مقاله انگلیسی مدیریت زباله و استفاده ان در پس از برداشت

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IN THE NAME OF GOD 

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WASTE MANAGEMENT & CULL UTILIZATION Master: Dr. Researcher: 

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PRINCIPLES FOR REDUCING r pos table 9. |): waste when Improve housekeeping. For example, some operations allow product to spill onto the floor. This wastes good-quality product, produce. solid waste, and unnecessarily uses water. Conveyers and transition points should be designed to prevent product spill. Change processing methods. In some situations there may be several alternative methods for accomplishing the same process er waste production in the selection process. Poorly designed machinery may damage product by allowing it to drop onto hard surfaces 01 be sheared as it moves past a protrusion. Some damaged product is removed as waste in packing. Other damage is not noticed until latei in the handling chain, and product may become unsalable at wholesale or retail marketing. Select packing and handling methods that produce less waste or produce waste that is easier to manage. For example. hydrocooling produces spent cooling water that must be posed of and requires water-resistant packaging (such as waxed fibers board boxes) that may not be easily recyclable. In contrast. forced-ai cooling requiresno cooling medium disposal and allows the use of regular fiberboard, which is recyclable. 

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DISPOSITION OF CULLED PRODUCT The most obvious way to reduce culls is to reduce the number of culls that reach the packinghouse. The producer should use the best cultural practices to produce a well-sized, unblemished commodity. Minimize the use of chemicals that contaminate waste and require special handling or disposal- Lye processing produces waste with a low pH that may need to be neutralized-Waste bline can be especially difficult to dispose of. Minimize wastewater flow. This is usually done by reusing and recycling water. Sometimes wash water can reused if solids are screened or settled out and disinfectants are kept at effective levels. As a general rule, the lowestwquality water should be used for initial cleaning of the product, and best-quality water should be used for the last step in processing. Minimizing water use may not decrease the total dry weight of solid waste but it does concentrate it. This may allow the use of smaller, less-expensive trealment systems and Ecrharencourage economical recovery of product because solid waste is more -concentrated. Segregate wastes. Wastes that require special processing or disposal should be kept separate from other wastes. Some wastes can be sc. — for byproducts and should be separaled from wastes that must be dis- posed of. 

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CATTLE FEED one Rte lc EUR le eet eR eV aan eT a eee TC Cee ی ی ا 000 تا ‎Ceo TE‏ ۱ enc Cece Rent cll aur cea et RM sce ce ‏ا ا‎ should be harvested and handled carefully to allows the feed to spoil quickly, If fed in large minimize injury, and ‏و‎ ace toate ae okt te eet ‏ا ل‎ mt 00 ی 000۴ ودنمحنطء فود ودنآ۵مهط ۵۶ صاعمی 20060 ۲۳6 ,معصنکدی عط م۵ ۴مابطتتاعنه انهاه» ۳6 برد ۵عاابی وطاعط کهاطهاه‌وع ‎lt sa rr‏ یر ۰ 200 ‏بجناهرمعدمم منجد خهضا کعوو ۵۱۲ عوهام3۵۷۵ علاتلعووم ۵ عوط عهاطهاعوع۷‎ as Detect ‏ی‎ tes ‏ل‎ tcto olm a teL ad Resear ae Cette mt Ree ‏ی ری .ی‎ Mey Cet soar aR ‏خمعاوی ۲عاه حون 6 ما عوهاهه3۵۷ اهتاعقامم‎ ee ea esc ‏انا‎ ‏ات ی تراک را‎ Lee Ro aL 

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Low protein levels in culled fruit limit the quantity that can be fed. Where rapid weight gain is important. in feed lots, example, only about 20% of the ration can be com posed of culled fruit- As a maintenance ration. up to 80% of the feed can be culls. Stone fruit pits rarely cause internal injuries or choking. Cattle spit out some pits while eating, and manv of the remaining pits are regurgitated with the cud and spit out. In fact, the main problem with pits is disposing of them. as they tend to fill feed troughs. Culled fruit is typically bought for $2 to S5 per ton: In terms of feed value, this is equivalent tobuying barley for $20 to $50 per ton. However, the costs of handling and transporting culls must be added to this cost. Also, some cost must be added to account for the uncertain effects of using a feed that has not been thoroughly tested for nutrient levels and trace chemicals. Culled potatoes are good source of reed for animals. Like stone fruits, they are high in water content (abOut 77%), high in energy value, and low in protein. Beef steers can be fed up to 50% potato waste in finishing rations and still have acceptable Weight gain. However, the steers must be carefully adapted to a potato ration, and the ration should not be changed rapidly. TO a limited extent cattle are also fed culled cantaloupes and other muskmelons. Cool-season vegetable culls have also been used as feed- These culls all have the same general limitations already discussed. 

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ALCOHOL PRODUCTION Most fruit and some culled vegetables (espeand tubers) can be used for alcohol production. Alcohol for human consumption has a much higher value than alcohol for motor fuel. Some culled pears, kiwifruits, and apples are used for fruit wine production in California, and some of the apple wine produced is converted to cider vunegar. The use of culls for fuel alcohol produclion is limited mainly by the low sugar content of most fruits and vegetables. The 8 to sugar content of most culled fruits results in an alcohol yield of about 42 Vmetric ton (10 gaVton) of fruit. Potatoes have one of the best yields of alcohol for culls at 83 to 104 Vmetric ton (20 to 25 gal/ton). but thisis still low compared to better feedstocks such as corn, which yield 375 Vmctric ton (90 gal/ton). The low yield makes it uneconomical to haul culls any significant distance. if production of fuel alcohol from culls is to be economical, it must bce done near the packinghouse. Low sugar content also results in 4 to 5% alcohol "wines," which require considerable energy per gallon of alcohol to process and distill. 

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CULL DISPOSAL Unfortunately, the limits to the use of culls often result in large portions of them being discarded. Improper disposal can cause sanitary and pollution problems. Flies and odor problems can be prevented by ensuring rapid drying. Fly maggots hatch into adults within 7 to 10 days, and odor problems can develop before flies appear. The culls should be crushed and spread no more than one or two layers deep; sometimes this is done on orchard roads or Tallow fields. Culls can be disked into the soil, although this tends to cover the fruit with soil and slows drying: also, insects or diseases that may have caused the fruit to be -—Cculled in the first place may infect a future crop. Disposal sites should be as far away from neighbors as possible. Flies can travel up to 8 km (5 m) from the place where they hatch. Culls should not be dumped near streambeds. Fruit dump sites can attract the dumping of many other kinds of refuse. If culls are deposited away from the point of production, use municipal solid waste disposal sites if available. 

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PACKAGES FOR HORTICULTURAL CROPS marketing and distributing horticultural products. They must protect fragile produCts against damage during distribution and must maintain their shape and strength, often for long periods at high RH and sometimes after water contact. Many are designed to allow rapid cooling or products from field temperatures to low storage or transport temperatures,-and- they-must allow for continual removal of heat produced by the contents. Packages must be adaptable to high-volume packing operatiorus. They convey information about their «contents and when used for display must be attractive to the consumer. 

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TODAY'S HORTICULTURAL PACKAGES inapact bauise on Anjou pears Bruising extends into the flesh and mayor Many materials, sizes, and are used in may not be visible on the surface. packages for horticultural products. In the United States alone, more than 500 different packages are used for produce. Past efforts at standardization have had limited success, but this situation is beginning to change in response to pressures from produce buyers. Major changes have been in response to economic considerations, the use of less- expensive materials, and the need to adapt to new packing and handling procedures. In he United States. most perishables are packed in corrugated fiberboard boxes, with a limited use. of plastic and wood boxes. Handpacking is used mainly for field-packed product. and most packinghouses employ mechanical packiag. Most products are unitized and shipped on pallets. 

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PRODUCT REQUIREMENTS Developing successful packages for horticultural products emphasizes the different requirements of various products. Although these requirements vary widely with the commodity, marketing program, packing method, and so on, there are many generalities that apply to most commodities. PROTECTION FROM INJURIES Physical injuries to the product must be avoided wherever possible during handling and distribution. Some of the more obvious open wounds (e.g., cuts or punctures) often occur before packaging and can be eliminated by good supervision and sorting. Certain bruises. however, may accumulate throughout all stages of handling, inclbding packaging and distribution. Impact bruises (fig. 10.*1). Impact bruising results from dropping the product onto a hard surface- Because impact injury may not be immediately visible on the surface, careful quality control is needed to protect against the product into the package is a common cause of impact injury during packing. Installing decelerator strips at filling chutes and designing fillers to raise empty boxes to reduce drop heights during volume-filling reduce the incidence and severity of impact bruising. Packaged products can also receive impact bruising from drops during manual or mechanical handling with chutes or convevors, or during transport as a vehicle runs over a curb or pothole. Unit handling reduces the number of times an individual package is handled and thus the number of impacts. Rough handling by machinery can also cause impact bruising. Corrugated fiberboard can انر 0 سجاه ال اد 

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FACILITATING SPECIAL TREATMENTS ‎ol tan]‏ ا ا ا ل ‎U Manca Oige‏ ل یر ‎MI aera cle‏ ره ‎amest‏ ریز ‎through which the fumigant can readily flow. Venting sufficient for rapid cooling is more than‏ ل ‎ECC team Meee else ltrta CCR meee‏ ‎Bears es time ote Mane ei iirc Moe cael aimee eet n)‏ ‎PV CURMisc IRM es Nace ‏ا ا ا ا‎ CN ent emit ceed lm ieee ‏ا‎ ce Nn Rial an ean eta Rea eur Pere Tena eetoran Meola tulle tt Sa: ECL Ag NaC agi tel toe leet cela oa ese Ta Ye Sener iene am Nene ra le Mem ‏ل‎ ele AT aU ‏ار ی‎ eure eile ReitTs 0 0 ‎0 ‏ت یر‎ ۱ sa racea temo kane tickets ha ‏ل‎ eric ein tac! Rieti ‏ار‎ oN -Mve te eet ‎Reece ‏ل ا‎ he neers ‎ 

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COMPATIBILFTYWITH HANDLING SYSTEMS Most boxes are hand-lifted at some point in the marketing chain, so package weight must be limited. A few commodities are packaged in units ‘designed only for mechanical lifts. For example, watermelons, bagged apples, and head lettuce for processing are shipped in pallet bins. Packaging may need special design features to make it compatible with packing equipment and handling procedures. For example, top flaps that extend upward may interfere with hand-nackina Tha nackada muct he sized to facilitate “| RETAIL DISPLAY |] Some packaging systems are designed for use in retail displays. Most notable examples are berries that are packed in small baskets, and apples, oranges, carrots that are bagged in consumer-sized units. Advantages of consurner packages are that they can be designed to modify the atmosphere around the product and extend shelf life, improve sanitation by reducing opportunity for human contact, increase RH around the product and reduce moisture loss, and protect the product from mechanical injury. Their that it may be difficult to sort out the occasional poor-quality product, high RH may foster growth of decay, and bags or consumer containers may slow cooling. Packages to be used in retail display must fit the needs of the retailer, so package appearance becomes much more important than for other types of packaging. 

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ECONOMIC CONSIDERATIONS Packaging costs include the Costs Of Product value costs include the costs * package components of + transportation + possible increase in product deterioration + package make-up, labor, and materials + discounts in sale price due to package + internal packaging materials (if needed) failu res + storage Of package components + possible negative impaCt on brand Packing costs include the costs of reputation related to package performance + adapting to mechanized package distribution + new or modified equipment and facilities at packing operation possible reduction in packing labor effi— ciency + increased number of packing steps required Palletizing and handling costs include the costs. Of + changes in pallet stacking efficiency + labor, materials, and equipment for unitizing pallets + compatibility with various pallet materials and substitutes Marketing costs include the costs of decreased load density in storage and in transport vehicles special labor or equipment for handling suitability of package as a display unit disposal of packages In considering the cost of any new package, all of the costs of adapting it into the marketing system must be considered- These costs include packaging material, labor, modifications in packing and handling operations. and potential changes in product condition. 

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COOLING HORTICULTURAL COMMODITIES err ‏ی ی‎ Maa ea core et) Rene oe Rui aac aa eee ae Reg nee eC Rae arc Pe ee aa enantio a Lt teen tae cee en onc etic Sed ga elt elise TAN Rec ictal mel! Mee See nea cmen ieee tetas een ns tC etn auc tours ۱3 ecue Ma et yaar irate oy ere a csr ec Rene erie Cece ene etree mis Rae eae el ited sa erence tend Erol cia kent nl un ae eM rece Tact gies B eso Me eet Neen a eens eet Racecar a cae ۱۳ ‏ره‎ este le aan iti mete Lar a) 

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Some commodities can withstand a fairlv long time between harvest and cooling. For example, apples placed in controlled atmosphere storage often do not reach optimal storage temperature until several days after harvest; exported California oranges may not reach best storage temperature until they have been at sea for several days. prod ucts that do not require fast cooling generally have slow respiration .rales, low moisture loss (transpiration) rates, and arc often grown in climates with mild temperatures. The first part of this chapter describes the variety Of cooling systems available for horticultural commodities and the issues that need to be understood in their use. The second part 65 for selecting a cooling svs| COOLING METHODS }"- Initial cooling of horticultural products to near their optimal storage temperature can bc done with scvcral cooling methods. including room cooling, forced-air cooling. hydrocooling, package icing. and vacuum cooling, Mechanical refrigeration in ships or refrigerated marine containers may bc uscd for cooling a few commodities during transport. A few cooling methods (e_g_. room cooling. forced-air cool ing, and hydrocooling) are used with a wide range of commodities. Some commodities can be cooled by several methods, but most come modities respond best to one or two coolino methods. 

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بصي 98 1 سوم ] of rape temperatura hares on the time needed forthe bes | | ter hanesel whe a ‏ما ی‎ grapes Ten ‏واه و93 ما‎ oss ty) 70 » ” 100 ۴ ROOM COOLING | Figure 112 Typical cooling cave for peihable products. Cooling tines are typical for large fut ite peaches, exposed to moderate amounts of aiov nial prod temperate Product temperature ‏وم‎ MB د 

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low air pressure within the tunnel. Cold air from the room moves through the openings in or between containers toward the lowpressure zone, sweeping heat away from the product. The exhaust fan is usually a permanent unit that also circulates air over the refrigeration coils and returns it to the cold room (fig. 11.6). The exhaust fan can also be a portable unit that is placed to direct the warm exhaust air toward the air return of the cold room or refrigeration evaporators COLD WALL This forced-air cooling system uses a permas nent air plenum equipped with exhaust fans (fig. 11.7). The air plenum is often located at one end or side of a cold room, with the exhaust fans designed to move air over the refrigeration coils. Because openings are located along the room side of the plenum, against which stacks or pallet loads cf containers can be placed (fig. 11.8), this method is not often used for products in bins. Various damper designs can be used to ensure that airflow is blocked except when a pallet is in place. Each palletstarts cooling as soon as it is in place, so there is no need to await deliveries to complete a tunnel. Shelves may be built so that several layers of pallets can be cooled. 

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HYDROCOOLING Ceo nate ‏یت رت‎ ‏مزا کاءباهه۲م ۲عتعمهاک-ااهطرو ۲۵۲ دعنمنه 10 278 ععصت وطناعمی کطاطونه5۵۷۵۱ هنم :(11.14 ۵00 11.13 .عو6)‎ cherries and up to | hour for large products such as melons. Hydrocoolers can use either an immersion or a shower Duo ‏و‎ ‎Per sce Ruut e enc aN ne em ec cl oR ‏ا ا‎ ‏ممع امعععغويي عم غدنامم وملاممعه برط مأ فعكن كاعم أماممء .ممكقع5 وملاممء ع1‎ ‎Tce‏ ل ا ل ا بو ‎en aR‏ 0 ‎Plgets ecg em ete RRNA oa ees Reems erect eae ea uate lm ace ae te‏ ‎ree CM ce ecm ed a Run men renee Ue teeasnet ener‏ ‎ec eS ut kei ei Re clccesecia Kurt Masia es aca ce Men A seg tori‏ ‎Ere Run eeu CnC tet toe lle es eee eon ern)‏ 0۷۵۲۵۵۵ 1۱۳0۵7۵100 ‎ ‎Biren eee um Coca ent eh cin emer ast eM ge eee cae es eRe PACU OP uy se Ret clade uci acc McInnes eeu ae) to accommodate two-high stacking of bins on the conveyors. Bulk product in shallow layers on a conveyor belt eee CCAR eee Nc uence sat ream sete a ene) Fate cu oestrone ‏ا ا ا‎ ۱ heuet ek Ona ner luni eae ecKcc miele ent ent ei Ceres ‏ره‎ ken CLT) 

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PACKAGE-ICING Some commodities are cooled by filling packed containers with crushed or flaked ice Initially, the direct contact between product and ice causes fast cooling. However, as the ice in contact with the product melts, the cooling rate slows considerably The constant supply of meltwater keeps a high RH around the product. Liquid ice, a slurry of ice and weater, distribute ice throughout the box, achieving better contact with the product (figs. 11.15and 11.16). Ice can be produced during off-peak hours when electricity is cheapest and stored for daytime usepackage-icing requires expensive, watertolerant packages. The packages should be fairly tight but should have enough holes to drain rneltwater. In small opentions the ice is hand-raked or shoveled into containers. Large operations use liquid-ice machines to automatically ice pallet loads of packed cartons. The process, which requires only a few minutes, is used for cooling some fieldpacked vegetables, particularly broccoli. The iced packages should be placed into a cold room after filling to minimize ice melt. 

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The product must be tolerant of prolonged exposure to wet conditions at OOC (320F). Some low-density products have excess space in which to load ice within the package, and ice not melted during cooling can remain in the package even after transport. This excess ice can keep the product cold if the cold chain is broken. However, this is an inefficient use of ice, and the weight of the ice can add significantly to the freight load, sometimes limiting the amount of product hauled. An ice weight equal to 20 to 30% of the product weight is needed for initial cooling, but liquid icing often adds an ice weight equal to the duct weight. Also, duri port of mixed load ter fi ating ic 0 

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SELECTING A COOLING METHOD RUS Gi ea Nera ee eau ae co ee ane ee Mee ۷۱ 000 ‏عط )موی عجهاهاهوم ناژ 309 عحجهعا که ععنهععط ۱0۵/5۲۵۲۵ ۲۵ عاهعام‎ kes ey ANG Leese akg te ‏ی ات‎ ete Rene ieee Ae ‘OOC (320F) room if it is removed from the cooler at 70C (450F) flesh temperature, It should then be Stored at 70C (450F). PE ea See Rn oe Re ee nee Let oes Cae Pat eee Rome fies es cnn er on steuN Ree Reems y COM eotoia ‏ی‎ enroll Sem gael lite teresa erie es curt en Maite rel telecon Meee tegen emai ۱ ‏ری‎ ent eh tM nie lecsie rnc lea We teckel cy CMe ‏ل ل‎ ‏لع أناوعء ناواعط قنع كلم مأ غعنافممم غعو مع مماغميعمه عط دأمكمم معط قمة بعط 6 5ومع؟ غعن لمم‎ م دعم بزالهنكن ذأ ععنا وهم غكعممهين عم ,دععامم ,زمدمعء042؟ عمبرط-اعممنة ما بعام تمق دم)ع *ع نعم عممعة ‎Piet ig teed eee etic aCe‏ COLD ROOMS Cooled product SMI! quickly warm up unless it is loaded directly into refrigerated transport - vehicles or placed in cold rooms. Rewarming wastes [he benefits of cooling: and cooled products left in a warm environment are also subject to condensation, which may lead to disease. To help solve these problems, a cold room should be associated with the cooler. In some cases, the cooler may-be a part Of the cold room, as with forced-air coolers, but this is not recommended. Small cold roorns can. be commercially constnxcted, purchased in prefabricated form and erected by growers, constnicted by growers, or purchased as used refrigerated transport Cars, trailers, or ‎ae CS aR ea Pa ety pe OD A ge‏ ی ل ل ل ا ا ا ‎ ‎ 

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] Effective cooling and temperature management requires a complete understanding of product and market requirements. and Oj the cooling methods available. Rapid thorough cooling and good product temperature management are essential [cr successful produce marketina. Cooling is part of 'the total system of handling pcrishables. Effects on cooling ratc must bc considered whcnever changc is made in packaging or handling. Requirements for cooling and cold differ, and thev should be considcrcd as two separate operations. Four cooling methods and variations arc available to achieve rapid cooling. Scicct a cooling method or methods that fit the needs of your customers and the rangc of commodities you handle. Fast cooling can Oftcn be achicvcd throu"h minor modifications of existing cooling facilities. Design requircmcnts should be determined bv a qualificd rcfrigcration engineer after evaluating the complete rcfrigeration system. The incrcascd costs involved in achieving faster coolina mav bc rclatively small when thc total cost o! the cooling system is considered. Cooling time can often be reduced by attention to details of air or water management, package packing material, and pallet stacking patterns. Keep careful records of cooling performance. Good cooler management requires systematic RR OPAL LAAT AE Rie. 

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REFERENCES Hardenburg, R- E. A. E Watada, and C. Y. Wang. 1986. The commercial Storage or fruits, vegetables, and florist and nursery stocks. USDA Handb. 130 pp. Isenberg. EM.R.E andj. E. Parson. 1982. Vacuum cooling vegetables. Cornell Univ. Coop. Ext. Bull. 186. 10 pp. Jeffrt%J.J. 1977. Engineering principles related to the of systems for air cooling of fruits and vegetables in shipping containers. Proc. 29th Intl. Conf. on Handling Perishable Agricul- tural Commodities. East Lansing: Mich. State Univ. 151-164. Rij, F. Thompson. and D. S. Farnham. 1979. Handling. precooling. and temperature manage ment of cut flower crops for truck transportation. Oakland: Univ. Calif. Coop. Ext. Leaflet 21058. Sargent. S. M. T. Talbot. and J. K. Brecht. 1989. Evaluating precooling methods for vegetable packinghouse operations. Proc. Fla. State Hot-L soc. 101:175-182. Thompson,}. E. and F. Kasmire. 1981. An evaporative cooler [or vegetable crops. Calif. Agric. Thompson. J. E, E G. Mitchell. T. R. Rumsey. R. E Kasmire. and C. H. Crisosto. 1998. Commercial cooling of fruits, vegetables and flowers. Oakland: Uniu Calif. Div. ot Ag. and Nat- Rex publ21567-61 pp. Watkins, J. B. , and S. Ledger. 1990. Forced-air cooling- 2nd ed. Brisbane. Australia: Queensland Dept. Of Primary Industries. 64 pp. 

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Author: James F. Thompson 

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*slow biological activity of the product by maintaining the lowest temperature that will not cause freezing or chilling injury and by_ controlling atmospheric composition. «slow the growth and spread of microorganisms by maintaining low Storage Systems temperatures and minimizing surface moisture on the product. *reduce product moisture loss and the resulting wilting and shrivel by reducing the difference between product and air temperatures and maintaining high humidity in the storage room. * reduce product susceptibility to damage from ethylene gas. 

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STORAGE CONSIDERATIONS TEMPERATURE The temperature in a storage facility normally should be kept within about *I°C (2°F) of the desired temperature for the commodities being stored. For Storage very close to the freezing point, a narrower range may be needed- Temperatures below the optimal range for a given commodity can cause freezing or chilling injury: temperatures 1 above it can shorten storage life. In addition, wide temperalure fluctuations can result in water condensing on stored products and more rapid water loss from them. Recommended temperatures and humidities for long-term storage of hOrticultural products are listed in appendix A. In many storage facilities, particularlv at and retail marketing, manv different products are held in a common rqom. Figure 12.2 groups commodities into four temperature and humidity groups for short-term storage. Maintaining storage temperatures within the prescribed range depends on several important design factors. The refrigeration system must be Sized to handle the maximum expected heat load. Undersized sys-terns allow the air temperature to rise during peak heat load condilions, but an oversized system is unnecessarily expensive. The system should also be designed so that air leaving the refrigeration coils is close to the desired temperature in the room. This prevents large temperature fluctuations as the refrigeration system cycles on and off. Large 

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Interior view ofa table grape cold storage. 

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When forklift openings are used for air dis- tribution. they must align along the entire length of the air path. The serpentine airflow system is the only one that forces air to flow through the product. This speeds initial cooling but may not be necessary for uniform product temperatures in long-term storage. Because air takes the path of least resistance. partially filled rooms often have poor air distribution. Large rooms can be divided into sections using uninsulated walls parallel to the direction of airflow. This allows product in one bay to be removed wih little effect on airflow in neighboring bays. Smaller rooms with packaged evaporator coils use an airflow pattern similar to the ceiling plenum design except that the plenum is not needed because high-capacity evaporator fans can discharge air 15 m (50 ft). The wall plenum is formed by stacking product 20 to 25 cm (8 to 10 in) away from the wall under the evaporator. Rooms cooled with roof-mounted packaged evaporative coolers can use ceiling-mounted paddle fans to distribute air downward past product bins some long-term controlled atmosphere storage, airflow is minimized by cycling evaporator fans off for as much as 85 to 90% of the time. In the winter in temperate climates, most refrigeration demand comes from heat released by evaporator fans and motors. Reducing fan operation time reduces heat input, which in turn reduces refrigeration operation. Tests conducted in the northwestern United States showed that fan cycling reduced electricity use by 65%. It may also increase humidity in the storage and reduce product moisture loss. 

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Temperature variation is minimized with adequate air circulation. Most storages are designed to provide an airflow of 0.052 per second and per metric ton (100 cfm/ton) of product, based on the maximum amount of product that can be stored in the room. This is needed to cool the product to storage temperature and may be needed if the products has a high respiration rate. Because this high airflow rate can cause excessive weight loss from products and fans are a significant source of heat, the system should be designed to reduce airflow to 0.0208 to 0.0104 m3 per second and per metric ton (20 to 40 cfm/ton) after the product has reached storage temperature. Systems that control motor speed, such as variable frequency controllers for AC motors, are often used to control fan speed. Operate fans at the 10WEt possible speed that prevents unacceptably warm product in the storage. The warmest product will tend to be near the top of the room next to a warm wall or roof, and farthest from the evaporator fans. Low circulation rates require that the system be designed to move air uniformly past. 

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Airflow systems used in cold storages The top two designs cause ar to flow through planned gaps between lanes of pallets or bins The bottom designs work with tightly stacked bins and force aic¢ through forklift openings ‘iaflow through spaces ‏تا‎ ‘eling pln wth tring vanes 1 “Vertical stots in supply plenum Aielow through forklift openings in bins penis _ ‏وه‎ tonal bs in sappy leu 

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HUMIDITY For most perishable commodities. the RH in a long-term storage facility should be kept at 90 to 95%. Humidities below this range result in unacceptable moisture loss. Humidities very close to 100% may cause excessive growth of microorganisms and surface cracking on some fruits, although it is unusual for a storage facility.to have relative humidities that are too high. Partially dried products such as garlic, ginger, and dry onion are held — at 65 to 75% RH. Dried fruits and nuts should be held at 55 - 65% RHFiberboard containers are weakened by prolonged exposure to the high humidity recommended for most horticultural cornmodifies. Typical fiberboard exposed to 95% RH has half as much strength as the same material exposed to 50% RH. The storage humidity for perishables can be lowered below recommended levels if the product is packaged in plastic bags or box liners to prevent ۳۱۵15۲۱۲6 ۰ Refrigeration equipment must be specially designed to ۳ ‏رت و‎ Tag pec Wer NO OP cn ‏م الا الك 10 ا ا‎ Sen ARS ar 

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EXPANSION VALVES Small mechanical refrigeration systems are controlled primarily by an expansion valve, which regulates the pressure of the refrigerant in the evaporator. Low pressures cause the liquid refrigerant to evaporate at low tempera tures. The valve also controls the flow of refrigerant, which affects the amount of refrigeration capacity available. Capillary tubes and thermostatic expansion valves are the two most common types of expatision valves. The capillary tube is used with very small refrigeration equipment (less than I HP). It is a tube 0.6 to 6 m (2 to 20 ft) long with a very small inside diameter of 0.6 to 2.3 mm (0.025 to 0.090 in). The resistance of the liq uid flowing through the tube creates the needed pressure drop between the low-pres sure and high-pressure sides of the system and regulates the flow of refrigerant. A capillary is inexpensive and has no moving parts to maintain, but it cannot be adjusted, ts subject to clogging, and requires a relatively constant weight of refrigerant in the system. A thermostatic expansion valve regulates the flow of refrigerant to maintain a constant temperature difference between the evaporator inlet (or evaporating temperature) and the coil outlet, maintaining a constant superheat. It allows the low-side pressure to va»r, sa that when high refrigeration loads are required, the temperature of the evaporator u coil increases. This type Of expansion valve is not well suited to obtaining high RH needed in long-term storage. Large refrigeration systems may use a flooded coil, an evaporator coil that is designed to always have liquid refrigerant in it. A flooded coil has a greater heat transfer efficiency than a nonflooded coil of equal size. Refrigerant flow is controlled primarily with a float control that ensures a constant level of refrigerant in the coil. The float control may operate in parallel with a thermostatic expansion valve. Other controls, such as suction pressure regulators, may be used conjunction with float controls. These are especially useful in maintaining the highest possible evaporator coil temperature in order to maintain high humidity in the storage room. 

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COMPRESSORS * The most common types of refrigeration compressors are reciprocating (piston) and rotarve screw (fig. 12.5). Reciprocating cornpressors come in a wide range of sizes and Can be set up to operate efficiently at varying refrigerant flow rates. Flow rates are varied by shutting off pairs of cylinders in a unit, which may have 6 to 12 cylinders. The main disadvantage of reciprocating compressoFS i4— their fairly high maintenance costs- Rotary screw compressors have low maintenance costs but are not available in sizes smaller than about 23 kW (30 HP). EVAPORATORS Modern cold storages usually use finned tube evaporators. Air from the Storage ts forced past the tubes by fans, which are a part of a complete evaporator unit. Evaporators operating below OOC (320F) build up frost that must be removed to maintain good heat transfer efficiency. Defrosting may be done by periodically flooding the coils with water, by electric heaters, by directing hot refrigerant gas to the evaporators, or by continuously defrosting with a brine or glycol solution. 

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The capacity of a refrigeration system is based on the sum of the heat inputs to a storage area, including heat conducted through walls, floor, and ceiling; field and respiration heat from the product; heat from air infiltration; and heat from personnel and equipment such as lights, fans, and forklifts. Details of heat load calculations are listed in ASHRAE handbooks and in Industrial Refrigeration Handbook (Stoecker 1998). Refrigeration equipment for storage facilities is generally not designed to remove much field heat from the product, since a large capacity would be required; a separate cooling facility is used for this purpose. 

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MECHANICA REFRIGERATION WWerescolele( Metall Me Meee coe eee ee ole Colac eMC NUTS eat tae ل ل ا ل of liquid nitrogen or liquid carbon dioxide in the storage area. As these liquids boil, they cause a cooling effect GR en eset ose reacties ial ‏ا‎ OPM aes keira mae EN Aneel ‏ی ی‎ le Mca iene acne cur ‏یت‎ M ‏ا‎ uence ‏ا ا‎ SS eto ‏زر‎ toner Ta Mater atenolol ta Figure 12.4 shows the components of a typical vapor recompression (or mechanical) refrigerationsystem. The ۱ ees enemies nC Mr Re ote se Reale eRe ects er eee Mau eM ‏سا رب ار‎ coll ra ere ‏ل‎ nam eM um Colge- le Cian sfoe-Coual Mero reall Metete-t Rear Ramet Men alate cae eC ‏ی رت ی‎ ۱ oma ics eect a Ml eee ena h ce gr) Neem cen emer M CMC Mente ‏ا ا ل‎ ۱3/۰۱۱۰۹۰۱۰ tales es reimeral ten 

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Mechanical humidifiers or fog spray nozzles are sometimes used-to add moisture to the storage room and reduce the drying effect of the evaporator coils. However, this added moisture results in the need for more frequent defrosting of coils. Humidifiers are needed in conditions where product is stored at a temperature warmer than the outside environment, such as cold-winter locations where heat must be added to prevent damage from low temperatures. Some refrigeration systems use a wet coil heat exchanger to maintain humidity. In this System, water is cooled to OOC (320F) or a higher temperature if higher room tempera- tures are desired. The water is sprayed down through a coil. and the storage area air is cooled and humidified to nearly 100% RH as it moves upward through the coil. However, as the air moves through the storage area it picks up heat, and the rise in temperature reduces RH. This system is usually limited to air temperatures above 0.20c (32.40F) and does not work for commodities that are held close to Or bclov.e OOC, without the use of compounds that lower the freezing point of water such as caustic soda 50 to 60C (| | OF) lower than the desired air temperature in the room. This causes an excessive amount of moisture to condense on the coils and can result in 70 to 80% RH in the storage room. Coils with a large system is vwey useful for this ‏کم ویس مت‎ 

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REFRIGERANTS * Cost of refrigerant. Halocarbon refrigerants are more expensive than ammonia. Environmental regulations restrict the availability of some halocarbon refrigerants. Compatibility. Ammonia cannot be used with metals that contain copper; halocarbon refrigerants cannot be usedwith alloys containing more than 2% magnesium and may damage some elastomeric materials. * Toxicity Ammonia at very low concentralions can injure perishable commodities. IL is toxic to humans, and government regulations may require ammonia systems to have equipment to contain accidental releases and a plan for protecting personnel and neighbors from a release. * Flammability. Ammonia is very flammable- Most commonly used halocarbon refrigerants are not flammable or have a low flammability. 

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CONDENSERS Condcnsers are categorized as air-cooled or water-cooled. Small Systems usually use an air-cooled unit. Many home refrigerators, for STORAGE SYSTEMS instance. have a coiled tube in the back that allows a natural draft of air to now past. Larger systems use a fan to provide airflow past the condenser. large condensers are more likely to be water cooled. Water is a better heat conductor than air, allowing water-cooled condensers to be smaller than forced-air units of equal capacity. However, water- cooled units may require large quantities of water. which can be expensive to obtain and dispose of. Evaporative condensers reduce water consumption by recycling the heated condenser water; they require close attention to water quality to maintain efficiency and to prevent damage to the heat exchanger. Energy use is minimized by selecting a condenser that cools the refrigerant fluid to as low a temperature as possible- For example, a facility maintaining OOC (320F) and a condensing temperature Of 520C (1250F) 50% more power than One that operates at a condensing temperature of 350 C (950 F). In Warm areas. well-watercooled or evaporatively cooled condensers should be selected over air-cooled units. 

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ALTERNATIVE REFRIGERATION SOURCES CONTROL SYSTEMS In many developing countries, where mechanical refrigeration is prohibitively expensive to instail, maintain, and operate, a number of other techniques can be used to produce refrigeration. In some cases, these techniques can provide cooling levels that approach recommended storage conditions. In others, they are a compromise between proper storage ee see CONG the ‏دم جومم‎ airs Ghacsted from vents slong “ABEND, incite bottom of the side walls Ee conventional systems, and brine solutions __ water loss. are corrosive. But they dramatically reduce the quantity of first-stage refrigerant needed -and confine it to the engine room. This a great asset in dealing with the flammability Evaporatively cooled sweet potato storage. Unit and safety issues of ammonia. Secondary rative coolers on the roc! continuously supp'y coded air refrigerant piping does not need to with- to the storage. Room air is exhausted from vents along the bottom of the side walls stand the pressure of primary refrigerants, and plastic piping can sometimes be used. The temperature of the heat exchanger can be precisely controlled with a mixing valve. Brines and glycol solutions are corrosive and must be used with corrosion inhibitors, and they should never come in contact with zinc. Sodium chloride and propylene glycol are food-grade materials: 

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