We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
Feb., 1950 ross : heating of films and slides 49
The slides would be less likely to break if they were made on plates of quartz or a heat-resisting glass like " Pyrex " (not a heat-absorbing glass). Such plates are liable to have small bubbles or blemishes and are costly, so that they would probably have to be re-used, either by transfer-sensitising them before printing, or by transferring on to them the finished print made on cut film. For studio process work it is preferred to use standard lantern plates, combined with an adequate slide cooler on the projector.
Action of the Air Stream
The action of the stream of air is shown diagrammatically in Fig. 7, blowing across a greatly enlarged view of one side of the slide. The air in contact with the slide is considered to be at rest, being " stuck " to the slide. Immediately above this " layer " is another, which " slides " on the first, and so on, layer after layer sliding on the previous one. Some distance from the slide these layers become no longer laminar and begin to become unsteady, and further still they become turbulent, eddying and swirling. This whole effect occurs within about 1/50 in. from the slide, within the " boundary layer."
Air is a very poor conductor of heat, which is therefore only to a small extent conducted through the first slow-moving " layers." Thereafter the heat is transferred with increasing effectiveness as the turbulence increases
AIR VELOCITY TEMPERATURE,
CURRENT OF AIR
SURFACE BEING COOLED Fig. 7. The action of air in cooling a surface. Left, air flow changes from slow-moving laminar flow to rapid turbulent flow ; centre, graph showing greatly reduced velocity near the surface ; right, graph showing distribution of temperature on passing from the surface out into the air-stream. The thin boundary layer acts as a blanket over the surface.
until the heated air is mixed thoroughly into the. main air stream. The distributions of velocity and temperature, on passing out into the air stream, are sketched in Fig.7.
The chief aim in forced air cooling is to reduce the effect of this slow-moving " blanket " of air over the slide, and this is mainly achieved by using a very high air-velocity. Consequently, the temperature of the main stream of air does not rise very much, and a relatively large amount of air has to be used. A great deal of data is available11 on cooling by air within pipes, which may be of circular or rectangular section. This data may be used if a glass window is placed on each side of the slide to form a tall but thin channel, and the air is blown through this.
The rate of cooling which may be obtained with such a system is equal to : 3Xt/0.75 ^0.75 Cp0-75. K0-25. T watts per sq. cm.
105 t0-25 where F=air velocity, cm/sec.
P= density =0 001 gm./cm.3 Cp=specificheat=0-24cal./gm. °C. K= conductivity =0 00006 cal./sec. cm.2 °C./cm. T= difference in temp, of slide above air, °C. f=thickness of each air passage, cm. It is calculated that in such a system the emulsion side of the slide is only 10° C. hotter than the far side, so that the total area cooled is twice the area of the gate.