Based on our fabrication process, background research and methodology for exploring coconut oil as a storehouse for latent heat, we hypothesize that the oil once heated, will absorb heat from the radiant heat lamp during its phase change. As the oil melts, we predict that the air temperature will increase at a slower rate than before the phase change. Once the heat lamp has been shut off and the temperature of the box and PCM begins to fall, we expect to see the air temperature inside the box cool slower than it would without the PCM. As the material resolidifies, heat absorbed by the coconut oil during its phase change transfers to the air, prolonging the cooling process. We identified several variables that may have an influence on the latent heat effect on air temperature: the quantity of PCM, the position of the testing tray within the box (to account for heat rising) and amount of heat input into the box. With our initial trials we test smaller amounts of PCM to determine the effect that the material’s latent heat storage potential produces for the interior air temperature. The amount of coconut oil used in these tests were 5oz and the bulb was turned on for approximately 20 minutes. The results from these initial tests were inconclusive to our hypothesis, as the air temperature and PCM temperature rose and fell at similar rates. In later tests, we increased the amount of PCM being tested and also the amount of energy input into the box. We predicted that by increasing the amount of material being tested, the influence on interior air temperature might be more visible in our data recorded by our two sensors. For this test, we placed the PCM sample in a central location in the box and input approximately .11kWh (396000 J) over the course of one hour (Figure 1). The bulb was shut off after this time and the box was left overnight to cool down while data was continuously recorded by the two sensors. Given coconut oil’s low melting point, we expected that the solidification process would take a substantial amount of time, in addition to the considerable amount of energy we introduced into the box. We returned to the box the following morning and found the coconut oil still most entirely in a liquid state. The data from the two sensors was overlaid to show the temperature of the PCM against the interior air temperature within the same time period (Figure 2).
Conclusion and Next Steps
The recorded temperatures for the air and coconut oil within the same time frame show the air temperature rising much faster than the PCM because of the direct proximity to the heat lamp within the box, while the coconut oil rose more gradually over time. Unfortunately our DHT sensor could not record the temperature of the box as the temperature of the air was reaching its peak, but resumed collecting data once the temperature in the box dropped below 140. In order to avoid this, we would reduce the amount of power input through the bulb to bring the air temperature curve back down closer to the range of the PCM material. We would suspect that heat transfer between the coconut oil and the air would begin to occur on the downward slope as temperatures for both air and material decrease, however the air temperature would have a slightly less steep slope as heat transferred from the oil radiates into the interior air. After allowing the test to cool overnight, the coconut oil was still liquid, with only slight resolidification. Coconut oil’s low melting point was the main reason the test was too long to be recorded by our sensors. The amount of heat introduced into the box was a primary control that obfuscated the data from this trial. Other considerations for presenting the data from this study include adding a control study demonstrating the air temperature changes within the box without a PCM inserted (Figure 3). This would illustrate the response in air temperature to the energy input through the heat lamp, and also show the cooling of the air once the bulb was switched off. We predict that by comparing two graphs, one control and one with the phase change material, we would demonstrate how the coconut oil slows the air temperature increase within the box, and how the cooling of the box would happen slower than the control once the bulb was turned off.