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Show -7- the extra-long tube lengths on the inspiration process must be taken into account in designing effective flare pilot burners. Regular inspirating pilot burners can be designed or analyzed on the basis of the Euler momentum equation, as applied to inspirators. This equation can be presented as: Eq.1 Note: Nomenclature appears at end of this paper. Taking into account the influence of a long mixture tube on the inspiration process can be done two ways. The first consists of entering the friction coefficient K, into equation 1. The second consists of applying a correlation for consideration of the influence of friction pressure upon excess air mixture. To evaluate the suitability of the aforementioned calculation concepts, extensive flare pilot tests have been conducted. One experimental setup represented an inspirating flare pilot of nominal 1-1/4" diameter with a mixture tube that could be varied in length from 9 to 1 00 ft. Natural gas/air flow rates, exit mixture velocities and static pressure drop in the mixture tube were measured. The excess air factor for the gas/air mixture was determined by gas/air flow rates and by analysis of gas/air concentrations in the mixture tube. Test results are presented in figures 1 and 2. Lengthening the pilot leads to an increase in the mixture pressure drop (fig. 1) and an appreciable decrease in the excess air factor (fig. 2). On the basis of obtained experimental data and equation 1, the value of friction factor f in the mixture tube was determined. It is obvious from fig. 3 ("Friction Factor vs. Pilot Length"), the value of friction factor f varies, essentially depending upon the mixture tube length. This fact contradicts the physical sense of friction factor, which for a constant Reynolds Number for a definite fluid , pipe diameter and pipe roughness. Thus, it is obvious: The introduction of the friction resistance coefficient K, into equation 1 cannot be used for a design procedure for long inspirating pilots. This phenomenon can be explained by the fact that equation 1 was developed primarily for flow potential conditions. Such conditions do not take into account a complicated vortex process in a mixing tube with the presence of significant hydraulic resistance. l |