Thermodynamic modification of CO2-based combined cooling and power cycle with ejector

Abstract

CO2-based combined cooling and power cycle (CCP) has received increasing attentions especially in scenarios with diversified energy desires for its excellent natural properties. In this paper, an ejector is introduced into a conventional CCP system to reduce exergy loss in refrigeration throttling. A refrigerated truck is selected as the typical application scenario. And the simulated results indicate that approximately 28% of the expansion work during throttling can be recovered by the ejector, concurrently saving 0.3kW and 0.7kW compression work with respect to 10.8kW and 6.5kW cooling load under the freezing and refrigeration conditions. To extend the application of CCP system in more general scenarios, the ejector based CCP system is further modified to suit single heat source conditions. Two modified ejector based CCP systems namely ME-CCP-I and ME-CCP-II are proposed to recover waste energy from the compressor discharge. The adaptations to various heat source and refrigerating temperature are comprehensively studied. And the results demonstrate the ME-CCP-II system will be more suitable for air-conditioning scenarios while the ME-CCP-I system is advanced in freezing scenarios. In addition, recovering waste energy from the compressor discharge contributes great to the total energy efficiency of the CCP system as well as the heat transfer in regeneration process. With the mass split ratio increased from 0.1 to 0.9, the total energy efficiency of the ME-CCP-I system can raise from 0.27 to 0.64 and the relative enhancement is ranging from 1.26% to 11.86% versus the baseline system. Meanwhile, the ME-CCP-I system can reduce 48.6% irreversible loss in the heat regeneration process versus the baseline one when the same amount of exhausted energy after expansion is recovered