Mylar straws from PPG and Pressure test Chiho
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Mylar straws from PPG and Pressure test Chiho Wang, Seog Oh Duke University
Mylar straws from PPG • • 6 μm Mylar + 6 μm polyester adhesive + 6 μm Mylar. Nomex wraps inside the straw for mandrel release Refrigerant type lubricant on mandrel (no Silicon) 25 pieces made: 5 mm ID x 150 cm length 9/1/11 Chiho Wang & Seog Oh 2
Pressure test • 4 straws on 15 psi N 2 9/1/11 Chiho Wang & Seog Oh 3
Leak rate 16 15. 5 15 PSI 14. 5 14 13. 5 13 12. 5 12 8/25/11 • • 8/26/11 8/27/11 8/28/11 8/29/11 8/30/11 8/31/11 9/1/11 Pressure drop = 0. 1757 psi / day @ ~15 psi (no env. corr. ) Leak rate = 0. 00813 m. Bar/min 1 straw: volume = 29. 45 cm 3, surface = 235. 62 cm 2 Leak rate / straw = 29. 45 * 8. 13 E-6 / 60(sec) = 4 E-6 cc/sec 9/1/11 Chiho Wang & Seog Oh 4
Permeability • Permeation Q = k p A / d § Q = permeation: cc/sec § P = pressure: atm § A = surface area: cm 2 § D = thickness: cm § K = permeability: cc/sec cm-2 cm atm-1 • 4 E-6 cc/sec = k * 1 atm * 253. 62 cm 2 / 18 E-4 cm • K = 2. 8 E-11 cc/sec cm-2 cm atm-1 @ 15°C 9/1/11 Chiho Wang & Seog Oh 5
Comparison • J. Vac. Sci. Technol. A, Vol 12, No. 4, Jul/Aug 1994 • • Temperature dependence : Our K at 15°C, 2. 8 E-11, is a factor of 6 smaller than 1. 8 E-10 If corrected for temperature, our value is even smaller. Note: in this table, aluminized Mylar has higher permeability than plain Mylar in CO 2 !! 9/1/11 Chiho Wang & Seog Oh 6
Discussion • O 2 and H 2 O diffusion into straws might compensate permeation of N 2 out of straws(? ) • Polyester adhesive might be more gas tight than Mylar(? ) • Residual of lubricant on straw wall might reduce the permeation(? ) • Will aluminizing Mylar help gas leak? • More study is needed. 9/1/11 Chiho Wang & Seog Oh 7
Plan • Add ~700 gram weight and continue the pressure test with 20 psi - to test the mechanical integrity. 9/1/11 Chiho Wang & Seog Oh 8
