Document pm257V9jzkRp9XZrG51OvqyKB

782 CHAPTER 49 B Bulletin published by Aluminum-Ore Co., East St. Louis, 111. and Aluminum Co. of A'mprire^ Pittsburgh, Pa. * Bulletin 121, Microtraps, Davison Chemical Division, W. R. Grace & Co. 17 W. A. Patrick and D. C. Jones (Journal of Physical Chem istry, 29, 1929, p. l). . ** W. A. Hammond.-.(Journal-.cf .Chemical Education, 12 (9) 1935, p.-446. Bulletin, W. A. Hammond Drierite Company, Yel low-Springs, Ohio). .* ** Bulletin, Linde Company, Division of Union Carbide Corp. " W. 0: Walker and W. R.- RinelU: U. S. Patent No. 2,163,901. W: 01 Walks'-: Latestideas'in' use of desiccants and diners (Refrigeration Service & Contracting* August 1963, p. 24). - - a A. J. GuIly, H.A -Tooke, and'L. H. Bartlett: Desiccant- refrigerant moisture equilibria (Refrigerating Engineering, April'1954, p. 62).0 " * Standard Method of Testing Desiccants far Refrigerant Drying (ASHRAE Standard 35A-1956); ` ,, u'Standard Methods of Rating and'Tesiing High Side Liquid Line.Driers (ASHRAE Standard 35B-1956). Standard for Rating Liquid Line Drier (Air-Conditioning and Refrigeration Institute Standard 7KK1964). 1965 Guide And Data Boole Standard Procedure far Servicing Hermetic-Motor Burnouts (Section 91. p. 9101, Service AfanuaLRefrigeration Service Engi neers Society, 433 No. Waller Ave., Chicago, Illinois). * J. E. Hoffman and B. L. Lange: Acid removal by various desiccants (ASHRAE Journal, February 1962, p. 61). nR. L Mays: Molecular sieve and gel-type, desiccants for Refrigerants 12 and 22 (ASHRAE Journal August 1962, p. 73). - u W. O.'Walker, J. M. Malcolm, and H. C. Lynn: Hydrophobic behavior of certain desiccants (Refrigerating Engineering, April 1955/p. 50).,. a W. O. Krause, A'B. Guise, and E. A Beachain: Time fao- tora in the removal of moisture from refrigerating systems with desiccant type driers (ASHRAE Transactions, VoI. 66,-1960, p. 465). H ., - . - "W.R. Brisken: Moisture'migration in hermetic refrigeration systems as measured' under various operating conditions' (Rr- frigeratingEngineering. July 1955, p. 42). " u W. A Pennington: Role of adsorption-type desiccant in re frigerating units (Refrigerating Engineering,- March <1951, p. 272). .......................... " Evan Jones: Determining pressure drop and refrigerant Sow capacities of liquid line driers (ASHRAE Journal, Febru ary 1964, p. 70). t CHAPTER 50 LUBRICANTS IN REFRIGERANT SYSTEMS Functions of Lubricant, Oil Properties, Viscosity, Viscosity Index, Solubility of Refrigerants in Oils, Effect of Dissolved Refrigerant on Viscosity and Sealing Function, Density of Off-Refrigerant Solutions, Thermodynamics of Refrigerant-Oil Solutions, Mutual Solubility of Oils and Refrigerants, Miscibility and Partial Miscibility, Fluidity of Off and Wax Separation at Low Temperatures, Solubility of Water and Air in Oils, Volatility, Soundary Lubrication, Oxidation and Refrigerant Resistance, Chemical Reactions in Off-Refrigerant Systems THE PRIMARY function of a lubricant is to minimise number of properties, such as color, viscosity, and pour point friction and prevent wear. In refrigerant systems a second are readily determined by the standard procedures published function is to seal the gas pressure between the high and low by the American Society for Testing and Materials (ASTM). pressure rides. Frequently a third useful function will be to However, many other properties important to refrigeration transfer heat from the compressor to the external environment use have not been standardized. A number of these nonstand- either through internal contact with the compressor shell ardized properties may be determined by special tests de wall or, in some instances, by means of external radiators. scribed in the refrigeration literature. But regardless of If two perfectly clean metallic surfaces are placed together and one is caused to slide over the other, a resisting force known as the force of friction is encountered during the mo rion. If the surfaces are then separated examined, either or both will show evidence of having been scraped, gouged, tom or otherwise eroded. This is known as wear. According to the currently accepted theory of lubrication, a lubricant reduces friction and prevents wear by interposing an easily sheared layer between the moving surfaces. Under ideal conditions, this layer or film of lubricant will com pletely prevent the metallic surfaces from actually touching each other. No real contact occurs. Under less favorable standard or special tests, experience has shown that the proper lubricating oil for a refrigerating system cannot be selected on the basis of laboratory tests alone. Performance tests in actual operating systems are necessary since changes in mechanical design often have an unsuspected influence on the behavior of the lubricant. Ordinarily, the specification of suitable lubricants for a given type of refrigerating equipment is the responsibility of tiie manufacturer. Servicing practice should follow his recommendations, and it is only rarely that an engineer who is concerned with installation, maintenance, or service will be obliged to depart from this policy. conditions when the lubricant layer may be unable to keep the surfaces apart during their motion, friction and wear are Viscosity Grades of Refrigerator Oils factors to be considered. Broadly speaking, refrigeration oils may be subdivided into OIL PROPERTIES two main types--paraffin base and naphthene base, depending on the preponderance of paraffin or naphthene hydrocarbons The properties of a lubricating oil may be classified as either in the refined'oiL Table 1 classifies these two types according physical or chemical. Among the physical properties impor to viscosity and other physical properties. Table 2 lists vis tant to refrigeration applications are: (1) viscosity, (2), cosity ranges which have long been recommended for re viscosity index, (3) mutual solubility with various refrigerants, frigeration systems of various types. (4) fluidity at low temperatures, (5) wax separation, (6) solu Id selecting a viscosity for a specific application the com bility of water in the oil, (7) solubility of air in the oil, (8) pressor designer must take into account the environment to volatility and (9) foaming tendency. Significant chemical which the oil will be exposed. The viscosity of the lubricating properties include: (1) boundary film-forming ability, (2) fluid is strongly influenced by temperature changes and also de oxidation resistance, (3) refrigerant resistance, and (4) effect pends on refrigerant concentration if the refrigerant dissolves of contaminants and additives. appreciably in the oil. The character of a lubricating fluid is largely,determined by its viscosity and film-forming characteristics. Its other Viscosity Index properties, such as pour point, acidity, refrigerant resistance, and solubility, are generally secondary factors in lubrication. But in a refrigerant system, these secondary factors may be very important. Specifications for a lubricant in a refrigerant system must therefore take into account both the primary and secondary factors in order to avoid harmful effects on the system. ' Whenever possible, it is desirable to specify the physical and chemical properties in terms of standard test methods.' A Viscosities of mineral offs decrease sharply with a rise in temperature. The conventional method of representing this effect is to plot viscosities vs. temperatures on a special type of graph paper uniquely scaled to produce straight line relations. Such a plot is shown for two different offs in Fig. I. The slope of the viscosity-temperature lines is different for different offs. This difference is ivunmnnly expressed as an empirical number called triscosity index (VI) (see ASTM D567). An oil with a high viscosity index (HVT) shows less Tb csatT4l responsibility (or this chapter b to TC 13, Lubrication. change in viscosity over a given temperature range than an 763