Search Results (5)

This paper presents a novel, integrated supercritical CO₂ system for shale gas development, comprising a supercritical CO₂ shale gas extraction system, a gas turbine system, a supercritical CO₂ power generation system, and a transcritical CO₂ refrigeration system. A comprehensive thermodynamic and economic analysis is conducted for this integrated energy development system. To enhance system performance across multiple dimensions, three objective functions are proposed for optimization: exergy efficiency, levelized energy cost (LEC), and heat transfer area per unit power output (APR). First, the effects of key operating parameters—including the gas turbine pressure ratio, gas turbine inlet temperature, supercritical CO₂ pressure ratio, the temperature difference between flue gas and the supercritical CO₂ top cycle, and the temperature difference between flue gas and the supercritical CO₂ bottom cycle—on system performance were analyzed through parametric studies. Next, the optimal system parameters were determined using a multi-objective optimization method based on a genetic algorithm. The optimization results reveal that, when exergy efficiency and LEC are used as dual-objective functions, the system achieves an optimal exergy efficiency of 60.5% and an LEC of 6.3 cents/(kW·h). Furthermore, when exergy efficiency, APR, and LEC are considered as objective functions, the system attains an optimal exergy efficiency of 59.5%, an APR of 0.21 m²/kW, and an LEC of 6.3 cents/(kW·h). The compound shale gas development system proposed in this paper demonstrates excellent economic viability, environmental sustainability and operational efficiency. The research outcomes offer an innovative solution for the development of shale gas and contribute to the advancement of research on new energy systems. Full article

This review focuses on the advancements of CO₂ transcritical cycle technology in building indoor environmental regulation, particularly in combined heating and cooling applications. The paper highlights the energy efficiency and environmental benefits of CO₂ as a natural refrigerant, which has zero ozone depletion potential (ODP) and very low global warming potential (GWP). It provides a comprehensive overview of recent optimization strategies, including distributed compression, the integration of ejectors and expanders, and the design improvements of key components such as gas coolers, compressors, and throttling valves. Through optimization strategies such as dual-system cycles, this technology can achieve a COP improvement of 15.3–46.96% in heating scenarios; meanwhile, with the help of distributed compression technology, its cooling capacity can be enhanced by up to 26.5%. The review also examines various operating conditions such as discharge pressure and subcooling, which significantly affect system performance. The paper concludes by identifying the current challenges in the application of CO₂ systems, such as high initial costs and system stability under extreme conditions, and suggests future research directions to overcome these limitations and improve the practical application of CO₂ transcritical cycles in the building industry. Overall, it is concluded that the development of expander-compressors holds great potential for achieving better performance and represents a promising direction for future advancements in this field. Full article

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

The air flow rate on the gas cooler side is one of the key parameters affecting the performance and running safety of transcritical CO₂ electric vehicle air conditioning systems. After experimentally analyzing the effects of the air volume flow rate in the gas cooler on the cycle parameters and system performance, a novel method to evaluate the optimal air flow rate was proposed. In addition, the effect of the gas cooler air volume flow rate on the key performance parameters of the system (e.g., optimal discharge pressure) was explored. Finally, the coupling effects of the compressor speed, ambient temperature and optimal air flow rate on the system performance was also exhaustively assessed. It was found that as the discharge temperature, the CO₂ temperature at the gas cooler outlet and the discharge pressure did not vary more than ±2%, the corresponding gas cooler air volume flow rate was optimal. For the single-row and dual-process microchannel evaporator used in this work, the recommended value of the optimal gas cooler air volume flow rate was 2500 m³·h⁻¹. The results could provide reference for the fan speed design of electric vehicle CO₂ air conditioning systems, especially for the performance under idling model. Full article

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