Carbon dioxide (CO2) can be considered at present as the most promising natural refrigerant alternative to the synthetic refrigerants characterised by a consistent direct warming impact. An unsolved technical problem with this refrigerant is the selection of the most suitable lubricant for each application. A good lubricant must contemporarily lubricate the mechanical moving parts and be soluble in the refrigerant so to ensure the return of oil to the compressor. Moreover, the presence of oil is affecting the heat exchange, especially in the evaporators. To properly select the lubricant and design the refrigeration system taking into account these problems, a better knowledge of the thermodynamic behaviour of the CO2 + lubricant system, with particular attention to the mutual solubility, is then required. Unfortunately, only few experimental data are available in the literature and they frequently refer to commercial oils with unknown composition. These data are not sufficient to build thermodynamic models able to predict the behaviour of the considered systems. For this reason, some pure ester oils, i.e. 2-methylbutyric ester oil, 2-methylvaleric ester oil and 2-methylhexanoic ester oil, were considered as pure precursors for commercial polyolester lubricants (POE), and the solubility of CO2 in these oils was measured at a temperature of 283 K. The experiments have been performed in an apparatus specifically built for the solubility measurements. It consists of a stainless steel equilibrium cell of about 180 ml capacity, equipped with glass windows for the visual observation of the mixture and for the determination of the liquid phase level inside the cell. The equilibrium cell is equipped with a magnetic stirrer, forcing the vapour through the liquid phase, with a controlled speed of rotation. The total internal free volume of the cell was carefully calibrated to within ± 0.1 ml. The cell is maintained at constant temperature by a water thermostatic bath. The estimated uncertainties of the measurements are ± 0.03 K for temperature, ± 2 kPa for pressure, and from ±0.001 (high CO2 mole fraction) to ±0.015 (low CO2 mole fraction) for mole fraction.
Solubility of Carbon Dioxide in 2-methylbutyric, 2-methylvaleric and 2-methylhexanoic ester oils
Sergio Bobbo;Laura Fedele;Mauro Scattolini;Roberto Camporese;
2006
Abstract
Carbon dioxide (CO2) can be considered at present as the most promising natural refrigerant alternative to the synthetic refrigerants characterised by a consistent direct warming impact. An unsolved technical problem with this refrigerant is the selection of the most suitable lubricant for each application. A good lubricant must contemporarily lubricate the mechanical moving parts and be soluble in the refrigerant so to ensure the return of oil to the compressor. Moreover, the presence of oil is affecting the heat exchange, especially in the evaporators. To properly select the lubricant and design the refrigeration system taking into account these problems, a better knowledge of the thermodynamic behaviour of the CO2 + lubricant system, with particular attention to the mutual solubility, is then required. Unfortunately, only few experimental data are available in the literature and they frequently refer to commercial oils with unknown composition. These data are not sufficient to build thermodynamic models able to predict the behaviour of the considered systems. For this reason, some pure ester oils, i.e. 2-methylbutyric ester oil, 2-methylvaleric ester oil and 2-methylhexanoic ester oil, were considered as pure precursors for commercial polyolester lubricants (POE), and the solubility of CO2 in these oils was measured at a temperature of 283 K. The experiments have been performed in an apparatus specifically built for the solubility measurements. It consists of a stainless steel equilibrium cell of about 180 ml capacity, equipped with glass windows for the visual observation of the mixture and for the determination of the liquid phase level inside the cell. The equilibrium cell is equipped with a magnetic stirrer, forcing the vapour through the liquid phase, with a controlled speed of rotation. The total internal free volume of the cell was carefully calibrated to within ± 0.1 ml. The cell is maintained at constant temperature by a water thermostatic bath. The estimated uncertainties of the measurements are ± 0.03 K for temperature, ± 2 kPa for pressure, and from ±0.001 (high CO2 mole fraction) to ±0.015 (low CO2 mole fraction) for mole fraction.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
