New capacity control technique for two-phase ejectors in transcritical CO2 condensing units: Preliminary experimental outcomes

Paride Gullo*, Martin Ryhl Kærn, Michael Birkelund, Ekaterini E. Kriezi

*Corresponding author for this work

Research output: Contribution to conferencePaperResearchpeer-review

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Abstract

With the ever-growing need for climate change mitigation, CO2 as the sole refrigerant (R744) has become an appealing future-proof option for several refrigeration and heat pump solutions. Currently transcritical CO2 systems offer, by far, the best energy and environmental performance in various medium- and large-capacity applications, provided that some of the available expansion work is recovered via two-phase ejectors. However, although similar benefits are expected for small-scale units (e.g. condensing units), at present no appropriate capacity control strategy is available for two-phase ejectors in these solutions. The aim of this work is to bridge this knowledge gap by presenting the first experimental results related to an innovative capacity control technique for two-phase ejectors in transcritical CO2 condensing units. The novel capacity control methodology is based on the pulse-width modulation (PWM) of the refrigerant flow through the ejector. At the compressor speed of 40 Hz, water temperature at the gas cooler inlet of 35 °C and ethylene glycol temperature at the evaporator inlet of 5 °C, it was found that the high pressure and the cooling capacity can be increased by up to about 20 bar and 17%, respectively. Furthermore, at the optimal operation condition the solution relying on the PWM ejector offered an increase in coefficient of performance (COP) by 14% compared to the unit with passive ejector and by about 29% over the standard system. In addition to the encouraging results obtained, the proposed strategy features low cost, simplicity, low vulnerability to clogging, no need to vary the nozzle throat area for flow control and major potential than its currently available competitors. Having no practical size or application constraints, the suggested capacity control mechanism could possibly lead to lay robust foundations for a significantly more sustainable future in the whole cooling and heating sector.
Original languageEnglish
Publication date2020
Number of pages10
Publication statusPublished - 2020
Event6th International Conference on Contemporary Problems of Thermal Engineering - Online
Duration: 21 Sep 202024 Sep 2020
https://www.s-conferences.eu/cpote2020

Conference

Conference6th International Conference on Contemporary Problems of Thermal Engineering
LocationOnline
Period21/09/202024/09/2020
Internet address

Bibliographical note

This work is related to ECO2-RAPJECT project (Project funded by the EU's Horizon 2020 research and innovation programme under the grant agreement No. 844924)

Keywords

  • Expansion work recovery
  • PWM
  • R744
  • Refrigeration
  • Small-capacity system

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