Rheological Properties of Oil/Refrigerant Mixtures in Refrigerant Environments

Transcription

1 MEMOIRS OF SHONAN INSTITUTE OF TECHNOLOGY Vol. 37, No. 1, 2003 * Rheological Properties of Oil/Refrigerant Mixtures in Refrigerant Environments Masayoshi MURAKI* Oil film thickness and traction characteristics of polyol ester in some refrigerants are determined with an EHD tester, where increase in refrigerant gas pressure decreases film thickness as well as traction in each refrigerant. When compared at an identical gas pressure, the film formability with refrigerant is HFC-125 HFC-134a HCFC-22, while that for the coefficient of traction is the same as film thickness. Oil film thickness and the coefficient of traction are inversely correlated with solubility of refrigerant in mole concentration. Then, by analyzing the traction measurements with the approximate formula, the rheological parameters are determined. As a result, the traction behavior is governed by the rheological parameters of refrigerant/polyol ester mixture at high pressures. The viscosity-pressure coefficient is inversely correlated while the representative stress positively with solubility of refrigerant in mole concentration. Finally, the relationship between the viscosity of the mixture and effective contact pressure at a constant gas pressure follows an entire curve described by the Roelands formula. Key words: Refrigerant, Rheology, Polyol ester, EHD, Traction, Viscosity-pressure coefficient. 1 (HFC) EHL EHL 1) 15) (CFC) (HCFC) HFC 4) 12) EHL, EHL 14) EHL *

2 mm 2 /s 25 C GPa Barus, 27.1 GPa 1 HCFC R-22 HFC R-134a R-125 Table 1. Properties of POE. Density, kg/m 9520 Refractive Viscosity, mm Viscosity Index 95 Viscosity-pressure coefficient, GPa 25C Fig. 1 (50 ml ) 1 Fig. 1. Viscometer for refrigerant/poe mixture. 2.3 EHL EHL Fig. 2 EHL DC 80 C 5MPa SUJ mm R max 0.02 mm 70 mm 8mm 25% 365 GPa

3 Fig. 2. Elasto-hydrodynamic lubrication tester. Fig. 3. Observation of EHL film. 16) t h h t/n (1) n Lorentz Lorenz 17) Hartung 18) Fig. 3 h c Fig. 4 3

4 37 1 Fig. 4. Principle of traction measurement and an example. DV/U DV/U U d sin b/u d cos b) tan b (2) y x m C N P m GPa 0 3% kpa m/s 0.1 m/s Fig. 5. Atmospheric viscosity vs. gas pressure. Fig. 5 R-22 R-134a, R- 125 R-22 R-134a, R-125 4

5 Fig. 6. Central film thickness vs. rolling speed. 3.2 Fig kpa R-22 R-134a, R-125 Hamrock Dowson h c 19) h c ka (h 0 U) 0.67 (3) k h 0 a 0, (3) Fig m/s R-22 R-134a R-125 Fig. 8 Fig. 7 Fig. 7. Influence of gas pressure on central film thickness. Fig. 8. Film thickness vs. solubility of refrigerant. 3.3 Fig. 9 Fig. 10 3% 5

6 37 1 Fig. 9. Traction curves in some refrigerants. Fig. 11. Distribution of non dimensional shear stress. 23) 21) ġ t t t g 0 sinh hn t 0 (4) Fig. 10. Influence of gas pressure on traction. R-22 R-134a, R GPa 20) EHL Fig. 9 h N t 0 h 0 a h N p h N h 0 exp(ap) (5) (4) t/t 0 Fig. 11 r* t m t n t e 6

7 t m t n t e 2h È t 0 Ê h ˆ Í1 1 2 ( ap ) h Á ln t H ÎÍ Ë 0 È 2 Ê 1 h ˆ 2h t Í 0 1 Á ln ln Í Ë ap H t 0 t 0 Î 2 t0ap 3 H È Ê 1 Í1 Í Á Ë ap Î H 3 h ˆ ln (6) t 0 a t 0 (6) Fig. 12 Fig. 12. Comparison between the measurements and the calculated results based on the simplified non Newtonian model. 4.2 P e h N a (5) P e Ú0 1 h N h 0 exp(ap H 1 r 2 )2rdr h 0 exp(ap e ) (7) P e P H (7) Fig. 13. Variation in viscosity-pressure coefficient with gas pressure. exp( aph ) Ê 1 ˆ 2 exp( ape ) ap Á1 ap Ë ( ap ) 2 H H H (8) a t 0 Fig. 13 a a R-22 a R-134a, R-125 a a t 0 Fig. a R-22 t 0 R-125 R-134a a t 0 a t 0 22),23) a t 0 Fig. 15 Fig. 16 a, t 0 7

8 37 1 Fig. 14. Variation in representative stress t 0 with gas pressure. Fig. 15. Viscosity-pressure coefficient vs. solubility of refrigerants in oil. 5.2 a Fig Fig. 13 (8) P e (5) P e a 20),25) Roelands 26) Fig. 16. Representative stress vs. solubility of refrigerants in oil. h h 0 exp(ln h ){( p) z } 1] (9) z Roelands Fig. 17. Variation in the viscosity of refrigerant/oil mixture with contact pressure. 8

9 6 (1) h 0 a t 0 R-22 h 0 a R-125 R-134a t 0 a (2) (3) (4) Roelands 1), 38, 2 (1993) ), 40, 9 (1995) 12. 3) S. Komatsuzaki and Y. Homma: J. STLE, 47, 3 (1991) ) 48, 9 (1994) 17. 5) T. Matsuzaki and M. Akei: Inter. Semi. On New Tech. Alter. Refr., Tokyo (1993) 27. 6) M. Muraki: Proc. Inter. Sym. R22 & R502 Alter. Refr., Japan (1994) ) H. O. Spaushus, D. R. Hendenson and D. F. Huttenlocher: Int. Semi. New Tech. Alter. Refr., Tokyo (1993) 33. 8) M. Sunami, K. Takigawa and S. Suda: Proc. Int. Refr. Conf., Purdue (1994) ) S. G. Sundaresan and W. R. Finkensatad: ASHRAE Trans., 92 (1992) ) T. Taken, K. Mizui and K. Takahata: Proc. Int. Comp. Eng. Conf., Purdue (1992) ) M. Muraki, K. Tagawa and D. Dong: Proc. Int. Refr. Conf., Purdue (1996) ) 43, 1 (1998) ) F. P. Wardle, B. Jacobson, H. Dolfsma, E. Hoglund and U. Jonsson: Proc. Int. Comp. Eng. Conf., Purdue, 2 (1992) ) 41, 5 (1996) ) M. Akei and K. Mizuhara: Tribol., Tras., 40, 1 (1997) 1. 16), (1991) ) C. A. Foord, W. C. Hammann and A. Cameron : ASLE, Trans., 11 (1968) ) P. S. Y. Chu and A. Cameron: J. Inst. Petrol., 49 (1963) ) B. J. Hamrock and D. Dowson: Trans. ASME. F, 99, 2 (1977) ) W. R. Jones, R. L. Johnson, W. O. Winer and D. M. Sanborn: ASLE, Trans., 18, 4 (1975) ) M. Muraki and D. Dong: Proc. Instn. Mech. Engrs, Part J: J. Eng., Trib., Vol. 213 (1999) ) 56, 528-C, (1990) ), 30, 1 (1985) ) R. Gohar: Elastohydrodynamics, Ellis Horwood. 9