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DO
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Removal
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by
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Partial
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Vacuum
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Purpose
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and
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Principle
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The
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purpose
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of
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this
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experiment
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was
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to
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determine
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the
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degree
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of
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dissolved
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oxygen
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removal
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from
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supersaturated
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water
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subject
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to
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a
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partial
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vacuum.
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Dissolved
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oxygen
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removal
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from
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the
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water
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occurs
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because
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the
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partial
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pressure
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of
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oxygen
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in
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space
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above
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the
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water
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was
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lowered
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by
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the
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partial
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vacuum.
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Thus,
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the
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dissolved
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oxygen
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would
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transfer
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out
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to
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the
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space
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above
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the
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water
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in
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order
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to
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restore
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equilibrium
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as
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stated
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in
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Henry's
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Law.
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Measuring
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the
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dissolved
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oxygen
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in
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the
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water
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over
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a
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period
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of
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time
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allowed
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us
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to
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observe
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the
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amount
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of
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dissolved
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oxygen
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removed
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and
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also
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to
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calculate
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the
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approximate
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rate
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of
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dissolved
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oxygen
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removal.
Procedure
We started the experiment by calibrating the dissolved oxygen probe and pressure sensor. This was done by vigorously aerating the water in the apparatus without the lid on for around 5 minutes to get the water to equilibrium DO saturation. This level of DO was set in EasyData to be 8.7 mg/L which is nearly the value of 100 percent oxygen saturation of pure water at atmospheric pressure. While using EasyData to monitor the pressure and dissolved oxygen, water originating from the large container above the sink filled with tap water was pumped out of the apparatus until the desired pressure was reached. The water was at around 20 degrees centigrade and constantly stirred. Once the desired pressure was attained, the pump was stopped and the apparatus was allowed to sit for a short period of time. This time was varied to determine, after being converted from time to distance based on a influent water velocity of 740 m/day, what the optimal vertical pipe length would be using our system. These values varied from seconds to a few minutes representing a pipe length of a fraction of a meter to a few meters. The system was then opened to the atmosphere by releasing the clamp on the pump that constricted the tube leading out of the apparatus. The dissolved oxygen was monitored and recorded for two to three minutes after this.
Results and Discussion
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h2. Procedure We started the experiment by calibrating the dissolved oxygen probe and pressure sensor. This was done by vigorously aerating the water in the apparatus without the lid on for around 5 minutes to get the water to equilibrium DO saturation. This level of DO was set in EasyData to be 8.7 mg/L which is nearly the value of 100 percent oxygen saturation of pure water at atmospheric pressure. While using EasyData to monitor the pressure and dissolved oxygen, water originating from the large container above the sink filled with tap water was pumped out of the apparatus until the desired pressure was reached. The water was at around 20 degrees centigrade and constantly stirred. Once the desired pressure was attained, the pump was stopped and the apparatus was allowed to sit for a short period of time. This time was varied to determine, after being converted from time to distance based on a influent water velocity of 740 m/day, what the optimal vertical pipe length would be using our system. These values varied from seconds to a few minutes representing a pipe length of a fraction of a meter to a few meters. The system was then opened to the atmosphere by releasing the clamp on the pump that constricted the tube leading out of the apparatus. The dissolved oxygen was monitored and recorded for two to three minutes after this. h2. Results and Discussion {float:left|border=2px solid black|width=350px} Click graphs to see larger. {anchor: Figure 1} [!E1T1DOVac.PNG|width=350px!|Experiment 1 Test 1 Results] h5. Figure 1: Experiment 1 Test 1, DO behavior under partial vacuum. {anchor: Figure 2} [!E1T1PressureVac.PNG|width=350px!|Experiment 1 Test 1 Results] h5. Figure 2: Experiment 1 Test 1, Pressure conditions under partial vacuum. {anchor: Figure 3} [!E1T1DOatm.PNG|width=350px!|Experiment 1 Test 1 Results] h5. Figure 3: Experiment 1 Test 1, DO behavior at atmospheric pressure. {float} |
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{float:left|border=2px solid black|width=350px}
Click graphs to see larger.
{anchor: Figure 4}
[!E1T2DOVac.PNG|width=350px!|Experiment 1 Test 2 Results]
h5. Figure 4: Experiment 1 Test 2, DO behavior under partial vacuum.
{anchor: Figure 5}
[!E1T2PressureVac.PNG|width=350px!|Experiment 1 Test 2 Results]
h5. Figure 5: Experiment 1 Test 2, Pressure conditions under partial vacuum.
{anchor: Figure 6}
[!E1T2DOVac.PNG|width=350px!|Experiment 1 Test 2 Results]
h5. Figure 6: Experiment 1 Test 2, DO behavior at atmospheric pressure.
{float}
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Graphs
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from
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two
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tests
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can
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be
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seen
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above.
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and
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depict
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the
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behavior
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of
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the
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dissolved
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oxygen
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concentration
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under
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negative
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pressure
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conditions
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profiled
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in
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and
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for
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test
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1
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and
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test
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2,
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respectively.
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and
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show
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the
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change
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in
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dissolved
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oxygen
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concentration
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after
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the
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reactor
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was
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opened
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to
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the
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atmosphere.
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The
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charts
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above
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both
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indicate
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a
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change
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in
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dissolved
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oxygen
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of
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about
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0.3
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mg/L
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over
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a
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minute
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to
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two
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minutes
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for
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water
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subject
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solely
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to
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partial
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vacuum.
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For
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the
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first
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test,
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the
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water
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was
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subject
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to
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a
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pressure
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drop
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from
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atmospheric
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to
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approximately
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-70
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kPa.
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A
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total
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pressure
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drop
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of
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-70
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kPa
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was
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also
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used
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in
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the
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second
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test
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though
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the
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water
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was
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kept
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at
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approximately
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-37
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kPa
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for
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about
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a
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minute
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in
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order
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to
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observe
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the
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effect
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of
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this
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pressure
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on
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the
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dissolved
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oxygen.
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It
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can
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be
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seen
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by
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juxtaposing
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the
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two
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curves
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on
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the
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same
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plot
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(
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)
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that
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the
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behavior
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of
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dissolved
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oxygen
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after
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being
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exposed
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to
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the
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partial
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vacuum
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are
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fairly
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similar.
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The
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first
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test
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was
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performed
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with
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a
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higher
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initial
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dissolved
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oxygen
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content
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in
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the
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water,
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so
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the
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graph
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is
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positioned
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slightly
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higher
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than
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the
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second
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test
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curve.
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{anchor: Figure 7} {float:left|border=2px solid black|width=600px} !E1T1T2Comparison.PNG|width=600px! h5. Figure 7: Graph comparing DO curves from Test 1 and Test 2. {float} \\ |
Also,
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the
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increase
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in
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dissolved
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oxygen
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concentration
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post
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vacuum
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was
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likely
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due
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to
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reincorporation
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of
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oxygen
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from
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tiny
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bubbles
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that
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formed
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on
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the
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interior
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walls
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of
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the
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reactor
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that
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were
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unable
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to
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float
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out
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of
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the
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reactor.
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Using
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this
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data
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as
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a
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baseline,
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a
...
second
...
experiment
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was
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run
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in
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which
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the
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water
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was
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aerated
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under
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partial
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vacuum
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and
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is
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described
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in
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...
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