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Sunday, March 13, 2011

ME2355 THERMAL CONDUCTIVITY OF INSULATING MATERIAL - LAGGED PIPE


THERMAL CONDUCTIVITY OF INSULATING

MATERIAL - LAGGED PIPE

AIM :
            To find the thermal conductivity of different insulating material.


DESCRIPTION OF APPARATTUS :

The insulation defined as a material, which retards the heat flow with reasonable effectiveness.  Heat is transferred through insulation by conduction, convection and radiation or by the combination of these three.  There is no insulation, which is 100% effective to prevent the flow of heat under temperature gradient.
The experimental set up in which the heat is transferred through insulation by conduction is under study in the given apparatus.
The apparatus consisting of a rod heater with asbestos lagging.  The assembly is inside as MS pipe.  Between the asbestos lagging and MS pipe saw dust is filled.  The set up as shown in the figure.  Let r1 be the radius of the heater, r2 be the radius of the heater with asbestos lagging and r3 be the inner radius of the outer MS pipe.
Now the heat flow through the lagging materials is given by
Q = K1 2 ΠL(Δt) / (In(r2)/r1) or
    = K2 2 ΠL(Δt) / (In(r3)/r2)
Where Δt is the temperature across the lagging.
K1 is the thermal conductivity of asbestos lagging material and
K2 is the thermal conductivity of saw dust.
L is the length of the cylinder.
Knowing the thermal conductivity of one lagging material the thermal conductivity of the other insulating material can be found.


TABULATION :

 

S.No

Heat temperature
Asbestos temperature
Sawdust temperature
Volts
Amps
1
2
3
avg
4
5
6
avg
7
8
avg










































































Specification:
Diameter of heater rod                                                            = 20mm
Diameter of heater rod with asbestos lagging                        = 40mm
Diameter of heater with asbestos lagging and saw dust         = 80mm
The effective length of the above set up of cylinders            =      500mm

PROCEDURE:
1.      Switch on the unit and check if all channels of temperature indicator showing proper temperature.
2.      Switch on the heater using the regulator and keep the power input at some particular value. 
3.      Allow the unit to stabilize for about 20 to 30 minutes.  Now note down the ammeter, voltmeter reading which given the heat input.
4.      Temperatures 1,2 and 3 are the temperature of heater rod, 4,5 and 6 are the temperatures on the asbestos layer, 7 and 8 are temperatures on the sawdust lagging.
5.      The average temperature of each cylinder is taken for calculation.  The temperatures are measured by thermocouple (Fe/Ko) with multi point digital temperature indicator.
6.      The experiment may be repeated for different heat inputs.
The readings are tabulated as below:

CALCULATIONS :
Lagged Pipe:

V         A         T1        T2        T3        T4        T5        T6        T7        T8

90        0.4       108      117      89        51        59        53        41        41

Avg. Temp. of heater                          = T1 +T2 +T3 / 3 = 104.6 o c
Avg. Temp. of Asbestos lagging        = T4 + T5 + T6 / 3 = 54.3 o c
Avg. Temp. of sawdust lagging          = T7 + T8 / 2 = 41 o c
The heat flow from heater to outer surface of asbestos lagging =
q          = k1 2 Πl (Δt) / ln (r2 / r1)
k1         = Thermal conductivity of asbestos lagging from data look at
= 110.5 X 10-3 w/mo k.
            = 54o c
r2         = Radius of the asbestos lagging = 20
r1         = Radius of the heater = 10 mm
l           = Length of the heater = 0.5 mtrs.

Substituting these values

q = 110.5 X 10-3 X 2 X Π X 0.5 X

Substituting this value of q to find the thermal conductivity of sawdust.

25.19 = k2 X 2 X Π X l X 13.3 / ln (r3/r2)

k2 = 25.19 X ln (40/20) / 2XΠX13.3X8.
     = 0.417


RESULT :
Thermal conductivity of
(i)                 Asbestas---------------W/mK
(ii)               Sawdust----------------W/mK

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