. Commercial dehydration of fruits and vegetables. Fruit Drying; Vegetables Drying; Fruit Processing; Vegetables Processing. DEHYDRATION OF FRUITS AND VEGETABLES 13 economical than conveying them through the tunnel on slides. The trucks and trays should fit snugly in the tunnel, so that all the air will pass between and across the trays. The loaded trucks are introduced through a door at one end of the tunnel, and the trucks of dried product are removed through a simi- lar door at the other end. Air locks may be built around these doors to conserve heat during loading and unloading. The doors
. Commercial dehydration of fruits and vegetables. Fruit Drying; Vegetables Drying; Fruit Processing; Vegetables Processing. DEHYDRATION OF FRUITS AND VEGETABLES 13 economical than conveying them through the tunnel on slides. The trucks and trays should fit snugly in the tunnel, so that all the air will pass between and across the trays. The loaded trucks are introduced through a door at one end of the tunnel, and the trucks of dried product are removed through a simi- lar door at the other end. Air locks may be built around these doors to conserve heat during loading and unloading. The doors may be in the side wall at each end of the tunnel, with the air ducts connected at the ends, or vice versa. Flexible movement of trucks is facilitated by transfer trucks, turntables, or pivoted truck wheels. The course of the air through the tunnel is usually opposite to that of the material to be dried, sometimes called the counter-current system of circulation. Some operators advocate circulating the air in the same direction as the material, in what may be called the concurrent system. Tunnels wide enough to hold several parallel lines of trucks have been built. In these the air is usually circulated across from one side to the other. Screens or vanes are sometimes installed. Fig. 6.—Tunnel drier (exterior) in tunnels at connecting points between air ducts and the drying chamber, so that inequalities in air distribution may be corrected. HEAT Heat plays an important part in the evaporation of moisture, first, in supplying the "sensible" heat needed to bring the temperature of the water to the point to which the material is raised during drying, and, next, in furnishing the "latent heat of evaporation," or the heat required to convert water into vapor at the temperature level reached by the drying material. The sum of the sensible heat and the latent heat of evaporation is called the "total heat of ; Heat also facilitates the transm
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