Modeling absorption of pure refrigerants and refrigerant mixtures in lubricant oil Tobias R. Gessner, Jader R. Barbosa Jr * Departamento de Engenharia Meca ˆnica, Universidade Federal de Santa Catarina, 88040-900 Floriano ´polis, SC, Brazil Received 6 June 2005; received in revised form 25 November 2005; accepted 1 December 2005 Available online 24 February 2006 Abstract This paper addresses the problem of absorption of refrigerant vapor in a stagnant layer of lubricant oil. The bulk motion of the solute is described in terms of apparent diffusion coefficients that encompass both molecular diffusion and possible macroscopic motion induced by liquid density instability and surface tension. In absorption of refrigerant mixtures, diffusion in the vapor and liquid phases are coupled with a thermodynamic model for interfacial equilibrium. Results are compared with experimental data available in the literature for absorption of several refrigerants in polyol ester oil (POE68). The adequacy of the formulation is assessed in the light of its basic assumptions and performance of the model. q 2005 Elsevier Ltd and IIR. All rights reserved. Keywords: Refrigeration system; Compression system; Modelling; Absorption; Refrigerant; Oil Mode ´lisation de I’absorption des frigorige `nes purs et des me ´langes de frigorige `nes par I’huile lubrifiante Mots cle ´s : Syste `me frigorifique ; Syste `me a ` compression ; Mode ´lisation ; Absorption ; Frigorige `ne ; Huile 1. Introduction In refrigeration systems where capillary tubes are used as expansion devices, the problem of refrigerant (vapor) absorption in lubricant oil in the compressor is of crucial importance to the determination of the system equalizing pressure. In reciprocating compressors, for example, high absorption rates of refrigerant are desirable since lower equalizing pressure means reduced torque and power required for compressor start-up. Solubility and vapour–liquid equilibrium (VLE) data for refrigerant–oil mixtures, as well as information regarding the transient behaviour during absorption, are important parameters in the selection of the most appropriate lubricants, especially those for HFC refriger- ants and their mixtures, i.e. the polyol esters (POE) and poly-alkylene glycols (PAG). Because of local density instability effects in the liquid phase [1], the complete description of refrigerant absorption in lubricant oil is an issue that still remains open. To overcome the difficulty in evaluating multi-dimensional effects within the flow field, a useful approach has been to define an apparent molecular diffusion coefficient for the refrigerant–oil mixture to describe both microscopic International Journal of Refrigeration 29 (2006) 773–780 www.elsevier.com/locate/ijrefrig 0140-7007/$35.00 q 2005 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2005.12.001 * Corresponding author. Tel./fax: C55 48 3234 5166. E-mail address: jrb@nrva.ufsc.br (T.R. Gessner).