Thermal Conductivity Of Pipe Insulation Using Lagged Pipe

Exp.No: Date: THERMAL CONDUCTIVITY OF PIPE INSULATION USING LAGGED PIPE APPARATUS AIM:

1. To determine the heat flow rate through the lagged pipe and compare it with the heater input for known valve of thermal conductivity of lagging material. 2. To determine the approximate thermal conductivity of lagging material by assuming the heater input to be the heat flow rate through lagged pipe.

APPARATUS REQUIRED: 1. Ammeter 2. Voltmeter 3. Thermocouple 4. Temperature indicator SPECIFICATIONS: 1. Heater diameter,

d1 = 20mm

2. Heater with asbestos diameter,

d2 = 40mm

3. Heater with asbestos + sawdust diameter, d3 = 80mm 4. Length,

L = 500mm

FORMULA USED:

Where, Q – Heat transfer rate, watts K1 – Thermal conductivity of asbestos in W/mK K2 – Thermal conductivity of sawdust in W/mK L – Length of the pipe, 0. 5 m ΔT– Temperature difference in K r1 – Heater radius, 0.01m r2 – Heater with asbestos, 0.02m r3 – Radius with asbestos and sawdust, 0.04m

Thermal conductivity of asbestos (K1)

Where, ΔT = T (Heater) – T (Asbestos) Thermal conductivity of sawdust (K2)

Where, ΔT = T (Asbestos) – T (Sawdust) Theory: The insulation is 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 understudy in the given apparatus.

The

apparatus consisting of a rod heater with asbestos lagging. The assembly is inside an MS pipe. Between the asbestos lagging and MS pipe, sawdust is filled.

PROCEDURE: 1. Connect the three pin plug to the 230 v, 50 Hz, 15 amps main supply and switch on the unit. 2.

Turn the Dimmer stat knob clockwise; set the heat input by fixing the voltmeter and ammeter readings and note down the heat input Q in the table.

3. Allow the unit to attain the steady state condition. 4.

When

the

steady

state

condition

is

reached

note

down

the

T 1 represents

the

temperature indicated by the temperature indicators. 5.

In

the

temperature

temperature

of

the

indicator, heater,

the

temperatures

T2 represents

the

temperature

of

the

asbestos and T3 represents the temperature of the sawdust lagging by using the multipoint digital temperature indicator. These values are noted in the table. 6. Calculate K1 (Thermal conductivity of asbestos) and K2 (Thermal conductivity of asbestos), by using the given formula and note the value in the table. 7. Repeat the experiment from step 2 to step 6 by varying the heat input to the system.

TABLE:

Voltmeter Readings

Ammeter Readings

Volts

Amps

V

I

Q=V x I

He ater Temp ˚C

Asbestos Temp ˚C

Sawdust Temp ˚C

T2

T3

S.No

1

2

3

4

Watts

T1

Asbestos K1 W/mk

Saw dust K2 W/mk

Figure 2. Lagged pipe apparatus

RESULT: 1. The heat flow rate through the lagged pipe and compare it with the heater input for known valve of thermal conductivity of lagging material. Q When (K1=0.15w/mk) = Q When (K2=0.698w/mk) = 2. The approximate thermal conductivity of lagging material by assuming the heater input to be the heat flow rate through lagged pipe. K1= K2= Thus the thermal conductivity of the given insulating material (Asbestos and Saw dust) has been calculated.