A generalized correlation for the effect of pressure on the isobaric heat capacity of gases

A generalized correlation is submitted for the deviation of the isobaric heat capacity of hydrocarbons from the ideal state. The range of conditions included is from reduced pressure = 0.2 - 15 and reduced temperature = 1.0 - 5.5. The curves presented have been based on data calculated from the Benedict - Webb - Rubin Equation of State, which is believed to be the most accurate method presently available for caleulating the heat capacity deviation. The results indicate that the order of magnitude of the correction ts quite large, especially in the critical region. The average absolute error of this correlation is approximately 4.2% from the data on which it was based, but errors as high as 16% may occur in the regions of high heat capacity deviation. This indicates that, whenever possible, specific data should be used in preference to a generalized correlation. Comparisons have been made with the correlations submitted by previous investigators, and the relative accuracies of all have been discussed. A comparison with experimental heat capacity data for nitrogen and oxygen has shown that the correlation is also suitable for non-polar gases; and there are indications, based on the experimental data, that this correlation is more accurate than the earlier correlations which have been published