## 12gram Pressure Chart

Post questions and info about pneumatic (compressed gas) powered launchers here. This includes discussion about valves, ratios, compressors, and anything else relevant to launchers powered by compressed gas.
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.
BC Pneumatics

Posts: 2391
Joined: Wed Dec 10, 2003 2:29 am
Location: USA

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.
Freefall

Posts: 3252
Joined: Tue Jul 29, 2003 4:46 pm
Location: USA

There we go. Thank you freefall.
BC Pneumatics

Posts: 2391
Joined: Wed Dec 10, 2003 2:29 am
Location: USA

Thanks for the explaination Freefall and BC.
acanz

Posts: 1191
Joined: Sun Mar 21, 2004 1:25 pm
Location: USA

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,
akb

Posts: 1055
Joined: Sun Sep 14, 2003 10:39 pm
Location: USA

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>
akb

Posts: 1055
Joined: Sun Sep 14, 2003 10:39 pm
Location: USA

Very nice akb! Much more percise it would seem. BC Pneumatics

Posts: 2391
Joined: Wed Dec 10, 2003 2:29 am
Location: USA

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
akb

Posts: 1055
Joined: Sun Sep 14, 2003 10:39 pm
Location: USA

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.
BC Pneumatics

Posts: 2391
Joined: Wed Dec 10, 2003 2:29 am
Location: USA

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
akb

Posts: 1055
Joined: Sun Sep 14, 2003 10:39 pm
Location: USA

PreviousNext 