Determination of Thermal Conductivity (Lagged Pipe)

Aim

To determine the thermal conductivity of the given Lagged pipe.

Specifications:

d₁- Heater diameter = 20mm

d₂- Heater with asbestos diameter = 40 mm

d₃- Asbestos & saw dust diameter = 80mm

Length = 500 mm

Apparatus Required:

1. Experimental setup
2. Stabilized power supply
3. Stop clock

Diagram:

Procedure:

1. Switch on the heater and set the voltage using the regulator.
2. The electrical heater transforms heat from the coil to the steel pipe filled with asbestos and it further transforms to the outer pipe filled with saw dust through conduction.
3. Wait for reasonable time for allow temperature at various points to reach steady state.
4. Measure the voltage current and temperature from t1 to t6 at equal intervals until the system reaches steady state.
5. Calculate the thermal conductivity of asbestos and sawdust.

Observations:

Formula Used

Heat Flow from the heater to outer surface asbestos lagging

Q = 2πL K₁(T_b -T_a/In [(r₂)/(r₁)] ) Watts

Q = Heat input in watts

K₁= Thermal Conductivity of the asbestos in W/m K

R₂= Radius of the asbestos pipe in m

R₁= Radius of the heater Pipe in m

T_b= Heater Temperature (T1+ T2+ T3) / 3

T_b= Asbestos Temperature (T4 + T5+ T6) / 3

K₂= ____ ____________________________W/m K

Result:

Thus the thermal Conductivity of the asbestos is (K₁1) _______ W/m k

Thermal Conductivity of the Sawdust is (K₂) __________________ W/m K

Viva-Voce Questions

What is steady-state condition?

Steady state implies that temperature at each point of system remains constant in due course of time.

What is heat conduction?

Conduction is the transfer of heat from one part of a substance to another part or to another substance in physical contact with it.

What is heat conduction?

Conduction is the transfer of heat from one part of a substance to another part or to another substance in physical contact with it.

What is heat conduction?

Conduction is the transfer of heat from one part of a substance to another part or to another substance in physical contact with it.

What is heat conduction?

Conduction is the transfer of heat from one part of a substance to another part or to another substance in physical contact with it.

What is heat conduction?

Conduction is the transfer of heat from one part of a substance to another part or to another substance in physical contact with it.

What is heat conduction?

Conduction is the transfer of heat from one part of a substance to another part or to another substance in physical contact with it.

What is thermal conductivity?

Thermal conductivity is the rate of heat transfer through a unit thickness of material per unit area per unit temperature difference

What is heat conduction?

Conduction is the transfer of heat from one part of a substance to another part or to another substance in physical contact with it.

Name the material having highest & least thermal conductivity?

Diamond & Freon-12.

Write down the equation for conduction of heat through a hollow cylinder.

Heat conduction is a mechanism of heat transfer from a region of high temperature to a region of low temperature within a medium [solid, liquid or gases] or different medium in direct physical contact

State Fourier's law of conduction

The rate of heat conduction is proportional to the area measured normal to the direction of heat flow and tothe temperature gradient in that direction Q = -kA dT /dxWhere, A- Area in m ². dT / dx,- Temperature gradient, K/m, K-Thermal conductivity, W/mK

Define Thermal conductivity

Thermal conductivity is defined as the ability of a substance to conduct heat

Write down the equation for conduction of heat through a slab or plane wall.

Heat transfer, Q = Toverall / R; Where, _ T = T₁- T₂

R = L / kAThermal resistance of slab, L- Thickness of slab; K-Thermal conductivity of slab; A- Area

Heat transfer, Q = _ Toverall / R, Where _ T = T₁- T₂; R = 1 / 2_Lk in [r₂ / r₁] Thermalresistance of slab,

L-Length of cylinder; k -Thermal conductivity; r₂-Outer radius, r₁Inner radius.