Modelling and analysis of a compression/resorption heat pump system with a zeotropic mixture of acetone/CO2

Industrial processes represent one of the most energy-consuming activities, which are related to fossil fuel uti-lization and the growing environmental problems. In this way, the heat waste energy recovery has been pre-sented as an efficient solution, to take advantage of low-grade residual heat, where the compressor-resorption heat pump technology has proven to achieve high-temperature levels with a considerable Coefficient of Per-formance. However, known working fluids such as hydrofluorocarbons represents an environmental hazard due to its Global Warming potential, these have been replaced by natural fluids such as ammonia, but they also have disadvantages like its toxicity. In this way, the CO2 is an available waste heat compound product of fossil combustions, therefore, this research is based on the utilization of novel fluids such as the zeotropic mixture of CO2/Acetone as an eco-friendly working fluid with low Global Warming Potential. Even more, the utilization of the mentioned compound represents the opportunity to explore the utilization of low-grade residual heat that sometimes is not used in subsequent applications. In this sense, the modelling of the binary vapor-liquid equi-libria of the mixture CO2/Acetone has been performed based on a thermodynamic model using the Peng -Robinson equation regarding the conditions of pressure, temperature, and concentration of the fluids for oper-ational industry applications. The modelling of the compression/resorption heat pump cycle is based on the mass and energy balance for each component with Engineering Equation Solver software (EES). In this way, the adjustment of equilibria for the mixture determinates the maximum average square deviation of 4.28 % and 8.70 % for a temperature range between 291 and 303 K and 333 to 393 K. The concentration of CO2 from 20 % to 50 % showed that the increasing molar fraction delivers a more efficient cycle, even reaching a coefficient of performance of 3 for a difference of 0.2 between the global concentration of CO2 and the poor solution, and a 20 degrees C temperature difference between source and sink. Even more, the COP obtained in the simulation was not affected by variations of steam mass flow rate and it was proven that the mathematical model proposed has a correlation with the literature.

Automated summary

In this study, a compress-resorption heat pump cycle with a novel CO2/acetone mixture as the working fluid is proposed, aiming to utilize low-grade residual heat in an eco-friendly way. The modeling of the vapor-liquid equilibrium of the mixture and the mass and energy balance of the cycle were conducted using the Peng-Robinson equation and Engineering Equation Solver software. The results showed that the model has a correlation with the literature and the proposed CO2/acetone mixture has a high coefficient of performance.