12gram Pressure Chart

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Postby BC Pneumatics » Tue Nov 02, 2004 11:23 pm

Okay, 0 psia only occurs in a vacuum, as it is the absolute (hence the 'a') pressure, and includes the atmosphere (~14.7psia). psig negates the atmosphere, so 12psig = ~26.7psia. Right Plasticex? (or some other higher being.)
BTW, It think the 'G' is for guage. I heard that once.
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Postby Freefall » Tue Nov 02, 2004 11:30 pm

Not always. PSIG is just a measure of pressure difference between two volumes of fluid. Generally, those volumes are some pressurized vessel and open atmosphere. If you took a vessel pressurized to 22.4 psig at sea level and put it under ~18 feet of water, it would now be 0 psig, even though what's inside hasn't changed. If you stuck a gage on the outside of the space station to measure the inside pressure, PSIG and PSIA would be identical, since the reference is 0 psi.

For many purposes though, PSIA = PSIG + 14.7 is adequate.
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Postby BC Pneumatics » Tue Nov 02, 2004 11:38 pm

There we go. Thank you freefall.
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Postby acanz » Wed Nov 03, 2004 1:34 am

Thanks for the explaination Freefall and BC.
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Postby akb » Sat Nov 06, 2004 10:02 am

Nice charts, BC, and a great idea to have it here as reference info.

I made some similar calculations in a different way with slightly different assumptions. The results are similar but there are some differences especially in the smaller chamber data.

It is a bit tricky to put Excel data on here, I'll give it a shot in another post.

-- akb

Have fun and be safe,
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Postby akb » Sat Nov 06, 2004 10:02 am

Analysis of CO<sub>2</sub> in 12 gram cylinder released into larger volume chamber

Assumptions
system allowed to equilibriate to one temperature
system volume includes CO2 cylinder plus chamber volume
chamber contains 1 atmosphere of CO2 prior to filling (not a vacuum)

Process
find moles of gas in CO2 cylinder (12/44)
find volume of CO<sub>2</sub> cylinder (pi * d^2/4 * length)
convert system temperature to Degrees Kelvin
find moles of gas in chamber N = PV/(RT)
add to moles of gas in CO<sub>2</sub> cylinder
find pressure of total moles in total volume; P = NRT/V
total volume is sum of chamber and CO<sub>2</sub> cylinder volumes
convert pressure to gauge pressure (subtract one atm, convert to psi)

Calculations
12 grams of co2 in cylinder
12 grams in mole of C
16 grams in mole of O
44 grams in mole CO<sub>2</sub>
0.273 moles in 12 gram cylinder CO2 (this is the N in PV=NRT)
0.767 volume of 12 gram cylinder cu in
8.2E-02 R in L-atm/mole deg C
61.0 cu in per liter
14.7 psi per atmosphere

<table border=1>
<tr><td colspan=5>
System at 30 deg F

<tr><td>Chamber <td>total N <td colspan=2>Pressure
<tr><td>cu in <td>mole <td>atm <td>psig
<tr>
<tr><td>10 <td>.280 <td>35 <td>506
<tr><td>20 <td>.287 <td>19 <td>262
<tr><td>30 <td>.295 <td>13 <td>177
<tr><td>40 <td>.302 <td>10 <td>134
<tr><td>50 <td>.309 <td>8 <td>107
<tr><td>60 <td>.317 <td>7 <td>90
<tr><td>70 <td>.324 <td>6 <td>77
<tr><td>80 <td>.332 <td>6 <td>67
<tr><td>90 <td>.339 <td>5 <td>60
<tr><td>100 <td>.346 <td>5 <td>54
<tr><td>110 <td>.354 <td>4 <td>49
<tr><td>120 <td>.361 <td>4 <td>45
<tr><td>130 <td>.368 <td>4 <td>42
<tr><td>140 <td>.376 <td>4 <td>39
<tr><td>150 <td>.383 <td>3 <td>36
</table>


<table border=1>
<tr><td colspan=5>
System at 50 deg F

<tr><td>Chamber <td>total N <td colspan=2>Pressure
<tr><td>cu in <td>mole <td>atm <td>psig
<tr>
<tr><td>10 <td>.280 <td>37 <td>526
<tr><td>20 <td>.287 <td>20 <td>273
<tr><td>30 <td>.294 <td>14 <td>184
<tr><td>40 <td>.301 <td>10 <td>139
<tr><td>50 <td>.308 <td>9 <td>112
<tr><td>60 <td>.315 <td>7 <td>93
<tr><td>70 <td>.322 <td>6 <td>80
<tr><td>80 <td>.329 <td>6 <td>70
<tr><td>90 <td>.336 <td>5 <td>62
<tr><td>100 <td>.343 <td>5 <td>56
<tr><td>110 <td>.350 <td>4 <td>51
<tr><td>120 <td>.357 <td>4 <td>47
<tr><td>130 <td>.365 <td>4 <td>43
<tr><td>140 <td>.372 <td>4 <td>40
<tr><td>150 <td>.379 <td>4 <td>38
</table>

<table border=1>
<tr><td colspan=5>
System at 70 deg F

<tr><td>Chamber <td>total N <td colspan=2>Pressure
<tr><td>cu in <td>mole <td>atm <td>psig
<tr>
<tr><td>10 <td>.280 <td>38 <td>547
<tr><td>20 <td>.286 <td>20 <td>284
<tr><td>30 <td>.293 <td>14 <td>191
<tr><td>40 <td>.300 <td>11 <td>144
<tr><td>50 <td>.307 <td>9 <td>116
<tr><td>60 <td>.313 <td>8 <td>97
<tr><td>70 <td>.320 <td>7 <td>83
<tr><td>80 <td>.327 <td>6 <td>73
<tr><td>90 <td>.334 <td>5 <td>65
<tr><td>100 <td>.341 <td>5 <td>58
<tr><td>110 <td>.347 <td>5 <td>53
<tr><td>120 <td>.354 <td>4 <td>49
<tr><td>130 <td>.361 <td>4 <td>45
<tr><td>140 <td>.368 <td>4 <td>42
<tr><td>150 <td>.375 <td>4 <td>39
</table>

<table border=1>
<tr>
<td colspan=5>
System at 90 deg F

<tr><td>Chamber <td>total N <td colspan=2>Pressure
<tr><td>cu in <td>mole <td>atm <td>psig
<tr>
<tr><td>10 <td>.279 <td>40 <td>568
<tr><td>20 <td>.286 <td>21 <td>294
<tr><td>30 <td>.292 <td>15 <td>199
<tr><td>40 <td>.299 <td>11 <td>150
<tr><td>50 <td>.305 <td>9 <td>120
<tr><td>60 <td>.312 <td>8 <td>101
<tr><td>70 <td>.319 <td>7 <td>86
<tr><td>80 <td>.325 <td>6 <td>76
<tr><td>90 <td>.332 <td>6 <td>67
<tr><td>100 <td>.338 <td>5 <td>61
<tr><td>110 <td>.345 <td>5 <td>55
<tr><td>120 <td>.351 <td>4 <td>51
<tr><td>130 <td>.358 <td>4 <td>47
<tr><td>140 <td>.364 <td>4 <td>43
<tr><td>150 <td>.371 <td>4 <td>41
</table>

<table border=1>
<tr>
<td colspan=5>
System at 105 deg F

<tr><td>Chamber <td>total N <td colspan=2>Pressure
<tr><td>cu in <td>mole <td>atm <td>psig
<tr>
<tr><td>10 <td>.279 <td>41 <td>583
<tr><td>20 <td>.285 <td>22 <td>302
<tr><td>30 <td>.292 <td>15 <td>204
<tr><td>40 <td>.298 <td>11 <td>154
<tr><td>50 <td>.305 <td>9 <td>124
<tr><td>60 <td>.311 <td>8 <td>103
<tr><td>70 <td>.317 <td>7 <td>89
<tr><td>80 <td>.324 <td>6 <td>78
<tr><td>90 <td>.330 <td>6 <td>69
<tr><td>100 <td>.336 <td>5 <td>62
<tr><td>110 <td>.343 <td>5 <td>57
<tr><td>120 <td>.349 <td>5 <td>52
<tr><td>130 <td>.356 <td>4 <td>48
<tr><td>140 <td>.362 <td>4 <td>45
<tr><td>150 <td>.368 <td>4 <td>42
</table>
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Postby BC Pneumatics » Sat Nov 06, 2004 10:15 am

Very nice akb! Much more percise it would seem. :D
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Postby akb » Sat Nov 06, 2004 10:17 am

Now if I could get decent formatting on it..

Well, it is at least better than it was. Excel sure puts out messy html.

At any rate, this method might produce more accurate numbers. Anyone have any real data to compare with??

-- akb
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Postby BC Pneumatics » Sat Nov 06, 2004 10:27 am

psst, ask PC, he did it for me ;)
Seriously, ally you need to do is set up a table. Look for an online guide to HTML if you dont know how.
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Postby akb » Sat Nov 06, 2004 10:51 am

A table is a good way to do it. Excel's table html output has too much formatting, so I did it by hand. Yuck. Was tempted to make a filter to reprocess Excel's html output, but didn't. Probably should have.

-- akb
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