Week 8

During Week 8, our group received the peltier we ordered in the mail. The following image is an image of a typical peltier.

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.**

Week 7

We had another meeting with Dr. Weyant this week in order to establish how the specifications would be figured out. After consulting several online resources and discussing the overarching idea behind the calculations, we were clear on what values we needed to account for in order to proceed with our design. From this point, we did some additional researching and made use of Fourier's Law [q = -kA(dT/dx)] in order to determine a temperature difference that a peltier would need to generate. With the values of the heat transfer coefficient of silicone (k), area of the interface (A), thickness of the interface (dx), and heat flow through the interface area (q), we were able to determine this temperature difference. From here, we used the temperature of the human body (roughly 98.6 degrees Fahrenheit) to find the temperature we would have to lower the interface to in order to create continual heat flow through our system. The next week will consist of meeting with additional faculty to solidify calculations, developing a model for the peltier-skin system, and testing the model several times to see if our calculations are correct.

Week 6

This week we had to severely reevaluate our design plan. After meeting with Dr. Weyant, we thought that we had a good idea of what our design would look like; however, after consulting with Dr. Allen, we realized that we had to have more concrete specifications before moving forward. Thus, for the upcoming week, we knew that we had to focus our efforts on calculations and additional specifications prior to the next meeting. In specific, we want to find the amount of heat the body, or a portion of the body, provides in a certain amount of time. We also discussed a primary list of items we needed to acquire for the final model construction.

Week 5

After talking with several faculty members at Drexel, many new ideas have been thought about and considered for our design. First of all, a few members of the group spoke with Dr. Primerano, a professor from Drexel's College of Engineering. We proposed our air ventilation system design to him and he gave us several tips and ideas to build onto our design. For example, he gave us a site that sold many different types of fans that we could implement into our ventilation system. He also suggested using a pelltier, which can be used to transfer hear. Later that week, we also talked to a member of the biomed department at Drexel, Dr. Seliktar. He is involved with prosthetics, therefore we thought he would be a great candidate to discuss our design with and receive ideas from. After telling him out design, he believed that our proposed system would not quite solve the problem at hand. He believed that a conductive material would be the best route to go down. Therefore, after speaking with Dr. Selikitar, Dr. Allen, and amongst ourselves, we now have decided to try to create a multilayer material that can remove heat and remove moisture. More so, one layer should wick away the moisture and another layer should absorb the moisture. We also thought of the possibility of having a compartment to collect the moisture, like shown in Figure 3 on the Brainstorming page. We will continue to research materials, especially conductors, that we can use to create a multilayer liner.

Week 4

During week 4, we decided on the approach we want to take to add air circulation to prostheses. Our design will include a small fan that will be connected to a series of medical tubing in order to deliver the air throughout the prosthesis. We purchased different sizes of medical tubing online. We also brainstormed ideas involving the fan. The fan could be made by use by using ProEngineer and developing our own fan blades. Then once printed, the fan blades could be attached to a small motor we received from elsewhere. For example, a motor from a fan inside an old computer could be used. We will continue to brainstorm ideas to create our fan system and will talk to other people with knowledge applying to our project, such as Dr. Primerano, for their input. We hope to make our air circulation system universal for any and all prostheses. As of now, we believe a fan is the best option for creating air flow to stop moisture build up.