The main objective of this experiment was to measure the temperature difference across a heat pipe and a solid conductor of the same material and size and under the same thermal conditions. Secondly, to use the data obtained herein to determine an effective thermal conductivity of the heat pipe.
Methodology
Apparatus
- Copper-water heat pipe
- Hot plate
- Thermocouple (3)
- Ring stand with clamps (2)
- Solid copper wire
- Glass beaker (2)
- Multichannel digital thermometer
- Vernier caliper
The copper water heat pipe apparatus is illutrated as shown below:
Figure 1: A Basic heat pipe
Description of the apparatus
heat pipes are passive heat transfer devices that utilize boiling and condensation for their operation. A Basic heat pipe, shown in Fig. 1, consists of three components: a container, a wick and a working fluid. A description of the heat pipes and their operating principle are given several references.
Results
Formula used:
Heat conduction is governed by Fourier law as expressed in Equation 1.
q=-KA∆t∆x (1)
where, q is the rate of heat input, ∆t is the temperature gradient between the ends, K is the thermo conductivity of the material in W/mK, A is the cross-section area and ∆x is the distance between the two ends.
The experimental data obtained in this experiment is presented in Table 1.
Calculations
Solid copper wire
The amount of heat transferred per unit length is computed as shown below:
q=-KA∆t∆x= KAT2-T1L
A=π*0.002971824=6.6874E-6 m2
q=287*6.9363*10-6*(61.5-54.3)1=0.01433
q=0.01433 watts/m
For the same rate of heat input the effective conductivity of the heat pipe is calculated as shown below:
q=-KAT2-T1L
0.01433 =-K*A*T2-T1L
A=π*0.003302 24=8.563356E-7 m2
Thus
0.01433 =-K*8.563356E-6*34.2-581
k is the only unknown. Thus, making K the subject of the formula
0.01433 =-K*8.563356E-7*34.2-581
K=704 W/m.K
Discussion of Results
In this experiment, the temperature difference across the heat pipe and copper wire were measured as shown in Table 1. From these results it is very clear that the temperature change is greater in the heat pipe as compared to the solid copper wire. The temperature drop for the heat pipe and solid copper wire are 23.8 oC and 7.2 oC respectively. This showed that the heat pipe is very effective in transferring the heat from the heat source to the heat sink.
This experiment have also shown that the effective thermal conductivity of the heat pipe is higher than that of drawn copper wire. This is consistent with theoretical and experimental studies that have shown that heat pipes have a high effective thermal conductivity as compared to drawn copper wire. This is because, heat pipes utilize evaporation and condensation of the working fluid that increases the rate of heat transfer from the heat source to heat sink. The evaporation of the working fluid at the evaporator creates a pressure gradient that makes the working fluid to flow to the cooler section of the pipe.
Conclusions
- When measuring the temperature using thermal couples the thermal contact established between the heat pipe/ copper wire could not have been effective because thermal paste was not used to increase the contact.
- In the experiment, the mass flow rate and the specific heat capacity of the coolant were not use in determining the actual amount of heat transferred in the heat pipe. This is very accurate.
- The temperatures measurements were supposed to be done at different locations along the length of the pipe. This is very important in comparative analysis of heat transfer between the heat pipe and solid copper wire.
