• Energy Research

Ejector refrigeration cycles offer an alternative to traditional systems for the production of cooling using low temperature heat. In this paper, a real gas thermodynamic model based on the mass flow rate maximisation is presented. This model has the advantage of simplifying the calculation algorithm and avoiding a complex description of the double choking mechanism taking place within the ejector. First, the model hypothesis and calculation algorithm are presented. The impact of each efficiency is evaluated and a tuning procedure is developed to calibrate the model on experimental data. Validation is performed on multiple datasets relative to two different fluids: R600a and R134a. The ejector model is then used to simulate a SERS (single ejector refrigeration system) cycle, to validate its robustness and capability to be used in the prediction of thermodynamic cycles performance. A comparative analysis of different fluids is carried out on the SERS, highlighting the important role played by the choice of the superheating. Finally, the model is used to predict performance in the case of a two-phase primary flow pointing out the limits of the model and the need of further experimental studies for the inclusion of appropriate semi-empirical corrections.

Ejector refrigeration cycles offer an alternative to traditional systems for the production of cooling using low temperature heat. In this paper, a real gas thermodynamic model based on the mass flow rate maximisation is presented. This model has the advantage of simplifying the calculation algorithm and avoiding a complex description of the double choking mechanism taking place within the ejector. First, the model hypothesis and calculation algorithm are presented. The impact of each efficiency is evaluated and a tuning procedure is developed to calibrate the model on experimental data. Validation is performed on multiple datasets relative to two different fluids: R600a and R134a. The ejector model is then used to simulate a SERS (single ejector refrigeration system) cycle, to validate its robustness and capability to be used in the prediction of thermodynamic cycles performance. A comparative analysis of different fluids is carried out on the SERS, highlighting the important role played by the choice of the superheating. Finally, the model is used to predict performance in the case of a two-phase primary flow pointing out the limits of the model and the need of further experimental studies for the inclusion of appropriate semi-empirical corrections.

International audience

International audience

The present experimental work investigates the impact of an innovative falling-film and plate combined generator, associating vapor production and purification, on the performance of an NH3–H2O absorption chiller of 5-kW cooling capacity. The impact of the flooding of the lower part of the exchanger on the performance of the machine is investigated: It decreases the COP by 33% and cooling capacity by 38%. Solution sub-cooling at the combined generator inlet improves the purity of the ammonia vapor produced, but degrades the performance of the chiller. A design of experiments is defined to characterize the performance of the combined generator, which is highly impacted by the solution mass flowrate and concentration. Then, two correlation forms are used to predict the performance, and the adapted NTU model yields better results. Finally, for an air-conditioning application, a low solution mass flowrate allows the energy consumption to be reduced by approximately 15% but it requires a higher temperature for the heat source; while the increase in the solution mass flowrate degrades the performance but enables the machine to self-regulate at a low heat source.

The present experimental work investigates the impact of an innovative falling-film and plate combined generator, associating vapor production and purification, on the performance of an NH3–H2O absorption chiller of 5-kW cooling capacity. The impact of the flooding of the lower part of the exchanger on the performance of the machine is investigated: It decreases the COP by 33% and cooling capacity by 38%. Solution sub-cooling at the combined generator inlet improves the purity of the ammonia vapor produced, but degrades the performance of the chiller. A design of experiments is defined to characterize the performance of the combined generator, which is highly impacted by the solution mass flowrate and concentration. Then, two correlation forms are used to predict the performance, and the adapted NTU model yields better results. Finally, for an air-conditioning application, a low solution mass flowrate allows the energy consumption to be reduced by approximately 15% but it requires a higher temperature for the heat source; while the increase in the solution mass flowrate degrades the performance but enables the machine to self-regulate at a low heat source.

This study presents the numerical development of a generator–rectifier combined component (called a “combined-generator”) composed of plate heat exchangers, designed and meant to be integrated in a single-stage ammonia–water absorption cooling system. Investigations are made to find the most compact and efficient design. Numerical simulations are presented describing parameters such as the ammonia fraction in the vapor produced and the combined generator efficiency as a function of the inlet temperatures or mass flow rate of the heat transfer fluid. The combined generator produces vapor with a high ammonia mass fraction and high mass efficiency for a solution inlet temperature range of [315–320 K] and a mass flow rate of the heat transfer fluid between [0.4 and 0.6 kg.s−1]. The impacts of the length and number of plates as well as the adiabatic/heated ratio of the plates are also examined. The ammonia fraction increases with the increase in the adiabatic/heated ratio, and the combined generator efficiency increases with the increase in the plate aspect ratio of length/width. The proposed system is developed to be operated in compact and medium-capacity absorption chillers (approximately 5 kW cold) for air-conditioning.

This study presents the numerical development of a generator–rectifier combined component (called a “combined-generator”) composed of plate heat exchangers, designed and meant to be integrated in a single-stage ammonia–water absorption cooling system. Investigations are made to find the most compact and efficient design. Numerical simulations are presented describing parameters such as the ammonia fraction in the vapor produced and the combined generator efficiency as a function of the inlet temperatures or mass flow rate of the heat transfer fluid. The combined generator produces vapor with a high ammonia mass fraction and high mass efficiency for a solution inlet temperature range of [315–320 K] and a mass flow rate of the heat transfer fluid between [0.4 and 0.6 kg.s−1]. The impacts of the length and number of plates as well as the adiabatic/heated ratio of the plates are also examined. The ammonia fraction increases with the increase in the adiabatic/heated ratio, and the combined generator efficiency increases with the increase in the plate aspect ratio of length/width. The proposed system is developed to be operated in compact and medium-capacity absorption chillers (approximately 5 kW cold) for air-conditioning.