A Simple Capillary Flow Meter Joseph W. Bozzelli a n d J o n a t h a n S n y d e r Department of Chemistry and Chemical Engineering, New Jersey Institute of Technology, Newark, NJ 07102
Capillary flow meters have been used in air pollution lab courses a t NJIT t o measure air sampling flow rates, t o determine flows of gas calibration standards entering a smog chamber, and t o determine gas flows through capillary GC columns in the research labs. They often can be used in closed or non-atmospheric pressure systems where a bubble meter flow or exposure to atmospheric gases would he a detriment to the experiment. This paper details manufacture of a simple flow meter without the requirement of machining, glassblowing, or tubefitting supplies. Capillary flow meters operate by measuring t h e pressure drop which occurs when gas flows through a restrictive orifi~e,'.~and they can operate over a wide to lo2 cm31sec) range of gas flows by utilizing different size capillaries. A specific capillary is only practical, however, over a flow range encompassing two orders of magnitude. T h e capillary used in construction of these flow meters is a length of stainless steel hypodermic syringe tubing.3 T h e table lists several measured flow ranges of air (0.2 5 AP 5 20 cm oil, sp. gr. = 1)versus tube gauge.
Figure 2.Bypass and valve for modificationof flow meter.
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Procedure To build the unit, construct the differential pressure manometer from clear, flexible, polyvinyl chloride tubing or a glass U-tube. Cover a wood or cardboard backing with graph paper, 10 lines to the cm, and support it vertically. Most simply, form a piece of % or 3/1s in. LD. X v32 in. wall thickness PVC tubing, 60 cm long, into a U-shape on the
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Figure 3,Flow
Flow Ranges ot Alr Versus Tube Gauge Length, cm.
Gauge
I.D.. in.
Flaw range, ccs-'
3 4 4 4
26 26 24 22
0.007 0.010 0.012 0.016
0.00052-0.043 0.0033 -0.317 0.0060 -0.529 0.0153 -1.61
hsck:ng and mount it ~ i t hnylon thread or thin wire ties Puncture the tuhing w~tha pin at [nu points on the i n d c uf the U approximatci) I cm from each end. Inrert a selected icngt h and gauge ofsyringe tubing into the punctures and apply a sealant (epoxy, silicone adhesive, ete.) as illustrated in Figure 1. No capillary blockage occurs using this technique, but if the capillary is removed and then remounted, the sealant may dog it. The flow meter is used by inserting it in series with the flowing gas usually but not necessarily keeping either the inlet or exhaust lines at 1 atm oressure. 'l'h~sflow meter manometer mn be improvrd or modified wirh a bvpnss and \,alveline and c,r by subsrituting a pr~-i
