A comparative study between Helmholtz and entropy scaling approaches for viscosity of natural gas mixtures based on the GERG-2008 equation of state

Abstract

This study compares the perfomance of Helmholtz scaling approach, the residual entropy scaling approach, and the modified entropy scaling approach proposed by Bell for predicting the viscosities of pure n-alkanes, as well as other light compounds, and natural gas mixtures at different pressure and temperature conditions. The modified entropy scaling approach showed the lowest global average absolute deviation (AAD) for pure components, with a value of 2.37%. In comparison, the Helmholtz scaling approach had a slightly higher value of 2.70%, while the entropy scaling approach produced the highest value at 4.02%. The predictive performance of different mixing rules was evaluated for a strongly asymmetric binary system (methane + n-decane), across a broad range of compositions, pressures, and temperatures. For all-natural gas mixtures, excellent results were achieved with similar AAD values obtained for entropy and Helmholtz scaling approaches, at 2.73% and 2.72%, respectively. The modified entropy scaling approach presented an AAD value of 3.12%. The results obtained with each of the binary and multicomponent mixtures allowed us to confirm the accuracy of the Helmholtz scaling, entropy scaling, and modified entropy scaling approach using GERG 2008 in the prediction of natural gas viscosities when appropriate mixing rules were selected for each approach.