Document V3OXMORy31Bby5Mxjm2v9D8Qg

568 CHAPTER 54 * W. T. Pentzer et al: Top-Icing Cantaloupe* (USDA, H. T.&S. Office Report No. 185, 1948). ' J. K. Stewart and W. J. Lipton: Factora Influencing Heat Los* m Cantaloupe* During Hydrocooling (USDA, Marketing Re search Report No. 421, 1960). I W. L. Smith et al: Peach Hydrocooling. Shipping and Fungi cidal Test* (USDA, Agricultural Marketing Service No. 199. 1957). * H. P. Hayes: High vacuum precooling method for produce (Ice and Refrigeration, May 1951, p. 49). u J. Kaufman et al: Vacuum cooling (Produce Marketing, August 1960, p. 10). II R. K. Showaiter: Effect of wetting and top-icing upon the quality of vacuum-cooled and hydrocooled sweet com (Proceed ing*, Florida State Horticultural Society, VoL 70, 1957, p. 214). " R. K. Showalter and B. D. Thompson: Vacuum cooling of Florida vegetables (Proceedings, Florida State Horticultural Society, VoL 69,1956, p. 132). " B. A. Friedman and W. A. Radspinner: Vacuum Codling 1962 Guide And Data Book Fresh Vegetables and Fruits (USDA, Agricultural Mart-z. Service Report 107, 1956). 14 W. R. Barger: Factor* Affecting Temperature Reduction --j Weight Loss of Vacuum-Cooled Lettuce (uSDA, Marketina search Report, 1961). ^ *** u W. T. Pentier et al: Precoolsno California Orn-nf* m. Refrigeration in Transit (USDA, 'Technical Bulletin, No. " A. L. Ryall: A study of packaging materials (Ice Refrii*-- Ron, August 1952, p. 11). u D. V. Fisher: Cooling rates of apples packed in different bushel containers and stacked at different epacinga in storam (Ashbab Journal, July 1960, p. 53). ^ l* G. F. Sainsbury and H. A. Schomer: Influence of Carton Stacking Patterns on Pear Cooling Rates (USDA, Markets. Research Report No. 17L1957). wn* M J. K. Stewart and W. R. Barger: Effects of cooling method and topacing on the quality of peas and sweet com (Proceeding American Society of Horticultural Science, Vol. 75, I960 n 470V ' CHAPTER 55 TRUCKS AND TRAILERS fypes of Refrigerated Tracks and Trailers, Body Design and Construction, Auxiliary Equipment, Types of Refrigerating Systems, Mechanical Refrigeration Equipment, Computation of Cooling Loads THE transportation of perishables in insulated refrigerated on a conventional truck chassis) are seldom over 16 ft long, trucks and trailers has grown to its present tremendous 8 ft wide and 7 ft high. Refrigerated buck bodies used for proportions in about 35 years. The ice cream industry prob ice cream delivery range in weight from about 3800 lb for 440 ably pioneered the first successful mechanically-refrigerated gal to about 7500 lb for 2200 gaL The smaller body, on a trucks, operated by methyl chloride units, electrically op medium duty truck chassis, will have a gross vehicle weight, erated from a gasoline engine-driven generator. Prior to this, including cargo, of about 10,500 lb and the larger body, on a various forms of ice-and-salt tanks, refrigerated barrels and heavy duty track chassis, will have a gross vehicle weight, other containers were used to transport frozen items in un including cargo, of about 25,500 lb. Refrigerated trailers and insulated trucks or wagons. Many of the early insulated ve semi-trailers are up to 45 ft long, 8 ft wide and 13H ft overall hicles were fitted with eutectic-filled refrigerating elements height. A 40 ft low temperature trailer will weigh between which were frozen by connection to ammonia lines from the 10,000 and 14,000 lb. Cargo space width is determined by the plant system when the vehicle was garaged. Present day sys allowance for insulation, the inside and outside wall thick tems are evolutions of these early basic types and a primary nesses and the depth of the side wall racks. Floor racks may consideration influencing changes has been the weight of the take up to two to four inches of load height, Anri if a forced* refrigerating mechanism in relation to payload. Petersen air system delivering air from the front end of the body with described, for ice cream trucks, the changing ratio of truck out ducts is used, the load height should be at least 12 in. weight per gallon of ice cream from 43 lb per gallon to 16 lb below the ceiling to permit cold air to circulate to the rear per gallon as improvements bad been made.1 Today's large portion of the load. On long trailers various forms of supply ice cream trucks are less than 10 lb per gallon. This is typical or return ducts have been used to improve the temperature for all refrigerated vehicle categories, and successful increase distribution throughout the load.7~u Some trailers with air in payload ratio has been a major factor in the growth of re distributed from the front end use a bulkhead to force return frigerated truck and trailer transportation. References 1 to 5 of air through the side walls and floor. Various designs of contain information on early developments in refrigerated envelope, semi-envelope, or perimeter construction, in which truck and trailer transportation. the cooling (or heating) air is circulated wholly or partially Stagg estimates that 18,000 trucks and 10,000 trailers were in ducts contained in the wails, ceiling and floor, are begin adapted to refrigeration in 1939.* Because of the large ning to appear in commercial use, both over-the-road and number of captive fleet vehicles today, an exact determination piggy-back.aM of the number of refrigerated vehicles in service is not avail The characteristics of the air distribution system which able, but one source in the trailer manufacturing industry affect the temperature distribution in a loaded low tempera estimates 250,000 trucks and 50,000 trailers in refrigerated ture trailer were discussed by Achenbach.14 Lents discussed service in 1961. laboratory and road performance tests of a loaded trailer.u TYPES OF REFRIGERATED TRUCKS AND TRAILERS USDA Handbook No. 106 gives recommended loading meth ods and temperatures for many perishable products.** Although tracks and trailers are usually considered a Practically every type of body, from bicycle-mounted and means of transportation only, the use of refrigerated bodies other peddler carts to 40 ft van and tank semi-trailers, has for terminal storage space is becoming increasingly im been insulated and equipped with means for refrigeration. portant in certain industries. The dairy industry first de Design temperatures ranging from 70 F and higher for per- veloped the idea for wholesale milk delivery, and later for aonnel, electronic gear, flowers, chicks, bakery products, retail delivery. Many companies found that they could ex etc., to below --100 F for solid carbon dioxide, liquid oxygen pand their business greatly without going to the expense of end other chemicals, have been used for special purpose building larger coolers by loading the milk directly into vehicles. trucks after bottling. When this was done in the afternoon The majority of refrigerated vehicles fall into one of three or evening, the tracks remained at the plant during the night, Seneral temperature classifications: 60 to 70 F, air condi and drivers got an early start in the morning without con tioned body; 35 to 40 F, medium temperature or perishable gestion at the dock. This method required much less handling produce body; and 0 F, low temperature or frozen food body. and, consequently, lowered labor costs. The meat packing _ Each state fixes by law the marimnm weight and dimen and ice cream industries soon adopted this same plan. sions of trucks and trailers that may be operated over its highways. A chart of current state size and weight limits for The entire transportation industry is undergoing many transitions which cut across truck, rail, air and ship trans trucks and truck-trailers is issued by the Track-Trailer Man portation fields. For example, at least one operation uses con ufacturers Association Inc.# tainers in the general size and form of a trailer body which Por practical operation, refrigerated track bodies (carried can be attached to a trailer chassis for land hauling, and trans- 569