Solubility characteristics of R22-DMF refrigerant-absorbent combination R. S. Agarwal and S. L. Bapat Keywords: refrigerants, absorbents, solubility, thermodynamic properties Caract6ristiques de solubilit6 du m61ange frigorigene-absorbant R22-dim6thylformamide Cet article pr#sente la solubilit# du m#lange R22-DMF (dim#thylformamide) mesur~e pour une grande plage de temperatures (de -25 ~ 120"C) et pour une s#rie complete de compositions. Les m(~langes pr#sentent une forte d#viation n#gadve par rapport ~ la Ioi de Raoult et il existe une grande difference du point normal d'#bullidon de ses composants. Ainsi ce m&lange convient aux syst~mes frigorifiques ~ absorption de vapeur. On a aussi #tabli le diagramme P- lIT et le diagramme temperature-composition pour les m~langes de R22-DMF ~ utiliser clans I'analyse des syst#mes ~ absorption de vapeur. This Paper presents the solubility data of Refrigerant 22 (R22) - dimethyl formamide (DMF) measured over a wide range of temperature (-25"C to 120"C) and over a complete range of composition. The mixtures show large negative deviation from Raoult's law and there is large difference in normal boiling point of its components. Thus this combination is suited for vapour absorption refrigerant systems. The In P-1/T diagram and temperature-composition diagram for the mixtures of R22-DMF have also been plotted for use in the analysis of vapour absorption systems. At present only a few working fluid combinations such as ammonia-water, water-lithium bromide, and ammonia-sodium thiocynate are used in vapour absorption systems. These combinations have a number of inherent drawbacks, e.g. high volatility of water (in the case of the ammonia-water system), corrosion, etc. The water-lithium bromide system has the additional requirement of maintaining extremely low pressures. With the use of the fluorocarbon-based refrigerant-absorbent combinations in vapour absorption systems most of the above drawbacks can be overcome. These refrigerants are also non-toxic, non-explosive, and with very low flammability characteristics. Eiseman 8 performed a comparative study of various probable fluorocarbon refrigerants for absorption systems. The refrigerants considered were R21, R22, R31, R133a, R30; R124a and R134. Dimethyl-ether - tetra-ethylene glycol (DME-TEG) was used as the absorbent which was proposed by Zellhoefer etaL 9. It was found that R21 is the best on the basis of its thermodynamic and physical properties. Unfortunately, its chemical stability is not good. R22, in second place in COP is excellent in chemical stability and is the preferred fluorocarbon refrigerant. RSAisfrom the Mechanical Engineering Department. liT, New Delhi - 110016, India. SLB is from the Mechanical Engineering Department, liT, Bombay- 400076, India. Paper received 12 November 1982. Further, it is desirable to keep the liquid circulation rate as low as possible to minimize liquid-pump power as well as heat losses from the system. This is possible only if the refrigerant is highly soluble in the absorbent. Albrightetal. 1 measured the solubilities of R22 in organic solvents containing an oxygen atom in the molecule, while Thieme and Albright~ measured the same in organic solvents containing a nitrogen atom in the molecule. The most promising solvents studied were the Di-N substituted formamides. Both dimethyl formamide (DMF) and diethyl formamide (DEF) showed large negative deviations from Raoult's law with R22. However, when the solvent capacity of DM E-TEG was compared with those of DMF and DEF, it was found to be better on a molar basis; but, the molecular weight of DME-TEG is 222 whereas the molecular weights of DMF and DEF are 73.09 and 101, respectively. Thus, when these solvents are compared on a weight basis, DMF is found to be better than both DEF and DME-TEG. The normal boiling points of R22 and DMF are -40.8°C and 153"C, respectively. Thus, the difference in boiling points is large (of the order of 200°C) which is desirable for vapour absorption system, both for space conditioning and refrigeration applications. Also, both the components are chemically stable over the entire temperature range used in the absorption refrigeration systems. Thus, DMF (absorbent) and R22 (refrigerant) seem to form one of the most promising combinations for the vapour absorption system. 0140-7007/85/030070-05S3.00 © 1985 Butterworth Et Co (Publishers) Ltd and IIR 70 Revue Internationale du Froid