Utilisation d'éjecteurs pour améliorer les performances des systèmes frigorifiques commerciaux fonctionnant au CO2

Résumé d'une communication présentée au Congrès International du Froid de l'IIF, téléchargeable dans Fridoc.
Expansion work recovery by means of a two-phase ejector is an attractive option for improving the efficiency of CO2 commercial refrigeration systems. Transcritical CO2 systems have relatively large throttling loss, meaning that they offer the greatest opportunity for improvement with an ejector.

However, the use of ejectors in a system subject to varying ambient conditions and capacity requirements presents a significant challenge, as ejectors have been seen to offer poor performance at off-design or reduced capacity conditions. For example, COP can decrease by up to 17% compared to its optimum at the given conditions if gas cooler pressure varies by 0.5 MPa.

In a paper presented at ICR2015, N. Lawrence and S. Elbel presented two different strategies to achieve higher ejector and cycle performance at varying capacity conditions: variable geometry ejector and parallel arrangement of multiple ejectors. They consider different ejector cycle options with two evaporation temperatures and different uses of the ejector. They have shown with a theoretical model that using an ejector to unload the medium-pressure compressors in a CO2 booster refrigeration cycle can result in 15% COP improvement, but using an additional ejector to unload the LP compressors resulted in little or no additional COP improvement compared to the single-ejector cycle.

Study on the use of ejectors for capacity modulation and performance improvement in CO2 commercial refrigeration systems, N. Lawrence, S. Elbel
Available via Fridoc: http://goo.gl/kFpW9K