Film condensation improved analysis

Laminar Free Convection. Sparrow and Gregg [33] were the first to use the boundary layer method to study laminar, gravity-driven film condensation on a vertical plate. They improved upon the approximate analysis of Nusselt by including fluid acceleration and energy convection terms in the momentum and energy equations, respectively. Their numerical results can be expressed as ... 

Promotion of Dropwise Condensation. Preliminary heat transfer experiments, using distilled water as feed, gave values of over-all heat transfer coefficient around 1000 B.t.u./sq. ft hr. ° F. and analysis indicated that the jacket condensate film provided the main resistance to heat transfer, due to filmwise condensation of the jacket steam. Following reports by Garrett (4) of successful tests using drop-wise condensation promoters, it was decided to use oleic acid for this purpose in the present experiments. The resulting improvement in jacketside coefficients enabled over-all heat transfer coefficients in excess of 5000 B.t.u./sq. ft hr ° F. to be achieved. 

The desired polyimide derivatives were prepared by condensation polymerization as shown in Scheme 1. The initial polyamic acids (PAA 1-4) could be spun onto a substrate and cured by ramping the temperature to 260 C. For those examples where X=(CF3)2C, the polyimide derivatives were soluble in organic solvents. These materials were usually spun in the preimidized form. The improved thermal stability of the arylamino substituted chromophores tethered to the polyimide backbone is obvious from the DSC analysis. The onset decomposition temperature measured by DSC of the aryl substituted polymer PI-2b is almost 40°C hi er than that of Pl-lb (Td = 376 vs 338T). Likewise, this stabilizing effect is apparent variable temperature, UV-visible spectroscopic studies of the polymer films. In this case, the absorbance at the max of the chromophore was monitored versus time at a variety of temperatures (18), While the absorbance of PI-2b (Amax 498 nm) was little changed after one hour at 275°C, that of Pl-lb (Amax 474 nm) decreased by almost 30%. In each case, the heating was conducted under an inert atmosphere. Studies such as these are the origin of the data shown in the last column of Table I. 

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