Thermal mass flow meters are broadly used in different parts of industry for flow metering objectives from very low up to very high flow rates. One of the most widely used thermal flow meters is capillary tube type which is more appropriate for measuring low mass flow rates. On the other hand, natural gas measurement accuracy in residential use has already been studied by the authors and it was found out that considerable amount of natural gas is lost over the year due to inaccurate flow metering. In order to resolve this problem, employing capillary tube mass flow meters instead of conventional counters in houses, assuming natural gas as pure methane, was proposed and investigated, resulting to satisfactory outcomes. Although pure methane well estimates natural gas behavior in many cases, it may not be an accurate assumption for heavy natural gas mixtures composed of lower methane fractions. Therefore, in this work, the effect of natural gas compositions variation on the performance of capillary tube thermal mass flow meters in residential use is studied. For this objective, various natural gas fields of Iran are considered and differential equations of natural gas stream and sensor tube are solved contemporary in Matlab. In the end, in order to validate the simulation approach and conditions, the simulation was accomplished for Nitrogen, for which experimental data was available in the literature. The results show that using an average specific heat capacity value for different mixtures causes a deviation below a maximum of only 1.8% and overall average error of 0.62% in measurement accuracy. It was also found out that changes in other properties of natural gas does not affect the accuracy.

Keywords