A horizontal thermal diffusion column is described in which the inefficiencies caused by the forgotten effect and parasitic remixing are avoided. Experimental results obtained on the separation of water‐ethyl alcohol mixtures are presented along with a phenomenological theory for the performance of the column.
A frequency domain analysis of reversible molecular diffusion in a granule or relatively stagnant drop of fluid reveals that for the larger values of time the rate equation reduces to
Compared with an earlier time domain result
the rate predicted is 15/π2 = 1.516 greater and this has been confirmed by results of experiment. An analysis of time constants shows that the dimensionless group relation
defines mathematically that which is meant by the larger value of time limitation.
A completely automated frost-dew point hygrometer with ultra fast response capability includes the hygrometer, refrigerant circulation system, integral two-stage low-temperature (-100°t o -125°F ) refrigerator, a cascaded controller of unconventional design, as well as ancillary automata. The continuous operating and recording range of the instrument is -100°to +200°F. The unique sensing element of the hygrometer combines a thin Invar buffer layer and a hemispherical silver thermal reservoir to permit reduction of the mass of the temperature-tracking element. A state of the art design is characterized by a first-order transfer function and time constant of 1.3 seconds. The internal control loop of the cascade control is temperature-activated and its design is based on final-value control principles. The outer loop is activated by a photoelectric deposit thickness monitor. The system tracks through the32°F transition temperature very smoothly without any indication of upset, instability, or tendency to hunt. The hygrometer and cascaded controller are completely compensated for nonlinearity to produce uniform response over the entire instrument range and the response speed is so great that thermodynamic equilibrium between
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