Li-ion battery is an essential component and energy storage unit for the evolution of electric vehicles and energy storage technology in the future. Therefore, in order to cope with the temperature sensitivity of Li-ion battery and maintain Li-ion battery safe operation, it is of great necessary to adopt an appropriate battery thermal management system (BTMS). In this paper, the current main BTM strategies and research hotspots were discussed from two aspects: small-scale battery module and large-scale electrochemical energy storage power station (EESPS). The practical application situation, advantages and disadvantages, and the future development trend of each heat dissipation method (air, liquid, PCM, heat pipe, hybrid cooling) were described in detail. Among them, the air cooling and liquid cooling were reviewed in-depth based on the engineering application. The PCM, heat pipe and hybrid cooling were reviewed extensively based on the latest explorations. The research provides a comprehensive understanding for the BTMS in all scales.

To achieve low-carbon economic operation of hydrogen-doped integrated energy systems while mitigating the stochastic impact of new energy outputs on the system, the coordinated operation mode of hydrogen-doped gas turbines and electrolyzers is focused on, as well as a hybrid energy storage scheme involving both hydrogen and heat storage and an optimized scheduling model for integrated energy systems encompassing electricity-hydrogen-heat-cooling conversions is established. A model predictive control strategy based on deep learning prediction and feedback is proposed, and the effectiveness and superiority of the proposed strategy are demonstrated using error penalty coefficients. Moreover, the introduction of hydrogen energy exchange and ladder carbon trading is shown to effectively guide the low-carbon economic operation of hydrogen-doped integrated energy systems across multiple typical scenarios. A sensitivity analysis is conducted based on this framework, revealing that increases in the hydrogen doping ratio of turbines and the carbon base price led to higher system operation costs but effectively reduce carbon emissions.

The development of azobenzene photoisomerization materials marks a pivotal advancement in solar-thermal conversion technologies. Their properties and performance, explored through comprehensive characterization, are vital for further progress. Despite extensive research in this area, a detailed summary of characterization methods for azobenzene materials remains largely unexplored. This review addresses this gap by detailing structural and performance characterization techniques. It provides an in-depth overview of various experimental methods, highlighting their objectives, operational mechanics, and practical applications. This detailed review sheds light on the complex relationship between the materials’ structure and their performance. Moreover, the review presents a critical analysis of these methods, assessing their strengths and limitations. By doing so, it highlights the revolutionary potential of azobenzene materials in the realm of solar energy conversion and underscores their significance in fostering sustainable energy solutions.

As an important and effective indicator of contact heat transfer, thermal contact resistance is a widespread phenomenon in engineering. It can directly affect product reliability, full-load performance, power consumption and even life cycle in energy, aerospace, electronic packaging, cryogenic refrigeration, etc. Therefore, enhancing the interface heat transfer and suppressing thermal contact resistance have become increasingly important. Against this background, this paper seeks to elaborate on conceptions of thermal contact resistance and the ways to reduce it. After reviewing the existing methods of measuring thermal contact resistance and characterizing the interface morphology, we highlight the theoretical underpinnings of thermal contact resistance, including the two-dimensional mathematic characteristics of the contact interface and the theoretical and empirical models for quantifying it. Three categories of influencing factors, i.e., thermal, geometrical and mechanical states, are then presented. Based on the macroscopic formation mechanism, the paper summarizes the existing methods for suppressing thermal contact resistance, with close attention paid to polymer composite thermal interfacial materials and metal interfacial materials filled with high thermal conductivity filler. In light of the findings, this review provides five promising directions for future research on thermal contact resistance. It suggests that the failure modes and service life of interface materials are essential to apply such technologies to suppress thermal contact resistance in practice. This review will be a guide for future research in thermal contact resistance and for the widespread use of composite interface materials.

A tandem blade configuration is a significant flow control method that delays the onset of flow separation. This study numerically investigates the effects of diffusion factor and percentage pitch on the flow structure of tandem blades. Diffusion factors vary from 0.328 to 0.484. Percentage pitches change from 0.80 to 0.92. Results show that the loss coefficient increases with diffusion factor and decreases with percentage pitch. There is a hub-corner stall of the forward blade in all cases. Gap flow determines the rear blade corner separation. Varying the percentage pitch and diffusion factor changes the momentum distribution of the gap flow. Corner separation of the rear blade is inhibited as low-momentum gap fluids are involved in the passage vortex along with the hub-corner stall of the forward blade. Increasing diffusion factor causes a change in incidence at the leading edge of the rear blade, resulting in a variation at the corner separation of the rear blade. A tandem blade is compared with the reference outlet vane. The performance of the tandem blade is superior to that of the reference outlet vane in all incidences, with a 26.35% reduction in the loss coefficient and a 7.89% enhancement in the pressurization at the designed incidence. Tandem blades stall at positive incidence because of the hub-corner stall of the forward blade. The intensity of the gap flow increases with incidence, preventing corner separation of the rear blade at positive incidences.

Recent research and development on ramjet and supersonic combustion ramjet (scramjet) engines is concerned with producing greater thrust, higher speed, or lower emission. This is most likely driven by the fact that supersonic/hypersonic propulsion systems have a broad range of applications in military sectors. The performances of such supersonic/hypersonic propulsion systems depend on a series of physical and thermodynamic parameters, such as the fuel types, flight conditions, geometries and sizes of the engines, engine inlet pressure/velocity. As a propulsion system, a stable and efficient combustion is desirable. However, self-excited large-amplitude combustion oscillations (also known as combustion instabilities) have been observed in liquid- and solid-propellant ramjet and scramjet engines, which may be due to acoustic resonance between inlet and nozzle, vortex kinematics (large coherent structures), and acoustic-convective wave coupling mechanisms due to combustion. Such intensified pressure oscillations are undesirable, since they can lead to violent structural vibration, and overheating. How to enhance and predict the engines’ stability behaviors is another challenge for engine manufacturers. The present work surveys the research and development in ramjet combustion and combustion instabilities in ramjet engines. Typical active and passive controls of ramjet combustion instabilities are then reviewed. To support this review, a case study of combustion instability in solid-fueled ramjet is provided. The popular mode decomposition algorithms such as DMD (dynamic mode decomposition) and POD (proper orthogonal decomposition) are discussed and applied to shed lights on the ramjet combustion instability in the present case study.

The absorption cycle is a promising technology for harnessing low-temperature heat, playing a crucial role in achieving the objectives of carbon peaking and carbon neutrality. As a significant element in distributed energy systems, the absorption cycle can utilize various types of low-grade heat to fulfill cooling, heating, and electrical energy demands. Therefore, it can be employed in diverse settings to unleash its substantial energy-saving potential. However, the widespread adoption of the absorption cycle is limited to specific scenarios. Hence, further efforts are needed to enhance its technological maturity, gain societal acceptance, and expand its application scope. Focusing on the utilization of different low-grade heat, this paper provides an overview of significant advancements in the application research of various absorption cycles, such as the absorption refrigeration cycle, absorption heat pump, absorption heat transformer, and the absorption power cycle. According to current research, absorption cycles play a critical role in energy conservation and reducing carbon dioxide emissions. They can be applied to waste heat recovery, heating, drying, energy storage, seawater desalination, refrigeration, dehumidification, and power generation, leading to substantial economic benefits. The paper also outlines the primary challenges in the current application of the absorption cycle and discusses its future development direction. Ultimately, this paper serves as a reference for the application research of the absorption cycle and aims to maximize its potential in achieving global carbon neutrality.

The selection of loss models has a significant effect on the one-dimensional mean streamline analysis for obtaining the performance of centrifugal compressors. In this study, a set of optimized loss models is proposed based on the classical loss models suggested by Aungier, Coppage, and Jansen. The proportions and variation laws of losses predicted by the three sets of models are discussed on the NASA Low-Speed-Centrifugal-Compressor (LSCC) under the mass flow of 22 kg/s to 36 kg/s. The results indicate that the weights of Skin friction loss, Diffusion loss, Disk friction loss, Clearance loss, Blade loading loss, Recirculation loss, and Vaneless diffuser loss are greater than 10%, which is dominant for performance prediction. Therefore, these losses are considered in the composition of new loss models. In addition, the multi-objective optimization method with the Genetic Algorithm (GA) is applied to the correction of loss coefficients to obtain the final optimization loss models. Compared with the experimental data, the maximum relative error of adiabatic the three classical models is 7.22%, while the maximum relative error calculated by optimized loss models is 1.22%, which is reduced by 6%. Similarly, compared with the original model, the maximum relative error of the total pressure ratio is also reduced. As a result, the present optimized models provide more reliable performance prediction in both tendency and accuracy than the classical loss models.

The supercritical carbon dioxide (sCO₂) cycle can be powered by traditional as well as clean energy. To help users obtain more accurate results than the literatures with pre-set compressor efficiency, we proposed a complete model to establish a link between the performance, sizes of compressors and parameters such as power W_C, inlet temperature T_in, inlet pressure P_in and pressure ratio ɛ. Characteristic sizes of compressors l_c, profile loss Y_p and clearance loss Y_cl are all proportional to powers of W_C with powers of 0.5, –0.075 and –0.5 to 0 respectively; the scaling laws are constant in the range of capacities from 20 MW to 200 MW. The compressor isentropic efficiency η_tt grows as the W_C increases, and the curves become gentle. Compressor efficiency improves over the full power range when the speed is changed from standard speed to the optimal speed; the η_tt curves turn soft as the n increase. As the P_in and T_in approach the critical point, the η_tt increase. Compressor efficiency follows a parabolic curve as the ɛ increases, this parabolic distribution results from the tradeoff between the change in losses and the pressure distribution of blades. The η_tt versus P_in, Tin and ɛ relations are similar at various capacities because of insignificant changes in the distribution of losses. Compressor efficiency maps facilitate the estimation of system performance, while scaling law for irreversible losses and characteristic lengths, along with constant criterion analyses, aid in comprehending the characteristics of compressors across various capacities.

With the advantages of low cost, excellent ability of heat and mass transfer and easy accessibility to the supercritical point, supercritical CO₂ has been applied in many engineering devices recently. Because of the sharply-varying thermophysical properties near the supercritical point, heat transfer and flow behavior of supercritical CO₂ in tubes become complex and have received a lot of research attention. The main purpose of this paper is to summarize the findings of the published works related to flow phenomena and heat transfer characteristics of supercritical CO₂. Firstly, influence parameters related to boundary conditions of supercritical CO₂ flowing in a smooth tube are introduced. Secondly, commonly-used turbulence and mathematic models dealing with internal flows of supercritical CO₂ are summarized. Then, research works on geometric effects of design parameters, shapes and configurations are introduced. The practical applications of supercritical CO₂ in recent years are presented. Finally, developments and future challenges of supercritical CO₂ in tubes are analyzed and summarized. This paper provides basic knowledge of heat transfer and fluid flow mechanisms and related practical applications of supercritical CO₂ in tubes.

Digital twin is a cutting-edge technology in the energy industry, capable of predicting real-time operation data for equipment performance monitoring and operational optimization. However, methods for calibrating and fusing digital twin prediction with limited in-situ measured data are still lacking, especially for equipment involving complicated multiphase flow and chemical reactions like coal-fired boilers. In this work, using coal-fired boiler water wall temperature monitoring as an example, we propose a digital twin approach that reconstructs the water wall temperature distribution with high spatial resolution in real time and calibrates the reconstruction using in-situ water wall temperature data. The digital twin is established using the gappy proper orthogonal decomposition (POD) reduced-order model by fusing CFD solutions and measured data. The reconstruction accuracy of the digital twin was initially validated. And then, the minimum number of measured data sampling points required for precise reconstruction was investigated. An improved uniform data collection method was subsequently developed. After that, the computational time required for the digital twin and the traditional CFD was compared. Finally, the reconstruction method was further validated by in-situ measured temperature from the in-service boiler. Results indicate that the established digital twin can precisely reconstruct the water wall temperature in real time. Thirty-nine sampling points are sufficient to reconstruct the temperature distribution with the original data collection method. The proposed uniform data collection method further reduces the mean relative errors to less than 0.4% across four test cases, and with the constrained technique, the errors decrease to 0.374% and 0.345% for Cases 1 and 3, which had poor reconstructions using the original sampling point arrangement. In addition, the reconstruction time of the digital twin is also considerably reduced compared to CFD. Engineering application indicates that the reconstructed temperatures are highly consistent with in-situ measured data. The established water wall temperature digital twin is beneficial for water wall tube overheating detection and operation optimization.

With countries proposing the goal of carbon neutrality, the clean transformation of energy structure has become a hot and trendy issue internationally. Renewable energy generation will account for the main proportion, but it also leads to the problem of unstable electricity supply. At present, large-scale energy storage technology is not yet mature. Improving the flexibility of coal-fired power plants to suppress the instability of renewable energy generation is a feasible path. Thermal energy storage is a feasible technology to improve the flexibility of coal-fired power plants. This article provides a review of the research on the flexibility transformation of coal-fired power plants based on heat storage technology, mainly including medium to low-temperature heat storage based on hot water tanks and high-temperature heat storage based on molten salt. The current technical difficulties are summarized, and future development prospects are presented. The combination of the thermal energy storage system and coal-fired power generation system is the foundation, and the control of the inclined temperature layer and the selection and development of molten salt are key issues. The authors hope that the research in this article can provide a reference for the flexibility transformation research of coal-fired power plants, and promote the application of heat storage foundation in specific coal-fired power plant transformation projects.

The modification with dark metallic oxide is identified as the crucial strategy to enhance optical absorptions of calcium-based materials for the direct solar-driven thermochemical energy storage. The effect of modification on the heat release behavior in carbonation of calcium-based material has been widely investigated, but its effect on the heat storage behavior in calcination is lacking of sufficient research, typically for low-cost calcium resource such as carbide slag. The Fe-modified and Mn-modified carbide slags for CaCO₃/CaO heat storage were synthesized and their optimum decomposition temperatures, effective heat storage conversions, heat flows and heat storage rates in endothermic stage were investigated. Although the Fe modification exacerbates the CaO sintering due to the formation of Ca₂Fe₂O₅, that is still effective in reducing the regeneration temperature of CaO in CaCO₃/CaO cycles. The Mn modification enhances significantly sintering resistance by forming the CaMnO₃ and its transformation into Ca₂MnO₄. The effective heat storage conversion of Mn-modified carbide slag after 30 cycles is 3.2 times as high as that of untreated carbide slag. Mn-modified carbide slag exhibits the lowest regeneration temperature and the highest heat storage rate after cycles. The loose and stable porous structure of Mn-modified carbide slag contributes to its superior endothermic performance. Therefore, Mn-modified carbide slag seems to be the potential candidate for calcium looping thermochemical heat storage.

Investigating the interaction between purge flow and main flow in gas turbines is crucial for optimizing thermal management, and enhancing aerodynamic efficiency. Measuring the high-speed rotating rotor poses challenges; however, employing the pre-swirl method to model rotational effect can facilitate experimental measurements. This study evaluates the validity of the pre-swirl method for modeling rotational effects. Numerical simulations are conducted under both stationary conditions, with seven swirl ratios, and rotational conditions. The investigation focuses on the underlying mechanisms of pre-swirl and rotation. Pre-swirl and rotation impart circumferential velocity to the purge flow relative to the blade, resulting in a diminishing effect on endwall cooling. On the other hand, pre-swirl reduces the adverse pressure gradient, and the rotation generates Coriolis forces acting on the passage vortex, both contribute to an increasing effect on endwall cooling. Under pre-swirl condition, the diminishing effect is dominant, while in rotational condition, neither the diminishing nor the increasing effect exhibits an overwhelmingly dominant trend.

With a broad range of application prospects, hydrogen fuel cell technology is regarded as a clean and efficient energy conversion technology. Nevertheless, challenges exist in terms of the safe storage and transportation of hydrogen. One proposed solution to this problem is the utilization of methanol on-line steam reforming technology for hydrogen production. In this paper, an integrated system for in-situ steam reforming of fuel coupled with proton exchange membrane fuel cells (PEMFC) power generation is proposed, and sensitivity analysis and exergy sensitivity analysis are conducted. Through the gradual utilization of waste heat and the integration of the system, fuel consumption is reduced and the power generation efficiency of the system is improved. Under the design operating conditions, the power generation efficiency and exergy efficiency of the system are achieved at 44.59% and 39.70%, respectively. This study presents a proven method for the efficient integration of fuel thermochemical conversion for hydrogen production with fuel cells for power generation, highlighting the advantages of complementary utilization of methanol steam reforming and PEMFC.

Supercritical carbon dioxide (SCO₂) centrifugal compressor is a key component of a closed Brayton cycle system based on SCO₂. A comprehensive understanding of the loss mechanism within the compressor is vital for its optimized design. However, the physical properties of SCO₂ are highly nonlinear near the critical point, and the internal flow of the compressor is closely related to its properties, which inevitably influences the generation of aerodynamic losses within the compressor. This paper presents a comprehensive investigation of the compressor’s loss mechanism with an experimentally validated numerical method. The real gas model of CO₂ embodied in the Reynolds-Averaged Navier-Stokes (RANS) model was used for the study. Firstly, the numerical simulation method was validated against the experimental results of Sandia SCO₂ compressor. Secondly, performance and loss distribution of the compressor were compared among three fluids including SCO₂, ideal CO₂ (ICO₂) and ideal air (IAir). The results showed that the performance of SCO₂ was comparable to IAir under low flow coefficient, however markedly inferior to the other two fluids at near choke condition. Loss distribution among the three fluids was distinctive. In the impeller, SCO₂ was the most inefficient, followed by ICO₂ and IAir. The discrepancies were magnified as the flow coefficient increased. This is due to a stronger Blade-to-Blade pressure gradient that intensifies boundary layer accumulation on walls of the shroud/hub. Furthermore, owing to the reduced sonic speed of SCO₂, a shock wave appears earlier at the throat region and SCO₂ encounters more intense boundary layer separation.

In this study, we perform a numerical investigation of a steady laminar stagnation flow flame stabilized at a wall with the consideration of heat transport, focusing on a lean hydrogen/air mixture with a fuel/air equivalence ratio 0.6. We discuss the NO emissions and their formation rates under various conditions, such as flow velocity and combustion pressure. It is found that the predominant reaction pathway for NO formation involves NNH radicals, though this changes near the wall surface. Beyond examining the wall’s influence on flame structures, the present work focuses on the impact of combustion process on materials. Specifically, the accumulation of atomic hydrogen at the wall surface is explored, which is significant for the consequent modeling of potential hydrogen embrittlement. Additionally, the growth rate of oxide layers on the material surface increases significantly if the combustion pressure and consequently the combustion temperatures are enhanced. These investigations offer valuable insights into how combustion processes affect material, which is useful for designing engineering components under high-temperature environments.

Thermally regenerative electrochemical cycle (TREC) is a novel and effective heat-to-electricity technology for harvesting low-grade heat. Currently, reported TREC analyses have been based on the Stirling cycle of ideal infinite heat source and infinite time for heat transfer. However, this will lead to inaccuracy when the scenario deviates from the ideal case. In this study, a systematic thermodynamic analysis on TREC is performed to address this problem. Based on different heat transfer situations, the description of thermodynamic processes and the corresponding mathematical models are established. At the same time, the TREC system, with the solar collector as the high-temperature heat source and the environment as the low-temperature heat source, is employed as a case. And the study delved into discrepancies arising from incongruences between the practical operational process and the traditional ideal analytical methodologies, along with an investigation of the different thermal environment impact on system performance. The findings suggest that the finite analysis method should be used when the actual operating time of the system is shorter than the desired equilibrium period. On the contrary, the use of the infinite analysis method, in this case, produces an error, the magnitude of which is directly related to the operating time, whereas when the time reaches 80% of the equilibrium time the error can be controlled to less than 2%. The influence of the heat source on the operating phase of the system is mainly in the temperature equilibrium and the rate of temperature equilibrium. This effect is proportional to the thermal capacitance and is also positively related to the system performance. Therefore, to improve system performance, it is recommended that a high-temperature heat source with a high ratio of thermal capacitance to system thermal capacitance should be selected and that the response time should slightly exceed the system equilibrium duration.

Supersonic wind tunnel experiment is one of the important measurements for developing advanced gas turbines, and supersonic multi-hole probes are sophisticated tools to measure pneumatic parameters in such experiments. However, shock waves form around the probe head in supersonic flow, which affect the accuracy of results. In this study, a supersonic five-hole probe is selected as the research object. Firstly, a compound five-hole pressure-temperature probe was designed and produced with 3D-printing technology. Then, the shock wave spectrum was numerically calculated by three methods, which were the Mach number, density gradient, and shock function; in contrast to the other two methods, the shock function could accurately identify the types and ranges of shock and expansion waves. The results show that a strong shock wave is formed at the front section of the probe head, and the shock wave generated around the pressure measuring tube affects the total pressure and Mach number of the flow field, which causes the increase of entropy. The intensity of the shock wave at the head of the pressure measuring tube is the largest, causing a decrease in the total pressure around the flow field. Afterwards, to reduce the calculation errors caused by neglecting the compressibility of gases and the entropy increase, a gas compression factor δ_s was introduced. It is proved that the error of the calculated pneumatic parameters is less than 5% and 10% in subsonic and supersonic condition, respectively, with the gas compression factor considered. The research results of this paper provide theoretical reference for the design and use of pneumatic probes during subsonic to supersonic flow.

The present study proposed a shaped sweeping jet (SJ) that possesses the merits of both SJ and shaped hole, which demonstrates significantly improved cooling effectiveness and anti-deposition performance. Compared to a classical 777 shaped hole, the shaped SJ exhibits a maximum enhancement of 70% in cooling effectiveness and a maximum reduction of 28% in particle deposition height, respectively. Owing to the periodic oscillation of coolant jet and higher streamwise jet momentum, the shaped SJ can provide much wider coolant coverage and therefore sweep the adhesive particle away from the wall. This study is the first attempt to reconcile the performance of film cooling and particle anti-deposition simultaneously, which offers a promising design concept for future engine cooling.

Numerical simulations of the flow and heat transfer characteristics of four shell-and-tube molten salt electric heaters with different perforation rates was conducted. Shell-and-tube electric heaters have the same geometry and tube arrangement, and all of them use single segmental baffles, but there exist four different baffle openings (φ), i.e., 0%, 2.52%, 4.06%, and 6.31%. The results indicated that the reasonable baffle opening could significantly reduce the shell-side pressure drop, effectively decreasing the shell-side flow dead zone area. They can eliminate the local high-temperature phenomenon on the surface of electric heating tubes, but the heat transfer coefficient is slightly decreased. All perforated schemes significantly reduce shell-side pressure drop compared to the baseline solution without open holes. In particular, the φ=6.31% scheme exhibits the optimal performance among all the schemes, with a maximum reduction of up to 50.50% in shell-side pressure drop relative to the unopened holes scheme. The heat transfer coefficient is the highest for φ=0%, exhibiting a range of 5.26% to 5.73%, 5.14% to 5.99%, and 7.31% to 8.54% higher than φ=2.52%, 4.06%, and 6.31%, respectively, within the calculated range. The composite index h/(Δp)^1/3 was higher for all open-hole solutions than that for the unopened-hole solution. The best overall performance was for φ=6.31%, which improved the composite index by 15.29% to 17.18% over the unopened-hole solution.

The exploitation of photovoltaic/thermal (PV/T) systems, which facilitate concurrent conversion of solar radiation into electrical and heat energies, presents substantial potential in the solar-abundant northwestern zone of China. This investigation endeavors to evaluate the efficacy of a micro heat pipe (M-HP) PV/T system via exhaustive experimental analysis conducted in Lanzhou. To improve the performance of M-HP-PV/T system, a comparison was made between the optimal angles for each day and the entire year. The system inside greenhouse exhibited an average photovoltaic conversion efficiency (PCE) and thermal conversion efficiency (TCE) of 12.32% and 42.81%. The system of external environment registered average PCE and TCE values of 12.99% and 21.08%. To further understand the system’s operational results, a mathematical model was constructed through the integration of experimental data, exhibiting good agreement between the simulated outcomes and empirical observations. The average solar irradiance of daily optimum angle was 728.3 W/m²; the annual optimum angle was 29° with an average solar irradiance of 705.6 W/m². The average annual total powers at the optimal angle outside the greenhouse and inside the greenhouse were 448.0 W and 398.7 W. The average annual total efficiencies at the optimal angle outside the greenhouse and inside the greenhouse were 40.8% and 56.9%. The total power in the greenhouse was lower by 49.3 W, while total efficiency in the greenhouse was higher by 16.1%.

Air source heat pump has insufficient heating performance under the low ambient temperature conditions;  meanwhile, the thermal storage device in heat pump system has a wide range of application. This study proposes a  thermal storage air source heat pump heating system (HSASHP) with a novel structure, and has established both the  mathematical models and simulation models of each component of the single-stage and the thermal storage air source heat  pump heating systems in MATLAB/Simulink respectively, with three operation modes proposed for the latter (i.e., the thermal storage air source heat pump heating system); by using the outdoor ambient temperature during the heating period in Baotou, China, the heating capacity of the two heat pump systems are simulated and the economy of both systems’ operation are investigated. The results show that within a 7-day heating period, the total heat production of the thermal storage heat pump unit and the single-stage heat pump unit is 442.58 kW·h and 355.68 kW·h, respectively, with HSASHP 24% higher; the average heating Coefficient of Performance (COP) of the two heat pump units is 2.11 and 1.51, respectively, with HSASHP 39.74% higher; the power consumption of the two heat pump units is 202.74 kW·h and 239.74 kW·h, respectively, with HSASHP 15.44% lower. These all illustrate the effectiveness of the new structure in improving the performance of heat pump units. However, the total power consumption and operational economy of both air source heat pump heating systems do not differ significantly.

As the total amount and share of new energy installed capacity continue to rise, the demand for flexible regulation capability of the power system is becoming more and more prominent. The current conventional molten salt energy storage system has insufficient peaking capacity. A solar-molten salt energy storage system based on multiple heat sources is constructed in this study. The heat generated from the solar field and the steams are used for the peaking process to further enhance the peaking capacity and flexibility. The installation multi-stage steam extraction and the introduction of an external heat source significantly improve the system performance. The simulation models based on EBSILON software are developed and the effects of key parameters on performance are discussed. The feasibility of the proposed system is further evaluated in terms of exergy and economy. The results demonstrate that the proposed SF-TES-CFPP (solar field, thermal energy storage system, coal-fired power plant) system exhibits the enhancement of peaking capability and flexible operation. In comparison with the conventional TES-CFPP, the integration of solar energy into the peaking process has enabled the SF-TES-CFPP system to enhance its peaking capacity by 20.60 MW while concurrently reducing the coal consumption rate by 10.26 g/kWh. The round-trip efficiency of the whole process of the system can be up to 85.43% through the reasonable heat distribution. In addition, the exergy loss of the principal components can be diminished and the exergy efficiency of the system can be augmented by selecting an appropriate main steam extraction mass and split ratio. The economic analysis demonstrates the dynamic payback period is 9.90 years with the net present value (NPV) across the entire life cycle reaching 1.069 02×10⁹ USD.

The rapid expansion of data centers has significantly increased energy consumption, with cooling systems accounting for about 40% of total use. Utilizing natural ambient cooling sources provides a simple and effective approach to enhancing energy efficiency. Radiative cooling (RC), though an emerging solution that can considerably reduce energy use, faces challenges in data centers due to the complex, multi-level nature of cooling systems, requiring careful adaptation across different scales, which hinders its widespread adoption in data centers. In this study, we designed radiative coolers for data center cooling systems to enhance efficiency, and then proposed an RC system integrating these structures and analyzed its energy-saving performance. The cooling properties of a real radiative cooling film applied to the cooler surface were experimentally tested, and the data were used for the simulation analysis of the proposed coolers. Five different radiative cooler structures were designed and optimized, and we conducted a comprehensive multi-level performance analysis of the optimized structures, including operational parameters such as flow rate and temperature, as well as the impact of location, climate, and regional adaptability. Subsequently, a novel hybrid cooling system incorporating radiative coolers for data centers was proposed. Comparative studies across different climate zones in China demonstrated that this hybrid system delivers substantial energy savings compared to traditional vapor-compression systems. Results showed that in Beijing, Urumqi, and Guangzhou, the annual temperature difference between the inlet and outlet of the radiative cooler ranges from 2.40°C to 3.28°C, making it feasible for radiative cooling throughout the year in most parts of China. The annual Power Usage Effectiveness (PUE) in Beijing using the novel RC system is 1.19, with an increase in Energy Efficiency Ratio (EER) of 60.74%. This study may contribute to the development of green, energy-efficient cooling technologies for future data centers.

The inferior flammability of coal gasification fine slag (CGFS) from entrained-flow gasifiers hampers its resourceful utilization. However, the reasons behind its poor flammability still need to be investigated. This paper conducted a comparative study on the combustion characteristics of three CGFS samples: CGFS_GSP, CGFS_SN, and CGFS_OMB (subscripts GSP, SN, and OMB representing different gasification processes), using experimental techniques such as TG/DTG and combustion kinetic model fitting methods. Additionally, a comprehensive investigation into the physicochemical properties of CGFS was conducted. The objective was to elucidate the causes behind the poor flammability of CGFS. The results revealed that CGFS exhibits lower volatile matter content and higher activation energy than their corresponding raw coal (RC), leading to a significantly higher ignition temperature. The ignition temperatures of RC1, RC2, and RC3 are 361.82°C, 378.66°C, and 404.99°C, respectively. In contrast, the ignition temperatures of CGFS_GSP, CGFS_SN, and CGFS_OMB are 549.08°C, 566.58°C, and 532.67°C, respectively. During the combustion reaction, the temperature (T_max) at which CGFS reaches its maximum weight loss rate is significantly higher than the temperature (T_maxIII) at which fixed carbon in raw coal reaches its maximum weight loss rate. The T_maxIII of RC1, RC2, and RC3 are 450.90°C, 457.19°C, and 452.77°C, respectively. In contrast, the T_max of CGFS_GSP, CGFS_SN, and CGFS_OMB are 583.55°C, 608.20°C, and 582.18°C, respectively. The maximum weight loss rate of different types of CGFS is also significantly lower than the fixed carbon combustion maximum weight loss rate of their respective raw coal samples. The physicochemical characterization results of CGFS demonstrate that, compared to the corresponding raw coal, there is a significant reduction in the proportion of active sites in CGFS. Simultaneously, the proportion of C-C/C-H on the surface of residual carbon in CGFS decreases. In contrast, the proportion of O=C-O significantly increases, suggesting a shift toward a more stable state of carbon-containing functional groups. This study is expected to offer essential theoretical support for the efficient combustion utilization of CGFS.

Metal foam promotes the heat transfer of phase change materials (PCMs) in the penalty of reducing the energy storage density of the composite PCMs. In this work, the effects of constant porosity (0.96, 0.94, 0.92, or 0.90) and pore density (PPI) of metal foam on heat transfer of composite PCMs are studied. Melting rate could be enhanced by employing with low porosity copper foam. Furthermore, aiming to the right bottom phase changing “dead region”, a regionalized enhancement strategy of cascaded metal foams is introduced. The dynamic melting performances of all the composite PCMs are comprehensively analyzed. The results reveal that the cascaded configuration is beneficial for optimization. Details show that the horizontal strategy enhances melting performance: a maximum of 17.98% reduction in total melting time could be reached when the rear part porosity is 90%. The energy storage density rate could be raised by 5.48%. Besides, the vertical strategy performs with a better average temperature uniformity of 0.441 and brings a lower temperature in the heated wall. To sum up, the regionalized enhancement of copper foam provides better performance in the phase change process. It shows significant potential for solar heat storage and thermal protection.

Axial overlap (AO) and percent pitch (PP) are considered as key position configuration parameters that affect the tandem cascade performance. The objective of the current study is to investigate the optimal design criteria for these two parameters in tandem cascades of subsonic highly-loaded two-dimensional compressors. Before that, the influence mechanisms of AO and PP are explored separately. Research results show that higher PP is beneficial for decreasing rear blade (RB) load, but an invalidity of gap flow occurs when it approaches 1. The change in AO has an influence on the adverse pressure gradient of the front blade (FB), and it also affects the gap flow strength and FB wake development. Then, the optimal design criteria for AO and PP are obtained in a large design space, which clarifies the matching relationship of the two parameters at different operating conditions. The best global range of AO is about –0.05 to 0.05 while PP is between 0.85 to 0.92, and PP should be smaller to avoid performance degradation as AO increases. According to the fault tolerance in practical applications, PP should be closer to the lower bound to ensure that the deterioration boundary is wide enough.

Turbulent agglomeration is viewed as a promising technology for enhancing fine particle removal efficiency. To better understand particle transport, agglomeration behaviors, and fluid-particle interactions, we numerically explored these phenomena under cylindrical vortex wake influence using a coupled large eddy simulation and discrete element method (LES-DEM) approach. The validity of the LES approach was verified by comparison with available direct numerical simulation (DNS) results. We adopted the Johnson-Kendall-Roberts (JKR) contact model for particle-particle interactions. The particle dispersion and agglomeration characteristics of particles with different diameters (d_p=2–20 μm) in the laminar and transition of shear layer (TrSL) flow regimes were analyzed. Fine particles were concentrated at the vortex centers, while larger particles accumulated around the vortices. The agglomeration efficiency exhibited an M-shaped profile spanwise (y-direction). With increasing Reynolds number, the agglomeration efficiency and turbulence intensity improve. The particle agglomeration efficiency peaks at a certain Reynolds number. However, at higher Reynolds numbers, reducing the residence time of particles in the flow field decreases the agglomeration efficiency.

As one of the hottest components of gas turbine, the blade tip is difficult to be cooled down for the complexity flow field in the tight tip clearance. The blade tip protection requires advanced tip structures. To develop new structures, the effect of ribs on blade squealer tip aerothermal performance and cooling performance were investigated. Ribbed squealers tips (1R, 2R and 3R, compared to the Basic case) were designed and their cooling ability under five coolant blowing ratios (M) were measured by the Pressure Sensitive Paint (PSP) technique, taking film cooling effectiveness (η) as the criterion. Numerical method was validated and then was adopted to analyze the flow field and aerodynamic loss in the tip gap. The results indicated that the cooling coverage and η increase with M for sufficient coolant supply. Compared to the Basic case, the η on the middle section is higher while that on the trailing part is lower for the ribbed squealer tips. The flow field analysis showed that the coolant flows downstream to the trailing edge in the Basic case, bringing additional cooling protect to the downstream region. The ribs induce vortices behind them to involve the local and upstream coolant and prevent upstream coolant from flowing down, leading to the improvement in the local and the degradation in the downstream for the film cooling performance. The aerodynamic results pointed out that the ribbed squealer tips are superior to the Basic case in terms of the aerodynamic performance, even though the tip leakage mass flow of these cases are larger than that of the Basic case. The maximum reduction on pressure loss coefficient is 16.2% for the ribbed squealer tip.

Paraffin (PA) is a common phase change material, which is widely used in battery thermal management systems (BTMS) because of its high latent heat and temperature uniformity, simple system structure, and no increase in battery energy consumption. In this work, sulfur-free expanded graphite (EG) is prepared by oxidation intercalation without H₂SO₄ in the preparation process, which avoids the harm to devices caused by the S element. The sulfur-free EG exhibits a high expanded volume of 324 mL·g^–1, which can adsorb PA well to prevent leakage. When the mass filling ratio of EG is 5.0%, EG/PA-5.0 composite films show high latent heat of phase transition (253.08 J·g^–1), and thermal conductivity (2.56 W·m^–1·K^–1). EG/PA films are attached to the external surface of the lithium iron phosphate battery for a heat dissipation performance test. When the discharge rate is 1C at room temperature, the surface temperature and maximum temperature difference between temperature measurement points of the battery with EG/PA-5.0 film are 32.1°C and 1.2°C. After charge-discharge at 1C for 100 cycles, the thermal properties of EG/PA remain basically unchanged, and it has good cycle stability. The simulation results are in good agreement with the actual temperature changes of the battery at different discharge rates. This work indicates that sulfur-free EG/PA composite has a good application prospect in BTMS of the power batteries.

To address the complex spatiotemporal characteristics of impeller axial clearance leakage flow in a liquid-ring vacuum pump, plasma actuation with radial centripetal, circumferential reverse, and counter discharge layout types was designed to control the leakage flow. The regulation effects and interference mechanisms of plasma actuation on clearance leakage flow were explored. The results show that under plasma flow control of the three layout types, the vacuum degree of the pump changes not obviously, but the shaft power is reduced and the efficiency is improved to a certain extent. Among them, the circumferential reverse has a more obvious control effect on the hydraulic performance of the pump and has more advantages in controlling the medium- and high-intensity leakage flow in the compression zone, while the radial centripetal has a more effective control effect on the low-intensity leakage flow in the transition zone. All three layout types of plasma actuation can effectively weaken the medium-intensity leakage flow near the beginning of the compression zone, but their suppression effect on the high-intensity leakage flow near the end of the compression zone is weak. Due to the weak leakage in the transition region, the plasma actuation induced airflow and low-intensity leakage flow are coupled with each other, which will further aggravate the complexity and variability of the flow in the clearance. For unsteady clearance leakage flow, the circumferential reverse has a more stable control effect. About the control of medium-intensity leakage flow, the radial centripetal plasma actuation effect is better than the circumferential reverse. The research results can provide theoretical and methodological references for the performance optimization of liquid-ring vacuum pumps.

In this study, a three-dimensional numerical investigation was conducted on the front and rear fans of a three-bypass variable cycle engine under various speeds and internal bypass conditions. The impact of internal bypass conditions and speeds on the matching characteristics of the front and rear fans, as well as the factors limiting the variation of bypass ratio, are summarized. The findings reveal that for near stall, design point, and near choke internal bypass conditions, the operating point of the front fan tends to move towards near-stall while that of the rear fan moves towards near-choke when increasing external bypass back pressure. At design speed, external bypass blockage is identified as a limiting factor for increasing the bypass ratio at the internal bypass design point. Additionally, blockage caused by a significant amount of low-energy fluid at the suction surface of the rear fan stator leads to rear fan stall which limits further increase in bypass ratio at external bypass near stall condition. Similarly, leakage flow overflow passage at the top section of first stage rotor blade in front fan results in front fan stall, which restricts decrease in bypass ratio at internal bypass near stall condition. As corrected speed decreases, there is an upper-left shift observed in the curve depicting variation in relative back pressure with respect to change in bypass ratio due to the phenomenon “pre-surge and post-choke”. This indicates increased air flow into external bypass resulting in higher values for lower speeds. Furthermore, limitation on further increase in bypass ratio at external bypass near stall condition with decreasing speed can be attributed to transition from rear fan stall to external bypass blockage.

Channel structure has a significant effect on the heat transfer performance of PCHE. In this study, a set of rectangular straight channel PCHEs with different cross-section aspect ratios had been tested on S-CO₂ heat transfer experimental platform, the effect of mass flow rate in both cold and heat sides, as well as the cross-section aspect ratio of the rectangular straight channel, on the heat transfer performance of PCHE was investigated. The results show that the comprehensive heat transfer performance of the rectangular cross-section is better than that of the semicircular cross-section; increasing the aspect ratio can improve the comprehensive heat transfer performance of PCHE, but the strengthening effect diminishes as the aspect ratio increases. Increasing the mass flow rate on both sides not only enhances the pre-cooler’s cooling capacity and heat transfer, but also raises the pressure drop. In addition, an improved heat transfer correlation for rectangular cross-section PCHE was proposed, considering the effects of cross-sectional aspect ratio and pseudo-critical temperature is proposed in the range of Re from 3169 to 48 474 and Pr from 0.98 to 12.5, the fitted results better predict the local Nu and f magnitudes and trends in the pre-cooler under different cooling conditions, outperforming the simulated data and Gnielinski and Blasius correlation.

In this work, the interactions between the environmentally friendly refrigerant propane (R290) and Polyol Ester (POE) including solubility parameters, diffusion coefficients, binding energies, and radial distribution functions were investigated using molecular dynamics (MD). Specifically, the effect of chain length of Pentaerythritol esters (PEC) as the representative component of POE on the interaction of PEC/R290 was discussed. The solubility parameters difference exhibits the PEC and R290 are more easily miscible as increasing chain length of PEC, and there is plateau as the chain lengths is above 8 units. In addition, it was also found that solubility parameters are various for the isomers due to the different spatial structure. Moreover, the presence of PEC would reduce the diffusion coefficient of R290 in the mixed system of R290/lubricant with the reduction of 20% on average. It is also found that van der Waals forces are dominant in the R290/PEC system. The PEC molecules start to be bound to the H atoms of R290 at the first neighbor shell layer with a radius of 0.219 nm. Finally, the molecular simulation model of POE22 considering various actual components was innovatively developed. The results showed that the solubility of R290 with typical POE lubricant is affected by the composition and proportions of based oil and additives.

Tubular moving bed heat exchangers (MBHEs) present inherent advantages for efficiently and stably recovering sensible heat from high-temperature granular bulk. In this study, we introduce a viable and practical approach based on the combined approach of Computational Fluid Dynamics with Discrete Element Method (CFD-DEM) and employ it to conduct a comprehensive investigation into the effects of operation parameters on tubular MBHEs. These parameters include inlet particle temperature (ranging from 500°C to 700°C), tube wall temperature (ranging from 50°C to 250°C), and particle descent velocity (ranging from 0.5 mm/s to 12 mm/s). Our analysis reveals that the heat radiation and gas film heat conduction predominantly govern the heat transfer process in the particle-fluid-wall system, collectively contributing to approximately 90% of the total heat flux of tube wall (Q_w^simu). The results indicate that increasing the inlet particle temperature and reducing the tube wall temperature intensify heat transfer by enlarging the temperature difference. More interestingly,   Q_w^simu exhibits three distinct stages as particle descent velocity increases, including an ascent stage, a descent stage, and a stable stage. Furthermore, the simulation attempts suggest that the optimal descent velocity for maximizing Q_w^simu  falls within the range of 1.3–2.0 mm/s. These findings not only uncover the precise influence mechanisms of operation parameters on heat transfer outcomes but also offer valuable insights for heat transfer enhancement efficiency in MBHE system.

The supercritical carbon dioxide (sCO₂) Brayton cycle system has become an emerging and highly promising method of thermal power conversion due to its efficiency advantage, system compactness, and excellent adaptability of the heat sources. For the low carbon sCO₂ Brayton cycle testbed with cycle output power approaching 3 MW, a relatively detailed dynamic simulation model of the entire system is constructed to explore the dynamic response characteristics of the system with different startup strategies and different buffer tank volumes during the startup process. The simulation results indicate that the smaller the volume of the buffer tank, the more rapid and obvious the parameter fluctuation in the buffer tank during the startup. Assuming the allowable relative deviation limit of density is 5%, then the ratio of the buffer tank volume to the volume of the entire closed loop should not be lower than 36.80%. The strategy of simultaneous temperature and speed increase during turbine bypass start can effectively reduce the fluctuation of compressor inlet parameters and reach the steady-state more quickly. This paper provides the recommended matching table for the opening of the turbine bypass valve (TBV) and the main regulating valve (MGV) to reduce the parameter fluctuation during the bypass switching. The effectiveness of the proposed turbine bypass and bypass switching startup strategy is verified by simulation, which may be used as a reference for test bench’s future debugging and operation.

Experimental and numerical investigations have been carried out on the effects of multi-swirl interaction patterns on self-excited unstable combustion characteristics based on a five-nozzle can combustor. The multi-swirl interaction patterns include equal swirl intensity interaction and strong-weak swirl interaction. The thermo-acoustic instability characteristics indicate that increasing the central nozzle swirl intensity transforms the interaction pattern from equal swirl intensity interaction to strong-weak swirl interaction, which can significantly weaken the thermo-acoustic coupling effect under low equivalence ratio conditions, and substantially reduce the dynamic pressure amplitude during unstable combustion. The instantaneous flame structures show that the multi-swirl flames exhibit chaotic oscillations under low equivalence ratio conditions. With equivalence ratios greater than 0.71, a clear flame interaction boundary appears, and the flames can exhibit periodic oscillations in a regular structure. However, different interaction patterns result in the completely different phase oscillations in the central and outer flames. The time-averaged flame structures also indicate that strong-weak swirl interaction leads to an increase in the flame angle and a decrease in the flame length for both the central and outer flames, and the variations in the flame angle and length have great impacts on the thermo-acoustic instability mode. The fuel-staging combustion characteristics demonstrate that the instability combustion conditions with a dominant frequency of 100 Hz are greatly broadened by the strong-weak swirl interaction pattern, and the overlapping operating conditions between this mode and other modes are greatly increased. This implies that it is more flexible to adjust the thermo-acoustic unstable mode, which is conducive to the passive suppression of thermo-acoustic instability.

Preheating combustion/gasification technology enables efficient and environmentally friendly utilization of coal resources, but the research on the flow and reaction characteristics of high-temperature gas-solid mixed fuels produced by the technology still needs to be further explored. The flame can intuitively show the jet, mixing and reaction of fuel and oxidant at the outlet of the burner. Therefore, this study investigates the jet flame characteristics of high-temperature gas-solid mixed fuels on a self-designed test platform. High temperature and gas-solid mixing are the special features of the fuel in this study, which are different from other studies. Therefore, we first qualitatively compare the jet flame characteristics of high-temperature gas-solid mixed fuel with traditional fuel. The preliminary results indicate that high-temperature gas-solid mixed fuels exhibit higher reactivity and a faster reaction rate compared to pulverized coal. As a result, it shows different characteristics in flame shape, ignition delay and ignition mode. The jet flame shape of high-temperature gas-solid mixed fuels closely resembles that of the pulverized coal group combustion flame, displaying a continuous cloud-like structure similar to the shape of a gas-fueled flame. Furthermore, the flame image does not show any significant ignition delay phenomenon. Building upon these results, this study also quantitatively analyzes the geometric parameters, temperature distribution and oscillation frequency of the high-temperature gas-solid mixed fuel jet flame under different secondary air equivalence ratios and primary air equivalence ratios, so that we can have a deeper understanding of the influence of operating parameters on the combustion/gasification process.

Upstream blade wake turbulence fluctuation may affect compressor blade forced response caused by wake sweeping. In order to investigate the effect of wake turbulence fluctuation and predict the blade vibration more accurately, this paper proposes a forced response calculation model that considers the excitation of upstream blade wake turbulence fluctuation on the basis of the conventional forced response calculation method. Using a three-stage axial compressor as the research subject, a quasi-three-dimensional large eddy simulation is conducted using the blade profile at 77.8% of the span of the inlet guide vane. Analysis of the flow field around the inlet guide vane indicates noticeable total pressure fluctuation in the wake of the inlet guide vane. The influence of upstream wake turbulence fluctuation is incorporated into the forced response calculation model in the form of total pressure fluctuation to obtain more accurate excitation forces. Specifically, the relationship between the amplitude of total pressure fluctuation and total pressure loss is established according to the results of large eddy simulation, and different formulas are set according to the position zoning of suction surface and pressure surface. Computational results show that, if only wake sweeping is considered, the maximum amplitude is 27% lower than the test result. However, when wake sweeping and wake fluctuation are considered, the calculated result better matches the test result, with only a 6% reduction compared to the test result. The results confirm the effectiveness of the proposed model.