Image 1
Image 1 is a standard peltier. As you can see, there are two wires, one positive (red) and one negative (black), to connect to the positive and negative ends of a voltage source.
We also purchased a 9 Volt battery. Testing the peltier was fairly simple; we just connected the red and black wires to the correct battery terminals. Soon, we could feel the effect of the peltier at work. One side of the peltier became much warmer than the other side. The following three figures and descriptions explain how a peltier device, or thermoelectric cooler, works.
Figure 1
Figure 1 diagrams the electron flow from the voltage source (i.e. a battery) to the peltier. The "blue" side of the peltier absorbs the heat and then transfers it to the "red" side, making the "blue" side cooler in the process. The "red" side must release the heat then.
Figure 2
Figure 2 better diagrams the actual components/materials that make up a peltier. As seen, a peltier contains P-type and N-type semiconductor pellets. Two types of semiconductor pellets are used in order to better maximize the heat pumping capability of the peltier. The N and P types are connected in couples and then the conductor tabs, usually plated with copper, form a junction between each N and P pellet couple. This is what allows for the heat to move in one direction. The technique of coupling allows for better efficiency as opposed to a simple series or parallel connection. Furthermore, ceramic is attached the conductive tabs.
Figure 3
Figure 3 shows the coupling of the N and P-type semiconductor pellets. The heat is exchanged between the pellets.
During our testing of the peltier, we used temperature probes and a software program to record the differences and changes in temperature occurring on both sides of the peltier. In a few minutes, we noticed that the cool side was getting relatively hot, almost as hot as the other side that was becoming hot to begin with. The hot side was still becoming increasingly warmer, to the point where it hurt to touch it. This obviously became a problem, since the cool side was no longer cool and the hot side would potentially be able to burn the prosthetic interface. After some research, we found out that typically a peltier in use also has a heat sink. For example, in a computer, there is a heat sink surrounded some sort of fan system. The purpose of the heat sink and fan system is for the hot or "red" side of the peltier to actually be able to release the heat, which occurs because the fan circulate the air and thus gets rid of some of the heat on the hot side. In our test of our peltier, the heat had no where to go after being transferred to the one side. Therefore, at a certain point, the hot side began to transfer the heat back to the other, or cool, side since the heat had no where else to go. Even more, the reason that the hot side was getting hotter even when the cool side began to get hot now is because the peltier is still connected to the battery and thus a current is still being moved throughout the peltier. In order to use the peltier for our cooling system in a prosthetic device, we will need to create some kind of heat sink (which could unfortunately be very bulky and thus improbable for use in a prosthetic) or perhaps figure out the correct voltage that needs to be applied to the peltier device so it works properly for a significant amount of time. Even more so, we may be able to create a design that allows for ventilation to occur in the prosthetic so the heat on the hot side of the peltier can be released into the air outside of the prosthetic. Though the peltier device comes with some challenges, we believe we are headed in the right direction for figuring out how to minimize the sweating that occurs at the contact area of a prosthetic and skin.
**Figures 1,2, and 3 and related info is from http://www.tellurex.com/technology/peltier-faq.php.**
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