A Self-Regulating Water Condensor

The point of my Senior Project is to construct a self-regulating water condenser. My mentor, Charles Kennemore, works at Viavi Solutions. Instead of going to Viavi Solutions to work with optic-based technology, Mr. Kennemore told me about a project he wanted to try: using a water condenser to water plants without any human intervention.

 

https://goo.gl/xnrUog

The idea is based off of the Peltier effect, named after Jean Charles Athanase Peltier. The Peltier effect occurs when an electric current is passed through two semiconductors. If the conductors are made of dissimilar materials and currents are passed through the free ends, heat moves from one end to the other. The heat wants to go from high energy states to low energy states, so the heat moves across the conductor system.

http://goo.gl/VxBoR2

In the above picture, "P" and "N" are referring to p-type and n-type semiconductors.

The Peltier effect can be used to manipulate the temperatures on either side of the Peltier cooler. The more current running through the cooler, the higher the temperature change that can be achieved. With this in mind, if we use a Peltier cooler at night, we could drop the temperature of the cooler to the dew point. The dew point is the temperature at which dew forms by condensing from the air. The dew point drops as the temperature drops, but stays roughly the same. By changing the temperature of the cooler to below the dew point, water will condense onto the cold side of the cooler.

So far, we've figured out that the most humid time of day is from 11 P.M. to 7 A.M. In that timeframe, the dew point is 19 degrees under the average temperature. Using graphs we found online, we determined that we would need at around 1.5 Amperes of current to get a 19 degree change. The amount of Volts we need may be large to draw that amount of current for such a long time, though.

 http://goo.gl/3NXp0y

The plan for this Peltier cooler is to start with a solar cell and a light sensor. During the day, the solar cell will charge the batteries. When the light sensor stops sensing the presence of light, it will open the circuit and not allow any more current to travel from the solar cell to the batteries. Then, at around 11 P.M., a timer will close its switch and complete the circuit, allowing current to flow from the batteries into the free ends of the cooler.

I have been instructed to look into several topics for this system. For instance, we need a way to disperse the heat from the hot side of the cooler. We could use a heat sink - a conductor with a moving coolant fluid inside that cools the material - or we could use a teethed-effect (as seen in the picture below) to maximize surface area and get rid of heat.

To be able to make the circuit self-regulating, we may need to employ thermistors. Resistors control the amount of current that pass through them. Thermistors do the same thing, but resist more current when they are at a lower temperature. With this in mind, we could have a heat sensor checking on the thermistor, and if it gets to a certain temperature and is letting too much current through, the heat sensor could open a switch to stop the circuit.

http://goo.gl/I3A4cO

An assortment of different thermistors.

I have also been looking into the best metals to use, which shapes have the most efficient volume-to-surface-area ratio, what kind of batteries we should use, and black-body radiation, among other things.

Next, we will work on testing circuits and constructing parts of the circuit itself. Mr. Kennemore mentioned testing which batteries work best and figuring out how much they will drain if we run 1.5 Amperes for eight hours. Before we actually start building the cooler and the circuit, we need to figure out how much room we will need, where we would want to put it, what we can do to minimize cost and materials, and how we can get the light sensor to work with the solar cell.