Determination of Thermal Conductivity (Insulating Powder)

Aim

To determine the thermal conductivity of the given Insulating powder.

Specifications:

• Radius of inner sphere : 37.5 mm
• Radius of outer sphere : 75 mm
• Insulating Powder : Magnesium oxide Powder

Diagram:

Procedure:

1. The apparatus consisting of concentric spheres made of copper. The inner Sphere is a heater, and in between the spheres insulating powder is (Magnesium oxide) filled and sealed.
2. There are two thermocouples fixed to the heater T1 & T2 and two thermocouples fixed on the inner wall of the outer sphere T3 & T4. A multiunit digital temperature indicator is provided to measure temperature at different locations.
3. The whole unit mounted on a laminated work bench with panel. An ammeter & voltmeter is provided to measure the input power and a dimmerstat is provided to vary the input power.
4. The Heater is switched on. The input voltage can be adjusted to a suitable level, which in turn will vary the input heat.
5. The heater supplies heat to the inner pipe, which in turn passes through the insulating powder to the outer pipe.
6. The Thermocouple readings are noted frequently till consecutive readings are same indicating steady has been reached.
7. After establishing the steady state, the input voltage is reduced and the power supply is switched off.

Observations:

Formula Used

Q = (T_i- T_i)

(r₂-r₁)/(4πKr₁r₂)

Where,

Q = Heat input in watts

K = Thermal Conductivity of the material in W/m K

r ₀= Radius of the Outer sphere in m

r _i= Radius of the Inner sphere in m

T ₀= Insulating powder Temperature (T₃+T₄+T₅+T₆)/4

T ₁= Heater Temperature (T₁+T₂) / 2

(K) = __ ______________________________ W/m K

Result:

Thus, the thermal Conductivity of the insulting powder is (K) ______ _______ 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 thermal conductivity?

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

What are the factors affecting the thermal conductivity?

a.Moisture b. Density of material c. Pressure d. Temperature e. Structure of material

Define heat flux

The quantity of heat transfer per unit time per unit area of the internal surface as Heat flux.

Define temperature gradient

The greatest temp variation is in direction normal to the iso thermal surface is known as temperature gradient.