Figures :

Figures :

Figure 1 : Schematic diagram of the device used.Data :

Cpw : Specific heat of water = 4180 J/kg.D : Diameter of aluminum specimen = 0.018 m

V : Collected water volume = 0.010 L

k : Thermal conductivity = 202 - 250 W/m. [1]

Tables :Table 1 : Experimental test results for measurement of thermocouple temperatures and theirs average temperature, inlet and outlet water temperatures and theirs average temperature, and time.

Try #T1()T2()T3()T4()Twi()Two()t

(s)

176.57063.857.723.625.98.94

276.369.863.757.623.726.09.19

376.369.963.757.623.926.19.09

476.369.963.857.724.126.39.25

Average76.3569.963.7557.6523.82526.0759.1175

Calculations :Sample calculation for T1 from table 1 :

T1 = = 76.35 CMass Flow Rate:

= =kg/sDifference between inlet and outlet water temperature:

=CCross sectional area of the specimen:A= == 2.5510-4 m2The rate of heat transfer to water tank:

WThe rate of heat transfer :

= Slope from figure 2 = - 207.5 C/m

The experimental thermal conductivity :

= W/m.CGraphs:

Figure 2 : The average temperature of the specimen vs. the distance from hear source .

Discussion :In this experiment, a thermal conductivity of aluminium has been measured by using thermocouples, temperature recorder, calorimeter, and electric heater. The aluminium is heated by electric heater and the temperatures of the aluminium at different locations have been measured by using thermocouples and the corresponding temperature value appears on the temperature recorder which is attached to the thermocouples. The temperature versus the distance x has been illustrated in Fig.1 where the slope indicates the change of the temperature with respect to the distance x. A linear fitting were used to fit the data where it shows that the data are distributed near the fitting line which means that the relationship between the temperature of the aluminium and the distance is linear. The temperature of the aluminium decreases as the distance increases which means that the temperature gradient has negative value. The heat transfer of the aluminium has been measured by passing water through a calorimeter that inlets at initial temperature and exits at the final temperature where the final temperature is greater than the initial one due to the heat transfer that takes place in this device. The mass flow rate of the water has been measured by using a bucket and a stopwatch. The direction of the heat transfer is perpendicular to the cross section area. Experimental test results for measurement of thermocouple temperatures and theirs average temperature, water temperatures and theirs average temperature, volume, and times and theirs average time have been tabulated in Table.1. Steady state has been reached after two and half hours, but actually the device does not reach the steady state since the temperature is change slightly with time. Then, more time is needed to reach steady state. Dewar bottle was used to minimize the heat loss during the heat transfer that takes place between aluminum and the water. Since the bottle was warm, this yields that the bottle is not perfectly isolated and there will be some heat loss to the atmosphere during heat transfer. The constant water flow rate has been reached by using a bucket at the top of the device instead of using a pump. The measured value of k is differed from the theoretical value due to some factors that influence the results. Theses factors are due to human error in measuring the time required to fill ten mille-letter, heat loss since the bottle is not perfectly isolated, and the steady state that is not reached yet. The value of the thermal conductivity of the aluminum that is obtained from this experiment is measured to be 155.34 W/m.K and the theoretical value is 237 W/m.K. The percentage error of the deviation between theoretical and measured value is calculated to be 34.46%. The results can be improved by using a bottle that is well insulated and more time should the experiment operates in order to reach steady state.

References :

[1] : Heat exchangers selection, rating and thermal design. By : Kaka , Liu. 1998.1

_1304882573.unknown

_1304882625.unknown

_1304882648.unknown

_1304882672.unknown

_1304882685.unknown

_1304882698.unknown

_1304882660.unknown

_1304882637.unknown

_1304882597.unknown

_1304882611.unknown

_1304882585.unknown

_1304882548.unknown

_1304882562.unknown

_1304882518.unknown