Amorphous hafnium dioxide (a-HfO₂) has attracted increasing interest in the application of semiconductor devices due to its high dielectric constant. However, the thermal transport properties of a-HfO₂ are not well understood, which hinders its potential application in electronics. In this work, we systematically investigate the thermal transport property of a-HfO₂ using the molecular dynamics method. The non-equilibrium molecular dynamics simulations reveal that the thermal conductivity of a-HfO₂ is length-dependent below 100 nm. Spectrally decomposed heat current further proves that the thermal transport of propagons and diffusons is sensitive to the system length. The thermal conductivity is found to increase with temperature using Green-Kubo mode analysis. We also quantify the contribution of each carrier to the thermal conductivity at different temperatures. We find that propagons are more important than diffusons in thermal transport at low temperatures (<100 K). In comparison, diffusons dominate heat transport at high temperatures. Locons have negligible contribution to the total thermal conductivity.

Hyperloop has become one of the key reserve technologies for future high-speed rail transit. The gas in the tube is compressed and rubbed, leading to a strong aerodynamic heating effect. The research on the flow field characteristics and aerodynamic heating effect of hyperloop is in its infancy, and that on the flow field structure is lacking. In this study, the nozzle theory was used to make a preliminary judgment on the choked flow phenomenon in the hyperloop. Based on the flow results obtained under different working conditions, the identification basis of the choked flow phenomenon in the hyperloop was obtained. Furthermore, the effect of the choked/unchoked flow on the flow structure, temperature, and pressure distribution of the annular space in the tube was analyzed. Based on traditional high-speed railway aerodynamics, according to relevant theories and calculation in aerospace field, and combined with the model test data, the reliability verification analysis on the characteristics of the flow field are carried out. The structure of the flow filed in the tube can be divided into choked and unchoked. The judgment is dependent on whether the throat reaches the speed of sound. Under the choked flow, a normal shock wave is formed in front of the tube train. The temperature rise of the local flow field exceeds 50 K; the temperature rise of the stagnation region exceeds 88 K, and the pressure is approximately 1.7 times that of the initial pressure in the tube. When the flow is unchoked, differences arise in the distribution of the flow field corresponding to different incoming Mach numbers. When the incoming flow is supersonic, the flow field maintains a supersonic speed, and a bow-shaped shock wave is formed at the front of the tube train. Owing to the shock wave or expansion wave, the local flow field exhibits significant fluctuations in temperature and pressure. Conversely, when the incoming flow is subsonic, the flow field in the tube maintains a subsonic speed, and no shock wave structure is observed.

In Iran, the intensity of energy consumption in the building sector is almost 3 times the world average, and due to the consumption of fossil fuels as the main source of energy in this sector, as well as the lack of optimal design of buildings, it has led to excessive release of toxic gases into the environment. This research develops an efficient approach for the simulation-oriented Pareto optimization (SOPO) of building energy efficiency to assist engineers in optimal building design in early design phases. To this end, EnergyPlus, as one of the most powerful and well-known whole-building simulation programs, is combined with the Multi-objective Ant Colony Optimization (MOACO) algorithm through the JAVA programming language. As a result, the capabilities of JAVA programming are added to EnergyPlus without the use of other plugins and third parties. To evaluate the effectiveness of the developed method, it was performed on a residential building located in the hot and semi-arid region of Iran. To obtain the optimum configuration of the building under investigation, the building rotation, window-to-wall ratio, tilt angle of shading device, depth of shading device, color of the external walls, area of solar collector, tilt angle of solar collector, rotation of solar collector, cooling and heating setpoints of heating, ventilation, and air conditioning (HVAC) system are chosen as decision variables. Further, the building energy consumption (BEC), solar collector efficiency (SCE), and predicted percentage of dissatisfied (PPD) index as a measure of the occupants’ thermal comfort level are chosen as the objective functions. The single-objective optimization (SO) and Pareto optimization (PO) are performed. The obtained results are compared to the initial values of the basic model. The optimization results depict that the PO provides optimal solutions more reliable than those obtained by the SOs, owing to the lower value of the deviation index. Moreover, the optimal solutions extracted through the PO are depicted in the form of Pareto fronts. Eventually, the Linear Programming Technique for Multidimensional Analysis of Preference (LINMAP) technique as one of the well-known multi-criteria decision-making (MCDM) methods is utilized to adopt the optimum building configuration from the set of Pareto optimal solutions. Further, the results of PO show that although BEC increases from 136 GJ to 140 GJ, PPD significantly decreases from 26% to 8% and SCE significantly increases from 16% to 25%. The introduced SOPO method suggests an effective and practical approach to obtain optimal solutions during the building design phase and provides an opportunity for building engineers to have a better picture of the range of options for decision-making. In addition, the method presented in this study can be applied to different types of buildings in different climates.

Printed circuit heat exchanger (PCHE) has been widely used in supercritical carbon dioxide (S-CO₂) power systems because of its high heat transfer efficiency and good compactness. However, due to the large variety of PCHE configurations, channel selection in practical applications lacks a basis. Therefore, this paper discussed the heat transfer and friction characteristics and the synergy of three fields in the channel under the guidance of the field synergy principle for four typical PCHE channels. Additionally, the comprehensive performance of four channels was compared. Finally, the heat transfer and friction factor correlations for S-CO₂ in four channels were established. The findings demonstrate that the synergy of velocity and pressure fields of the straight channel PCHE is better (β≈180°), so its resistance loss is relatively small. The zigzag and sinusoidal wavy channels and the airfoil fins can reduce the angle α between the temperature gradient and velocity, thus enhancing the heat transfer. The sinusoidal wavy channel can reduce flow resistance compared to the zigzag channel due to the rounded corners. The streamlined airfoil structure can guide the flow and reduce backflow, thus reducing resistance losses. In the range of Re studied in this paper, the maximum error of the proposed heat transfer and friction factor correlations of PCHE is 7.0%, which shows good fitting accuracy. The research in this paper can provide a reference for the selection and design of PCHE with different channel configurations.

Plastic crystal neopentyl glycol (NPG) exhibits colossal barocaloric effect with high entropy changes. However, their application is restricted in several aspects, such as low thermal conductivity, substantial supercooling effect, and poor springback properties. In this work, multi-walled carbon nanotubes (MWCNTs) with ultra-high thermal conductivity and high mechanical strength were selected for performance enhancement of NPG. The optimal mixing ratio was determined to be NPG with 3 wt% MWCNTs composites, which showed a 6 K reduction in supercooling without affecting the phase change enthalpy. Subsequently, comprehensive performance of the composites with optimal mixing ratio was compared with pure NPG. At 40 MPa, 390 J·K^–1·kg^–1 change in entropy and 9.9 K change in temperature were observed. Furthermore, the minimum driving pressure required to achieve reversible barocaloric effect was reduced by 19.2%. In addition, the thermal conductivity of the composite was increased by approximately 28%, significantly reducing the heat exchange time during a barocaloric refrigeration cycle. More importantly, ultra-high pressure release rate resulted in a 73.7% reduction in the springback time of the composites, offering new opportunities for the recovery of expansion work.

Liquid desiccant systems are promising methods to recover water and waste heat simultaneously from flue gas. Prior research found that the reduction of particulate matter could occur during the absorption processes. In the present paper, experiments were carried out to explore the effect of removing fine particulate matter (PM2.5) in a liquid desiccant dehumidifier. Aqueous calcium chloride (CaCl2) was used as the desiccant in the experiments. The discrepancies in mass and energy conservation were within ±10% and ±15%, respectively, which showed the good reliability of the experimental results. Additionally, 23.5%–46.0% of the PM2.5 and 23.9%–45.1% of the moisture in the flue gas were removed. By comparing the desiccant solution and water, it was found that they could minimally remove PM2.5 through washing the flue gas. Regardless of whether the flue gas was dehumidified by water or the solution, the removal fractions of PM2.5 of these two methods could be very close if they achieve the same fraction of moisture removal. From the results of a parameter analysis, it was found that the removal fraction of PM2.5 was nearly proportional to the removal fraction of moisture within the experimental range.

The coal gasification fly ash (CGFA) is an industrial solid waste from coal gasification process and needs to be effectively disposed for environmental protection and resource utilization. To further clarify the feasibility of CGFA to prepare porous carbon materials, the physicochemical properties of ten kinds of CGFA from circulating fluidized bed (CFB) gasifiers were analyzed in detail. The results of proximate and ultimate analysis show that the CGFA is characterized with the features of near zero moisture content, low volatile content as low as 0.90%–9.76%, high carbon content in the range of 37.89%–81.62%, and ultrafine particle size (d₅₀=15.8–46.2 μm). The automatic specific surface area (SSA) and pore size analyzer were used to detect the pore structure, it is found that the pore structure of CGFA is relatively developed, and part of the CGFA has the basic conditions to be used directly as porous carbon materials. From SEM images, the microscopic morphology of the CGFA is significantly different, and they basically have the characteristics of loose and porous structure. XRD and Roman spectroscopy were used to characterize the carbon structure. The result shows that the CGFA contains abundant amorphous carbon structure, and thus the CGFA has a good reactivity and a potential to improve pore structure through further activation. Through thermal gravimetric analysis, it can be concluded that the order of reactivity of the CGFA under CO₂ atmosphere has a good correlation with the degree of metamorphism of the raw coal. The gasification reactivity of the CGFA is generally consistent with the change trend of micropores combined with the pore structure. According to the physicochemical properties, the CGFA has a good application prospect in the preparation of porous carbon materials.

The unsteady cloud cavitation shedding in fuel nozzles greatly influences the flow characteristics and spray break-up of fuel, thereby causing erosion damage. With the application of high-pressure common rail systems in diesel engines, this phenomenon frequently occurs in the nozzle; however, cloud cavitation shedding frequency and its mechanism have yet to be studied in detail. In this study, a visualization experiment and proper orthogonal decomposition (POD) method were used to study the variations in the cavitation shedding frequency and analyze the cavitation flow structure in a 3 mm square nozzle. In addition, large eddy simulation (LES) was performed to explore the causes of cavitation shedding, and the relationship between cavitation and vortices. With the increase of the inlet and outlet pressure differences, and fuel temperatures, the degree of cavitation intensified and the frequency of cavitation cloud shedding gradually decreased. LES demonstrated the relationship between the vortices, and the development, shedding, and collapse of the cavitation clouds. Further, the re-entrant jet mechanism was found to be the main reason for the shedding of cavitation clouds. Through comparative experiments, the fluctuation of the vapor volume fraction in the nozzle hole accurately predicted the regions with stable cavitation, re-entrant jet, cavitation cloud shedding, and collapse. The frequency of cavitation shedding can then be calculated. This study employed an instantaneous POD method based on instantaneous cavitation images, which can distinguish the evolution process and characteristics of cavitation in the nozzle hole of diesel engines.

To overcome the huge drag on an airfoil in transonic flow, a hybrid flow control method using suction and loaded leading edge (SLLE) is proposed and its active feedback control effect is studied in the different operation conditions. The loaded leading edge structure can redistribute the pressure as a passive flow control technique, while the suction slot is used to control shock wave’s position and flow separation, which can be conducted actively and automatically using feedback control system. Firstly, the investigation is conducted in steady flow, and a significant drag reduction performance is obtained. The highest drag reduction rate of 22.5% can be got when attack angle is 5°, and the increasing of lift-drag ratio can be obtained in each attack angle case. Secondly, a heuristic approach to feedback flow control is conducted in off-design inflow conditions, where a feedback-based SLLE control method is introduced. The results show the SLLE control can achieve a fair drag reduction performance which is over 10%, which indicates to a flow control method with good applicability in changing flow conditions.

In this research paper, a solar air heater with triangular fins has been experimentally analysed and optimized. Initially, an experimental set-up of a solar air heater having triangular fins has been developed at the location of 28.10°N, 78.23°E. The heat transfer rate through fins and fins efficiency has been determined by the Finite Difference Method model equations. The experimental data and modeled data of response parameters have been optimized in MINITAB-17 software by the Response Surface Methodology tool. For creating the response surface design, three input parameters have been selected namely solar intensity, Reynolds number, and fin base-to-height ratio. The range of solar intensity, Reynolds number, and fin base-to-height ratio is 600 to 1000 W/m², 4000 to 6000, and 0.4 to 0.8 respectively. The response surface design has been analyzed by calculating the outlet temperature, friction factor, Nusselt number, fin efficiency, thermal performance factor, and exergy efficiency. The optimum settings of input parameters: solar intensity is 1000 W/m²; Reynolds number is 4969.7, and the fin base to height ratio is 0.6060, on which these response: namely outlet temperature of 92.531°C, friction factor of 0.2350, Nusselt number of 127.761, thermal efficiency of 50.836%, thermal performance factor of 1.4947, and exergy efficiency of 8.762%.

Supercritical carbon dioxide printed circuit board heat exchangers are expected to be applied in third-generation solar thermal power generation. However, the uniformity of supercritical carbon dioxide entering the heat exchanger has a significant impact on the overall performance of the heat exchanger. In order to improve the uniformity of flow distribution in the inlet header, this article studies and optimizes the inlet header of a printed circuit board heat exchanger through numerical simulation. The results indicate that when supercritical carbon dioxide flows through the header cavity, eddy currents will be generated, which will increase the uneven distribution of flow rate, while reducing the generation of eddy currents will improve the uniform distribution of flow rate. When the dimensionless factor of the inlet header is 6, the hyperbolic configuration is the optimal structure. We also reduced the eddy current region by adding transition segments, and the results showed that the structure was the best when the dilation angle was 10°, which reduced the non-uniformity by 21% compared to the hyperbolic configuration, providing guidance for engineering practice.

The design of thermal conductivity enhancers (TCE) is quite critical to overcoming the disadvantage of the poor thermal conductivity of phase change materials (PCM). The main contribution of this study is firstly to discuss how to actively enhance natural convection of the melted PCM in cellular structure by the fin formed in the structure under the condition of the same metal mass, apart from simultaneously improving heat conduction, which can boost the heat transfer performance. Also, a tailored hybrid fin-lattice structure (HFS) as TCE is designed and fabricated by additive manufacturing (AM). A two-equation numerical method is applied to study the heat transfer of the PCM, and its feasibility is validated with the experimental data. The numerical results indicate that enhanced natural convection and improved heat conduction can be obtained simultaneously when a well-designed fin is embedded into a lattice structure. The enhanced natural convection results in the improved melting rate and the decreased wall temperature; e.g., the complete melting time and the wall temperature are reduced by 11.6% and 19.7%, respectively, because of the fin for metal aluminum. Moreover, the parameters of HFS including the porosity, pore density, and fin dimension have a great impact on the heat transfer. The enhancement effect of the fin for HFS on the melting rate of the PCM increases as the thermal conductivity of the base material decreases. For example, when the fin is introduced into the lattice structure, the complete melting time is reduced by 24.1% for metal titanium. In summary, this study enables us to obtain a good understanding of the mechanism of the heat transfer and provides necessary experimental data for the structural design of HFS fabricated by AM.

The low net efficiency of oxy-fuel circulating fluidized bed (CFB) combustion is mainly due to the addition of air separation unit (ASU) and carbon dioxide compression and purification unit (CPU). High oxygen concentration is one of the effective methods to improve the net efficiency of oxy-fuel combustion technology in CFB. In this research, a series of calculation and simulation were carried out based on Aspen Plus platform to provide valuable information for further investigation on the CFB oxy-fuel combustion system with high oxygen concentration (40%, 50%). A CFB oxy-fuel combustion system model with high oxygen concentration was established including ASU, CPU and CFB oxy-fuel combustion and heat exchange unit. Based on the simulation data, energy and exergy efficiency were analyzed to obtain the following results. The cross-sectional area of furnace and tail flue of 50% CFB oxy-fuel combustion boiler are 43% and 56% of the original size respectively, reducing the construction and investment cost effectively. With the increase of oxygen concentration, the net efficiency of power generation increased significantly, reaching 24.85% and increasing by 6.09% under the condition of 50% oxy-fuel combustion. The total exergy loss increases with the increase of oxygen concentration. In addition, the exergy loss of radiation heat transfer is far higher than convection heat transfer.

Syngas fuel generated by solar energy integrating with fuel cell technology is one of the promising methods for future green energy solutions to carbon neutrality. This paper designs a novel solar-driven solid oxide electrolyzer system integrated with waste heat for syngas production. Solar photovoltaic and parabolic trough collecter together drive the solid oxide electrolysis cell to improve system efficiency. The thermodynamic models of components are established, and the energy, exergy, and exergoeconomic analysis are conducted to evaluate the system’s performance. Under the design work conditions, the solar photovoltaic accounts for 88.46% of total exergy destruction caused by its less conversion efficiency. The exergoeconomic analysis indicates that the fuel cell component has a high exergoeconomic factor of 89.56% due to the large capital investment cost. The impacts of key parameters such as current density, operating temperature, pressure and mole fraction on system performances are discussed. The results demonstrate that the optimal energy and exergy efficiencies are achieved at 19.04% and 19.90% when the temperature, pressure, and molar fraction of H2O are 1223.15 K, 0.1 MPa, and 50%, respectively.

The costs of conventional fuels are rising on a daily basis as a result of technical limits, a misallocation of resources between demand and supply, and a shortage of conventional fuel. The use of crude oil contributes to increased environmental contamination, and as a result, there is a pressing need to investigate alternate fuel sources for car applications. Biodiesel is a renewable fuel that is derived chemically by reacting with the sources of biodiesel. The present research is based on analyzing the effect of fish oil biodiesel-ethanol blend in variable compression engine for variable compression ratio (VCR). The processed fish oil was procured and subjected to a transesterification process to convert fatty acids into methyl esters. The obtained methyl esters (biodiesel) were blended with ethanol and diesel to obtain a ternary blend. The ternary blend was tested for its stability, and a stable blend was obtained and tested in VCR engines for its performance, combustion, and emission characteristics. In the second phase, experiments are conducted in the diesel engine by fueling the fish oil methyl ester and ethanol blended with diesel fuel in the concentration of 92.5 vol% of Diesel+7.5 vol% of Fish oil+1.25 vol% ethanol, 92.5 vol% of Diesel+7.5 vol% of Fish oil+5 vol% ethanol, 87.5 vol% of Diesel+12.5 vol% of Fish oil+1.25 vol% ethanol, 87.5 vol% of Diesel+12.5 vol% of Fish oil+5 vol% ethanol, 82.5 vol% of Diesel+17.5 vol% of Fish oil+1.25 vol% ethanol, 82.5 vol% of Diesel+17.5 vol% of Fish oil+ 5 vol% ethanol to find out the performance parameters and emissions. Because the alternative fuel performs better in terms of engine performance and pollution management, the percentage chosen is considered the best mix. The results showed that the use of a lower concentration of ethanol in the fish oil biodiesel blend improved the engine thermal efficiency by 5.23% at a higher compression ratio. Similarly, the engine operated with a higher compression ratio reduced the formation of HC and CO emissions, whereas the NO_x and CO₂ emissions increased with an increased proportion of biodiesel in diesel and ethanol blends.

The objective of this paper is to understand the benefits that one can achieve for large-scale supercritical CO₂ (S-CO₂) coal-fired power plants. The aspects of energy environment and economy of 1000 MW S-CO₂ coal-fired power generation system and 1000 MW ultra-supercritical (USC) water-steam Rankine cycle coal-fired power generation system are analyzed and compared at the similar main vapor parameters, by adopting the neural network genetic algorithm and life cycle assessment (LCA) methodology. Multi-objective optimization of the 1000 MW S-CO₂ coal-fired power generation system is further carried out. The power generation efficiency, environmental impact load, and investment recovery period are adopted as the objective functions. The main vapor parameters of temperature and pressure are set as the decision variables. The results are concluded as follows. First, the total energy consumption of the S-CO₂ coal-fired power generation system is 10.48 MJ/kWh and the energy payback ratio is 34.37%. The performance is superior to the USC coal-fired power generation system. Second, the resource depletion index of the S-CO₂ coal-fired power generation system is 4.38 μPR_china,90, which is lower than that of the USC coal-fired power generation system, and the resource consumption is less. Third, the environmental impact load of the S-CO₂ coal-fired power generation system is 0.742 mPE_china,90, which is less than that of the USC coal-fired power generation system, 0.783 mPE_china,90. Among all environmental impact types, human toxicity potential HTP and global warming potential GWP account for the most environmental impact. Finally, the investment cost of the S-CO₂ coal-fired power generation system is generally less than that of the USC coal-fired power generation system because the cost of the S-CO₂ turbine is only half of the cost of the steam turbine. The optimal turbine inlet temperature T₅ becomes smaller, and the optimal turbine inlet pressure is unchanged at 622.082°C/30 MPa.

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.

The operating principles of Circulating Fluidized Bed (CFB) boilers involve a significant amount of heat accumulation, which forms the thermal inertia of the boiler and hinders the improvement of its variable load response rate. This study aims to characterize the thermal inertia of CFB boilers by evaluating the change in the boiler’s heat accumulation corresponding to the change in unit power generation. The thermal inertia of a 330 MW CFB boiler was determined through the collection of operating data under four different operating conditions of 30%, 50%, 75%, and 100% load. The study proposes to substitute the existing refractory material with a metal grille to reduce the thermal inertia of the boiler. The effect of the metal grille on heat transfer was confirmed through verification on a 440 t/h CFB boiler, and its performance change and thermal inertia reduction were further predicted. The results indicate that over 50% of the total thermal inertia of CFB boilers originates from the refractory material. The use of metal grille in place of refractory material improved heat transfer in the furnace, resulting in a decrease of the furnace chamber temperature by 13°C in the 330 MW CFB boiler. This reduction of thermal inertia by 30%–35% will facilitate faster load lifting and lowering of the boiler, fulfilling the requirement for flexible peaking.

Turbulent two-phase combustion is widely encountered in spray and pulverized-coal combustors, and large-eddy simulation (LES) becomes a powerful CFD method for its simulation, because LES can give unsteady flame structures and more reasonable statistical results than Reynolds-averaged modeling. Present combustion models in LES either lack of generality or are computationally too expensive. A statistical moment model based on the idea of turbulence modeling called “second-order moment (SOM) combustion model” was developed by the present authors for LES of two-phase combustion. In this paper, a review is given on our published research results for SOM-LES of two-phase combustion, including the description of the SOM-LES model, its application, validation of statistical results by experiments, as well as the phenomena obtained by instantaneous results.

In this research, a solar hybrid combined cooling heating and power (CCHP) system is proposed considering the different scenarios of Prime Movers (PMs) and the part-load performance of PMs is validated by the designed values from the manufacturer of Volvo. Moreover, a multi-optimization model based on a genetic algorithm is developed in order to select both the most promising performance PM and the most cost-effectiveness, environmentally friendly number of collectors for the proposed CCHP system, simultaneously. Then the hourly performance of this solar hybrid CCHP is determined through a case study of a hotel in Shanghai. Results show that the highest efficiency of the PM with larger capacity has the most promising performance and the collector number of 90 turns out to be a superior value for the hotel building based on the primary energy saving ratio of 61.61%. Moreover, on a typical summer day, the recovered waste heat and the solar energy can provide all the thermal energy demands, while, an auxiliary boiler should be started to fulfill the energy gap in both typical transition and winter days. From the simulation result, the CO2 emissions can be reduced by 856.2 t/a due to the solar energy introduced into the system. Besides, the dynamic investment payback period will change from 3.01 years to 3.56 years when the fuel price (Pfuel) ranges from 0.8Pfuel to1.2Pfuel.

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.

Understanding the residence time distribution (RTD) of a continuous hydrothermal reactor is of great significance to improve product quality and reaction efficiency. In this work, an on-line measurement system is attached to a continuous reactor to investigate the characteristics of RTD. An approach that can accurately fit and describe the experimental measured RTD curve by finding characteristic values is proposed for analysis and comparison. The RTD curves of three experiment groups are measured and the characteristic values are calculated. Results show that increasing total flow rate and extending effective reactor length have inverse effect on average residence time, but they both cause the reactor to approach a plug flow reactor and improve the materials leading. The branch flow rate fraction has no significant effect on RTD characteristics in the scope of the present work except the weak negative correlation with the average residence time. Besides, the natural convection stirring effect can also increase the average residence time, especially when the forced flow is weak. The analysis reveals that it is necessary to consider the matching of natural convection, forced flow and reactor size to control RTD when designing the hydrothermal reactor and working conditions.

Phase change materials (PCMs) are a kind of highly efficient thermal storage materials which have a bright application prospect in many fields such as energy conservation in buildings, waste heat recovery, battery thermal management and so on. Especially inorganic hydrated salt PCMs have received increasing attention from researchers due to their advantages of being inexpensive and non-flammable. However, inorganic hydrated salt PCMs are still limited by the aspects of inappropriate phase change temperature, liquid phase leakage, large supercooling and severe phase separation in the application process. In this work, sodium acetate trihydrate was selected as the basic inorganic PCM, and a novel shape-stabilized composite phase change material (CPCM) with good thermal properties was prepared by adding various functional additives. At first, the sodium acetate trihydrate-acetamide binary mixture was prepared and the melting point was adjusted using acetamide. Then the binary mixture was incorporated into expanded graphite to synthesize a novel shape-stabilized CPCM. The thermophysical properties of the resultant shape-stabilized CPCM were systematically investigated. The microscopic morphology and chemical structure of the obtained shape-stabilized CPCM were characterized and analyzed. The experiment results pointed out that acetamide could effectively lower the melting point of sodium acetate trihydrate. The obtained shape-stabilized CPCM modified with additional 18% (mass fraction) acetamide and 12% (mass fraction) expanded graphite exhibited good shape stability and thermophysical characteristics: a low supercooling degree of 1.75°C and an appropriate melting temperature of 40.77°C were obtained; the latent heat of 151.64 kJ/kg and thermal conductivity of 1.411 W/(m·K) were also satisfactory. Moreover, after 50 accelerated melting-freezing cycles, the obtained shape-stabilized CPCM represented good thermal reliability.

The low power consumption of the near-critical compressor is the key factor for the high efficiency of supercritical CO₂ Brayton cycle. In the numerical simulation of the compressor, the rapid changes in the thermophysical properties of the CO₂ near the critical point make it difficult to capture the condensation phenomenon. This paper investigates the influence of fluid physical properties on the condensation phenomenon. Firstly, the differences in the physical properties of CO₂ in the SRK EOS (equation of state), PR EOS, and SW EOS are compared. Then, the simulation of nozzles and compressors were carried out and discussed. Results show that the condensation positions predicted by the three EOSs are basically the same. Compared with SW EOS, the disparities between the maximum condensation mass fraction predicted by the PR and SRK EOSs is 5.7% and 11.5%, and that of total pressure ratio is 0.3% and 3.8%, respectively. The results show that PR EOS can be considered for numerical simulation in engineering practice. Since its physical property calculation results are closer to the actual physical properties while the physical properties change more gently, it has considerable accuracy and numerical stability.

The specific heat capacity of working fluid is an important influence factor on heat transfer characteristic of the pulsating heat pipe (PHP). Due to the relatively large specific heat capacity of micro encapsulated phase change material (MEPCM) suspension, a heat transfer performance experimental facility of the PHP was established. The heat transfer characteristic with MEPCM suspension of different mass concentrations (0.5% and 1.0%) and ultra-pure water were compared experimentally. It was found that when the PHP uses MEPCM suspension as its working fluid, operating stability is impoverished under lower heating power and the operating stability is better under higher heating power. At the inclination angle of 90°, the temperature at heating side decreases compared to ultra-pure water and the temperature at heating side decreases with the raising of MEPCM suspension mass concentration. The heat transfer characteristic of the PHP is positively correlated with the inclination angle and the 90^° is optimum. The unfavorable effect of the inclination angle decreases with heating power increasing. When the inclination angle is 90^°, the PHP with MEPCM suspension at 1.0% of mass concentration has the lowest thermal transfer resistance and followed by ultra-pure water and MEPCM suspension at 0.5% of mass concentration has the highest thermal transfer resistance. When the inclination angles are 60^° and 30^°, the effect of gravity on the flow direction is reduced to 86.6% and 50% of that on the inclination angle of 90°, respectively, and the promoting effect of gravity on the working fluid is further weakened as the inclination angle further decreases. Due to the high viscosity of MEPCM suspension, the PHP with ultra-pure water has the lowest heat transfer resistance. When the inclination angles is 60^°, the thermal resistance with MEPCM suspension at 0.5% of the mass concentration is lower than that at 1.0% at the heating power below 230 W. The thermal resistance of MEPCM suspension tends to be similar for heating power of 230–250 W. At the heating power above 270 W, the thermal resistance with MEPCM suspension at 1.0% of the mass concentration is lower than that at 0.5%.

Based on the COMSOL Multiphysics simulation software, this study carried out modeling and numerical simulation for the evaporation process of liquid metal lithium in the vacuum free molecular flow state. The motion of lithium atoms in the evaporation process was analyzed through a succession of studies. Based on the available experimental values of the saturated vapor pressure of liquid metal lithium, the relationship between saturated vapor pressure and temperature of liquid lithium in the range of 600 K–900 K was obtained. A two-dimensional symmetric model (3.5 mm×20 mm) was established to simulate the transient evaporation process of liquid lithium at wall temperatures of 750 K, 780 K, 800 K, 810 K, 825 K, and 850 K, respectively. The effects of temperature, the evaporation coefficient, back pressure, and length-to-diameter ratio on the evaporation process were studied; the variation trends and reasons of the molecular flux and the pressure during the evaporation process were analyzed. At the same time, the evaporation process under variable wall temperature conditions was simulated. This research made the evaporation process of liquid lithium in vacuum molecular flow clearer, and provided theoretical support for the space reactor and nuclear fusion related fields.

A 2 MW gas turbine engine has been developed for the distributed power market. This engine features a 7:1 pressure ratio radial inflow turbine. In this paper, influences of various geometry features are investigated including turbine tip and backface clearances. In addition to the clearances, the effects of the inducer deep scallop and exducer rounded trailing edge are investigated. Finally, geometric features associated with a split rotor (separate inducer and exducer) are studied. These geometry features are investigated numerically using CFD. Part of the numerical results is also compared to experimental data acquired during engine test to validate the CFD results.
Results indicated that for this specific turbine, the influences of the exducer radial tip clearance, inducer axial tip clearance, and even scalloped blade backface clearance all have negligible influences on performance. In all cases, 1% increase in clearance only attributes to approximately a 0.1% lower efficiency. This finding is very different from former published papers with low pressure ratio turbines, indicating different flow physics apply for a turbine with a relatively high-pressure ratio.

Compressed Air Energy Storage (CAES) is one of the methods that can solve the problems with intermittency and unpredictability of renewable energy sources. A side effect of air compression is a fact that a large amount of heat is generated which is usually wasted. In the development of CAES systems, the main challenge, apart from finding suitable places for storing compressed air, is to store this heat of compression process so that it can be used for heating the air directed to the expander at the discharging stage. The paper presents the concept of a hybrid compressed air and thermal energy storage (HCATES) system, which may be a beneficial solution in the context of the two mentioned challenges. Our novel concept assumes placing the thermal energy storage (TES) system based on the use of solid storage material in the volume of the post-mining shaft forms a sealed air pressure reservoir. Implementation of proposed systems within heavily industrialized agglomerations is a potential pathway for the revitalization of post-mine areas. The potential of energy capacity of such systems for the Upper Silesian region could exceed the value of 10 GWh. In the paper, the main construction challenges related to this concept are shown. The issues related to the possibility of storing air under high pressure in the shaft from the view of the rock mass strength are discussed. The overall concept of the TES system installation solution in the shaft barrel is presented. The basic problems related to heat storage in the cylindrical TES system with a non-standard structure of high slenderness are also discussed. The numerical calculations were based on the results of experiments performed on a laboratory stand, the geometry of which is to reflect the construction of a TES tank in a post-mining shaft. The article presents the results of numerical analysis showing the basic aspects related to difficulties that may occur at the construction stage and during the operation of the proposed HCATES system. The paper focuses on the methodology for determining the energy and exergy efficiency of a section of a Thermal Energy Storage tank, and presents the differences in the performance of this tank depending on its geometric dimensions, which are determined by the different sizes of mine shafts.

Ejector refrigeration cycle (ERC) with advantages of simple structure and low cost holds great application potential in cascade/hybrid cycles to improve the overall system performance by removing or recovering the heat from the main cycle. In this paper, a theoretical and experimental investigation of the ERC as a part of a cascade system was carried out. The operating parameters were optimized. The experimental ERC test rig was designed, developed and investigated at high evaporating temperatures and wide ranges of operating conditions. The influence of operating conditions on the efficiency of the ejector and ERC was analyzed. Experimental results and analysis in this study can be helpful for the application and operating condition optimization of ERC in cascade/hybrid refrigeration systems.

Oxidation of acetylene (C2H2) has been investigated in a high-pressure jet-stirred reactor (HP-JSR) with equivalence ratios Φ=0.5, 1.0, 2.0 and 3.0 in the temperature range of 650 K–900 K at 1.2 MPa. 18 products and intermediates were analyzed qualitatively and quantitatively by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Generally, with Φ increasing, the production of intermediates increases significantly. CH₄, C₂H₄, C₂H₆, C₃H₆ and C3H8 were important intermediates, which were formed abundantly at Φ=3.0. Sufficient light hydrocarbon intermediates could be an important reason for significant formation of cyclopentadiene, benzene, toluene and styrene at Φ=3.0. A detailed kinetic mechanism consisting of 299 species and 2041 reactions has been developed with reasonable predictions against the present data and previous results obtained at 0.1 MPa. According to flux and sensitivity analysis, H and OH radicals play important roles in the consumption of C₂H₂. The combinations among light hydrocarbons and their free radicals are the main generation pathways of aromatics. C₃H₃, IC₄H₅ and AC3H5 are important precursors for the formation of aromatics. By comparing the results of atmospheric pressure and high pressure, it can be found that increasing the pressure is conducive to fuel consumption and aromatics generation.

Infrared thermography, velocity and impingement pressure measurements alongside numerical modelling are used in this study to resolve (heated) surface temperature distributions of turbulent swirling impinging jets for two Reynolds numbers (Re=11 600 and 24 600). Whilst building upon earlier discoveries for this same geometry, this paper provides three new contributions: (1) identifying the role of impingement distance (H/D) as a deciding factor in the trade-off between more efficient heat transfer (at high swirl numbers) and achieving better substrate temperature uniformity (lower gradients), (2) developing correlations to predict Nusselt number for swirling and non-swirling cooling jets, and (3) predicting the underlying mixing field in these jets and its interplay with the thermal distributions resolved.
Results indicate substrate temperature uniformity varies based on H/D and swirl intensity (S) with a significant level of thermal non-uniformity occurring in near-field impingement (H/D=1) at stronger swirl (S=0.59 and 0.74). Four correlations describing the effects of S, Re, and H on the average heat transfer and stagnation heat transfer are developed and yield accuracies of 8% and 12%, respectively. Flow recirculation near the impingement surface is predicted at H/D=1 for stronger swirl jets which disappears at other substrate distances. The peak wall shear stress reduces and the flow impingement becomes radially wider at higher H/D and S. Stronger turbulence or eddy viscosity regions for non-swirling jets (S=0) are predicted in the shear layer and entrainment regions at  H/D=1, but such turbulence is confined to the impingement and wall jet regions for strongly swirling flows.

Condensation temperature is one of the crucial parameters determining the performance of an organic Rankine cycle. It is necessary to consider the differences in the working fluids themselves when setting the condensation temperature of organic Rankine cycle. In current study, temperature-entropy (T-s) diagram is employed to describe the difference in working fluids. Three areas of dry and isentropic fluids in a temperature-entropy (T-s) diagram, which are the area denoting net output work of cycle (A₁), the area denoting net output work of the Carnot cycle (A), and the curved triangle in superheated region denoting condensation characteristics (A₂), are defined. On this basis, the ratio of A₂ to A1 and the ratio of A₁ to A are calculated. Logarithmic Mean Difference of the above two ratios is obtained to determine the operable ideal condensation temperature of 66 dry and isentropic fluids employed in Organic Rankine Cycle. The findings indicate that the operable ideal condensation temperatures for the majority of dry and isentropic fluids are in the range of 305 K to 310 K. The work presented in this study may be useful for designing and establishing an Organic Rankine Cycle system.

In order to effectively widen the high-altitude operating limits of the multi-swirl staged combustor, the ignition and lean blow-out (LBO) performances of the model combustor were experimentally acquired under the conditions of room temperature and sub-atmospheric pressure with the altitude ranging from 0 km to 12 km. Moreover, the isothermal flow fields inside a staged model combustor with different sub-atmospheric conditions were simulated. Experimental results show that the minimum ignition and LBO fuel-air ratio (FAR) increase rapidly with the increase of simulated altitude. In addition, as the relative pressure drop of injector increases from 1% to 3%, the ignition and LBO performances are gradually improved. Side visualization of the flame by high-speed camera shows that the time-averaged flames under stable combustion have a similar distribution pattern under different pressure drops. The luminous intensity is stratified into dim-bright-dim layers along axial direction. The flame near LBO shrinks to the outlet of pilot stage with a great reduction in luminous intensity. The numerical results reveal that with the decrease of air pressure, the air mass flow rate involved in atomization and combustion is significantly reduced, and the aerodynamic shear force of swirling air is weakened, which are adverse to atomization and fuel-air mixing for airblast atomizer and further lead to the deterioration of ignition and LBO performances.