ME2355 THERMAL CONDUCTIVITY APPARATUS-GAURDED HOT PLATE METHOD - Computer Programming

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Sunday, March 13, 2011

ME2355 THERMAL CONDUCTIVITY APPARATUS-GAURDED HOT PLATE METHOD


THERMAL CONDUCTIVITY APPARATUS-GAURDED HOT PLATE METHOD

AIM:
To find the thermal conductivity of the specimen by two slab guarded hot plate method.

DESCRIPTION OF APPARTUS:
The apparatus consists of a guarded hot plate and cold plate.  A specimen whose thermal conductivity is to be measured is sand witched between the hot and cold plate.  Both hot plate and guard heaters are heated by electrical heaters.  A small trough is attached to the cold plate to hold coolant water circulation.  A similar arrangement is made on the other side of the heater as shown in the figure.  Thermocouples are attached to measure temperature in between the hot plate and specimen plate, also cold plate and the specimen plate.
A multi point digital temperature indicator with selector switch is provided to note the temperatures at different locations.  An electronic regulator is provided to control the input energy to the main heater and guard heater.  An ammeter and voltmeter are provided to note and vary the input energy to the heater.
The whole assembly is kept in an enclosure with heat insulating material filled all around to minimize the heat loss.

SPECIFICATION:
Thickness of specimen  = 2.5mm
Diameter of specimen (d) = 20cm

T
 
T
 
T
 
T
 
T
 
T
 
T
 
T
 


MODEL CALCULATIONS:
FORMULA USED:
Since the guard heater enables the heat flow in uni direction
q = KA dT/dx
Where A = surface area of the test plate considered for heat flow = m2 
dx = thickness of the specimen plate = m
dt = average temperature gradient across the specimen = c
q = Q/2 since the heat flow is from both sides of the heater = watts
Tavg1 = T1 + T2 / 2 ; Tavg2 = T3 +T4 / 2
Q = V.I. Watts
Q = K1 A. dT / dx (for lower side)
Q = K1. пd2/4 (Tavg1 – T5)/dx
Where dx = 2.5mm  = 0.0025m
Diameter of specimen
          d = 20cm = 0.2m
Q = K2 пd2/4 . (Tavg2 –T6)/dx ( for upper side)
KAvg   = (K1 + K2 )/ 2
PROCEDURE:
1.     Connect the power supply to the unit.  Turn the regulator knob clockwise to power the main heater to any desired value.
2.     Adjust the guard heater’s regulator so that the main heater temperature is less than or equal to the guard heater temperature.
3.     Allow water through the cold plate at steady rate.  Note the temperatures at different locations when the unit reaches steady state.  The steady state is defined, as the temperature gradient across the plate remains same at different time intervals.
4.     For different power inputs is in ascending order only the experiment may by repeated and readings are tabulated as below.



















result:
          The thermal conductivity of the specimen is found to be ------------- W/mK.


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