Question
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at FLOW MEASUREMENT Mechanical Flowmeters ws are ACIMITIES Name Activity 20-1-Rotameter Selection The proper sel Date ection of a rotameter from a manufacturer's catalog can be more confusing and difficult than expected The capacity values shown in manufacturer's catalogs are for water or for air flowing at 14.7 psia and 70 F If a liquid to be measured has a higher specific gravity than water, the additional buoyancy on the fleat g the effective weight of the float; at the same time, the higher specific gravity increases the es are almost always at a higher pressure than 14.7 psia of gas must pass through the rotameter to lift the ntum of the flowing liquid. The result is that it takes a lower flow to lift the float to the top of the compared to water. When measuri and are most likely to be at a t specific gravity. Gas at higher pressure means that more sefm float to the top of the scale. g gas flow, the gases al erent temperature. The gas may not even be air, which then ch In some cases it may be necessary to Float Specific Gravity Hastelloy" C = 8.94 Teflon® 2.31 Liquid Flow. The change in liquid flow caused by a change in liquid specific gravity is calculated as follows: 316 SS 8.02 Monel 8.84 Foriginal flow F, = new flow p, float specific gravity = original fluid specific gravity (water or air) p.-new fluid specific gravity The change in liquid flow caused by a change in float specific gravity andwor weight is calculated as follows where F, original flow. F2 = new flow. original float weight = new float weight original float specific gravity P, new float specific gravity p fluid specific gravity
Explanation / Answer
consider 316 SS Float
rhof = 8.02
1. for 4 gpm water rotameter
f1 = 4 gpm
rho2 = 1.1
rho1 = 1
hence
f2 = f1*(sqroot((rhof - rho2)rho1)/(rhof-rho1)rho2)
f2 =3.786 gpm
2. for monel float
rhof = 8.84
rho 2= 1.2
f1 = 3.5 gpm
hence
f2 = 3.1540318 gpm
3. 2.3 gpm brine should be 0.75 of full capacity
f2 = 2.3/0.75 = 3.06667 gpm
rhof = 8.02
rho2 = 1.2
hence
f1 = 3.4082 gpm
hence we should use the 3.5 gpm rotameter
4. f2 = 37.5 scfm
P = 60 psig
T = 95 F
original temperature = To = 298 C = 568.4 F
original pressure Po = 1atm = 14.6959 psig
hence
PC = sqroot((14.7 + 60)/(14.7 + 14.6959)) = 1.5941
TC = sqroot((460 + 568.4)/(460 + 95)) = 1.361239
GC = 1 specific gravity new not given
hence
f2 = f1*PC*TC
f1 = 17.281489 scfm
