Sierra Series 830/840/860 Side-Trak™ and ... - Sierra Instruments

Appendix ASeries 830/840/860 Instruction ManualCalculating Dual Gas MixturesEquation (6) is used for gas mixtures, but we must calculate N/ρC pfor the mixture. The equivalent values of ρ, C p , and N for a dualgas mixture are given as follows:The equivalent gas density is:! = ( m• / m• 1 T)! 1+ ( m• 2/ m• T)! 2Where:m•T = m•1 + m•2 = Total mass flow rate (gm/min),( ) 1 = Refers to gas #1, and( ) 2 = Refers to gas #2The equivalent specific heat is:C p = F 1 C p1 + F 2 C p2Where:1 m• !1 1 m•T !2 m• ! 2 2m•T !F = ( )/( ) andF = ( )/( )The equivalent value of N is:! = ( m•/ m• 1 T ) ! 1 + ( m• 2 / m• T ) ! 2The equivalency relationships for ρ, C p , and N for mixtures ofmore than two gases have a form similar to the dual-gas relationshipgiven above.IMPORTANT NOTE ABOUT K-FACTORS:Please note that if you have a transducer calibrated for a gas suchas methane and wish to use the K-factors to measure a gas such asair, that the inaccuracy of the measurement can range from ±5 to10%. The use of K-factors is, at best, only a rough approximationand should not be used in applications that require a better than ±5to 10% accuracy.It should also be noted that certain gases, in similar “families,” willwork exceptionally well with K-factors; however, those instancesare only true when similar thermal properties of the gas are present.A-6 IM-83/84/86-H