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790 CHAPTER 50 1965 Guide And Data. Book Lubricants in Refrigerant Systems If 791 | fj Fig. 9.... Solubility of Refrigerant 12 in a 240 SUV Paraffin Base Oil of German Origin10 Four general'rules may be stated for partially miaciMn re frigerant-oil mixtures: 1. In the miscible range of.compositions, the four rules stated earlier for completely miscible mixtures may be applied; ' 2. Under equilibrium conditions in the immiscible range, there are only two possible solution compositions at each given tem perature, and the mixture will proportion itself accordingly;: . 3. The vapor pressure over the immiscible range is constant at a given temperature, no matter what proportion of refrigerant is mixed with the oil within that range. '4. The immiscible range is usually narrowed by increasing the temperature; and if so, a critical solution temperature will usually befound. - Totally tmmiacible refrigerants and oils', or both,-are defined for the purpose of this chapter as being completely immiscible or,"at most, only very slightly miscible. In such mixtures, the immiscible'range is so broad that mutual solubility effects may be ignored in practice.' Critical solution temperatures are seldom found in mixtures of the totally immiscible type. Ex* amples are ammonia and oil, and carbon dioxide and oiL- Rg.. 10 .... Solubility of Refrigerant. 12 in Refrigeration Tig., 12 Viscosity-Temperature Chart for Solutions of Oils Refrigerant ,12 in 300 SUV Naphthene Base Oilf*7 Fig. 13 .... Solubility of-Refrigerant 13 in 150 SUV Oils Solubility Curves and MisdbiHty Diagrams Published reports usually have not shown-mutual solu bility relations of partially miscible refrigerant-oil mixtures all on one diagram as is shown on graph (b) of Fig. 5. The model curves in this graph are pictured as extending over the whole range of refrigerant-oil concentrations, whereas in de-.termining actual data, it has been a more common practice to conduct separate investigations of the miscible and im miscible ranges. Data for the miscible range of oil-rich com positions, Le., the region lying to the left-of the broken line (OC), are ordinarily plotted as pressure-temperature-eolubility curves just as was done for completely miscible refriger ant-oil mixtures. Such curves must terminate for partially miscible mixtures when they meet the broken line (OC), since any attempt to further increase the refrigerant concen tration then merely causes' a second liquid phase,' richer in refrigerant, to drop out of solution. Terminating points of this type can.be seen in the Refrigerant 22 solubility curves at tributed to H. J. Lfiffler (see Fig. 23); however it must be kept in mind'that the position of the broken line marking the presumed beginning of the immiscible region'will be different for different oils. The immiscible range for a given temperature may be broad or narrow, according to the nature of the refrigerant and the nature of the oiL Oh the oil-rich side, however, even those refrigerants which exhibit broad immiscible ranges may dis solve significantly in the oil. Thus, Refrigerant 13, is classed as a low miscibility refrigerant (see Table 5 and Reference 8) but dissolves in mineral oil to the extent of about 20 weight percent at 50 F and 360 psia (see Fig. 13). The immiscible range itself is generally plotted in the form f &tejnperatw-c-rniscibility curve, or, as it is sometimes called, a critical solubility curve. As a matter of convenience, the scale on the vertical axis of the miscibility curve is tempera ture rather than refrigerant pressure, as was tiie ww? in Braph (b) of fig. 5. Otherwise the miscibility curve is amply the dome (OCR), once the refrigerant pressure is fixed and determined by the mixture temperature at all equilibrium Rg. 14 .... Viscosity of Mixtures of 60 SUV Naphthene Base Oil and Refrigerant 13M points within' the immiscible range (Rule 3). Likewise for convenience, the composition scale on the horizontal axis is often reversed from that shown in graph (b), and proceeds from left to right as the oil concentration is increased. The top of the dome may be read directly as the critical solution - Refrigerant 13"