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Blending Theory

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Blending Theory

- Requirements
- Basics – empty cylinder
- Basics – partially empty cylinder
- Calculations
- Mixing Chart

- Decide method
- Assemble equipment
- Check suitability
- Need to know:
- What have in cylinder
- What want in cylinder
- What is final mix in cylinder
ANALYSE – ANALYSE - ANALYSE

- Have: Empty Cylinder
- Want: EAN32 to WP 230 bar
- How much oxygen?
0.32 x 230 = 73.6 bar O2 in final mix

- Top up with air (pPO2 = 0.21)
- Calculate O2 content in air top up
- Use formula

- To account for top up:
Final mix FO2 - Top up FO2 x Fill Pressure

Top up FN2

0.32 - 0.21x 230 0.79

= 32 bar oxygen plus 198 bar of air

- Check calculation:
32 bar oxygen = 1.0 x 32 = 32

198 bar air = 0.21 x 198 = 41.6

Total oxygen in EAN32 @230 bar

32 + 41.6 = 73.6 bar oxygen

- Use formula for any top gas
- Analyse to check mix

- Contains air – same as empty
- Contains nitrox mix – empty or analyse
- Find oxygen remaining in cylinder
- Subtract from required oxygen

- Have EAN34 @70 bar
0.34 x 70 = 23.8 bar O2

- Want EAN32 @ 230 bar
0.32 x 230 = 73.6 bar O2

- O2 wanted 73.6 – 23.8 = 49.8 bar
- Fill pressure 230 – 70 = 160 bar
- Require 49.8 bar O2 in 160 bar

- Work out FO2 - use pressure ‘T’
49.8 = 0.311

160

- Use top up formula
0.311 - 0.21x 160

0.79

= 20.5 bar O2

- Top up with 139.5 bar air

- Check calculation
EAN34 @ 70 bar = 23.8

Add 20.5 bar O2 = 20.5

Air @139.5 bar = 29.3

Total = 73.6 bar O2

Want EAN32 @ 230 bar = 73.6 bar O2

- Mixing chart – Appendix 1
- Oxygen in mix for pPO2 and fill pressure
- Use to calculate O2 needed
- Use to calculate O2 left in cylinder
- Accounts for O2 in air for top up
- Removes errors in calculation

We have covered:

- Requirements
- Basics – empty cylinder
- Basics – partially empty cylinder
- Calculations
- Mixing chart

Questions?