #3 insulation asbestos tape 69.5 mm outer diameter
Pipe #4 insulation chrome finished
Data recording sheet:
Time Steam Pipe#1 Pipe #2 Pipe #3 Pipe #4
Min Temp
(°C)
Hc
(cm)
Temp
(°C)
Hc
(cm)
Exter
Temp
(°C)
Inter
Temp
(°C)
Hc
(cm)
Exter.
Temp
(°C)
Inter.
Temp
(°C)
Hc
(cm)
Temp
(°C)
Hc
(cm)
0
5
10
15
20
Av.
Requirements:
- find out the lagging efficiency for all of the 4 pipes
- calculate the K thermal conductivity for the 2nd and the 3rd pipe's lagging materials
- compare the last results of the K thermal conductivity with the same materials in the
indexes.