Viscosity TRAPP

The principle of corresponding states for viscosity is based on the idea that there is universal relation between a suitably defined dimensionless (or reduced) viscosity and a set of dimensionless parameters, such as reduced temperature and pressure. Among the important corresponding states prediction methods for viscosity is that of Ely and Hanley [15], which evolved into the TRAPP method. Others have suggested modifications to the Ely-Hanley method in recent years [3,16,17,18,19]. The TRAPP method and its modifications are useful for wide ranges of fluids and from the dilute gas to the compressed liquid. However, the mathematical complexity... 

There have been two approaches to modeling the effect of pressure on the viscosity of mixtures. Either the effect of pressure is implicitly included in the model (for example, as in the case of Cao et al. or in the TRAPP method, in which the effect of pressure on density directly affects the viscosity), or viscosities are first calculated at low pressure (from saturation to a few atmospheres) and then corrected... 

In the TRAPP procedure (Ely Hanley 1981b, 1983), the viscosity of a fluid at density p, temperature T (and for a mixture, of composition x, ) is equated to the viscosity of a hypothetical pure fluid. (The hypothetical pure fluid is obtained through the use of mixing and combining rules and is discussed later.) The hypothetical pure... 

Semiempirical modification SUPERTRAPP As will be shown in the next section, the modified TRAPP is very successful for the majority of fluids tested the exception is that the viscosity prediction for cyclic compounds and some highly branched alkanes is not satisfactory. To correct this and slightly improve the overall representation of the data, a further modification is proposed. It is semiempirical and requires thermophysical property data as input. If these data are not available, however, the modified procedure will revert to TRAPP. The modifications are implemented in a computer program SUPERTRAPP (Ely Huber 1990) and are as follows ... 

A full discussion on the original TRAPP equations plus extensive comparisons of the method with pure fluid and mixture data were given in the papers of Ely Hanley (1981a,b, 1983) and will not be repeated here. Table 12.1 gives a comparison of experimental viscosity data for selected pure fluids with the modified TRAPP model and the SUPERTRAPP model, in terms of the average absolute percent deviation AAD and the average percentage error BIAS. For all fluids except the cyclic compounds and... 

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