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**To**:**<Aquatic-Plants at actwin_com>****Subject**:**CO2 loss through silicone tubing (was multi tank CO2)****From**:**"Joe Kopanski" <kopanski at earthlink_net>**- Date: Mon, 26 Nov 2001 22:33:28 -0500
- Importance: Normal
- In-Reply-To: <200111262048.fAQKm1g10087 at actwin_com>

It has been suggested that I modify my previous post in the following way: “The pressure difference you need to calculate is the difference between the CO2 pressure in the line and the partial pressure of CO2 in air. And 15 psi is a more realistic pressure. The gauge is reading the pressure *above* room pressure.” The CO2 permeability of silicone tubing is 10132 (units: 10^-10 cc-mm/sec-cm^2-cm Hg). A better choice is FEP (fluorinated ethylene propylene) tubing (CO2 permeability: 5.9). So, is it worth it to use FEP instead of silicone tubing? I’ve wondered about it myself, so here’s my shot at a calculation (I’m sure someone will let me know if I’m wrong): CO2 flow rate 1 bubble/sec 0.06 cc/sec (my measurement) Room pressure 14.7 psi 76.0 cm-Hg Partial pressure CO2 in air 4.0 cm-Hg CO2 Line Pressure 15.0 psi 78 cm-Hg 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 Fick’s Law: Flow = Permeability * Area * (Pressure Difference)/ Thickness = 10131*10^-10*45.96*(78+76-4.0)/0.8 Tube length CO2 loss (silicone tubing) 1 ft 0.0087 cc/sec (ml/sec) 2 ft 0.017 4 ft 0.035 8 ft 0.070 10 ft. 0.087 100 ft. 0.87 So, you lose about 58% (!) of your CO2 with 4 ft of silicone tubing per tank and virtually none with FEP. With multiple tanks, the percentage loss is the same, but the total volume lost is greater. CO2 is cheap (I just paid $13.65 for a 10# refill) -- but you’re also saving the cost (annoyance) of getting your tank refilled more often. Well, that’s a huge loss… I’m I still doing something wrong? Wrong equation, wrong assumptions? Joe K.

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