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Advances in Supercritical Carbon Dioxide Cycle
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Advances in Supercritical Carbon Dioxide Cycle

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "J: Thermal Management".

Deadline for manuscript submissions: 25 August 2025 | Viewed by 780

Special Issue Editors

Dr. Xiang Qin

E-Mail Website
Guest Editor
1. School of Mechanical and Power Engineering, Zhengzhou University, Zhengzhou 450001, China
2. Environmental System Research Laboratory, Faculty of Engineering, Hokkaido University, N13-W8, Sapporo 060-8628, Japan
Interests: integration and control of transcritical CO2 heat pump system; applications of jet refrigeration technology; characteristics of supercritical CO2 heat transfer
Dr. Xu Peng

E-Mail Website
Guest Editor
School of Mechanical and Power Engineering, Zhengzhou University, Zhengzhou 450001, China
Interests: fluid flow and enhanced heat transfer; optimization of thermal management for new energy vehicles; carbon dioxide heat pump air-conditioning technology
Dr. Jiaheng Chen

E-Mail Website
Guest Editor
School of Mechanical and Power Engineering, Zhengzhou University, Zhengzhou 450001, China
Interests: new energy-saving technologies for refrigeration/heat pumps; thermal management for new energy vehicles; optimization and application of injector structures

Special Issue Information

Dear Colleagues,

Supercritical carbon dioxide (sCO2) cycles have attracted significant attention in the energy conversion field due to high efficiency, compactness, and wide applicability. Compared with traditional steam power cycles, sCO2 cycles offer higher thermal efficiency and smaller equipment size, making them particularly promising for applications in nuclear power, solar energy, gas turbines, high-grade heating, and waste heat recovery. Current research on sCO2 cycles mainly focuses on system optimization, key component development, and operational control strategies. Despite notable progress, challenges remain in cycle optimization configuration, system stability, and economic feasibility. Future development trends include enhancing cycle efficiency, optimizing system integration, expanding application areas, and optimizing control strategies to drive the commercialization of sCO2 cycles and support the transition to low-carbon energy solutions.

Topics of interest for publication include, but are not limited to, the following:

  • Thermodynamic optimization of cycles (different sCO2 cycle configurations, influence of key parameters, multi-objective optimization, etc.);
  • Development of key components (high-efficiency compressors and expanders, compact and high-performance heat exchangers, cooling and sealing technologies for critical components);
  • Control strategies and operational stability (modeling and simulation of the dynamic behavior of sCO₂ cycle systems, advanced control algorithms to enhance operational stability, optimization of transient operations and startup/shutdown strategies);
  • Expansion of application areas;
  • Economic and engineering feasibility analysis;
  • Composite utilization of renewable energy.

Dr. Xiang Qin
Dr. Xu Peng 
Dr. Jiaheng Chen
Guest Editors

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

  • supercritical CO2 cycles
  • thermodynamic efficiency
  • system integration
  • control strategy
  • energy conversion

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Published Papers (3 papers)

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Research

20 pages, 3672 KiB  
Article
Comparative Analysis of Transcritical CO2 Heat Pump Systems With and Without Ejector: Performance, Exergy, and Economic Perspective
by Xiang Qin, Shihao Lei, Heyu Liu, Yinghao Zeng, Yajun Liu, Caiyan Pang and Jiaheng Chen
Energies 2025, 18(12), 3223; https://doi.org/10.3390/en18123223 - 19 Jun 2025
Abstract
To promote renewable energy utilization and enhance the environmental friendliness of refrigerants, this study presents a novel experimental investigation on a transcritical CO2 double-evaporator heat pump water heater integrating both air and water sources, designed for high-temperature hot water production. A key [...] Read more.
To promote renewable energy utilization and enhance the environmental friendliness of refrigerants, this study presents a novel experimental investigation on a transcritical CO2 double-evaporator heat pump water heater integrating both air and water sources, designed for high-temperature hot water production. A key innovation of this work lies in the integration of an ejector into the dual-source system, aiming to improve system performance and energy efficiency. This study systematically compares the conventional circulation mode and the proposed ejector-assisted circulation mode in terms of system performance, exergy efficiency, and the economic payback period. Experimental results reveal that the ejector-assisted mode not only achieves a higher water outlet temperature and reduces compressor power consumption but also improves the system’s exergy efficiency by 6.6% under the condition of the maximum outlet water temperature. Although the addition of the ejector increases initial manufacturing and maintenance costs, the payback periods of the two modes remain nearly the same. These findings confirm the feasibility and advantage of incorporating an ejector into a transcritical CO2 compression/ejection heat pump system with integrated air and water sources, offering a promising solution for efficient and environmentally friendly high-temperature water heating applications. Full article
(This article belongs to the Special Issue Advances in Supercritical Carbon Dioxide Cycle)
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16 pages, 2980 KiB  
Article
Comprehensive Performance and Economic Analyses of Transcritical CO2 Heat Pump Water Heater Suitable for Petroleum Processes and Heating Applications
by Dongxue Zhu, Chaohe Fang, Shejiao Wang, Yafei Xue, Liaoliang Jiang, Yulong Song and Feng Cao
Energies 2025, 18(12), 3070; https://doi.org/10.3390/en18123070 - 10 Jun 2025
Viewed by 252
Abstract
With the intensification of the global energy crisis, the application of air-source transcritical CO2 heat pumps has attracted increasing attention, especially in cold regions. Existing research mainly focuses on the evaluation of steady-state performance while paying less attention to the dynamic characteristics [...] Read more.
With the intensification of the global energy crisis, the application of air-source transcritical CO2 heat pumps has attracted increasing attention, especially in cold regions. Existing research mainly focuses on the evaluation of steady-state performance while paying less attention to the dynamic characteristics of the system during the actual operation process. In order to deeply study the dynamic performance of the air-source transcritical CO2 heat pump system under the winter climate conditions in the Yan‘an area, this study established a system simulation model with multiple parameter inputs and systematically analyzed the influences of ambient temperature, discharge pressure, and inlet and outlet water temperatures on the heating capacity and COP. The research starts from both dynamic and steady-state perspectives, revealing the variation law of system performance with environmental temperature and conducting a quantitative analysis. As the ambient temperature rose from −11 °C to 2 °C, the COP of the system increased by approximately 15% and exhibited significant dynamic response characteristics, indicating that the increase in ambient temperature significantly improved system efficiency. At different ambient temperatures, the optimal discharge pressure increased with the rise in temperature. At the highest ambient temperature (2 °C), the optimal discharge pressure was 11.7 MPa. Compared with the optimal discharge pressure of 11.0 MPa at −11 °C, the performance improved by nearly 13.3%. Through the dynamic simulation method, theoretical support is provided for the optimization of energy-saving control strategies in cold regions, and thoughts are offered regarding the application of transcritical CO2 systems under similar climatic conditions. Full article
(This article belongs to the Special Issue Advances in Supercritical Carbon Dioxide Cycle)
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19 pages, 2782 KiB  
Article
Numerical Study of the Condenser of a Small CO2 Refrigeration Unit Operating Under Supercritical Conditions
by Piotr Szymczak, Piotr Bogusław Jasiński and Marcin Łęcki
Energies 2025, 18(11), 2992; https://doi.org/10.3390/en18112992 - 5 Jun 2025
Viewed by 261
Abstract
The paper presents a numerical analysis of a tube-in-tube condenser of a small refrigeration system. One of the challenges in designing such units is to reduce their dimensions while maintaining the highest possible cooling capacity, so the research presented here focuses on the [...] Read more.
The paper presents a numerical analysis of a tube-in-tube condenser of a small refrigeration system. One of the challenges in designing such units is to reduce their dimensions while maintaining the highest possible cooling capacity, so the research presented here focuses on the search for and impact of the appropriate flow conditions of these two fluids on condenser performance. The refrigerant is supercritical CO2, which is cooled by water. Thermal-flow simulations were performed for eight CO2 inlet velocities in the range of 1–8 m/s, and four cooling water velocities of 0.5–2 m/s. The main parameters of the exchanger operation were analyzed: heat transfer coefficient, Nusselt number, overall heat transfer coefficient, and friction factor, which were compared with selected correlations. The results showed that the condenser achieves the highest power for the highest water velocities (2 m/s) and CO2 (8 m/s), i.e., over 1000 W, which corresponds to a heat flux on the tube surface of approx. 2.6 × 105 W/m2 and a heat transfer coefficient of approx. 4700 W/m2K. One of the most important conclusions is the discovery of a significant effect of water velocity on heat transfer from the CO2 side—an increase in water velocity from 0.5 m/s to 2 m/s results in an increase in the heat transfer coefficient sCO2 by over 60%, with the same Re number. The implication of this study is to show the possibility of adjusting and selecting condenser parameters over a wide range of capacities, just by changing the fluid velocity. Full article
(This article belongs to the Special Issue Advances in Supercritical Carbon Dioxide Cycle)
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