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Gas Mixing & Blending: ‘Kwik Kalucations’ with K-Factors


Oct 18, 2011

‘Kwik Kalucations’ with K-factors make gas mixing with a single gas mass flow meter simple.

If you’re looking to improve flexibility and save money when it comes to gas mixing and blending applications, consider applying a “K-Factor.” A dimensionless numerical relation of a specific gas vs. air or nitrogen, a gas K-factor never changes. If K-factors will work in your application, you can use one gas mass flow controller calibrated on air or nitrogen for several gasses by simply applying the K-factor.

K-factors, in general, do not change and are used for measurement and control of mass flow rate in units of SCCM and SLPM.  For example, if you calibrate your capillary-sensor gas mass flow controller with air for 0-100 SLPM, but intend to run 100 SLPM of argon through it, you will only get an output of 69 SLPM for the instrument. That’s because the physical properties of argon that effect heat transfer (the standard gas density and specific heat) are different than air. Furthermore, when you run enough argon through the instrument so that it indicates 100 SLPM, you will actually find the flow of argon is 145 SLPM. Thus, the K-factor of Argon is always 145/100 = 1.45.

Every gas has its own K-factor, but there can be slight differences across various brands of instruments. Is the K-factor a perfect linear function? Well, we assume so, but in reality that is not always true, especially with lower-cost flow sensors and flow meters for gas on the market today. Errors can be up to 7% on very specific light gasses like hydrogen or helium for these lower performing instruments.

In contrast, the Smart-Trak 100 is a premium instrument with a high level of reliability with K-factor behavior enabling such technologies as Dial-A-Gas, multi gas capability.  This makes the Smart-Trak 100, together with the advanced digital communication possibilities of the Compod, an ideal choice in gas mixing and blending applications.

In my next post, I will discuss Dilution in Gas Mixing and Blending applications.

Paul de Waal, Managing Dir., Sierra Europe
Written By:
Paul de Waal, Managing Dir., Sierra Europe
Sierra Instruments

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