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756 CHAPTER 46 -1965 Guide And Data Book Small systems can use antiseptic materials such aa bleaching powder if proper care is taken. The dosage should be calcu lated on the basis of applying not over 1 ppm chlorine to the water in the system. By starting with a low dosage and observing the results, the quantity can progressively increase until control is obtained, without damage to the system. Sodium pentachlorophenate is effective in concentrations of about 30 ppm. It is not harmful to' the system if used in ex cess, but it is a pollution hazard in the blowdown. ' Most fouling of refrigerating condensers is due to biological growth rather than to scale deposition. An alga/adp. shmdH be applied when an abnormal increase in head pressure is noted. If biological fouling is present, chlorination will give almost immediate results since the organic matter will be destroyed. A more complete discussion of Water Treatment appears in Chapter 15. . WOOD DETERIORATION Wood is widely used in cooling towers because few materials compare with it in cost or durability. It is less subject to chemical deterioration than most other materials in the sys tem! But it is also attacked by microorganisms causing decay. The incidence' of wood deterioration is more prevalent in cool ing towers operating with an alkaline water. This observation led to th> supposition that the alkali canard a lwTniial attack similar to the process used in the manufacture of paper pulp. Later investigations11'1* have shown that wood-destroying organisms are usually present in the deteriorated wood. Heart redwood contains natural preservatives that are toxic to these organisms. The toxic materials are soluble in water, and the solubility increases under alkaline conditions. This.indicates that a high alkalinity will accelerate the leaching and render the wood, susceptible to decay rather than'cause a purely rKpmiral attack. ` This conclusion is supported by the fact that an aTVfllina water does not lead to deterioration when treated lumber is involved. Preservatives are applied to new lumber by pressure treating processes to assure the required'retention and pene1 tration of the preservatives. Most commercial preservatives may also be applied to wet lumber by the diffusion process which results in comparable retentions and penetration. The diffusion treatment provides a mmmn of protecting printing towers built of untreated lumber, and it is being used ex tensively. The use of pressure treated lumber adds about 10 percent to the cost oi a new tower. The cost of a diffusion treatment is usually slightly less. REFERENCES . 1S. Hori, U. A. Patchett, and L. M. K. Boelter: Deaign of spray cooling ponds (ASHVE Journal Sbctxos, Heating, Piping and Air Conditioning, October 1942, p. 624). * D. R. Baker and-It A. Shryock: A comprehensive approach to the analysis of cooling tower performance {ASMS Transac tion*. Journal of Heat Transfer. August 1961, p. 339). - 1F. Merkel: Verdustunss kuhlung (Porsehungarbetien. No 275, 1925). * Joseph Lichtenstein: Performance and. selection ;af me. chanicaf-draft cooling towers {ASMS Transactions, 1943, d 779). * - * W.-K. Lewis: The evaporation of a liquid into a gas {ASME Transactions. VoL 44,1922, p. 325). . * D. R. Baker and L. T., Mart:* Analysing cooling tower -performance, by the. unit-volume coefficient {Chemical En gineering, December 1952,'p. 196). ' * H. S. Mickley: Design of forced draft air conditioning equip- msnt (Chemical Engineering Progress, VoL 45, 1949,p. 739). J. C. Albright and .D. R. Baker: Summer Weather Data (The Mariey Co., 1944). . * Evaluated Weather Data for Cooling Equipment Design (fluor Products Company, 1958). ,a D.-R. Baker: Use charts to evaluate cooling towers {Pe troleum Refiner, November 1962). U-R. H. TWrf-hW and C. A. Richards: Deterioration of.wood in cooling towers {ASMS Transactions, VoL 73, 1951, p. 1055). " B. L. Browning and L. O. Bublitz: Extent and nature of rod- wood deterioration (Industrial and Engineering Chemistry,- VoL 45, 1953, p. 1516). BIBLIOGRAPHY F. H. Armstrong and J. G. Savory: The influence of fungal decay on the properties of timber. Effect of progressive decay by the soft-rot fungus, chaetomium globosum, on the strength of Beech. {Hdzforsckung, 13:84-89)._ R. M. Atchley: Protect cooling tower lumber with preservatives ('Power Engineering, May 1961, p. 72). R. H. Baechler, J. 0. Blew, and C. GrDuhcan: Cause and pre vention of decay of wood in cooling towers {ASME Petroleum Division Conference, 1961). D. R. Baker: Wood deterioration in cooling towers (Regional Meeting, ASME, April 1950) {Petroleum Engineer, April 1951). ' C. G. Duncan: Wood-attacking Capacities and Physiology of Soft-rot Fungi (Forest Products L*boratary Report No. 2173). J. R. Goff and J.'S. Excell: Chemically treating cooling tower lumber protects against decay {ASME Petroleum Division Con ference, September 1961). 1 J. Koch: Unterschung *n4 Berecbnung -von Euehlwerken ' (VUT Foreehungwhaft No. 4A4, Berlin, 1940). H. B. Nottage: Merkel's cooling diagram as a performance correlation for air-water,evaporative coding'systems {ASHVE Transactions, VoL 47,1941, p.' 429). J. G. Savory and R. H. Farmer: Susceptibility of attack by chaetomium globosum of timber treated with chlorine (Princes Risborough, FI*ILL., 1959). . B. F. Skexna and B. L. Browning: Study of deteriorated red wood specimens from <wiling towers (Institute of Paper Chem istry, Project 1561, Progress Report Three. 1952). * W. H. Walker, W. K. Lewis, W. H. McAdams, and EL R. GQffiaad: Principles of Chemical Engineering (McGraw-Hill Co., New York, 1937, p. 480). . D. Q. Rem: Process Heat Transfer (McGraw-Hill Co., New York, 1950, p/563). CHAPTER 47 FACTORY DEHYDRATING, CHARGING AND TESTING Ddrydrafion by Heat, Vacuum and Dry Air, Combination Methods, Special Considerations; Moisture Measurement; Charging; Testing of Leaks: Leak Detection Methods, Special Considerations; Performance Testing: Compressor Testing, Testing of Complete Systems, Testing of Components ECAUSE of the inherent complexities of a refrigeration tures must be high pnnngh for the removal of water adsorbed B system the proper processing of components and units on the various surfaces. is extremely'criticaL Not only must close tolerances and fits Obviously, the relative humidity of the air in the oven be met, as is normal to many manufacturing cycles, but ex must be maintained at low leveL Also, the moist air must be treme care must be taken to see that the chemical, electrical exhausted and replaced with dry air, to prevent vapor from and Tp^hanir-al segments of the system are processed in such bong recondensed on the treated parts when they are removed a m,nn<`r that they will remain compatible through an ex from the oven. As soon as the parts have been removed from tensive warranty period. Improved designs or clever innova the oven, they must be capped or dosed, in order to prevent tions can be completely nullified by archaic or careless factory moisture from entering them during cooling. This is not procedures. The three processing techniques peculiar to the necessary when the parts are directly removed to an area refrigeration industry, and ones that play a major role in the ultimate success or failure of a unit, are dehydration, charging with low humidity. The dehydrating method using vacuum is primarily used for and testing. Since a complete design must normally specify systems or parts which can be dosed and made leak-tight. The end results required, such as allowable moisture content, re boiling point of water is lower under vacuum, heing only 77 F frigerant quantities, and performance, this chapter will con at 29 in. of mercury, and 59 F at 29.5 in. Therefore the mois cern itself only with the methods that can be used to secure ture can be converted into vapor and moved to the vacuum a specified result rather than how to establish-limits. DEHYDRATION pump at reasonably low ambient temperatures. If dry air or nitrogen is used for dehydration, the air or nitrogen drawn or blown through the equipment removes The danger of excessive moisture in refrigeration systems is well known. In low temperature applications, incomplete dehydration may lead to capillary or expansion valve freezeup. Other results of incomplete dehydration are the formation of sludge in the system, flapper-valve breakage, and hermetic motor burn-out. Since all these effects, with the exception of freeze-up, cannot ordinarily be detected during a standard factory test, it is extremely important to use a dehydration technique which results in a safe moisture leveL In addition to this technique, an accurate method of measuring moisture' content in the system must be established. (See Table 1.) The acceptable moisture content depends upon many factors, such as size of the unit, its application, and the type of refrigerant used. Table 1 shows moisture limits specified by several mannl facturers for various systems, with the average limit of 15 ppm for Refrigerant 12, and 25 ppm for Refrigerant 22. When the cold trap method of moisture determination is used prior to the addition of oil and refrigerant, the moisture limit varies between 0.01 and 1.0 cc. moisture by becoming totally or partially saturated. The three methods described in the foregoing have certain disadvantages which will now be discussed. In the first method (oven heat), time and escape area are criticaL If the system or the parts to be dehydrated are large, it may be diffi cult to heat them to the correct temperature, with the result that either production is limited or a large operating area is needed. Also, since water vapor must escape by its own momentum, a complete system will normally have* a small opening for vapor escape as compared to the volume which must move through it. Where spring-mounted compressors are used, the use of oven heat alone may become prohibitive due to the time involved in heating the compressor parts and motor windings by radiation and convection. The necessity of handling the parts soon after they leave the oven presents an additional hazard which must be averted. The use of vacuum presents a number of problems. In nor mal shop ambient temperature, the boiling point requires a fairly high vacuum, and the amount of moisture that can be moved per unit time at this point is of course limited by both Dehydration by Heat, Vacuum, and Dry Air Several satisfactory methods of adequately dehydrating refrigeration systems and components are available, and the' final choice of the method used depends on the desired mois ture level, size, production quantities, tima, and cost. Heel, vacuum, and dry air are used for moisture'removal, either separately or in different combinations. Heat is applied by placing the equipment in an oven. The method is pri marily used for the dehydration of open parts, such as tubing,' driers, and other components. Sufficient time must be allowed to convert all the water present into vapor, and tempera- the size of the pump and the of the opening and linaw through which the vacuum is drawn. The length of piping re quired may also become a limiting factor. Dry air or nitrogen sweeping is an effective way of removing moisture, but in systems with several passages or with blind passages, there may not be sufficient flow. As a general rule, the rate of flow should be high enough to avoid complete saturation of the air in order to minimiae the danger of depoa-. tinn of moisture in some cooler portion of the equipment. On the other hand; there is little to be gained by the use of a very high rate of air flow, since the amount of water removed per' unit of air will be small. Also, moisture may remain in the .Tfae (eauil rapcuftaEty for Una ebaotv fe ***"4 f#*ry Conprwor Unit*. to TC A.A Hectare pores of the metal due to surface Viscosity.1 This may also happen when the vacuum method is used.. .