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Energies
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Improvements on CO2 Vapour Compression Cycles
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Improvements on CO2 Vapour Compression Cycles

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "B3: Carbon Emission and Utilization".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 12137

Special Issue Editor

Dr. Daniel Sánchez García-Vacas

E-Mail Website
Guest Editor
Department of Mechanical Engineering, Universidad Jaume I, Castellon de la Plana, Spain
Interests: commercial refrigeration; natural refrigerants; CO2; transcritical cycles; Low-GWP refrigerants; hydrocarbons; subcooling; energy performance; thermoelectric; booster systems; cascade systems

Special Issue Information

Dear colleagues,

As a guest editor, I am pleased to invite you to submit your scientific works to this Special Issue of Energies entitled “Improvements on CO2 vapour compression cycles” focused on CO2 technology in subcritical and transcritical conditions.

At present, carbon dioxide is being positioned as one of the most promising natural refrigerants in the field of refrigeration and heat pumps systems. Its excellent heat transfer and transport properties, together with its A1 classification and environmentally friendly behaviour, make this refrigerant unique among all the artificial refrigerants used to date. Moreover, the worldwide extended prohibition on using fluorinated gases was the principal starting point of the progressive increase in the use of carbon dioxide and hydrocarbons.

Despite its strengths, carbon dioxide has intrinsic drawbacks that must be solved when it is implemented in refrigeration facilities or heat pumps systems. The low critical temperature and the corresponding transcritical cycle provide low energy performance in the vapour compression cycles, which should be revised in order to make this technology competitive and attractive, especially in warm countries.

In this context, this Special Issue named “Improvements on CO2 vapour compression cycles” will encompass scientific works devoted to analysing the CO2 vapour compression cycle and to enhancing its energy efficiency. Furthermore, studies about the CO2 heat transfer phenomena and heat exchanger design are also welcome. Original works should be submitted following the journal submission process and will be peer-reviewed by international researchers.

Looking forward to your submissions!

Prof. Dr. Daniel Sánchez García-Vacas
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • CO2
  • transcritical cycles
  • subcooling
  • IHX
  • ejector
  • parallel compressor
  • gas-cooler
  • heat transfer phenomena
  • energy performance
  • booster systems

Published Papers (4 papers)

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Research

15 pages, 4636 KiB  
Article
Experimental Investigation of the Effect of a Recuperative Heat Exchanger and Throttles Opening on a CO2/Isobutane Autocascade Refrigeration System
by Michał Sobieraj
Energies 2020, 13(20), 5285; https://0-doi-org.brum.beds.ac.uk/10.3390/en13205285 - 12 Oct 2020
Cited by 10 | Viewed by 2327
Abstract
An experimental evaluation of an autocascade refrigeration (ACR) system was carried out. A zeotropic mixture of isobutane and CO2 was employed as a working fluid in an autocascade refrigeration (ACR) system. An experimental system was designed and built to study the influence [...] Read more.
An experimental evaluation of an autocascade refrigeration (ACR) system was carried out. A zeotropic mixture of isobutane and CO2 was employed as a working fluid in an autocascade refrigeration (ACR) system. An experimental system was designed and built to study the influence of the recuperative heat exchanger (RHX) and openings of the throttle valves on the system performance. The use of RHX facilitated the condensation process and improved the cycle characteristics. The working mass concentration of CO2 was higher, as it was closer to the nominal concentration and the discharge pressure was lower by 19% to even 39% when the RHX was employed in the system. An increase of up to 20% in the coefficient of performance (COP) was observed. Furthermore, the effects of the openings of the throttle valves on the system characteristics were studied. The change in the openings of the expansion valves affected the mass flows and the working mixture composition. The working CO2 mass fraction increased with higher openings of the evaporator throttle. The subcooling degree of liquid CO2-rich refrigerant increased with higher openings of the expansion valve under the phase separator. The results of the present work should be helpful for design and optimization of autocascade systems working with natural and synthetic refrigerants. Full article
(This article belongs to the Special Issue Improvements on CO2 Vapour Compression Cycles)
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29 pages, 10631 KiB  
Article
Improvements in CO2 Booster Architectures with Different Economizer Arrangements
by J. Catalán-Gil, L. Nebot-Andrés, D. Sánchez, R. Llopis, R. Cabello and D. Calleja-Anta
Energies 2020, 13(5), 1271; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051271 - 09 Mar 2020
Cited by 11 | Viewed by 4187
Abstract
CO2 transcritical booster architectures are widely analyzed to be applied in centralized commercial refrigeration plants in consonance with the irrevocable phase-out of HFCs. Most of these analyses show the limitations of CO2 cycles in terms of energy efficiency, especially in warm [...] Read more.
CO2 transcritical booster architectures are widely analyzed to be applied in centralized commercial refrigeration plants in consonance with the irrevocable phase-out of HFCs. Most of these analyses show the limitations of CO2 cycles in terms of energy efficiency, especially in warm countries. From the literature, several improvements have been proposed to raise the booster efficiency in high ambient temperatures. The use of economizers is an interesting technique to reduce the temperature after the gas cooler and to improve the energy efficiency of transcritical CO2 cycles. The economizer cools down the high pressure’s line of CO2 by evaporating the same refrigerant extracted from another point of the facility. Depending on the extraction point, some configurations are possible. In this work, different booster architectures with economizers have been analyzed and compared. From the results, the combination of the economizer with the additional compressor allows obtaining energy savings of up to 8.5% in warm countries and up to 4% in cold countries with regard to the flash-by-pass arrangement and reduce the volumetric displacement required of the MT compressors by up to 37%. Full article
(This article belongs to the Special Issue Improvements on CO2 Vapour Compression Cycles)
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23 pages, 7954 KiB  
Article
Investigation of the Impact Factors on the Optimal Intermediate Temperature in a Dual Transcritical CO2 System with a Dedicated Transcritical CO2 Subcooler
by Yulong Song, Haidan Wang and Feng Cao
Energies 2020, 13(2), 309; https://0-doi-org.brum.beds.ac.uk/10.3390/en13020309 - 08 Jan 2020
Cited by 8 | Viewed by 2206
Abstract
As a natural fluid with superior environment advantages, CO2 is used to constitute a dual transcritical system to reduce performance deterioration under high gas-cooler outlet temperature. Aiming at the system configuration, improvement potential, and optimization, the proposed system is deeply analyzed, and [...] Read more.
As a natural fluid with superior environment advantages, CO2 is used to constitute a dual transcritical system to reduce performance deterioration under high gas-cooler outlet temperature. Aiming at the system configuration, improvement potential, and optimization, the proposed system is deeply analyzed, and corresponding coupling models are presented in detail. First, the veracity of simulation models is completely verified by comparing with previous measurements. Then, the existence of the optimal intermediate temperature is validated, while the optimal values are found to increase with the augmentation in ambient and water-feed temperatures. Moreover, the negative effects of the pinch point on the heat transfer inside the gas cooler could be greatly reduced by using the dual gas cooler. Finally, a predictive correlation for optimal intermediate temperature determination with ambient and water-feed temperature as independent variables is proposed, which provides a theoretical basis for the proposed system to realize efficient control in the industrialization process. Full article
(This article belongs to the Special Issue Improvements on CO2 Vapour Compression Cycles)
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17 pages, 6088 KiB  
Article
Thermodynamic Analysis of the Air-Cooled Transcritical Rankine Cycle Using CO2/R161 Mixture Based on Natural Draft Dry Cooling Towers
by Yingjie Zhou, Junrong Tang, Cheng Zhang and Qibin Li
Energies 2019, 12(17), 3342; https://0-doi-org.brum.beds.ac.uk/10.3390/en12173342 - 29 Aug 2019
Cited by 12 | Viewed by 2612
Abstract
Heat rejection in the hot-arid area is of concern to power cycles, especially for the transcritical Rankine cycle using CO2 as the working fluid in harvesting the low-grade energy. Usually, water is employed as the cooling substance in Rankine cycles. In this [...] Read more.
Heat rejection in the hot-arid area is of concern to power cycles, especially for the transcritical Rankine cycle using CO2 as the working fluid in harvesting the low-grade energy. Usually, water is employed as the cooling substance in Rankine cycles. In this paper, the transcritical Rankine cycle with CO2/R161 mixture and dry air cooling systems had been proposed to be used in arid areas with water shortage. A design and rating model for mixture-air cooling process were developed based on small-scale natural draft dry cooling towers. The influence of key parameters on the system’s thermodynamic performance was tested. The results suggested that the thermal efficiency of the proposed system was decreased with the increases in the turbine inlet pressure and the ambient temperature, with the given thermal power as the heat source. Additionally, the cooling performance of natural draft dry cooling tower was found to be affected by the ambient temperature and the turbine exhaust temperature. Full article
(This article belongs to the Special Issue Improvements on CO2 Vapour Compression Cycles)
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