Direct pore-scale and volume-averaging numerical simulations are two methods for investigating the performance of porous volumetric solar receivers. To clarify the difference in the prediction of heat transfer processes, a direct comparison between these two methods was conducted at both steady state and transient state. The numerical models were established based on X-ray computed tomography scans and a local thermal non-equilibrium model, respectively. The empirical parameters, which are indispensable to the volume-averaging simulation, were determined by Monte Carlo ray tracing and direct pore-scale numerical simulations. The predicted outlet air temperature of the receiver by the volume-averaging simulation method corresponded satisfactorily to that in the direct pore-scale simulation. The largest discrepancies were observed when the receiver’s working temperature was elevated, with differences of 5.5% and 3.68% for the steady state and transient state simulations, respectively. However, the volume-averaging method is incapable of capturing the local temperature information of the air and porous skeleton. It underestimates the inlet temperature of the receiver, leading to an overestimation of the receiver’s thermal efficiency, with the largest difference being 6.51%. The comparison results show that the volume-averaging model is a good approximation to the pore-scale model when the empirical parameters are carefully selected.

Energy storage technology is an essential part of the efficient energy system. Compressed air energy storage (CAES) is considered to be one of the most promising large-scale physical energy storage technologies. It is favored because of its low-cost, long-life, environmentally friendly and low-carbon characteristics. The compressor is the core component of CAES, and the performance is critical to the overall system efficiency. That importance is not only reflected in the design point, but also in the continuous efficient operation under variable working conditions. The diagonal compressor is currently the focus of the developing large-scale CAES because of its stronger flow capacity compared with traditional centrifugal compressors. And the diagonal compressor has the higher single stage pressure ratio compared with axial compressors. In this paper, the full three dimensional numerical simulation technologies with synergy theory are used to compare and analyze the internal flow characteristics. The performance of the centrifugal and diagonal impellers that are optimized under the same requirements for large-scale CAES has been analyzed. The relationship between the internal flow characteristics and performance of the centrifugal and diagonal impellers with the change of mass flow rates and total inlet temperature is given qualitatively and quantitatively. Where the cosine value of the synergy angle is high, the local flow loss is large. The smaller proportion of the positive area is the pursuit of design. Through comparative analysis, it is concluded that the internal flow and performance changes of centrifugal and diagonal impellers are different. The results confirm the superiority and feasibility of the off-design performance of the diagonal compressor applied to the developing large-scale CAES.

The complementary of biomass and solar energy in combined cooling, heating and power (CCHP) system provides an efficient solution to address the energy crisis and environmental pollutants. This work aims to propose a multi-objective optimization model based on the life cycle assessment (LCA) method for the optimal design of hybrid solar and biomass system. The life-cycle process of the poly-generation system is divided into six phases to analyze energy consumption and greenhouse gas emissions. The comprehensive performances of the hybrid system are optimized by incorporating the evaluation criteria, including environmental impact in the whole life cycle, renewable energy contribution and economic benefit. The non-dominated sorting genetic algorithm II (NSGA-II) with the technique for order preference by similarity to ideal solution (TOPSIS) method is employed to search the Pareto frontier result and thereby achieve optimal performance. The developed optimization methodology is used for a case study in an industrial park. The results indicate that the best performance from the optimized hybrid system is reached with the environmental impact load reduction rate (EILRR) of 46.03%, renewable energy contribution proportion (RECP) of 92.73% and annual total cost saving rate (ATCSR) of 35.75%, respectively. By comparing pollutant-eq emissions of different stages, the operation phase emits the largest pollutant followed by the phase of raw material acquisition. Overall, this study reveals that the proposed multi-objective optimization model integrated with LCA method delivers an alternative path for the design and optimization of more sustainable CCHP system.

The application of thermal diodes, which allow heat to flow more readily in one direction than the other, is an important way to reduce energy consumption in buildings and enhance the battery heat dissipation of electric vehicles. Depending on various factors including the specific design, materials used, and operating conditions, the convective thermal diode can exhibit the best thermal rectification effect in intended applications compared to the other  thermal diodes. In this study, a novel convective thermal diode with a wick was proposed based on the phase change heat transfer mechanism. This design takes advantage of both capillary forces provided by the wick and gravity to achieve enhanced unidirectional heat transfer performance for the designed convective thermal diode. The effect of the filling liquid ratio on the thermal performance of the thermal diode was experimentally investigated, which was in good agreement with the theoretical analysis. The research findings showed that with an optimal liquid filling ratio of 140%, the thermal diode with a wick can achieve a better thermal rectification ratio when subjected to a lower heating power, and the maximum thermal rectification ratio of 21.76 was experimentally achieved when the heating power of the thermal diode was 40 W.

Tuning the surface acidity of ZSM-5 catalyst is essential to achieve desired propene selectivity and yield. Here several ratios of Zr were utilized to modify ZSM 5 via flame spray pyrolysis technique coupled with a pulse spray evaporation system. The interaction between Zr and ZSM 5 in the flame influenced the physicochemical and acidity properties of the Zr/ZSM-5. The increasing Zr ratio in ZSM 5 shows coated layers of irregular nano-sized Zr with an increase in crystallite sizes due to the synergetic effect between Zr and ZSM 5. The surface chemical analysis revealed increased lattice oxygen on the Zr modified ZSM 5 (1:4) sample compared to other catalysts. The acidity analysis revealed the Lewis and Brønsted acid distribution in the weak and medium acid sites on the catalyst surface. However, the increase in Zr loading decreased the concentration of Brønsted acid sites and tuned the catalyst surface to more Lewis acidity, promoting propene selectivity and hindering the over-oxidation of propene. The modified ZSM-5 catalysts were examined in a fixed bed reactor within 300°C–700°C at a gas hourly space velocity (GHSV) of 6000 mL·g(catalysts)^–1·h^–1 for the oxidative dehydrogenation of propane (ODHP) to propene. Among the catalysts, Zr/ZSM 5 (1:4) exhibited the best propene yield, with 57.19% propane conversion and 75.54% selectivity to propene and the highest stability. This work provides a promising strategy for tuning the surface acidity of ZSM 5 with Zr for ODHP applications.

In this paper, the efficient utilization of liquefied natural gas (LNG) vaporization cold energy in offshore liquefied natural gas floating storage regasification unit (FSRU) is studied. On the basis of considering different boil-off gas (BOG) practical treatment processes, a cascade comprehensive utilization scheme of cold energy of LNG based on the longitudinal three-stage organic Rankine cycle power generation and the low-grade cold energy used to frozen seawater desalination was proposed. Through the comparative analysis of the effects of the pure working fluid and eight mixed working fluids on the performance of the new system, the combination scheme of system mixed working fluid with the highest exergy efficiency of the system was determined. Then, the genetic algorithm was used to optimize the parameters of the new system. After optimization, the net output power of the LNG cold energy comprehensive utilization system proposed in this paper was 5186 kW, and the exergy efficiency is 30.6%. Considering the power generation and freshwater revenue, the annual economic benefit of the system operating is 18.71 million CNY.

The linear Fresnel reflector concentrator (LFRC) is widely used in the field of solar energy utilization due to its simple structure, low cost, and excellent wind resistance. Nevertheless, the LFRC operates outdoors all year round, and the dust accumulation on the mirror will reduce the optical efficiency of the system, so it needs to be perfected and improved. In this paper, a focal plane energy flux experimental device was designed to test the energy flux of the system under different dust accumulation times. The results indicate that, the dust density on the mirror increased and the energy flux on the focal plane decreased with increase of dust accumulation time. After undergoing dust accumulation for 35 days, the dust density on the mirror reached 4.33 g/m2 and the average energy flux on the focal plane decreased to 1.78 kW/m2. Additionally, the variation of reflectivity caused by dust accumulation on mirror was taken as the quantitative index, and a prediction model for the impact of dust on the optical efficiency of the system was proposed. The results will provide guidance for improving the optical efficiency of the LFRC.

As a variable-condition adjustment technology, the adjustable vaned diffusers (AVDs) can expand the working flow range of the compressor in the compressed air energy storage (CAES) system and improve its aerodynamic performance. In order to investigate the regulatory mechanism of AVDs and capture the details of vane loading distribution for the diffuser design optimization, additively manufactured AVDs for testing in a centrifugal compressor closed test facility are designed and implemented. Firstly, the regulation law of AVDs was summarized by numerical analysis and experimental support, and the corresponding vane loading data was extracted for the distribution law. Then, based on the distribution characteristics, 3D diffuser models were designed suitably for the adjustable components. Then, the laser selective melting (SLM) technology and die steel material 1.2709 were selected for metal printing according to the actual operating environment. Finally, performance testing and accuracy detection were performed on the finished test pieces, almost all inlet hole’s deviations were within the 0.3 mm tolerance. The research results indicated that additive manufacturing can significantly improve the accessibility of the internal flow channels of the diffuser, and derive the load of the blade on the pressure surface and suction surface in detail, also provide adjustable functions for variable operating conditions. It can not only break through the traditional processing bottleneck of the complicated internal flow channels of AVDs but also improve the design matching degree with adjustable components; simultaneously, it ensures high performance with high precision and effectively shortens the long lead time.

The thermal stress-induced deformation issue of receiver is crucial to the performance and reliability of a parabolic-trough (PT) concentrating solar power (CSP) system with the promising direct steam generation (DSG) technology. The objective of the present study is to propose a new-type receiver with axially-hollow spiral deflector and optimize the geometric structure to solve the above issue. To this end, optical-flow-thermal multi-physics coupling models have been established for the preheating, boiling and superheating sections of a typical PT-DSG loop. The simulation results show that our proposed new-type receiver demonstrates outstanding comprehensive performance. It can minimize the circumferential temperature difference through the spiral deflector while lower the flow resistance cost through the axially hollow structure at the same time. As quantitatively evaluated by the temperature uniformity improvement (ε∆T) and the performance evaluation criteria (PEC), different designs are achieved based on different optimal schemes. When ε∆T is of primary importance, the optimal design with torsional ratio of 1 is achieved, with ε∆T=25.4%, 25.7%, 41.5% and PEC=0.486, 0.878, 0.596 corresponding to preheating, boiling, superheating sections, respectively. When PEC is of primary importance, the optimal design with torsional ratio of 6–6.5 is achieved, with PEC=0.950, 2.070, 0.993 and ε∆T=18.2%, 13.3%, 19.4% corresponding to preheating, boiling, superheating sections, respectively.

Hydrogen production via a two-step thermochemical cycle based on solar energy has attracted increasing attention. However, the severe irreversible loss causes the low efficiency. To make sense of the irreversibility, an in-depth thermodynamic model for the solar driven two-step thermochemical cycles is proposed. Different from previous literatures solely focusing on the energy loss and irreversibility of devices, this work decouples a complex energy conversion process in three sub-processes, i.e., reaction, heat transfer and re-radiation, acquiring the cause of irreversible loss. The results from the case study indicate that the main irreversibility caused by inert sweeping gas for decreasing the reduction reaction temperature dominates the cycle efficiency. Decreasing reduction reaction temperature without severe energy penalty of inert sweeping gas is important to reducing this irreversible loss. A favorable performance is achieved by decreasing re-oxidation rate, increasing hydrolysis conversion rate and achieving a thermochemical cycle with a lower equilibrium temperature of reduction reaction at atmosphere pressure. The research clarifies the essence of process irrrversibility in solar thermichemical cycles, and the findings point out the potential to develop efficient solar driven two-step thermochemical cycles for hydrogen production.

Thermal energy storage (TES) using phase change materials (PCMs) is a powerful solution to the improvement of energy efficiency. The application of Ammonium alum (A-alum, NH₄Al(SO₄)₂·12H₂O) in the latent thermal energy storage (LTES) systems is hampered due to its high supercooling and low thermal conductivity. In this work, modified A-alum (M-PCM) containing different nucleating agents was prepared and further adsorbed in expanded graphite (EG) to obtain composite phase change material (CPCM) to overcome the disadvantages of A-alum. Thermal properties, thermal cycle stability, microstructure and chemical compatibility of CPCM were characterized by differential scanning calorimetry, thermal constant analysis, scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The cold rewarming phenomenon of CPCM was established and explained. Results showed that the latent heat and melting point of CPCM were 187.22 J/g and 91.54°C, respectively. The supercooling of CPCM decreased by 9.61°C, and thermal conductivity increased by 27 times compared with pure A-alum. Heat storage and release tests indicated that 2 wt% calcium chloride dihydrate (CCD, CaCl₂·2H₂O) was the optimum nucleating agent for A-alum. The result of TG and 30 thermal cycles revealed that CPCM exhibited favorable thermal stability and reliability during the operating temperature. The prepared modified A-alum/EG CPCM has a promising application prospect for LTES.

Ice accretion on surfaces of the aircraft and engine is a serious threat to the flight safety. In this paper, a novel hot air anti-icing method is proposed based on the porous foam. Taking the NACA0012 airfoil as an example, the traditional thermal protection structure is proved to exist the deficiency in balancing the heat exchange caused by route loss of the heat. By dividing the hot chamber into multiple regions to fill with various foam metal, flow resistance characteristics and heat transfer characteristics for this protection mode are analyzed in order to derive the maximized benefit in anti-icing process. The calculation results reveal that, under the same condition, the region filled with foamed copper not only improves the temperature uniformity on the anti-icing area, but also achieves a better protection effect for enhancing heat transfer between the tube and the hot gas, averagely above 20°C higher than it without porous foam filling in surface temperature. Additionally, the minimum mass flow rate of the protection hot air is reduced by 16.7%. The gratifying efficiency of the porous filler in fortifying heat transfer confirms the potential of replacing the efficient but complex heat transfer design with simple structure filled with foam metal.

The flow field at the inlet of compressors is generally encountered combined total pressure and swirl distortion for either aircraft engine with S-duct or gas turbine with lateral air intake. This inevitably deteriorates compressor aerodynamic performance, including not only the efficiency or pressure ratio but also the operation stability. In order to conquer this issue, appropriate measures such as integrating flow control techniques and modifying inlet or compressor design are of benefits. Due to this motivation, this article develops a full-annular two-dimensional (2D) and a partial-annular three-dimension (3D) optimization strategy for non-axisymmetric vane design. Firstly, two numerical simulation methods for evaluating performance of full-annular 2D vane and compressor with partial-annular 3D vane are developed. The swirl patterns at the inlet of a 1.5-stage axial compressor are analyzed and parametrized, and the parameterization is transferred to characterize the circumferential distribution of geometrical parameters of the vane profile. These approaches dramatically reduce computational simulation costs without violating the non-axisymmetric flow distortion patterns. Then various full-annular 2D sections at different radial locations are constructed as design space. The designed vane is reconstructed and 3D numerical simulations are performed to examine performance of the non-axisymmetric vane and the compressor with it. Also, partial annular 3D optimization is conducted for balancing compressor efficiency and stall margin. Results indicate that the designed non-axisymmetric vane based on full-annular optimization approach can decrease the vane total pressure loss under the considered inlet flow distortion, while those using partial-annular optimization achieve positive effects on compressor stall margin.

Integrating a high proportion of intermittent renewable energy provides a solution for the higher peak-shaving capacity of coal-fired power plants. Oxy-fuel combustion is one of the most promising carbon reduction technologies for coal-fired power plants. This study has proposed a novel oxy-fuel power plant that is coupled with both liquid O₂ storage and cold energy recovery systems in order to adapt to the peak-shaving requirements. The liquid O₂ storage system uses cheap valley electricity to produce liquid O₂ for a later use in the peak period to enhance the peak-shaving capacity. Meanwhile, the cold energy recovery system has been introduced to recover the physical latent energy during the phase change of liquid O₂ to increase the power generation in the peak period. Technical economies of three power plants, i.e. a 330 MW (e) oxy-fuel power plant as reference (Case 1), the same power plant coupled with only liquid O₂ storage system (Case 2), and the same power plant coupled with both liquid O₂ storage and cold energy recovery systems (Case 3), have been analyzed and compared. Thermodynamic performance analysis indicates that the peaking capacity of Case 3 can reach the range of 106.03 to 294.22 MW (e), and the maximum peak-shaving coefficient can be as high as 2.77. Exergy analysis demonstrates that the gross exergy efficiency of Cases 2 and 3 reaches 32.18% and 33.57%, respectively, in the peak period, which are significantly higher than that of 26.70% in Case 1. Economic analysis shows that through selling the liquid O₂ and liquid CO₂, combined with carbon trading, the levelized cost of electricity (LCOE) of the three cases have been greatly reduced, with the lowest one of 30.90 USD/MWh shown in Case 3. For a comprehensive consideration, Case 3 can be considered a future reference of oxy-fuel power plant with the best thermodynamic and economic performance.