Extended hard-sphere model for predicting the viscosity of long-chain n-alkanes

Abstract

An extended hard-sphere model is presented that can accurately and reliably predict the viscosity of long chain n-alkanes. The method is based on the hard-sphere model of Dymond and Assael, that makes use of an universal function relating reduced viscosity to reduced volume. The existing expression for the molar core volume is extrapolated to long chain n-alkanes, while the roughness factor is determined from experimental data. A new correlation for roughness factor is developed that allows the extended model to reproduce the available experimental viscosity data on long chain n-alkanes up to tetracontane (n-C 40 H 82 ) within ±5 %, at pressure up to 30 MPa. In the dilute gas limit a physically realistic model, based on Lennard-Jones effective potential, is proposed and used to evaluate the zero-density viscosity of n-alkanes to within ±2.4 %, that is better than currently available.

Models for viscosity, thermal conductivity, and surface tension of selected pure fluids as implemented in REFPROP v10.0

“…The procedure described in Riesco and Vesovic (Riesco & Vesovic, 2016) was used to estimate the Lennard-Jones parameters. This method is tuned for long-chain alkanes.…”

Reference Correlation of the Viscosity of n-Hexadecane from the Triple Point to 673 K and up to 425 MPa

“…115 Although the expressions for the second virial coefficients were developed using data for much smaller molecules, the use of scaling parameters of Riesco and Vesovic model that successfully employs effective spherical potentials to mimic the interaction between long chains, give us some justification in estimating the initial density term by means of the second viscosity virial coefficient. 44,46 The first set of measurements 44 were carried out in the capillary viscometer operating in the absolute mode at pressure of 0.5 bar in the temperature range (551 to 723) K. The purity of the sample was indicated to be in the range of 98-99%.…”

Preliminary models for viscosity, thermal conductivity, and surface tension of pure fluid constituents of selected diesel surrogate fuels

“…The equation of state is implemented in the REFPROP text file included in Supplementary materials. Lennard-Jones parameters were estimated with a new method developed especially for long-chain alkanes (97). The liquid-phase viscosity data of references (85,87,98) were used to provide the coefficients in Table 3, and a deviation plot for data up to 100 MPa is shown in Figure 22.…”

“…The equation of state is implemented in the REFPROP text file included in Supplementary materials, and was used to provide density in the formulations for viscosity and thermal conductivity. Lennard-Jones parameters were estimated with a new method developed especially for long-chain alkanes (97). This method involves only the molecular weight and the number of carbons, so the LJ parameters for 2-methylheptadecane are the same as n-octadecane.…”

“…The equation of state is implemented in the REFPROP text file included in Supplementary materials. Lennard-Jones parameters were estimated with a new method developed especially for long-chain alkanes (97). Liquid-phase data at pressures up to 50 MPa (the upper limit of the EOS for isohexadecane) from references (48,(106)(107)(108)(109) were fit with n-octane as a reference fluid to obtain the coefficients in Table 3.…”