In the pursuit of bridging the energy demand gap and striving for a pristine environment, ammonia fuel has emerged as one of the most promising fuels of the future. Zero carbon emissions, high energy density, and low production and transportation costs make it a promising candidate. However, challenges persist regarding the overall efficiency of pure ammonia combustion. This paper proposes a regenerative cycle in an ammonia gas turbine that matches the reheat Rankine cycle, considering the maximum temperature of the exhaust gas from the turbine and phase transition temperature of liquid ammonia in the turbine cycle. We conducted a thermodynamic analysis and evaluated the system performance based on the first and second laws of thermodynamics and analyzed the influence of the inlet temperature and pressure of the ammonia gas turbine on the overall cycle performance. The results indicate that the combined cycle has improved the efficiency of the ammonia gas turbine by up to 33.38% and the maximum efficiency achieved by the combined thermodynamic cycle is 60.13%,when the inlet temperature of an ammonia gas turbine does not exceed 1 400 ℃ and the inlet pressure remains below 0.5 MPa. Furthermore, the combined cycle exhibits outstanding thermodynamic properties and energy recovery rates. Additionally, the efficiency of the regenerative cycle increases with increasing the inlet temperature and pressure of the ammonia gas turbine, provided that the inlet pressure does not exceed 5 MPa. New perspectives have been proposed to enhance the operational efficiency of ammonia-powered gas turbines and promote the efficient utilization of ammonia as a fuel. This study proposes novel perspectives towards enhancing the efficient utilization of ammonia fuel and the actual efficiency of ammonia gas turbine cycles, providing a forward-looking exploration for the energy utilization of ammonia gas turbine systems.

Currently, the steam pipelines in cigarette factories are characterized by numerous points, extensive lengths, and broad coverage. The thermal conversion factor of these pipelines is high, and their steam energy consumption accounts for a large proportion of the total energy consumption. Therefore, investigating the performance of the insulation layer of steam pipes is of considerable importance for improving steam utilization efficiency and reducing heat loss in the steam pipe network. In this study, the thermal conductivities of insulation layers made of four insulation materials were measured using the steady-state method at different temperatures to elucidate the relationship between the thermal conductivity of an insulation material and the steam temperature, thereby identifying the efficient insulation materials suitable for application scenarios. The appropriate insulation layer thickness was determined using the maximum allowable heat loss method and economic thickness method. Moreover, the thermal conductivities of insulation layers with different service lives were measured. Results indicate that the thermal conductivity increased linearly with the increasing service life. Factors causing the deterioration of insulation layer performance were incorporated into the model to study the relationship between the operating cost of an insulation layer and its outer diameter and service life. For insulation layers with different designed service lives, their optimal outer diameters and operating costs were calculated using the economic thickness method. Results show that considering material aging factors in the design of insulation layer thickness can reduce cumulative costs by 10.7% within the designed service life. However, when the service life expires, the operating cost of a design that considered the aging issue is higher than that of a design that did not consider the aging issue owing to increased heat loss as a result of aging of the insulation layer. The insulation layer can be designed to reduce steam heat loss and improve steam utilization efficiency as well as provide theoretical guidance for the green, low-carbon, and high-quality development of cigarette factories.

Supercritical CO₂ plays an important role in many applications such as nuclear power generation, solar power generation, cryogenic refrigeration, and aerospace. Currently, the majority of studies on supercritical CO₂ convective heat transfer in tubes focus on the temperature range near the critical point, while the heat transfer patterns at high temperature and pressure far from the critical point remain unclear and need to be further studied. In this study, numerical simulations were performed to analyze the effects of mass flow, inlet temperature, system pressure, heat flux density, and tube diameter on the convective heat transfer coefficient at high temperature and pressure, as well as the effects of buoyancy and flow acceleration caused by operating conditions on the heat transfer characteristics. The results show that the convective heat transfer coefficient increases with increasing mass flow, inlet temperature, system pressure, and heat flux density. The difference in convective heat transfer coefficient gradually grows along the flow direction under different heat flux densities. Convective heat transfer coefficient decreases with increasing tube diameter. Compared with the heat transfer patterns near the critical point, heat flux density and tube diameter exert different effects on the convective heat transfer coefficient. In general, the effects of pressure on the convective heat transfer coefficient are small. This study provides significant values to understand the law of supercritical fluid heat transfer and guide the design of efficient and safe heat exchanger.

Energy and environment problems are becoming increasingly prominent, renewable energy is developing rapidly, and its intermittency is one of the key problems restricting its development. Advanced adiabatic compressed air energy storage (AA-CAES) is an effective method to address the intermittency of renewable energy. In this study, a mathematical model for the energy storage stage of AA-CAES is established, and dynamic and sensitivity analysis of the conservation of energy, energy balance, and key parameters of each component are conducted. The results reveal that the proposed mathematical model follows the laws of conservation of energy and exergy balance; the exergy loss of the compressor is greater than that of the heat exchanger; energy and heat are mainly stored in heat transfer oil and high-pressure air, respectively; the deviation between compressor operating and design condition reduces the efficiency; the effect of the air flow rate and inlet temperature of the first-stage turbine on the operation time is greater than that of the storage temperature, adiabatic efficiency and stored air mass. This paper provides reference for adjusting parameters and optimizing energy storage system according to actual demand.

Submerged combustion evaporation technology is a heat exchange technology that uses high-temperature flue gas as the heat source to evaporate the liquid in direct contact with it. However, existing research lacks thermal state simulations of the immersed combustion evaporation process and investigations on the impact of the inclination angle of the distribution disc inside the evaporator on the evaporation. In this study, we conducted a thermal state numerical simulation on the structural parameters of the distributed disc-type submerged combustion evaporator using the Euler method. Herein, the flue gas distribution inside the evaporator was obtained by studying the gas-liquid two-phase flow. Additionally, the impact of different distribution disc inclination angles on the evaporation amount and pressure fluctuation was explored. The numerical simulation results indicate that the angle of the distribution disc affects the distribution of flue gas in the liquid. Moreover, the pressure fluctuation at the inlet of the submerged tube can be reduced by increasing the distribution disc’s angle, thereby increasing backpressure stability in the burner. Conversely, the heat exchange effect between gas and liquid can be enhanced by decreasing the distribution disc’s angle, thereby enhancing evaporation efficiency.

To overcome the shortcomings of traditional absorption refrigeration working pairs, ionic liquid refrigeration working pairs have been widely developed and used as ideal substitutes. Herein, the gas-liquid phase equilibrium properties of the [EMIM]BF₄/CH₃OH ionic liquid binary system were investigated using static experiments and molecular dynamics simulations. The results reveal that this binary solution shows favorable gas-liquid phase equilibrium properties, and its saturated vapor pressure is experimentally measured to be approximately 21% lower than that of other alcohol-based ionic liquid solutions. In addition, the simulation results exhibit the same order of magnitude and trend as the experimental results, and the relative errors are generally less than 8%. These findings provide physical property database for screening ionic liquid refrigeration working pairs and studying the theoretical cycle system as well as a new method for simulating and predicting the basic properties of ionic liquids.

As a novel energy storage method, compressed supercritical carbon dioxide (sCO₂) energy storage offers several advantages, such as high energy storage density, compact structure, long service life, and negative carbon emissions. Therefore, it has a broad application prospect in the energy storage and conversion. In this study, a dynamic mathematical model for the compressed sCO₂ energy storage system (SC-CCES) was established based on the mass conservation and energy conservation laws and the reliability of the model was verified. Additionally, dynamic simulations of the SC-CCES system with single-stage compression and single-stage expansion were performed using Matlab/Simulink. Under the designed operating conditions, the energy storage efficiency of the SC-CCES system was found to be 51.98%, with an energy storage density of 447.8 kWh/m³. The energy storage density of the SC-CCES system was more than 20 times higher than that of a traditional compressed air energy storage system. Furthermore, the impact of different high-pressure tank inlet pressures on system performance was analyzed. The results showed that the energy storage efficiency increases with the increase of the inlet pressure of the high-pressure storage tank, while the energy storage density is exactly the opposite. This study provides a basis for the development of compressed carbon dioxide energy storage.