Document V3ge2720x6M1Or064bwVrL4vZ

798 CHAPTER 50 1965 Guide And-Data Book fig.' 31 .... Critical Solubility of Refrigerant 13B1 and Naphthenic 03* solubility of water in a refrigeration grade 150 SUV naphthene haoil has been estimated to fail-between 50 and 70 parts per million by weight.** If it is desired to measure and control the amount of dissolved water below the solubility limit, a quantitative test such as the Earl Fischer method must be employed.1* A moisture content of 20 parts per million is frequently specified as the maximum permissible in refrigera tion oUs, but according to Divers*0 economical considerations and practical refinery handling practice limit the minimum moisture content of refrigeration oils to about 30 parts per million at the present time. The solubility of water in mineral oils increases with in creasing-temperature. Unfortunately, the published literature rfintAing no reference to temperature-moisture solubility relationships as specifically applied to refrigeration oils. How ever, Clark's data" on'the solubility of water in transformer oil (Fig. 41) may be used as a general guide. Spot checks on refrigeration oils have agreed reasonably well with points on Clark's curve. In refrigerator manufacturing plants, oils can be dried below the solubility limit by several methods. Blotter pressing will remove a substantial portion of the dissolved moisture, provided the filter papers are carefully dried at an elevated Rgi -32 .... Temperature-Composition Diagram Showing Misdb3ity of Refrigerant 22 with Four Oils17 fiedrown front 19. Fig. 33 .... Temperature-Miscibility Relations at Low Oil Concentrations in Refrigerant 22-03 Mixtures temperature just before use and are installed in the frame while still hot. For minimum moisture content a vacuum dry ing process may be used. Vacuum drying of the oil provides an' added advantage since dissolved air is'alsb removed (see Chapter 47). When refrigeration repair-work is done in the field it is not always possible to' protect the oil from access of moisture, and redrying is impractical. However, when opening of the system is necessary, this usually, exposes other parts of the system (e.g.`, motor windings) which also are vulnerable to moisture absorption. Hence it is common practice in repair work'to inctAll a desiccant-type dryer of a size adequate to redehy drate the whole system (see Chapter. 49). Solubility of Air in Oil ` . > Refrigerating systems should not contain excessive amounts of air or-other noncondensable gases. Hie oxygen present in air reacts quite readily with oil and this in itself is a valid reason for removing and excluding air. A more compelling reason, however, is that air, or at least the 79 percent nitrogen which it contains and which does not react with the oil, con stitutes a honcondensable gas which', even in'amounts so small asto cause no concern over'posable oil oxidation, can inter fere with the proper performance of refrigerating machines. (See Chapter 47). In some systems the tolerable volume of noncondensables is very lowland if.the oil is.added after the system is'evacuated, it must not contain too much dissolved air or, .for that matter, too much of any, other, noncou-. densable gas. As mentioned in thb preceding section, dis solved air is removed when a vacuum process is employed to dry the oil. However, if the deaerated oil is subsequently stored under dry air pressure, it will reabsorb air in proportion to the pressure. Fig. 42 shows the volume of air under standard conditions that can be absorbed (be., dissolved) in mineral oil over'a' range of pressuresi*,The data in Fig. 42 were de termined at 68 F but are applicable" also to other tempera- Urbricants in Refrigerant Systems . REFRIGERANT II4-50OVIS KVI REFRIGERATION OIL \ / /><\ REFRIGERANT 114.600 vis l\\' NAPHTHENIC OIL REFRIGERANT 114-ISO WISH' REFRIGERATION OILN. KH V RE FRIGERA NT 114*1 SO VIS N PHTHE* tc 20 40 60 60 100 PERCENT WEIGHT REFRIGERANT 114 Rg. 34 .... Critical Solution Temperatures of Refrigerant 114-03 Mixtures1 tores since there is only a minor variation in solubility between 20 F ond 120 F. Volatility--Flash and Fire Points ' - Some indication of volatility may be obtained by determin ing the flash and fire points of the oil which ordinarily are not particularly important in refrigerant systems.: However, some refrigerants such as sulfur dioxide, ammonia and methyl* chloride have a high ratio of specific heats cp/c, and conse quently have a high adiabatic compression temperature. It has been reported that these refrigerants frequently produce carbonization of oils with low flash- and fire points when operating in high ambient temperatures.1 Foaming and Antifoam Agents .Excessive, foaming of the lubricant is 'undesirable in re frigeration systems. Brewer*7 has pointed out that an ab normal tendency to foam with refrigerant reduces the effec tiveness of the oil in cooling the motor windings and removing heat from the compressor. Also, too much foaming may cause too much oil to pass through the pump and enter the low side. Foaming in a pressure oiling system may result in starved lubrication under some conditions. However, it has also been claimed that moderate foaming is beneficial in refrigeration systems. There is no general agreetoent as to what constitutes excessive foaming, or how it should be prevented. Some manufacturers add nm!1 amounts of an antifoam agent; such as a silicone fluid, to refrigerator oils, but others believe that foaming difficulties are more easily corrected by equipment design than by the "use of antifoam agents available at the present time.** The use of crankcase heaters to reduce oil foaming h*R been discussed by Neubauer** and others.** Boundary Lubrication and Rim Formation An important function of the lubricant in many types of B5rv*ce is to prevent wear under conditions of boitndary frio"on- The boundary condition-is manifested by a sharp in? crease in friction coefficient as the relative speed of the moving 0 20 .40 60 60 100 WEIGHT PERCENT OF OIL Rg. 35 .... Critical Solubility of Refrigerant 502 Naphthenic 03*