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65 C, the wheel temperature was found to be 48.5 C. This checks very closely with the computed curve. The deviation from the computed curve, as observed in the experiments, appears to be, therefore, solely a function of the temperature difference between the air and the wheel. It might be noted here that the difference in temperature between the wheel and film was very small and in the order of not more than 5 C.
Fig. 8. Type K-4 turbulent-air highspeed film drier.
In order to assure operation of the wheel at the exact required temperature, a new model film drier (type K-4) was built as shown in Fig. 8. In this unit heating elements were installed in the wheel which were energized through slip rings. Approximately 2 kw of power was required to maintain the drum at the required temperature. The air was introduced directly into the slots in the rear of the unit and was forced over the film in a number of passages and exits in the front. The passages are formed by a number of movable blocks so that the duct width of the passage over the film can be varied. The diameter of this wheel was reduced to 6 in. from 16 in., since the calculations indicated that this would be sufficient to dry the film.
Satisfactory results were obtained
with the K-4 film drier and considerable experimental data were obtained drying film at 100 fpm. However, an insufficient safety factor was allowed to permit the use of greatly different types of film. Up to this point the only film that had been used for the experiments was Du Pont Film, Type 628B. It was found that the amount of moisture which could be absorbed in the film during the photographic process varied considerably with different batches of film, with the amount and type of developer used, and with the amount of light exposure on the film.
In order to perform satisfactory experiments all tests described above were done with undeveloped film which was soaked in a wetting tank at constant temperature. It was found that only under these conditions could reproducible results be obtained.
The final design of a turbulent-air film drier which permits a sufficient safety factor for the use of almost any film of the 35-mm type is shown in Figs. 9 and 10. This unit (model K-6) incorporates a 14-in. wheel with approximately 3 kw of heaters inside the wheel
Fig. 9. Type K-6 turbulent-air highspeed film drier.
L. Katz: Drying Film by Turbulent Air
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