4. Discussion

4.1    Key findings

Although the relative humidity in both boxes increased throughout the duration of Experiment 1,2 and 3, the relative humidity in Box A increased at a faster rate. After concluding each experiment we made changes to the dehumidifier such as removing the lining of silica gel from the pipes, but the relative humidity in Box A continued to rise at a higher gradient than that of Box B. This shows that our project did not meet the engineering goals as the relative humidity in Box A does not decrease.


4.2    Explanation of key findings


The faster increase in relative humidity in Box A as compared to Box B could only be possible if the humidity from inside to the dehumidifier is escaping into Box A, since Box A is completely sealed up and humid air from the outside environment is unable to enter the box. The silica gel could be contributing to the humidity since it may contain moisture from the water vapour it evaporates.  Also, the dehumidifier is not decreasing the relative humidity in Box A, as it is supposed to. This could be because of the silica gel as well. The silica gel inside the desiccant wheel has turned pink, reaching its fullest absorption capacity, and is unable to absorb any moisture from the air in Box A. The hair dryer is supposed to warm the silica gel so that the water vapour from the silica gel is evaporated and the silica gel regenerates. However, the hair dryer is only able to reach a temperature of 60ºC ( Labat, 2009 ) while the silica gel has to be heated to 90ºC - 110ºC for it to regenerate and regain its absorption capacity (Sicco Desiccators and Drying Cabinets, 2014 ). This means the silica gel would not have regenerated as desired, causing the silica gel to be insignificant and the moisture contained inside of it to be contributing to the relative humidity in Box A. Hence the humidity in Experiment 1,2 and 3 increases instead of decreasing. To tackle this problem, we should have switched on the hair dryer 1 hour prior to the experimentation so that it is able to remove as much water vapour from the silica gel as possible by steadily increasing the temperature of the silica gel. This will increase the absorption capacity if the silica gel, allowing it to absorb more water vapour from the humid air of Box A and thus decrease the relative humidity inside of it.


4.3    Evaluation of engineering goals


The project has failed to meet 3 goals but it has met 1 of the goals of the project.
Specifically,
a) The dehumidifier should turn on when the amount of humidity in the surrounding atmosphere is higher than a certain level (45%).
b) Once the level of humidity has been brought down to a certain level (45%) the dehumidifier should automatically switch off.
c) The dehumidifier should decrease the amount of humidity in the surrounding atmosphere.
d) Build the structure of a dehumidifier.

The structure of the dehumidifier has been built successfully with all the parts in proper working conditions, fulfilling goal d. However, goals a, b and c were unfulfilled.

This could be due to a 1 flaw in the design which is due to the hair dryer not warming the silica gel to the required temperature. For the water vapour to evaporate from the silica gel so that the silica gel can absorb a larger amount of moisture from Box A, the hair dryer needs to be able to warm the silica gel to a temperature of 90ºC - 110ºC (Sicco Desiccators and Drying Cabinets). However, the hair dryer switches off automatically (HowStuffWorks, 2014) once it reaches a temperature of 60ºC (Labat, 2009).


Due to the lack of time, the automation of the dehumidifier, which consists of connecting the hair dryer, the fan and the motor to the relay, which is connected to the arduino, and programming the arduino using the right codes such that the dehumidifier switches on and off at above 45% relative humidity and below 45%v relative humidity respectively, was not possible. Therefore, the dehumidifier is not automatic but instead manually turning on a single switch is necessary to switch it on.


4.4    Areas for improvement


Currently we are using a 240V computer fan to channel the air inside the box into the dehumidifier. The fan may be too weak and not have enough wind power to blow the humid air into the desiccant wheel and the dehumidified air out of the desiccant wheel and into the the air outside. This could be one reason as to why the relative humidity in Box A was not decreasing. This could be solved by switching the computer fan for a more powerful fan, such as a small table fan.


The hairdryer we are using to warm the silica gel constantly switches off every 5 seconds or so and switches on after 5-10 minutes. This is because the hair dryer consists of a switch called the thermal cutout switch, a safety feature, that shuts off the hair dryer if it gets too hot (HowStuffWorks, 2014). This would cause the silica gel to be warmed only at certain intervals, which would not allow the water vapour from the silica gel to be evaporated to increase the absorption capacity of the silica gel so that it can absorb more moisture from the air. By removing the thermal cutout switch, it is possible to prevent the hair dryer from switching off on its own so that the hair dryer is able to make the temperature of the silica gel rise to the point whereby it can be ridded of its existing moisture.

The amount of silica gel inside the desiccant wheel might be too much, causing the air spaces in between them to be too miniscule to allow airflow. This would result in the air from inside Box A, blown into the desiccant wheel by the fan, and the warm air from the hair dryer to be unable to pass through the thick layer of silica gel into the other side of the desiccant wheel and back into Box A and outside of Box A respectively. We can reduce the amount of silica gel inside the desiccant wheel to ensure that there is ample air spaces between the silica gel for the air to flow through. This way the humid air can easily be blown over the silica gel so that the silica gel can absorb the moisture from the air and the dehumidified air can then be blown back into Box A. Not only that, the warm air from the hair dryer will also be able to flow into the silica gel and out of the desiccant wheel to be expelled into the air outside of Box A with more ease.

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