Trade-offs between design complexity and performance impacts for transcritical R744 ejectors

Francesco Botticella, Zishen Liu, Stefan Elbel

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

It is well known that the transcritical CO2 cycle has higher intrinsic throttling losses than comparable subcritical cycles. Replacing the expansion valve with a two-phase ejector greatly improves cycle performance by reducing throttling losses. However, ejectors have yet to be successfully applied to low-capacity systems (approximately 1 to 5 kW), such as bottle coolers, window air conditioners, beverage dispensers, heat pump water heaters or similar. It is a real challenge to integrate ejectors into mass produced systems of small capacity in a cost-effective manner due to the relatively complex design of an ejector in comparison to simpler expansion devices. In addition to presenting system level results obtained with a transcritical CO2 bottle cooler with ejector, another aim of this paper is to systematically determine the possibilities for cost reduction by identifying performance trade-offs of less complex ejector designs. In a first step, a simplified diffuser design was investigated in combination with a conventional motive nozzle having converging-diverging design. Resulting system COPs and the impact on ejector efficiency are reported.

Original languageEnglish (US)
Title of host publication8th Conference on Ammonia and CO2 Refrigeration Technologies, Ohrid 2019 - Proceedings
PublisherInternational Institute of Refrigeration
Pages227-234
Number of pages8
ISBN (Electronic)9782362150340
DOIs
StatePublished - 2019
Event8th Conference on Ammonia and CO2 Refrigeration Technologies, Ohrid 2019 - Ohrid, Macedonia, The Former Yugoslav Republic of
Duration: Apr 11 2019Apr 13 2019

Publication series

NameRefrigeration Science and Technology
Volume2019-April
ISSN (Print)0151-1637

Conference

Conference8th Conference on Ammonia and CO2 Refrigeration Technologies, Ohrid 2019
Country/TerritoryMacedonia, The Former Yugoslav Republic of
CityOhrid
Period4/11/194/13/19

Keywords

  • COP
  • Carbon Dioxide (CO2
  • Design Trade-offs
  • Ejector
  • Ejector Efficiency
  • R744)

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Electrical and Electronic Engineering
  • Mechanical Engineering
  • Condensed Matter Physics

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