Mahmood Moshfeghian John M. Campbell & Co. Norman, Okla. To develop a generalized correlation for natural gas heat capacity, the author conducted an extensive investigation of heat capacity as a function of temperature, pressure, and composition. To aid in understanding the impact of variables on heat capacity, the existing phase for each case was determined. Heat capacity is widely used for heat-exchanger duty determination in plant and engineering calculations. As expected, abnormal behavior was evident at low temperature, at which two-phase gas and liquid co-existed, and at high pressures when the system was in dense phase. These abnormalities vanished for lower relative-density n...