Document dYdJr6V4vQb9gqeX0gX5qQGr9

336 CHAPTER 30 (Building Materials and Structures Report 145, U. S. Department of Commerce, April 2, 1056). BIBLIOGRAPHY B. W. Scribner: Summary Report of Research at the National Bureau of Standards on the Stability and Preservation of Records on Photographic Film (National Bureau of Standards Publication M162. May 1939). J. t. Crabtree and C. . Ives: Hie storage of valuable motion picture film (Journal of Society of Motion Picture Engineers, March 1938, p. 303). 1962 Guide And Data Boole Prevention and Removal of Fungus Growth on Processed Ph^ graphic Pilm (Eastman Kodak Co., 1954). Hazard in (he Handling and Storage qf Nitrate and Safety Motion Picture Film (Eastman Kodak Co., February 1951). J- M. Calhoun: Air conditioning in storing and handling motion picture film (Heating and Ventilating, October 1949, p. 66) J. M. Calhoun: Cold storage of photographic film (Phatograohie Science and Technique, October 1952. j>. Rfi). ^ American Standard Practice for Storage of Microfilm (American Standards Association, PH 5.4-1957). Stonge and Preservation of Motion Picture Film (Eastman Kodak Co., March 1957). CHAPTER 31 MEAT AND FRESH FISH Carcass Chifling and Holding: Cooler, Systems Used; Beef Carcass: Chilling, Holding, Cooler Layout, Drying, Design Conditions, Refrigeration Load; Hog Carcass: Chilling, Tempering, Cooler Design, Refrigeration Equipment, Spray Deck Coolers; Lamb and Calf: ChiH/ng, Processing Variety Meats, Refrigeration Load; Hog Cutting; Pork Trimmings; Smoked Meat; Fresh Pork; Sausage Dry Rooms; Lard Chilling; Hide Curing; Refrigerating Machinery; Fresh Fish: Care Aboard Vessels, long Fish, Shore Plant Procedure THIS chapter deals with the processing of meat and fish equipment designed to minimize glycol losses. Sludging in the particularly with care, cleanliness, and refrigeration re concentrator may become a difficult operating problem; to quirements for maintenance of quality. Chilling, holding, avoid it, additives must be used and pH closely controlled. storage, handling methods.are described and load calcu Finned coils are usually used with propylene glycol. lations are explained in detail. Because of its non-corrosiveness in comparison with sodium chloride, the use of propylene glycol greatly reduces the cost refrigeration systems for carcass of unit cooler construction as well as maintenance of space CHILLING AND HOLDING COOLERS equipment. However, propylene glycol is expensive, and the Refrigeration systems in common use in carcass chilling and holding rooms are operated with ammonia, at a system pres sure of 20 to 25 psig, as the primary refrigerant, and are of three general types: chilled brine spray, sprayed coil, and dry coils. In chilled brine spray systems sodium chloride brine--nor mally 70 Salometer (about 20 percent) solutions--is used as. the secondary refrigerant. It is chilled by the primary refriger-. ant to 15 to 20 F in shell-end-tube coolers or in large central tnnlfg equipped with pipe coils. From these it is pumped to' banks of brine sprays placed in overhead spray decks or in ver tical floor-mounted bunkers in the chill rooms, and returned by gravity to the central tanks. The air is chilled directly by the sprays, in which tb brine temperature usually rises 3 to 4 F deg in the process. The brine is constantly diluted by mois ture condensed out of the spaces being refrigerated, and must therefore be strengthened (i.e. concentrated) regularly. Chilled brine spray systems are generally being abandoned in favor of other systems described due to large building space required, inherent low capacity, brine carry-over tendencies, and difficulty of control. Nevertheless, many such systems are still in use. Sprayed coil systems comprise the majority of shilling am] holding room installations in use today. These employ unit coolers equipped with coils, brine spray banks, eliminatore to prevent brine carry-over, and fans for air-vapor circulation. The units usually are mounted (without ductwork) either on the floor, or overhead on converted brine spray decks. cost of equipment requiredto reconcentrate the spray solution is high. Dry coil systems have been used very little in chilling and holding rooms until recently, although they are widely used in other applications. Early attempts at dry coil chilling were unsuccessful, largely because the coil capacity provided was inadequate for dry coil operation. Dry coil systems usually include unit coolers equipped with coils, defrosting means, and fans for air-vapor circulation. Because the coils are operated without continuous brine spray, eliminators are not required. Coils are usually of the finned type with fins limited to 3 or 4 per in. to avoid icing difficulties. The units may be mounted on the floor, overhead on the rail beams, of over head on converted brine spray decks. A feature of all dry coil systems operated at surface tem peratures below 32 F is that moisture condensing on the coil surfaces results in the gradual build-up of a coating of frost or ice. Beyond a point, this causes substantial reduction in air flow and consequent capacity loss. The coils must therefore be defrosted periodically. to maintain capacity, normally every 4 to 24 hours for coils having 3 or 4 fins per inch. The rate of build-up, and hence the defrosting frequency, de creases with large coil capacity and high evaporating pres sure. Successful dry coil operation at frosting temperatures therefore requires far more coil surface than does sprayed coil operation. Defrosting may be done manually or automatically as follows: Refrigeration is supplied by the primary refrigerant in the coils. Chilled or non-chilled recirculated brine is continually sprayed over the coils, thus eliminating ice formation and oeed for periodic defrosting. The brine predominantly -used is sodium chloride, with caustic soda or other additive for control of pH. Because the sodium chloride brine is very corrosive, bare-pipe coils (with out fins) are usually used. The brine is also highly corrosive to the rail system and other cooler equipment. Another coil spray solution, recently finding some use in competition with sodium chloride, is propylene glycol with Added inhibitor complexes, available commercially under vari ous trade names. As with sodium chloride brine, it is constantiy diluted by moisture condensed out of the spaces being refrigerated, and must be concentrated by the evaporation of ^ater from. it. The reconcentration process requires special 1. Hot gas defrost is accomplished, with fans either on or off, by introducing hot gas direct from the system compressors into the evaporator coils. The evaporator suction is throttled to maintain a coil pressure of about 60 to 75 psig (approximately 40 to 50 F). The coils then act as condensers and supply the heat for molting the ice coating. Other evaporators in the system must supply the load for the compressors during this period. Hot gas defrost is rapid, normally requiring 5 to 15 minutes for com pletion. 2. Cod spray defrost is accomplished (with the fans turned off) by spraying the coil surfaces with water, which supplies the heat required to melt the ice coating. Suction and feed lines are closed off, with pressure relief from the coil to the suction line, to minimi** refrigeration effect. Enough water at 50 to 75 F must be used to avoid freezing on the coils, and care must be taken that freeze-up does not occur in the drain lines. The sprayed water tends to produce some fog in the refrigerated space. Coil spray defrost is fully as rapid as hot gas defrost. 3. Room air defrost b accomplished with the fans kept running while tiie suction and feed lines are closed off, with pressure 337