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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
...
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. 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 mg/L which is approximately the value of 100 percent oxygen saturation of 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 700 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 from two tests can be seen above. #Figure 1 and #Figure 3 depict the behavior of the dissolved oxygen concentration under negative pressure conditions profiled in #Figure 2 and #Figure 5 for test 1 and test 2, respectively. #Figure 3 and #Figure 6 show the change in dissolved oxygen concentration after the reactor was opened to the atmosphere.
The charts above both indicate a change in dissolved oxygen of about 0.3 mg/L over a minute to two minutes for water subject solely to partial vacuum. For the first test, the water was subject to a pressure drop from atmospheric to approximately -70 kPa. A total pressure drop of -70 kPa was also used in the second test though the water was kept at approximately -37 kPa for about a minute in order to observe the effect of this pressure on the dissolved oxygen. It can be seen by juxtaposing the two curves on the same plot (#Figure 7) that the behavior of dissolved oxygen after being exposed to the partial vacuum are fairly similar. The first test was performed with a higher initial dissolved oxygen content in the water, so the graph is positioned slightly higher than the second test curve.
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The graphs above indicate a change in dissolved oxygen of about 0.3 mg/L over a minute to two minutes for water subject solely to partial vacuum. For the first test, the water was subject to a pressure drop from atmospheric to approximately -70 kPa. A total pressure drop of -70 kPa was also used in the second test though the water was kept at approximately -37 kPa for about a minute in order to observe the effect of this pressure on the dissolved oxygen. It can be seen by juxtaposing the two curves on the same plot that the behavior of dissolved oxygen after being exposed to the partial vacuum are fairly similar. The first test was performed with a higher initial dissolved oxygen content in the water, so the graph is positioned slightly higher than the second test curve. {float:left|border=2px solid black|width=600px} !E1T1T2Comparison.PNG|width=600px! h5. Figure 67: Graph comparing DO curves from Test 1 and Test 2. {float} \\ |
Also,
...
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
...
baseline,
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a
...
second
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experiment
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was
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run
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in
...
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
...
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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