The Estimation of Heat-capacity Ratios of Hydrocarbon Gases Using a Simple Predictive Tool

Abstract

All compression processes of practical importance are normally adiabatic. The term adiabatic does not adequately describe this process, since it only implies no heat transfer. The ideal process also follows a path of constant entropy and should be called isentropic. The heat capacity varies considerably with temperature, since the temperature of the gas increases as it passes from suction to discharge in the compressor. For a multi-component gas, the mole weighted average value of molar heat capacity must be determined at average temperature; however, if only the molecular weight of the gas is known and not its composition, an approximate value for heat-capacity ratios of hydrocarbon gases or isentropic exponent (k) is required as a function of temperature and molecular weight for engineering calculations. The aim of this study is to develop a simple-to-use predictive that is easier than existing approaches and less complicated with fewer computations for predicting the approximate heat-capacity ratios of hydrocarbon gases. Results show that the proposed predictive tool has a very good agreement with the reported data where the average absolute deviation percent is 0.3%. The proposed method is superior owing to its accuracy and clear numerical background, wherein the relevant coefficients can be retuned quickly if new data become available. This proposed simple-to-use approach can be of immense practical value for engineers and scientists to have a quick check on approximate value for heat-capacity ratios of hydrocarbon gases or isentropic exponent (k) for wide range of operating conditions without the necessity of any experimental trials. In particular, practice engineers would find the proposed approach to be user friendly involving transparent calculations with no complex expressions for their applications compression process.

Keywords:

• compression process
• gas compressor
• heat-capacity ratio
• isentropic exponent
• isentropic system