Heat Transfer Lab. Experiment 1

Heat Transfer Lab. Experiment 1

EXPERIMENT NO. 1

OBJECT:-

Conductive thermal resistance of the given system.
Thermal conductivity of a given insulating powder.
Critical thickness of insulation.

APPARATUS:-

The apparatus consists of two thin walled concentric copper spheres. The inner sphere houses the heating coil. The insulating powder (Asbestos powder) is packed between the two shells. The power supply to the heating coil is by using a dimmer stat and is measured by Voltmeter and Ammeter. Thermo-couples are use to measure the temperatures. Thermocouples 1 to 6 are embedded on inner sphere and 7 to 12 are on outer sphere. Temperature readings enable to find out the Thermal Conductivity of the insulating powder as an isotropic material.

FORMULAS:-

For the prescribed spherical geometry shown in diagram:

Heat input can be expressed as -

Thermal Resistance

Using equation (1) & (2)

Where,

Radius of inner sphere r_i= 50 mm = 0.05 m

Radius of outer sphere r_o= 100 mm = 0.1 m

Critical thickness of insulation is given as:

h_o, convective heat transfer coefficient at outer surface, can be calculated from

T_sur= Surrounding temperature of air around the sphere.

PROCEDURE:-

Switch on the heater and adjust the voltage and current to a given limit.

Observe the thermocouples readings after frequent intervals of time till the steady state condition is achieved.

To achieve quick steady state condition higher heating input can be given for small initial period.

OBSERVATION:-

Voltage reading, V = (Volts)

Ammeter reading, I = (Amperes)

T_sur = ºC

CALCULATIONS:-

Heat input Q_r = VI = (Watts)

Average inner surface temperature,T_i = (T₁+ T₂+ T₃+ T₄+ T₅+ T₆)/6 = ºC

Average outer surface temperature,T_o = (T₇+ T₈+ T₉+ T₁₀+ T₁₁+ T₁₂)/6 = ºC

Thermal conductivity of a given insulating powder, k =

Thermal resistance, R_t =

Critical thickness of insulation, r_c=

RESULT:-

DISCUSSION:-

Heat Transfer Lab. Experiment 2
Heat Transfer Lab Experiment 3

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