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SummaryThis investigation demonstrates the Peltier priniciple. A Peltier device is supplied with different

voltages and then the temperature difference from the hot and cold sides is observed. The

investigation finds that the temperature difference increases very slowly with voltage increases.

Aims and ObjectivesThe aim of this experiment is to demonstrate the Peltier principle, which is widely used in electrical

and electronic cooling equipment.

IntroductionThe Peltier effect is one of three reversible thermoelectric pheonomena (or thermoelectric effects).

Jean Peltier (1785-1845), who was a French physicists, discovered it in 1834 hence the name the

Peltier effect.

Jean Peltier observed that when junctions of two different metals were subjected to heating or

cooling, dependant on the direction of the electrical current passed through them, that the heat

generated by the current flowing in one direction, would be absorbed if the direction of the current

was changed. This would only work when the junctions were in pairs. The size of the Peltier Effect is

found to be proportional to the size of the current

around the circuit.

An example of the Peltier Effect is shown to the left.Under the conditions shown in the diagram, the right

hand side junction would be heated and the left hand

side junction would be cooled. At the right hand

junction the heating effect is seen has the electrical

energy changes to thermal energy and on the left hand

side cooling is observed as the thermal energy is

converted into electrical energy. If the current were to

be reversed the cooling would be on the right and the

heating on the left.(Daviddarling, 2010)1

When an electric current flows across a junction of two dissimilar conductors, heat is liberated or

absorbed. When the electric current flows in the same direction as the Seeback current, heat is

absorbed at the hotter junction and liberated at the cooler junction. The Peltier Effect is defined as

the reversible change in heat content when one coulomb crosses the junction.

The direction in which the current flows determines whether heat is liberated or absorbed. This

effect is reversible and is independant of the shape or dimensions of the materials composing the

junction. It is a function of the compositions of the materials and the temperature of the junctions,

not of the contact.

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It is interesting to note that Peltier, using a thermocouple made of antimony and bismuth, was able

to freeze a droplet of water. This was the first demonstration of thermoelectric refridgration. Peltier

devices, made from suitably doped semi conductors, are widely used to cool sensitive, solid state

electronic circuitry, such as that used in computers. These have low thermal effencies, but are

virtually trouble free and lend themselves to simple control. In reverse mode, junctions with large

Peltier effects have been used for power generation where thermal efficiency is not of primary

importance. Use has been made of this to power satellites.(Pollock, D.D., 1985)

MethodologyThe Peltier device was setup in a circuit as shown below. The two fans above the Peltier device were

to act as heat sink cooling fans.

First the heat sink cooling fans were turned on. It is important that this is done first as it will prevent

the device from overheating and becoming damaged. Secondly the power supply was turned on and

set to 14 volts and allowed 5 minutes to settle down. Once the temperature readings had settled

down a reading was taken for the voltage, current and temperatures on both sides on the device.

After this readings were taken with the power supply set to 13, 12, 11 and 10 volts. Between each

reading the device was given time to settle down.

Results and Discussion

As more power is supplied to the peltier device the greater the temperature difference is. The power

being supplied in the investigation increases by nearly 50 Watts but the temperature difference only

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mperatureDiff(C)

Power Supplied (w)

Temperature Diff vs Power Supplied

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increases by 1 C. The increase in the temperature difference is proportional to the power supplied.

In the circled result there appears to be a small error.

Above is a graph of current against power transferred by the unit. As the current increases more

power is transferred by the unit. This pattern is similar to typical peltier devices.

ConclusionIn this investigation it can be seen the peltier principle works well enough to be measured andobserved experimentally. There is one error which has been outlined. This error could possibly be

from the changing of the reading display (flicking between two numbers). Errors like this could have

been avoided if more time was given to the peltier to settle.

References1http://www.daviddarling.info/encyclopedia/P/Peltier_effect.html[Accessed: 05/12/2010, 15:13]

2Pollock D.D., (1985) Thermoelectricity: theory, thermometry, tool ASTM International.

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Current(I)

Power Transferred (W)

Power Supplied vs Current