Theoretical Investigation of Al2O3 Nanoparticle Slip Mechanisms in High-Viscosity Two-Component Mixture in Two-Phase Flow

Abstract

The need for higher energy efficiency is driving the space conditioning and refrigeration industry toward the use of advanced technologies. Vapor compression cycles work with a mixture of refrigerant and lubricant, and although oil in heat exchangers affects negatively the performances of the system, its presence is unavoidable. The studies of colloidal solutions showed promising results to enhance the heat transfer capabilities of the liquids in which nanoparticles are dispersed, and current experimental research revealed that the increase in thermal conductivity is not enough to explain the enhancements observed in heat transfer. In order to further understand the nanoparticles' contribution to the heat exchange phenomena, this paper analyses slip mechanisms that nanoparticles can be affected by when dispersed in the liquid phase of a high-viscosity oil–refrigerant mixture undergoing evaporation inside a horizontal tube. The study was conducted for Al2O3 nanoparticles dispersed in refrigerant R410A and polyolester (POE) oil at different mass concentrations. Depending on the flow regime, the slip mechanisms related to Brownian motion and thermophoresis were found to provide the largest contributions to nanoparticles' redistribution within the liquid phase of the mixture.