The following were the main objectives of this experiment:
Methodology
The following apparatus were used in this experiment:
- Copper-water heat pipe
- Hot plate
- Thermocouple (3)
- Ring stand with clamps (2)
- Solid copper wire
- Glass beaker (2)
- Multichannel digital thermometer
- Vernier caliper
Figure 1 below shows the illustration of copper-water heat pipe:
According to Fig. 1, The three main components of a heat pipe are the working fluid, vacuum tight containment vessel and the capillary/wick vessel. The operation of these three elements ensures the efficient and even heat transfer between heat source and sink. The wick structure that line up the inner surface of the heat pipe carries the working fluid. The work of the wick structure is to provide a capillary action that returns the working fluid from the heat sink to the heat source. The working fluid boils at the evaporator taking up the heat.
Results
Governing equations
A summary of the formulations used in this work is presented in this section:
qin=K.AcT2-T1L1
where, qin represents the heat input from the heater, K is the thermal conductivity of the pipe, L is the effective length, Ac is the cross-section area T2 and T1 respectively are temperatures of the wire at heat source and at end (sink). The effective thermo conductivity of the copper wire is computed from the following formula:
Keff=qin.LAc(T2-T1)2
Experimental data
Calculations
The quantity of heat input to the wire is computed as shown below by considering the copper wire:
qin=K.AcT2-T1L
diameter=0.17 inches=0.0029718 m
Ac=π*0.002971824=6.6874E-6 m2
qin=287*6.6874E-6*(61.5-54.3)L =0.0138189
q=0.0138189 watts/L
The effective thermo conductivity of the copper heat pipe thus becomes:
Keff=qin.LAc(T2-T1)
diameter=0.13 inches=0.003302m
Ac=π*0.003302 24=8.563356E-7 m2
Thus
Keff=0.0138189/L*L8.563356E-7*(58-34.2)
Keff= 678 W/m.K
Discussion and Conclusion
This experiment involved the measurement of temperatures drop on copper heat pipe and solid copper wire between the heat source (T1) and heat sink (T2). According to Table 1, the temperature drop (difference between T1 and T2) is greater in copper heat pipe as compared to copper wire. This was in consistent with our expectations. This ascertains the fact that heat pipes are efficient in transferring heat between one points to another as compared to solid wire. Thus, heat pipes applications in different areas for instance in computer motherboards to remove the heat from the processor.
The effective thermal conductivity of copper heat pipe has been determined as 678 W/m.K while that of solid copper wire is 287 W/m.K. This was consistent to our expectations. The working fluid in the heat pipe facilitates the transfer of heat from the heat source to sink. This explains the higher effective conductivity in copper heat pipe as compared to solid copper wire. The objective of the experiment were achieved. The temperature difference and the effective thermal conductivity were well accurately measured and determined in this experiment. In addition, the results obtained in this experiment compare well with theoretical data published in difference manuals. The experimental errors obtained in this work are listed below:
- Thermal paste was not used to increase the contact between the thermocouples and heat pipe/copper wire/ this could have affected the temperature obtained.
- For solid copper wire, the conduction of heat to the environment has been neglected ion this study.
- For the heat pipe, the mass flow rate and specific heat capacity of the working fluid should be used to determine the heat input to the heat pipe.
