(84a) High-Pressure Soret-Modified Hydrocarbon Mass Transport across Non-Isothermal Gaseous Boundary Layers | AIChE

(84a) High-Pressure Soret-Modified Hydrocarbon Mass Transport across Non-Isothermal Gaseous Boundary Layers



Motivated, in part, by supercritical pressure combustion applications, we deal here with species mass transport across non-isothermal compressed gas 'films'---mainly hydrocarbon fuel vapor transport across non-isothermal N2 boundary layers at pressures up to ca. 300 atm. We show that because of the significant pressure sensitivity of the dimensionless Soret factor, mass transfer coefficients become quite sensitive to pressure level when one leaves the familiar domain of "ideal gases"[Rosner and Arias-Zugasti, AIChE J(2007)].

We first examine the expected pressure dependence of the binary Soret factor for each of the n-alkanes (CH4 to C20H42) dilute in compressed N2, exploiting a rational formulation for 'correcting' Chapman-Enskog-derived Soret factors to higher pressures based on the thermodynamics of irreversible processes (TIP) combined with a virial equation of state (VES). Our TIP-VES-predicted Soret factors are then used to demonstrate the pressure sensitivity of expected "Soret-modified" mass transfer coefficients (Sherwood numbers) for the illustrative case of C12H26(g) transport across N2(g) at temperature ratios between 0.3('cold'-wall) and 2.0 ('hot'- wall) at pressures up to 300 atm.

Because of the growing importance of compact, dense vapor systems in many ChE fields (including supercritical fluid extraction and even cryogenic distillation) our present results demonstrate that reliable mass transfer rate predictions in non-isothermal dense vapor systems will require systematic inclusion of non-Fickian molecular mass transport mechanisms.