Week 9

This week we worked to figure out how we could get the peltier thermoelectric cooler could work properly, as in that the hot side of the peltier would not transfer the heat back to the cold side. This week we needed to determine an amount of voltage that will make the peltier work better and more efficiently. We also worked to collect data about temperature difference between the two sides of the peltier and whether or not a heat sink helped to maintain the significant hot and cold temperature difference between both sides.

The following image shows the device we used in order to adjust and apply a voltage (volts) and also electric current (amps) to the peltier. However, the displayed voltage and current are not the established voltage needed for the peltier to work at its best.

Image 1

Image 1 shows the peltier wires, red and black, attached to the device to apply a voltage and current of our choice.

The next image shows the heat sink we purchased and used on the peltier to help the hot side of the peltier release its heat better instead of transferring it back to the cold side.

Image 2

Image 2 is a small heat sink, about the same size as the peltier, that was placed underneath the hot side of the peltier.

The third image is of the set up we established in order to run tests and collect data on the temperature difference between the two sides of the peltier.

Image 3

Image 3 shows the relative set up used for testing. heat sink was placed underneath peltier's hot side. One of each temperature probes were placed on one side of the peltier. The peltier is hooked up to the device. THe temperature probes are hooked up to a laptop that contains a software program that collects temperature readings over time and graphs the data. 

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.

Week 3

During week three of class, sketches of possible designs were drawn up.  The three different designs can be seen by clicking on the Brainstorming tab above. Each design includes how it is meant to work.  However with each design there are constraints that need to be overcome.  Our main design is shown in Figure 1 and 2, an air ventilation system used in conjugation with a liner. Between the prosthetic and liner would be an layer that allows for air to circulate throughout and thus onto the skin that is in contact with the prosthetic directly. Several other ideas and designs have been created also. Figure 3 shows a liner that can draw the moisture and perspiration down into one collecting area. This collection area could then be emptied. Figure 4 is solely for lower extremities prostheses. A mechanical pump would be inserted to create air flow. The pump would be activated and thus air flow would occur by the natural forces of pressure created when weight is pushed down onto the prosthetic from walking.

Week 2

It has been decided that the main project will be to create a ventilation system that can easily be inserted into existing prosthetic devices and also easily be applicable between different types of prosthetic devices.  Another possible solution to the problem is a liner that can cover the area of the body that is being inserted into the prosthetic device. Many liners exist already, however they are usually made up of silicon gel. The silicon gel adds cushion to the user, however it causes much perspiration since the material cannot breathe and no air is circulating in the prosthetic. Other liners are of cotton-like material that also add comfort. These can became wet quickly as the sweat is absorbed, and then must be changed regularly.

Week 1

In week one of lab, group 04 of section 012 was formed.  Once the group was formed, the main topic for the design project was chosen: human assist devices.  After much brainstorming of devices needed in the medical field to create or improve upon, the group chose to pursue creating a porous material that would allow for breathable prosthetics and orthotics. This will allow for people wearing the devices to be more comfortable in every day wear, especially during the warmer months when perspiration occurs readily. It was realized that the contact area between the skin and prosthetic easily perspires and then easily becomes irritated. We hope to add substantial comfort to all prosthetic users with our final design.