How to Correct Flow Data after Choosing the Wrong Gas

Correct your flow data after choosing the wrong gas in Gas Select

Like most flow meter technologies, Alicat mass flow meters need to know which gases are flowing through them for their flow readings to be accurate. Our differential pressure-based technology uses the known absolute viscosity of the gas or gas mixture (stored in Gas Select), combined with the measured absolute pressure and temperature to produce flow readings.

If you accidentally selected a preloaded gas calibration that was different from the gas you actually flowed through the instrument, your flow data will be corrupted by approximately the ratio of the viscosities of the two gases. This article shows you how to correct your data by multiplying each reading by the ratio of the selected gas’s viscosity to the desired gas’s viscosity.

How to correct your flow data if you accidentally selected a different gas in Gas Select

Procedure

Let’s start by defining a few variables:

Qindicated = Flow rate recorded by your device
ηselected = Absolute viscosity of the gas you incorrectly selected
ηactual = Absolute viscosity of the gas that actually passed through your device
Qactual = Actual (corrected) flow rate of the gas that passed through your device

To get to the corrected flow rate of the gas flowing through the unit (Qactual), multiply the indicated flow rate by the ratio of the gas viscosities:

Qactual = Qindicated x (ηselectedactual)

Your Alicat product manual lists the absolute viscosity (η) of each gas that is part of Gas Select, at reference temperatures of both 0 °C and 25 °C. If your process operates near room temperature, the viscosity at 25 °C is a good choice, but note that viscosity does change with temperature.

Example

You flowed a natural gas mixture of 95% CH4/3% C2H6/1% N2/1% CO2 (Gas Select #190, Nat Gas-2), but you accidentally had Gas Select set to air. Your gas was close to room temperature, and you recorded a flow rate of 1.00 slpm.

Qindicated = 1.00 slpm
ηselected = 184.8989 (absolute viscosity of air)
ηactual = 111.5557 (absolute viscosity of Nat Gas-2)

Using the equation above, we come up with the following corrected flow value:

Qactual = 1.00 x (184.8989/111.5557) = 1.6575 slpm

 

Learn more

Pure Non-Corrosive GasesGas data (at 25°C)
Gas number (if available)Short NameLong NameRP10 Mol. Wt.RP10 AbsoluteViscosity (uP) at 25°CRP10 Density at 25°CCompressibility at 25°CAdiabatic index (Cp/Cv)
0AirAir28.958601184.8992441.1840110.9996981.401783
1ArArgon39.948226.2399491.6338640.9993661.669574
2CH4Methane16.0428110.7595460.6568820.9982471.306166
3COCarbon Monoxide28.0101177.6799151.1452980.9996411.401279
4CO2Carbon Dioxide44.0098149.1462111.807970.9949551.294092
5C2H6Ethane30.0690492.3395461.2384560.9923991.1939
6H2Hydrogen2.0158889.0029830.0823481.0005941.405358
7HeHelium4.002602198.4561390.1635231.0004841.666546
8N2Nitrogen28.01348178.0474061.1452450.9998021.401283
9N2ONitrous Oxide44.0128148.4448241.8088710.9945331.280409
10NeNeon20.179317.1301710.8244091.0004711.666923
11O2Oxygen31.9988205.5020731.3087870.9993531.396654
12C3H8Propane44.0956281.2261871.8320360.9838051.136398
13nC4H10n-Butane58.122273.7614012.4492930.9699491.105253
14C2H2Acetylene26.03728103.2024181.0706920.9939821.228674
15C2H4Ethylene (Ethene)28.05376103.1838981.153290.9942551.246119
16iC4H10i-Butane58.122274.9784592.4402770.9735331.105199
17KrKrypton83.798253.4057323.4322810.9979271.67221
18XeXenon131.293230.5364435.3950080.9947121.677336
19SF6Sulfur Hexafluoride146.055419152.2020166.0383040.9886681.098367
210D2Deuterium4.0282125.8692070.1645531.000581.398484
Pure Corrosive GasesGas data (at 25°C)
Gas number (if available)Short NameLong NameRP10 Mol. Wt.RP10 AbsoluteViscosity (uP) at 25°CRP10 Density at 25°CCompressibility at 25°CAdiabatic index (Cp/Cv)
30NONO (Nitric Oxide)30.006190.05951.2267160.9997971.386
31NF3NF3 (Nitrogen Trifluoride)71.019175.4252.9133640.9963861.1876
32NH3Ammonia17.03052100.88280.7035160.9894681.316454
33Cl2Chlorine70.906135.29632.9353990.9873331.339572
34H2SHydrogen Sulfide (H2S)34.08088123.86891.4037550.9923561.330967
35SO2Sulfur Dioxide64.0638128.58272.6635740.9830961.281358
36C3H6Propylene (Propylene)42.0797485.60711.7450880.9856061.156696
801ButenButylene (1-Butene)56.1063277.1342.3590510.9721251.122513
81cButenCis-Butene (cis-2-butene)56.1063276.288672.3660720.9692411.13195
82iButenIso-Butene56.1063278.487632.358960.9721631.117015
83tButenTrans-Butene56.1063276.325792.3659510.969291.120934
84COSCarbonyl Sulfide60.0751123.62762.4832150.9888441.260677
85DMEDimethylether46.0684491.965141.9182120.9816451.156324
86SiH4Silane (SiH4)32.11726115.9441.3200230.99451.4
Welding GasesGas data (at 25°C)
Gas number (if available)Short NameLong NameRP10 Mol. Wt.RP10 AbsoluteViscosity (uP) at 25°CRP10 Density at 25°CCompressibility at 25°CAdiabatic index (Cp/Cv)
20C-2525% CO2 / 75% Ar40.96345205.15521.6765780.998661.505324
21C-1010% CO2 / 90% Ar40.35418217.64311.6509040.9991071.592406
22C-88% CO2 / 92% Ar40.27294219.34471.6474920.9991611.60637
23C-22% CO2 / 98% Ar40.02924224.50261.6372670.9993161.652559
24C-7575% CO2 / 25% Ar42.99435166.71781.7635270.9964941.340763
25He-2525% He / 75% Ar30.96165231.56291.2654581.0000511.66819
26He-7575% He / 25% Ar12.98895234.6060.5306191.0005491.666839
27A102590% He / 7.5% Ar / 2.5% CO27.698687214.90650.314511.0005311.645543
28Star29Stargon CS  90% Ar / 8% CO2 / 2% O240.11396219.03731.6409870.9991611.598911
140C-1515% CO2 / 85% Ar40.55727213.42741.6594460.9989661.560182
141C-2020% CO2 / 80% Ar40.76036209.26511.6680040.9988181.53132
142C-5050% CO2 / 50% Ar41.9789185.35511.719750.9977251.40648
143He-5050% He / 50% Ar21.9753236.07610.8978521.0004071.667353
144He-9090% He / 10% Ar7.597142222.09660.3103581.0005411.666637
Refrigerant GasesGas data (at 25°C)
Gas number (if available)Short NameLong NameRP10 Mol. Wt.RP10 AbsoluteViscosity (uP) at 25°CRP10 Density at 25°CCompressibility at 25°CAdiabatic index (Cp/Cv)
100R-11Trichlorofluoromethane137.368101.60485.8235950.9641451.13912
101R-115Chloropentafluoroethane154.4664125.14786.4329180.9814631.088332
102R-116Hexafluoroethane138.0118137.81735.7009580.9895011.088952
103R-124Chlorotetrafluoroethane136.475115.93115.7282020.9738291.103392
104R-125Pentafluoroethane120.0214129.61744.9816830.984761.103591
105R-134ATetrafluoroethane102.032118.18824.2578280.9794811.119533
106R-14Tetrafluoromethane88.01172.44683.6108480.9962551.160565
107R-142bChlorodifluoroethane100.495104.20194.2163090.9742261.124503
108R-143aTrifluoroethane84.041112.13373.49450.9830011.12861
109R-152aDifluoroethane66.051100.81322.7590240.9785241.154922
110R-22Difluoromonochloromethane86.468126.30393.5867940.9853641.184702
111R-23Trifluoromethane70.01385149.13162.8840340.9922731.201092
112R-32Difluoromethane52.024126.13142.153140.9875961.252257
113RC-318Octafluorocyclobutane200.04117.1238.4291920.9700161.064227
114R-404A44% R-125 / 4% R-134A / 52% R-143A97.6038120.83134.0573870.9832591.118293
115R-407C23% R-32 / 25% R-125 / 52% R-134A95.02751122.80433.95130.9830081.129835
116R-410A50% R-32 / 50% R-12586.0227133.54423.5644280.9864411.146601
117R-507A50% R-125 / 50% R-143A98.85916121.70234.1087210.9834631.117223
WordPress Video Lightbox Plugin