Carbon capture, utilization and storage (CCUS) refers to the separation of CO₂ from energy utilization systems, industrial production or the atmosphere followed by purification and transport to facilities using CO₂ or to storage sites to achieve long-term separation of the CO₂ from the atmosphere. The Intergovernmental Panel on Climate Change (IPCC) recently stated that CCUS systems are a "foundation" technology for carbon emission reduction and carbon neutrality. CCUS technologies are indispensable key technologies in China's "two-carbon" goal for a carbon neutral China. This paper reviews the key heat and mass transfer issues for carbon dioxide geological storage, CO₂ enhanced tight oil/shale gas/deep geothermal energy recovery in recent years by major international and domestic research groups including the authors' research group. These studies have used theoretical analyses, simulation methods including molecular dynamics, lattice Boltzmann, and computational fluid dynamics, as well as experimental methods including pore-scale visualization experiments, core-scale nuclear magnetic resonance investigations, and supercritical pressure fluid convection heat transfer investigations. These studies have analyzed the multiphase, multicomponent flow and heat and mass transfer mechanisms of supercritical CO₂ in micro-nano porous structures for reservoir conditions at various scales. The influences of mineral reaction, CO₂ exsolution, fluid physical properties, and scale effects on the CO₂ geological storage, oil displacement, gas displacement, and heat recovery have been analyzed to provide theoretical and technical support for CO₂ geological storage and utilization.

Hydrogen energy is an widely used, abundant, green, low-carbon energy carrier. Hydrogen is gradually becoming one of the most important energy carriers for our future green energy transformation. This paper provides a detailed introduction to the basic and applied research achievements in various fields related to hydrogen production made by the Department of Energy and Power Engineering, Tsinghua University. A pyrochrite catalyst was synthesized for hydrocarbon fuel reforming with prototype hydrogen reforming units then used to evaluate the catalyst effectiveness. An elevated temperature purification process was developed for elevated temperature hydrogen production using both a nitrogen-modified activated carbon hydrophobic adsorbent and a layered double hydroxide based adsorbent for the entire temperature range which can provide on-site H₂/CO₂ separation using elevated temperature pressure swing adsorption. For electrolysis using renewable energy sources, the co-electrolysis of carbon dioxide and water to produce hydrogen was realized in a solid oxide electrolytic cell with the energy consumption of the alkaline water electrolysis reduced by raising the temperature to reduce the theoretical water decomposition voltage. These results contribute to the international hydrogen fuel cell industry developing efficient hydrogen production technologies that will boost the transformation of future energy utilization systems as a crucial step towards building a low-carbon, safe and efficient modern energy system.

The combustion of zero-carbon and low-carbon fuels such as hydrogen, ammonia, electronic fuels, and biofuels is fundamental to achieving carbon neutrality. The efficient utilization of synthetic jet fuels, fused-ring hydrocarbons, and multiple mixed fuels is then important for developing advanced aerospace technologies. Combustion kinetics studies of these new fuels are essential for understanding the combustion process and for developing new combustion modes and burners. The development of predictive kinetics models for these new fuels presents many challenges. On one hand, accurate experimental data under a wide range of conditions, especially under extreme conditions and multi-physics conditions, are needed; on the other hand, effective tools for uncertainty qualification and model optimization are highly desired. This paper reviews the fundamental experimental methods and uncertainty quantification/reverse uncertainty quantification methods developed by the authors' group in recent years. These experimental methods include the acquisition of more detailed speciation information, measurements of fuel ignition data at lower temperatures and species diagnostics in plasma-assisted combustion systems. The analysis methods include model dimensionality reduction, global sensitivity analyses, uncertainty quantification, and model optimization of combustion kinetics models.

Fluid machinery is widely used in many fields with clean hydro power turbines producing more than 16% of the total residential electricity consumption and rotating machinery consuming around 30% of the total electrical energy consumption every year. Therefore, the development of advanced, efficient rotating fluid machinery can promote the rapid increase of renewable energy sources such as wind power and photovoltaic power by improving the stability of hydro turbines and pumped storage units over wider operating ranges and increasing the efficiencies of fluid machinery through design optimization and smart controls to support reaching the "double-carbon" targets in China. This paper introduces the challenges and development trends in fluid machinery to develop environmentally friendly, efficient hydropower equipment and safe, stable pumped storage systems through design optimization and smart system controls. This paper also summarizes the recent advances in fluid machinery design to provide guideline for future key fluid machinery development.

The organic Rankine cycle (ORC) is a mainstream technology for efficient heat-power conversion of low-to-medium temperature thermal energy below 200℃. Zeotropic mixtures effectively reduce the heat transfer exergy losses, complement the advantages of pure components, and extend the working fluid useful temperature range. Thus, zeotropic mixtures are being rapidly accepted into the ORC field. This paper summarizes the research progress by the authors' team in optimizing the design of ORC systems using zeotropic mixtures. Conventional ORC systems using zeotropic mixtures have been expanded by the introduction of dual-pressure evaporation cycles to improve the temperature matching during evaporation and significantly reduce the heat transfer losses. The liquid-separation condensation method is also used to increase the condensation heat transfer rate of the zeotropic mixtures which greatly reduces the system cost. In summary, zeotropic mixtures can significantly improve the thermodynamics of ORC systems while the liquid-separation condensation method can effectively reduce the large heat transfer areas and improve the poor thermo-economic performance of systems using zeotropic mixtures. Thus, zeotropic mixtures then have favorable prospects for use in ORC systems.

Gas-solid reactions have a very wide range of scales that significantly challenge computational models. This paper presents a first principles based rate equation theory that connects the various scales and couples the chemical reactions with the diffusion of the solid state ions. The theoretical models cross all the 'atom→grain→particle' size scales with efficient algorithms. The results show a discrete island growth mechanism of solid product on surfaces or interfaces. The rate equation theory is applied to CFD models of oxidation/reduction kinetics in chemical looping combustion, surface and interfacial phenomenon in thermal chemical energy storage, pollutant control, coal combustion and dual fluidized bed reactors.

Heavy crude oil is a valuable energy resource that is very abundant but also very viscous which complicates exploitation of these resources. One efficient and environmentally friendly heavy oil recovery technique uses exothermic oxidation reactions with a small amount of the oil reacting with oxygen in the injected pressured air. However, the lack of a thorough fundamental understanding of the complex multiple physicochemical and thermal processes in the reservoir limits broad use of this technique. In the past decade, our research group has conducted fundamental research in this field, including "The basic heat release characteristics and key factors affecting moderate temperature oxidation", "coke formation and chemical properties", "reaction model for low asphaltene heavy oil", "combustion regimes for high temperature oxidation at various operating conditions", and "reservoir scale simulations of the moderate temperature oxidation technique". Experimental systems were constructed to measure the heat release, the product properties and the transport properties during the heavy oil oxidation. Multiscale numerical simulations were developed for pore-scale, lab-scale and reservoir-scale studies to understand the coupling mechanisms at different scales. These research results have improved our fundamental understanding and promoted industrial applications of this heavy oil recovery technique in China.

The application of flue gas desulfurization (FGD) gypsum to ameliorate saline-alkaline soils not only provides a new use for FGD gypsum, but also provides a new method for improving saline-alkaline soils. This paper reviews the development of this technology for ameliorating saline-alkaline soils over the past 20 years including the basic theory, key technologies, short and long-term effects, environmental safety and industrialized applications of treating saline-alkaline soils with FGD gypsum. This paper also presents the future research needs to address current problems for large-scale applications. Efficient and safe treatments of large saline-alkaline soil areas using FGD gypsum should reduce the application rate of FGD gypsum per unit land area, increase long-term positioning of test points and formulate national standards for agricultural application of FGD gypsum.

The latest generation of Artificial Hearts are using centrifugal blood pumps to provide important support for patients with cardiovascular diseases. This paper describes the advances in the development of Artificial Hearts in the Department of Energy and Power Engineering of Tsinghua University. A pump design optimization method was proposed based on the maximum scalar shear stress for the hemolysis standard to raduce the calculational load and improve the optimization efficiency. A blood-cell-damage model based on the turbulent viscous dissipative stress was developed for better prediction. Both extracorporeal pumps with bearings and left ventricular assist device (LVAD) prototypes with magneto-hydraulic suspensions have been developed with studies of their hydraulics. Model predictions agree with the experimental data with an error of 3.6%. A medical fluid flow experimental system has been developed to improve research on Artificial Heart prototypes through evaluations of the physiological effects of new Artificial Heart designs.

Single- and multi-phase turbulent flows occur throughout nature as well as in engineering applications. These are strongly influenced by complicated boundaries and extreme conditions. This study shows that the turbulent structures and the transport efficiency are influenced by the complex conditions in various systems, such as the atmosphere, oceans, the earth core, aero-engines, oil extraction, and chemical production. This paper reviews the advances in turbulent flow studies for complicated boundaries and extreme conditions in terms of the effects of the complex boundaries on the thermal turbulence, the influence of supergravity and porous media on the turbulent structures and transport efficiency, and the dynamics of particles in turbulent flows and turbulent emulsions. This paper then also identifies future research directions.

Through-flow and computational fluid dynamics (CFD) calculations are the main approaches used for aerodynamic design and analyses of turbomachinery. In this study, an integrated through-flow and CFD optimization design method using an in-house through-flow code was used to analyze highly loaded multi-stage axial compressors. This method uses a multi-level aerodynamic analysis process that combines the through-flow and CFD calculations in a design optimization process that combines 3D blade design and intelligent optimization algorithms. The method is applied to a 3-stage transonic compressor and reasonably categorizes the flow problems resulting from the boundary layer separation along the transonic rotors. The analysis is used to optimize the first rotor (R₁) and third rotor (R₃) designs with the optimized designs giving 0.1 percent point and 0.3 percent point increases in the efficiencies of the 3-stage compressor. This study shows that this method is capable of synthesizing the advantages of the through-flow and CFD methods to simultaneously consider the characteristics of the aerodynamic configuration and flow structures. The compressor flow fields and performance can be efficiently categorized based on their relationships to the blade profile and aerodynamic configurations to provide guidance on how to optimize the design.

The flame dynamics strongly affect the accurate prediction and control of self-excited oscillations in combustion systems. This paper introduces the authors' research on the theoretical modeling and experimental verification of the flame dynamics characteristics for various practical application backgrounds, including ideal non-premixed jet flames, bluff body premixed flames, main/piloted flames and flames with multi-dimensional disturbances. This review presents a distributed flame transfer function for non-premixed flames developed using the Green's function method. The interaction mechanism between the vortex and the flame surface was studied using the flame surface equation and the discrete vortex model. The interaction mechanism between the pilot flame and the main flame was studied through modeling. The response characteristics of flames to disturbances in various directions were also studied. The flame dynamics model was combined with an acoustic network model to show that the flame dynamics have different effects on the thermoacoustic modal stability.

Gas turbines and aero engines are known as the jewels of the industrial crown and their development is an important symbol of a country's technological level and national strength. Turbine inlet temperatures are rapidly increasing to improve the turbine efficiency, so the turbine blades are being exposed to higher temperatures. Efficient blade cooling methods are then needed for the blades to work safely at temperatures much higher than the material melting point. This paper reviews the development of high-efficiency cooling methods for gas turbines and presents a three-dimensional research framework for gas turbine cooling methods. This paper also reviews the research results of the present authors on the flow and heat transfer characteristics of cooling units, blade cascades and multiple cooling component interactions. This paper then presents a design method for efficient experimental data-driven cooling structure design. The characteristics and development trends of next generation cooling methods using double wall cooling are also described.

China's peak carbon and carbon neutrality policy targets are accelerating the low-carbon transition of China's energy system. A clear, complete picture of the future low-carbon energy system is needed to provide forward-looking guidance for coordinated country-wide actions. However, there are few studies of the characteristics and sensitivities of China's future low-carbon energy supply. This paper presents a coupled energy-material flow analysis with a sensitivity analysis as a measurement basis for the 2050 low-carbon energy supply system that shows the overall energy flows and the carbon dioxide sources and sinks with analyses of the impacts on the total carbon dioxide emissions caused by changing the structures and efficiencies of the main components. The results indicate that the low-carbon energy system will have some key patterns including a primary energy and power generation structure dominated by non-fossil fuel energy supplies and a high proportion of electricity use in end-use sectors. The carbon dioxide emissions will include negative emissions by the power sector and large emissions by the industrial sector. The total carbon dioxide emissions of this system are most sensitive to changes in the share of electricity use by the industrial sector and changes in the fossil energy power generation efficiencies, followed by the proportion of wind power generation, carbon capture and sequestration (CCS) for coal power generation, and the use of waste heat power generation. Therefore, the government needs to strictly control the direct end-use of fossil energy, accelerate low-carbon power generation development, strengthen the development of low-carbon pathways for difficult to reform emission sectors, and increase non-electric utilization of non-fossil energy sources. The government must also encourage the vigorous development of smart energy systems to ensure multi-energy usage systems.

China seeks to reach peak emissions in 2030 and to be carbon neutral in 2060. All industries and regions in China need to develop low-carbon energy system development plans according to their own resources and development expectations to reduce the costs of carbon emission reductions. This paper presents an energy system development planning model based on the superstructure modeling method for planning how to control the emission peak goal. This model starts with the regional energy system structure and infrastructure. The model then considers various energy supply, transformation, transmission, and storage methods and possible changes in consumption technologies during different periods to obtain the best low-carbon development path with the optimal total energy system cost. This study then determines the best energy system development path from 2021 to 2035 for a typical city which controlled the peak carbon emissions to 179 million tons and reduced carbon emissions by 150 million tons within 15 years.