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RE: CO2 loss through silicone tubing (was multi tank CO2)
I wanted to post this one last time, since I caught some mistakes and
finally got the calculation “correct.” I redid the calculation for low
pressure and high pressure systems; also for thick walled tubing.
Fick’s Law:
Flux = Permeability * Area * (Partial Pressure Difference)/ Thickness
CO2 Permeability silicone tubing 20132 (10^-10 cc-mm/sec-cm^2-cm Hg)
CO2 Permeability FEP tubing 5.9
(specs from Cole-Parmer catalog)
CO2 flow rate 1 bubble/sec 0.06 cc/sec (my measurement)
Room pressure 14.7 psi 76.0 cm-Hg
CO2 High Pressure Systems 15.0 psi 77.6 cm-Hg
CO2 Low Pressure Systems 1.0 psi 5.1 cm-Hg
Partial pressure of CO2 in air 4.0 cm-Hg
thin wall tubing
tube wall thickness 1/32 inch 0.8 mm
ID of tube 3/16 inch 4.8 mm
Area 1 ft of tube 7.07 inch^2 45.96 cm^2
thick wall tubing
tube wall thickness 1/16 inch 1.6 mm
ID of tube 1/8 inch 3.2 mm
Area 1 ft of tube 4.71 inch^2 30.64 cm^2
Flux_hp_thin wall = 20131*10^-10*45.96*(77.6+76.0-4.0)/0.8 = 0.0173 cc/sec
Flux_lp_thick wall = 20131*10^-10*30.64*(5.1+76.0-4.0)/1.6= 0.00297 cc/sec
CO2 flux through tube
Tube length thin wall, HP thick wall, HP thick wall, LP
1 ft 0.0173 cc/sec 0.00577 0.00297
2 0.035 0.012 0.0059
4 0.069 0.023 0.012
8 0.138 0.046 0.024
10 0.173 0.058 0.03
Percent CO2 loss (if aquarium use is continuous 1 bubble (0.06 cc) per
sec**)
Tube length thin wall, HP thick wall, HP thick wall, LP
1 ft 22% 9 5
2 37 16 9
4 54 28 17
8 70 43 28
10 74 49 33
**The percent loss is a function of use rate. For example, if you use 5
bubbles per second at LP with 4 ft of tubing, your loss rate would be only
4%.