Existing methods of calculating the Joule–Thomson coefficient for natural gas are analyzed. A procedure
for use in calculations of gas flow rate employing the variable pressure drop method is proposed which
gives increased measurement accuracy by eliminating the additional error in determining the temperature
of the natural gas.
Key words:Joule–Thomson coefficient, flowmeter, natural gas.
The variable pressure drop method is mainly used to measure the flow rate and quantity of natural gas in large-diam-
eter pipelines. The new standards [1–6], which standardize the measurement of the flow rate and quantity of flowing media
using this method, provide the possibility of taking into account the systematic component of the error in measuring gas flow
rate due to the difference between the temperature of the gas at the point where it is measured after the constricting device
and the temperature before the constricting device. In accordance with the requirements in , the temperature after the con-
stricting device must be corrected when there is a loss in pressure in the constricting device greater than 160 kPa, i.e., this
correction is obligatory. According to the standard , the correction for the change in temperature of the gas when it flows
through a constricting device must be introduced if “… high accuracy in measuring the flow rate is required, and also if there
are considerable pressure losses in the constricting device.” Hence, in the standard  there is no limitation on the value of
the pressure loss as in , while the correction for the change in the gas temperature, measured after the constricting device,
is recommended only when a higher accuracy in measuring the flow rate is necessary. The same may apply when measuring
flow rate as described in .
The main obstacle to introducing such a correction has been the lack of a simple method of calculating it using a
calculation of the Joule–Thomson coefficient. Below we present a fairly simple method of calculating this coefficient, which
can be achieved using microprocessor calculators of the flow rate and quantity of a gas.
As is well known, the flow of a gas through the constricting device is accompanied by a change in the parameters of
the state of the gas (the pressure, temperature and density) along the measuring part of the pipeline. A change in the tempera-
ture of the gas in the throat of the constricting device and after it along the length of the pipeline means that the constricting
device of the flowmeter and its measuring temperature converter, placed a distance of 5–15 internal diameters of the measur-
ing pipeline  after the constricting device, are situated in a zone of different temperatures of the gas flow. It is impossible to
measure the gas temperature immediately in front of the constricting device, as required by the variable pressure drop method,
without distorting the kinematic structure of the flow. Hence, the temperature difference of the gas immediately in front of the
constricting device and at the point where the converter is situated are found [5, 6] by calculation using the integral
Measurement Techniques, Vol. 52, No. 5, 2009
DETERMINATION OF THE JOULE–THOMSON
COEFFICIENT IN PROBLEMS OF MEASURING
THE FLOW RATE OF NATURAL GAS
E. P. Pistun, F. D. Matiko,
and O. Ya. Masnyak
Lviv National Politechnic University (Lvivska Politekhnika), Lviv, Ukraine; e-mail: firstname.lastname@example.org. Translated
from Izmeritel’naya Tekhnika, No. 5, pp. 46–49, May, 2009. Original article submitted March 11, 2009.
2009 Springer Science+Business Media, Inc.