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These calculations yield a total realized heating power for our system of 316.2 watts, a 34%
efficient conversion of sunlight to thermal energy. With this conservative estimate of
power, the estimated water pasteurization ability of the device was 4.19 liters/hour. Since
these tests were run during winter days with low ambient temperatures, this value likely
represents the lower estimate of the power of the device.
Figure 1: Temperature curve for trough absorber
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The thermostat purchased is rated at 91°C, which was later verified to be the temperature
the device begins to open at. In the system, the valve remains shut during periods when
the water has not reached a high enough temperature to be considered safe. However,
once the water reaches 91°C, well above the pasteurization temperature, the valve begins
to allow the flow of water into the clean reservoir. If the system falls below this
temperature, the valve closes again, and the water will not pass until the system heats back
up. With the thermostatic valve and the geometry of the trough, this device can be
completely passive, and purify water throughout the day without human intervention.
Figure 2: Schematic of Modified Thermostat. The blue blocks represent the silicone "gasket" addition to the
thermostat.
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Once the valve opened, the back pressure of the system needed to be adjusted in order to
reach steady state. If the pressure on the outlet side of the valve is not adjusted, the
temperature of the water near the valve rises to approximately 102 °C, the valve opens and
the water is rapidly expelled from the system, and then the valve closes. The system
operating in this fashion does not reach steady state. In order to reach a continuous flow,
the pressure on the outlet side of the valve must be adjusted to reach steady state and a
continuous flow rate. When this was done, a sustainable flow was achieved around 52
minutes into the experiment and was maintained until the end of the experiment at 75
minutes. Constant flow would have been maintained as long as solar irradiance was
maintained at a similar level. The flow rate was calculated to be 465mL over a five-minute
time span, which is equivalent to 5.58 L per hour. In addition, water was calculated to be
at sufficient pasteurization temperature for a period of approximately 81 seconds before
exiting the system.
Figure 3: Plot of temperature versus time for the water pasteurization trough
system. The red data points indicate internal temperature near valve and blue data
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