PRESERVATION OF FRUITS AND VEGETABLES 25 



to the different trays, passing from the top down and horizontally 

 across the trays, then down through a port in the bottom into a return 

 duct, by which it is returned to the radiators and reheated the few 

 degrees lost in one circuit. 



As the air is divided among the six compartments each one gets 

 one-sixth of the total amount, or 3,000 cubic feet. This amount is 

 divided by a sluice that gives 1,500 cubic feet to each half of the 

 chamber, which is further divided by the vanes on each side into 

 three equal parts, or 500 cubic feet to five trays. Each tray being 

 30 inches square, takes one-fifth of the 500 cubic feet, or 100 cubic 

 feet, which is spread over the 30-inch surface at the rate of 3% cubic 

 feet per inch per minute. This 3}i cubic feet of air per minute passes 

 over a strip of the tray surface 1 inch wide by 30 inches long, coming 

 in drying contact with only 30 square inches of material in one 



Figure 6. — Trays in rack on loading-platform truck, ready to ba pushed into 

 one of the drying chambers. 



complete cycle. Thus use is made of a fundamental principle of 

 heating and ventilating, that it is cheaper to move air than to heat it. 

 Temperature control is effected by an indirect-acting duct thermo- 

 stat of the intermediate or gradual-movement type. This gives a 

 gradual motion to the valve in the steam line and holds it firmly in 

 any intermediate position, provided that the desired temperature 

 prevails at the thermostat. The temperature of the air is controlled 

 by the amount of steam which passes the diaphragm valve on its way 

 to the vento heaters. The flexible thermostatic disk is in the outlet 

 duct leading from the fan and is filled with a low-boiling liquid. 

 When the temperature of the air surrounding the disk in the duct 

 leading from the fan rises, the disk expands, owing to volatilization 

 of the liquid within, and flexes a diaphragm which opens a valve in 

 the thermostat. This valve permits air to pass through the air 

 line from the air-compressor storage tank to the diaphragm valve 

 on the main steam supply line, closing it. When the temperature 

 of the air in the duct drops, the thermostatic disk contracts, and the 



