Percolation Rate
Flow Rate: With a series of plaster pots created, we can first examine the rate of flow in the pots.
The purpose of this inquiry is to determine the best chemical compositions to recommend for the plaster pots based on water needs for a person for each day. We will test the rate of flow for each pot and then calculate the time necessary to produce enough potable water for one person for one day.
The materials you will need for this part will be your filters, a screen and cup to hold the filter, a graduated cylinder, stopwatch or clock, water, and STEM Notebook for recording procedure and data. Set up your apparatus as shown in the picture below. Follow the procedure below for the initial trials of percolation tests.
FLOW RATE (PERCOLATION TEST) PROCEDURE 1
1) Because your plaster pots have cured and dried, they will need to be thoroughly soaked before they are tested. Immerse the pots in clean water for several minutes so that the plaster is thoroughly wetted.
2) Place the wet pot on the screen holder above a clean cup so that all the percolated water can be caught.
3) Determine an amount of water to add to the cup. In our example we found that 60 ml would fit inside the filter with a little room to spare. We measured 60 ml in a plastic cup and then poured the water into the filter and the immediately clicked the stopwatch.
4) Decide on a method for determining when all the water is out of the filter--when to call "time". We called "time" when any part of the plaster at the bottom of the filter became visible (no water on it). It is important to be consistent in the way you decide when percolation ceases.
The data we collected from our trials were as follows:
PERCOLATION RATE FOR 5 FILTERS USING 60 ml
*g/reactant refers to the mass of baking soda and cream of tartar used
to create pores in the plaster. Time refers to minutes and seconds that
60 ml of water took to percolate through the filter.
5) Students will note variation in the times based on several variables. The plaster may not have been stirred sufficiently to distribute the bubbles, the paper cup mold may not have been centered, or the depth of the cup may not have been equal in each circumstance. In the example above it was noted that the .55 filter was misshapen--one side of the filter was thinner than the other. This may cause an anomaly in the data.
6) From the data, determine the percolation rate per hour. We did this by charting the data again noting that if 60 ml percolated in a certain number of, minutes, the rate per hour could be determined by dividing 60/minutes to determine the number of 60 ml dumps per hour. To get an hourly dump measure then multiply the #60 ml dumps per hour X 60.
7) Humans require anywhere from 2000-3000 ml of water per day. From the data table above students can then determine what rate may be acceptable to produce enough water for an average family. Students can also make some calculations about scaling-up the size of the filter. Is the filtration rate linear based on internal surface area? Does the depth of the water make a difference because the pressure is higher?
Students can extend the percolation test by measuring the rate of flow in a different way:
PERCOLATION TEST PROCEDURE 2
Another way to measure percolation rate is to keep the level of water the same in the filter while setting a specific time on the filtration.
1) Prepare the apparatus as before in steps 1 and 2 above.
2) Make sure the cup that accepts the effluent (the water that comes out of the filter) is empty.
3) Pour water into the filter at a designated level that is marked inside the filter. You determine this arbitrarily. Have an assistant keep track of the time.
4) Keep water poured into the filter so that it stay as the level determined in 3 above.
5) Time the process for a set period of minutes, say 5 minutes.
6) Remove the filter and measure the effluent in the cup. This will give a measure of filtration when the filter is always full. If you know how much water passes in 5 minutes, then the per hour rate can be determined by multiplying by 12.