(449f) High-Pressure Transport-'shifted' Dew-Point Temperatures For Surfaces Exposed To Hydrocarbon-Containing Vapors

We show that high-pressure molecular TRANSPORT phenomena will not only influence the interpretation of hot gas/'cold' surface 'dew-point' measurements, they will significantly raise the temperatures at which containment- or immersed-surfaces must be maintained to avoid the ravages of corrosive or insulating inorganic condensates (see, eg., Rosner, et al. , Comb. Sci. Tech.,1979)).

Our earlier studies demonstrated that Soret-driven species transport causes concentration non-uniformities in the immediate vicinity of 'cold' surfaces immersed in undersaturated vapor-containing streams. These concentration non-uniformities, in turn, altered corresponding condensation onset temperatures by as much as 30K (i.e., ca. 3%) in previously studied, near-atmospheric pressure combustion systems (see, e.g., Rosner and Nagarajan (Chem E. Sci, 1985)). However, because high pressures often cause remarkable increases in the relevant binary Soret factors (Rosner and Arias-Zugasti (AIChE J, 2007)), we investigate here the importance of such vapor phase 'transport' effects for 'compressed' N2 streams containing dilute quantities of an alkane such as: C12H26 (n-dodecane). We invoke the 'virial'-EOS to now predict the dramatic effect of gas phase non-ideality on previously available ideal-gas binary Soret factors. Our illustrative numerical results, valid for, say, nominally 1000K N2 streams up to pressures of ca. 300 atm, now reveal that high-pressure Soret 'shifts' in Tdp can amount to ca. 70 percent, even at surface temperatures above the freezing points of such condensates.

It is also interesting to note that the present theory could itself be used to experimentally study the pressure dependence of the binary Soret factor, at least for systems with well-characterized saturation vapor pressure.