Thermodynamic properties of Al2O3 nanolubricants: Part 1—Effects on the two-phase pressure drop

Abstract

In vapor compression cycles, a small portion of the oil circulates with the refrigerant throughout the system components and penalizes the heat transfer as well as increases the pressure losses. Nanolubricants—lubricants with dispersed nanoparticles—are expected to provide enhancements in heat transfer. While solubility and miscibility of refrigerants in polyolester lubricant are well-established knowledge, there is a lack of information regarding if and how nanoparticles dispersed in the lubricant affect these two properties. This article presents the experimental data of solubility and miscibility of three types of Al2O3 nanolubricants with refrigerant R410A. The nanoparticles were dispersed in polyolester lubricant by using three different surfactants. The data identified optimum combinations to achieve stable and uniform dispersions. The associated viscosity was also measured. The viscosity was about 2.6 higher at 5°C. The nanolubricants had also lower refrigerant R410A solubility with respect to polyolester oil, and surfactants slightly affected the viscosity and solubility properties of the nanolubricants. Finally, this article presents data of pressure drop for two-phase flow boiling in a horizontal tube with internally enhanced heat transfer surfaces and discusses the effect of the nanoparticles on the pressure drop of the mixture. Nanolubricant did not increase the two-phase pressure drop with respect to polyolester lubricant, and at low and medium mass flux, the pressure drop of nanolubricant were lower than the corresponding two-phase pressure drop of refrigerant R410A and polyolester oil mixture. Two correlations from the literature predicted well the pressure drop data of the refrigerant R410A and polyolester oil mixture of the present work, while their accuracy for the nanolubricant mixture was slightly over ±20%.