Does V Planner Blender include a fudge factor?

[ardhill]

Hi

I was just working out my blending calcs and decided for some reason to try a couple of blender programmes.

I normally use V Planner, but tried a couple of others as well.

- Empty tanks
- I want 210 bar 27% Nx

V Planner gives me 21 bar O2 and top with air

Other blender programmes give me 16 bar O2 and top with air

Now that I think about it, do normally use V Planner, but also normally over fill the air part to get the blend.

Is this right, does it include the fudge factor that many people add or is there a glitch in my copy (I use the PDA version).

Thanks

[nickb]

<Edited in the light of Ross's reply below>

I use Nigel's Blender program with the Van der Waals equation of state option.

[ardhill]

Nigel's app says 16 bar as well. It appears to be only the V Planner one that is giving me 21 bar.

[David]

Originally Posted by ardhill

- I want 210 bar 27% Nx

V Planner gives me 21 bar O2 and top with air

Other blender programmes give me 16 bar O2 and top with air

can someone not do this long hand ?


12 liter cylinder = 12 * 210 = 2520 liters free gas
16 * 12 = 192 liters

2520 - 192 = 2328 liters of 21% 02 and 79 N2

now I am stuck :-) help please

[David]

Originally Posted by David

can someone not do this long hand ?


12 liter cylinder = 12 * 210 = 2520 liters free gas
16 * 12 = 192 liters

2520 - 192 = 2328 liters of 21% 02 and 79 N2

now I am stuck :-) help please

192 o2
488.88 o2
1839.12 n2

680.88 o2
1839.12 n2

2520 total but the answer is in there somewhere :-)

2520*0.27 =680.4

so thats about 27% will someone who knows more than I do sort this please



where is Gloc when you want maths done wrong :-)

[ardhill]

Originally Posted by David

can someone not do this long hand ?

Yep:

210 bar

27% of which is O2
73% of which is N2

73% of 210bar = 153.3bar

convert to air pressure...

(153.3 / .79) * 1 = 194

So, Air = 194 bar

210 - 194 = 16 bar O2


But my question was what is going on with V Planner as it gives me 21 bar O2

[nickb]

V-Planner's asking me for 17 bar of 02 (v3.80)

Just checked v3.81 and it's the same

[A. Berk]

To work on it 'longer-hand' look at it this way, you need to isolate the PN2 in you final mix as this comes from your 'air' source and its partial pressure never changes though the O2 partial pressure will 'cos you are adding pure O2.

So, a 27% mix has 73%N2 at 210 bar. Therefore 210 x .73 = 153.3 bar N2 will be in final mix. This N2 brings with it 21% O2 (in air) so, divide the PN2 by 79 (the % N2 in air) and x by 21 (% O2 in air) and you have 40.7 bar O2 that comes with the air. Add these together 40.7 O2 + 153.3 N2 = 194 bar Air. Therefore the shortfall from 210 bar is 16, which is the pressure of 'pure' O2 that you must add. Voila - 210 bar of 27%!!!

Add it all up;

153.3 N2
40.7 O2 from air
16.0 Pure O2
210.0 bar Nitrox 27%

Berko

[ardhill]

Originally Posted by nickb

V-Planner's asking me for 17 bar of 02 (v3.80)

Thanks Nick, I will email Vplanner then.
.

[nickb]

<Edited in the light of Ross's reply below>