tag:blogger.com,1999:blog-5157088340069292858.post1309878539175408079..comments2014-09-26T11:27:31.500-05:00Comments on Madison Beer Review: Five Gallons At A Time: Draught System BalanceJeffhttp://www.blogger.com/profile/02125346445306449573noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-5157088340069292858.post-10803578702131897052013-02-18T20:30:53.544-06:002013-02-18T20:30:53.544-06:00I figured you assumed zero roughness because of wh...I figured you assumed zero roughness because of where Re = 11,000 and f = 0.031 intersect on the Moody Chart. Sorry about that! Anyway, I think the biggest difference between our calculations is that mine are based on 2 fl-oz/sec instead of ~1.35 fl-oz sec. If I change my flowrate to match yours, I calculate ~1.3 psi/ft for 3/16" ID vinyl. When you used my roughness assumption, did you convert it to relative roughness before you determined the friction factor? If you did, I'd guess that most of the remaining 0.4 psi/ft difference between our calculations is because I used the Swamee-Jain equation (http://en.wikipedia.org/wiki/Darcy_friction_factor_formulae) to calculate friction factor instead of looking it up in a Moody Chart.Joe Waltshttps://www.blogger.com/profile/18115431808379517101noreply@blogger.comtag:blogger.com,1999:blog-5157088340069292858.post-55568887963704363552013-02-18T18:03:08.361-06:002013-02-18T18:03:08.361-06:00Thanks for the link, and nice catch regarding my a...Thanks for the link, and nice catch regarding my assumptions of kinematic viscosity. I wasn't able to find a reference for beer. I did want to point out that I used a roughness of 0.0025 mm for vinyl tubing, though at the flow rates involved it hardly matters.<br /><br />Incorporating your assumed values for roughness and viscosity, the theoretical resistance for 3/16" ID vinyl is still only about 0.9 psi/ft. Any thoughts on why there's such a discrepancy? In my experience (a few kegerators and one long-draw beer gas system) assuming a value of 2-3 psi/ft would be far from a balanced pour.Sean Terrillhttp://seanterrill.comnoreply@blogger.comtag:blogger.com,1999:blog-5157088340069292858.post-72425591477448903922013-02-04T07:34:35.352-06:002013-02-04T07:34:35.352-06:00Yup, I meant fluid oz/sec and it's now fixed (...Yup, I meant fluid oz/sec and it's now fixed (all three times... ugh). Thanks!Joe Waltshttps://www.blogger.com/profile/18115431808379517101noreply@blogger.comtag:blogger.com,1999:blog-5157088340069292858.post-31821513577547644472013-02-04T06:32:03.324-06:002013-02-04T06:32:03.324-06:00Really interesting post. One quick correction -- ...Really interesting post. One quick correction -- I think you mean 2 fluid oz/sec instead of 2 fluid oz/min?tophmcknoreply@blogger.com