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Title: A Proposed Standard For Natural Gas Viscosities
Author: William Johansen
Source: American Gas Association 2010
Year Published: 2010
Abstract: The natural gas flowmetering community does not have a standard method to calculate viscosity. The error levels in current viscosity models frequently exceed 25 %. Moreover, one of the prevalent methods to compute viscosity produces values that are consistently smaller than measured values. This bias inviscosity computations leads to biases in the Reynolds number which ultimately result in flow measurement biases that can be 0.1% or more. The errors in Reynolds numbers have also led to numerous flowmeters being calibrated in the wrong Reynolds number range. We demonstrate that limiting the Reynolds number errors to 5 % is sufficient to reduce flowmeter measurement biases to less than 0.028 % for commonly used flowmeters e.g., critical flow Venturis, orifice meters). We show that the NIST-maintained database REFPROP 8.1 and a viscosity model developed at CEESI both agree with published natural gas viscosity data within 5% or less at temperatures from 270 K to 330 K and at pressures up to 12 MPa for a wide range of natural gas mixtures. Based on these results we propose that REFPROP 8.1 be adopted as the standard for calculating natural gas viscosities.

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