Last week was Midterms week and thus we spent the week away from the MnT lab! With our academic struggles out of the way for the moment, we spent our Recess week working on our project.
During this week, we tested the circuitry using terminal blocks and mosfets. One improvement from last week was that we now had a functioning code that could turn the set-up off. However, we realised that our fan code was not fully complete as when we tried to control the fan speed of the cold side fans, we could only increase the speed and not decrease it. We also set-up the closed water pump system for the Peltier blocks. Although it is quite an insignificant portion of our project, it takes 2-3 people to fill the system, ensure that there are no air bubbles, before hurriedly attaching the remaining open tube to the pump to close the circuit. After multiple attempts, we finally obtained a satisfactory lack of bubbles in our water system. We sealed the tubes with silicone sealant (which is unbelievable messy), and reinforced it with zip ties.
Fig. 1: Closed water pump system
We carried out a few tests to obtain data on our prototype. First, we tested wind speed against distance (0-50cm) for different current supplies and plotted the corresponding graphs. We found that an increase in distance from the fan results in a very slow decrease in wind speed felt. Next, we test temperature against time, measuring the air leaving both the hot and cold side fans. We obtained a consistent 4°C temperature difference between the hot and cold side, with a 2°C temperature decrease from ambient temperature (28°C) with a fan current of 0.85A. We found that the decrease in temperature was not as stark as previous experiments. Thinking that the limiting factor was that fan was blowing air out too fast for it to be sufficiently cooled, we changed the fan current to 0.34A to decrease the fan speed. We reached a decrease in temperature much faster with the lowered current being supplied to the fan. The cold side temperature was the same as the previous test, but the hot side temperature had increased, making the ΔT 5°C. We had been testing the set-up for close to 2 hours and thus concluded that a lower cold side temperature could probably be obtained if we ran the system at a lower cold side fan current from the beginning, as heat would not have accumulated in the system yet.
Fig. 2: Graph of Windspeed against Distance
Fig. 3: Plot of Temperature against Time
Lastly, we set the intended cold side temperature to 27°C and tested whether the code would be able to regulate current such that the cold air that was exiting the set-up was kept at a constant temperature. The code for this function worked, which could be seen from the jumps, to and fro, in Peltier current from 0.8A to 4.0A .
While testing, we found out that the touch screen function of our original screen was faulty – we were unable to find the driver to download the touchscreen function. It also did not help that most documents in the SD card were in Chinese, making it extremely difficult for us to identify which file was the correct one. After a few hours of trying, we gave in and placed an order for another screen, which is due to come next week. We also placed an order for a new 20V 41A PSU as our current one was heavy duty enough to power an entire CPU!