HVAC&R Equipment Performance Group
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Improved Thermal Boundary Layer Parameter for Semi-Theoretical Refrigerant/Lubricant Pool Boiling Model
Improved Thermal Boundary Layer Parameter for Semi-Theoretical Refrigerant/Lubricant Pool Boiling Model (156 KB)
Kedzierski, M. A.
International Congress of Refrigeration , August 17-22, 2003 , Washington, DC - August 01, 2003
Keywords:Refrigerants , lubricants , mixtures , pool boiling , heat transfer , excess surface density , predictions
Abstract:This paper outlines the framework for an improvement in the thermal boundary layer parameter for a semi-theoretical model for predicting the pool boiling heat transfer of refrigerant/lubricant mixtures on a roughened, horizontal, flat pool-boiling surface. Refrigerant/lubricant pool boiling is significantly influenced by the excess lubricant that resides in a thin layer on the boiling surface. The model is based on lubricant excess surface density measurements and a mass balance on lubricant deposition and removal from the wall. The original thermal boundary layer parameter that was derived for R123/lubricant mixtures predicts the R134a/lubricant data presented here for superheats below 6 K. The improvement in the thermal boundary layer enables the model to predict the full range of superheats for the R134a/lubricant mixture measurements. Further work on the new thermal boundary layer parameter is necessary to include the effects of the lubricant composition, viscosity, and critical solution temperature with the refrigerant. These effects were included in the original thermal boundary layer parameter. The new thermal boundary layer parameter increases the range of superheats for which the model is valid for the R134a/lubricant pool boiling heat transfer measurements presented here.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899
