Page 44 - Handbook of Natural Gas Transmission and Processing Principles and Practices

(1.27)

where µ is the viscosity of the gas mixture at the desired temperature and atmospheric pressure,
ga
y is the mole fraction of the ith component, µ is the viscosity of the ith component of the gas
i
ga
mixture at the desired temperature and atmospheric pressure, M is the molecular weight of the ith
gi
component of the gas mixture, and N is the number of components in the gas mixture.
This viscosity is then multiplied by the viscosity ratio to obtain the viscosity at reservoir
temperature and pressure.

1.6.2. Thermodynamic Properties
The principles of thermodynamics find very wide application in predicting the properties of
hydrocarbons. The properties of greatest interest are specific heats of natural gas and its Joule–
Thomson coefficient.

1.6.2.1. Specific Heat
Specific heat is defined as the amount of heat required to raise the temperature of a unit mass of a
substance through unity. It is an intensive property of a substance. It can be measured at constant
pressure (C ), or at constant volume (C ), resulting in two distinct specific heat values. In terms of
p
v
basic thermodynamic quantities:

(1.28)

(1.29)

where H is the molal enthalpy (BTU/lbmole), U is the molal internal energy (Btu/lbmole), C is the
p
o
molal specific heat at constant pressure (BTU/lbmole- R), and C is the molal specific heat at
v
o
constant volume (Btu/lbmole- R).
Both heat capacities are thermodynamically related. It can be proven that this relationship is
controlled by the P–V–T behavior of the substances through the following relationship:

(1.30)

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