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Effect of Refrigerant Oil Additive on R134a and R123 Boiling Heat Transfer Performance and Related Issues for GSA.


pdf icon Effect of Refrigerant Oil Additive on R134a and R123 Boiling Heat Transfer Performance and Related Issues for GSA. (3508 K)
Kedzierski, M. A.

NISTIR 7132; 63 p. June 2004.

Keywords:

refrigerants; additives; heat transfer; alternative refrigerants; boiling; enhanced heat transfer; fluorescence; non-adiabatic lubricant excess surface; refrigerants/lubricant mixtures; polyolester lubricant; naphthenic mineral oil

Abstract:

This paper investigates the effect that an additive had on the boiling performance of an R134a/polyolester lubricant (POE) mixture and an R123/naphthenic mineral oil mixture on a roughened, horizontal flat surface. Both pool boiling heat transfer data and lubricant excess surface density data are given for the mixture of R134a and a POE for before and after the addition of the additive. A spectrofluorometer was used to measure the lubricant excess density that was established by the boiling of an R134a/POE lubricant (98% by mass/2% by mass) mixture on a flat boiling test surface. The measurements obtained from the spectrofluorometer suggest that the additive increases the total mass of lubricant on the boiling surface. The heat transfer data shows that the additive caused an average and a maximum enhancement of the R134a/POE heat flux between 5 kW/m2 and 22 kW/m2 of approximately 73% and 95%, respectively. Conversely, for nearly the same heat flux range, the additive caused essentially no change in the pool boiling heat flux of an R123/mineral oil mixture. In addition, a maximum degradation of the heat flux for the R123/mineral oil mixture was observed to be approximately 27% at a heat flux of 73 kW/m2. The lubricant excess surface density and interfacial surface tension measurements were used to hypothesize a physical explanation for the enhancement/degradation mechanism associated with large liquid-vapor surface-tension additives. The results of a compatibility study of the additive with common refrigerants and lubricants are included along with a survey of chiller manufactures on the use of additives.