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Symbols, Definitions, Dimensions and Values
A = area normal to heat or mass trans k
fer, sq ft Pr
B = thickness of stagnant layer, ft Re
C = concentration, % Sc
Cp = specific heat, Btu/lb°F T
D = diameter, ft V
Ea = rate of mass transfer, Ib/hr 5
g = acceleration of gravity, ft/secj n
h = heat transfer coefficient Btu/hr p
sq ft — °F 0
thermal conductivity Prandtl number, Cpn/k Reynolds number, Schmidt number, up/8 temperature, °R velocity, fpm diffusivity, sq ft/hr viscosity, Ib/ft hr density, Ib/cu ft partial pressure, atm
turbulent fluids might well provide an important time gain in the rapid processing of photographic film and that further investigation would the justified. It was, therefore, decided to embark on a research program in which an effort would be made to isolate the results which were solely attributable to the effect of turbulence so that a proper evaluation could be made.
Scope of the Investigation
Although it was realized from the beginning that the effects of turbulent flow would be more useful if they were combined with other changes, such as increased concentration of developer, different emulsions, different temperatures, etc., it was decided to limit this first investigation solely to the investigation of the effects of turbulence. Consequently, the following standards were established :
1. The film to be used was Kodak Super-XX Aerographic Film.
2. The developer to be used was Kodak Developer D-19.*
3. The temperature at which the film was to be processed was to be maintained at 68 F (66 F to 70 F).
4. The fixer to be used was Kodak Fixing Bath F-6.*
5. The developing time under turbu
lent conditions was the time measured between the initiation of turbulent flow and the cessation of turbulent flow.
6. The fixing time was determined as the time to clear the film completely of opalescence.
7. Washing time was determined by silver nitrate tests.**
8. Small samples of film approximately l| in. wide by 6j in. long, on which a photographic wedge had been exposed, were used in a stationary mount.
Theory
The treatment of photographic emulsion by means of various chemicals to perform the functions of developing, fixing, washing and drying and other basic functions can, in general, be separated into two basic phenomena as follows:
1 . The chemical reaction taking place between the particles contained in the photographic emulsion and the particles introduced by external means.
2. The diffusion by which these chemicals are transported from the surrounding atmosphere into and out of the gelatin to permit the accomplishment of the chemical reaction.
Photographic film can be considered as consisting of a base which absorbs practically no fluids, and a gelatin
* See Photo Lab Index, Henry M. Lester, Sect. 6, Morgan & Lester, New York, 12th ed., 1952.
** The Theory of the Photographic Process, C. E. K. Mees, Macmillan, New York, 1942, p. 532.
106
February 1953 Journal of the SMPTE Vol. 60