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rules of thumb for process engineering

asked Dec 31, 2015 in Process by cobiesmith (3,310 points)

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answered Dec 31, 2015 by cobiesmith (3,310 points)
 
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Following are the 17 rules of thumb for process engineering:

  1. Vapor pressure doubles every 20 degC.

  2. The latent heat of vaporization of steam is five times that of most organics.

  3. If two liquids are immiscible, the infinite dilution activity coefficient is > 8.

  4. 10% salt in water doubles the activity coefficient of a dissolved organic.

  5. Infinite dilution is essentially < 1000 ppm of dissolved organic.

  6. Freezing temperature may be suppressed 1 degC for every 1.5 mol % impurity present.

  7. A ratio of impurity concentration between a solid/liquid phase i 0.2 is probably due to solid solution.

  8. Dissolving 2–20% organic solute usually reduces the interfacial tension.

  9. The Prandtl number for gases is approximately 1; for liquids 1 to 3.

  10. The thermal conductivity of hydrogen = 10 x value for most organic vapors.

  11. For distillation, the condenser cooling water usage is 15 L/kg of steam to the reboiler.

  12. Polymer melts can be classified based on their viscosity: low viscosity melts for polyacylamide; polyethylene, polypropylene and polystyrene; medium viscosity melts for ABS, cellulose acetate, POM and styrene butadiene; and high viscosity melts for polycarbonate, polymethylmethacrylate, polypropylene oxide and polyvinyl chloride.

  13. The Hamaker constant for liquid surfaces is about 10–20 J and is relatively independent of temperature.

  14. The disjoining pressure for films is negligible for fluid films i 0.1 mm thick. 

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