. Department bulletin. Agriculture; Agriculture. 28 BULLETIN" 1141, U. S. DEPARTMENT OF AGRICULTURE. inclination of the trays. In consequence there is a rapid and un- impeded air movement throughout the whole apparatus. The temperature of the air falls rapidly as it passes through the tunnel, as a result of the heat expenditure in vaporizing water, while tin' amount of water vapor carried by it of course increases. The difference in temperature at opposite ends of the tunnel is usually from 25° to 30° F. In consequence, the fruit at the lower end of the tunnel dries rapidly, while the rat
. Department bulletin. Agriculture; Agriculture. 28 BULLETIN" 1141, U. S. DEPARTMENT OF AGRICULTURE. inclination of the trays. In consequence there is a rapid and un- impeded air movement throughout the whole apparatus. The temperature of the air falls rapidly as it passes through the tunnel, as a result of the heat expenditure in vaporizing water, while tin' amount of water vapor carried by it of course increases. The difference in temperature at opposite ends of the tunnel is usually from 25° to 30° F. In consequence, the fruit at the lower end of the tunnel dries rapidly, while the rate of drying decreases steadily with decrease in air temperature toward the upper end. When the tunnel is first charged with fruit the trays nearest the air inlet become dry, while those next them still contain much moisture, and those at the upper end are scarcely wTell started to dry. While this delays start- ing, it is of advantage once operation is well under way. The dry. Cent*** Fig. 11.—A section through the tunnel drier. trays are removed at the lower end, the whole series moved down the length of one tray, and trays of fresh fruit inserted in the spaces thus made at the upper end. The heat supplied is now increased until the temperature at the lower end of the tunnel becomes as high as is safe to employ in completing the drying, since the fruit nearest the air inlet has lost the greater part of its moisture. The operation now becomes continuous; an exposure of one to three hours to the maximum temperature completes the drying of the fruit on the trays directly exposed to it, and as they are removed the whole series is moved down by the insertion of fresh trays at the upper end. For maximum efficiency, it is essential that the baffle-platelike ar- rangement of the trays over the air inlet, termed by operators " bank- ing" or " offsetting.^ be carefully maintained and that the trays on each runway be pushed closely together, so that the air is forced to
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