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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

The impact of turbine guide vanes on a three-dome combustor’s lean blowout limit and blowout process was experimentally investigated. The parameters studied include the presence of the turbine guide vanes or not and the blockage ratio of turbine guide vanes. It is shown that the presence of turbine guide vanes and an increase in the blockage ratio increase the lean blowout fuel-to-air ratio. From the images of flame spontaneous emission captured by the high-speed camera, the coupling of the combustor with turbine guide vanes can alter the sequence of the blowout among the three domes, and localized tiny flame lumps have been observed to develop into larger flames during lean blowout. However, flames within the combustor are established independently near blowout, and no reignition is observed. Furthermore, the turbine guide vanes have been found to shorten the duration of the blowout process and enhance the likelihood of blowout by increasing the lean fuel-to-air ratio.

Non-Fourier heat conduction models are extended in response to heat transfer phenomena that cannot be accurately described by Fourier’s Law of heat conduction. This paper provides a review of heat conduction in functionally graded materials (FGMs) employing non-Fourier models. FGMs are designed materials with a gradual transition in composition, microstructure, or thermal conductivity throughout their volume. The spatial variation in thermal conductivity can lead to deviations from Fourier’s Law, resulting in non-Fourier heat conduction behavior in certain situations, such as at very short time scales or in materials with high thermal conductivity gradients. Researchers utilized various models, such as, Cattaneo-Vernotte, parabolic two-step model, hyperbolic two-step, phonon kinetic, dual-phase lag, and three-phase lag models to describe non-Fourier heat conduction phenomena. The objective of this review is to enhance the understanding of non-Fourier heat transfer in FGMs. As a result, the analytical studies conducted in this particular area receive a greater emphasis and focus. Various factors affecting non-Fourier heat conduction in FGMs including gradient function, material gradient index, initial conditions, boundary conditions, and type of non-Fourier model are investigated in various geometries. The literature reviews reveal that a significant portion of research efforts is centered around the utilization of dual phase lag and hyperbolic models in the field of non-Fourier heat conduction within FGMs. 

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 triple spark ignition scheme was first designed on a three-cylinder 1.5-L dedicated hybrid engine (DHE). On this basis, the effect of different ignition modes on engine combustion and emission characteristics was studied, especially under high dilution condition. The results tested at 2000 r/min and 0.8 MPa BMEP (brake mean effective pressure) show that with highly increased in-cylinder flow intensity, using only passive prechamber (PPC) has a lower lean limit than that with single central spark plug (CSP), thereby leading to slightly higher minimum fuel consumption and nitrogen oxides (NO_x) emissions. Adding side spark plugs (SSP) based on PPC can result in improved capability of lean limit extension and engine performance than CSP. However, the improvement level is lower than that with triple spark plugs (TSP). As the excess air ratio λ increases, the advantage of PPC and PPC with SSP in improving the combustion phasing compared with CSP gradually weakens. Correspondingly, the increasing tendency of their ignition delay and combustion duration is more obvious. The added SSP based on PPC can effectively shorten the ignition delay of leaner mixture, but the combustion duration can be only slightly improved. As a result, under extremely lean condition, the advantage of PPC and PPC with SSP in terms of combustion characteristics over CSP becomes much smaller. In contrast, the TSP ignition can achieve much shorter ignition delay and combustion duration simultaneously under this condition. Due to the highest available dilution level, the TSP ignition achieves the lowest raw NOx emissions. Moreover, it can also reduce the raw carbon monoxide (CO) and hydrocarbons (HC) emissions compared to CSP due to a more thorough combustion of the end gas mixture. Based on the excellent performance of TSP, the highest engine brake thermal efficiency (BTE) was further explored. The results show that with normal RON 92 fuel, the engine finally achieved 43.69% and 45.02% BTE under stochiometric mode with exhaust gas recirculation (EGR) and lean-burn mode respectively. When using RON 100 fuel, the highest BTE was further increased to 45.63% under lean-burn mode.

Cold sintering as a new technology for the fabrication of ceramic composites could overcome the shortcomings of traditional high temperature sintering approach and achieve dense structure in the composite at a relatively low temperature (<200°C). In this work, a shape stabilization phase change composite is fabricated and investigated by dint of such new fabrication approach, in which a mixed nitrate salt of NaNO₃-KNO₃ is used as phase change material and magnesia powder is acted as structure skeleton. Using of deionized water as sintering additive, the effects of sintering agent content, sintering temperature, uniaxial pressure and time on the composite microstructure characteristics and macroscopic properties are evaluated. The results show that the liquid salt could be effectively accommodated in the magnesia skeleton, forming a dense and stable structure in the composite. There is existence of optimal cold sintering parameters at which a benign combination of mechanical strength and thermal cycling performance could be attained in the composite. Under the sintering temperature of 150°C, duration time of 8 min, uniaxial pressure of 150 MPa, and water mass content of 7%, the fabricated composite exhibits a heat storage density of 610 kJ/kg at its potential utilization temperature range of 30°C–580°C and a compressive strength over 240 MPa with a dense density higher than 98%, demonstrating that it can be a viable alternative used in thermal energy storage domains.

The green transition of power systems relies on the accurate measurement of the economic cost associated with the deep peak-shaving process in coal-fired power plants. To evaluate the variation in the coal consumption rate during low-load operation, a model of a 300 MW coal-fired unit was established, with less than 1% deviation from the actual operation value. The results indicate that the coal consumption rate at 20% load can increase to 1.48 times the full-load value. When the excess air coefficient is reduced by 0.3 at low-load conditions, between 40% and 20% load, the exhaust gas temperature is reduced by approximately 5°C, leading to a decrease in the coal consumption rate. In addition, elevating the steam temperature to the design value can reduce the coal consumption rate by 6% to 13%, and increase the inlet temperature of Selective Catalytic Reduction (SCR) process by 10°C. Improving the turbine efficiency during peak-shaving significantly reduces the coal consumption cost, and the enhancement of the mean steam temperature is an efficient approach. This study offers a theoretical reference for the retrofitting, design and economic operation of coal-fired units in peak-shaving, thereby supporting energy system transitions.

The effect of different fuel mixtures (C₂H₂, C₃H₆, C₃H₈, C₂H₂+C₃H₆, C₂H₂+C₃H₈) on the acceleration of the gas detonation flame under the same detonation tube gun structure has been studied using numerical simulation. The trends of the internal parameters of the gun, as well as the variations of the gas flow velocity, temperature and pressure at the gun outlet with time were analyzed. At equivalence ratio of 1, the simulation results demonstrate that acetylene fuel produces the shortest detonation time and reaches the highest average gas flow velocity of 1031.6 m/s at the gun exit, and the acetylene detonation reaches the highest average temperature of 2750.6 K. The fastest speeds of OH and other parameters were produced by the detonation of C₂H₂ and its mixture fuels, which represents the fastest flame propagation. Propane detonation at the outlet of the gun to reach the maximum pressure of 0.66 MPa; internal to the gun, detonation of CO₂ produced by the majority of the distribution of the wall region. Different fuel compositions lead to variations in the detonation spray effects, and altering the fuel composition can meet diverse requirements for detonation and spray particle characteristics.

The junction film cooling has been proposed to deal with the situation of insufficient film cooling performance under limited coolants. Numerical investigations are performed for baseline case and four junction film hole cases (3_junction, 4_junction, 5_junction and 6_junction cases) at the coolant mass flow rate varying from 0.0016 kg/s to 0.0064 kg/s. From the results, due to the expanded film hole exit and the interactions between branch film jets, junction film hole cases can suppress the “injection phenomenon” of film jet and the “entrainment effect” of mainstream, thus to improve film cooling performance, especially the film spanwise coverage. By comparison, under low coolant mass flow rate, the 5_junction case can generate the most obvious film cooling performance improvement. To be specific, at the coolant mass flow rate of 0.0016 kg/s, it achieves 76.92% improvement in area-averaged adiabatic film cooling effectiveness, and at the coolant mass flow rate of 0.0032 kg/s, the improvement is up to 703.85%. Through flow loss analysis, the results show that at low coolant mass flow rate, the junction film hole cases improve film cooling performance and pay a little cost of pressure loss; but under high coolant mass flow rate, they can improve film cooling performance and reduce total pressure loss concurrently. Among them, the 5_junction case generates the lowest total pressure loss coefficient; corresponding to the coolant mass flow rate of 0.0048 kg/s and 0.0064 kg/s, it decreases by 15.90% and 41.58% respectively. Through this study, the junction film cooling for improving cooling performance is provided, which is conducive to further raising turbine intake temperature, thereby improving the kinetic and thermodynamic properties of gas turbines.

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.

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 improvement of composite phase change materials in energy storage density and thermal conductivity is significant for the efficient use of energy. This study proposed novel composite materials based on forsterite with high specific heat as matrix materials, chloride salts (NaCl-KCl) with high latent heat as phase change materials and SiO₂ nanoparticles as fillers. The results indicated that forsterite and chloride salts exhibited excellent chemical compatibility, and the composite materials containing 40% (in weight) chloride salts achieved an energy storage density of 882.5 J/g within the range of 100°C to 800°C, a latent heat of 108.1 J/g, and a thermal conductivity of 0.68–0.81 W/(m·K) at 300°C–500°C. Furthermore, the addition of SiO₂ enhanced the thermal conductivity and energy storage density of composite materials due to the formation of unique nanostructures. More importantly, the removal of structural water during heat-treatment process resulted in the formation of micropores and increased specific surface area of forsterite particles, which facilitated the adsorption and stabilization of molten chloride salts. Combined with the stabilization effect of forsterite and synergistic effect of SiO₂ nanoparticles, the obtained composite materials with 2.0% (in weight) SiO₂ nanoparticles exhibited good thermal stability with 1.80% weight loss and 2.34% reduction in latent heat after 150 cycles, indicating a promising application in high-temperature thermal energy storage.

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.

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.

The influence of partitioned profiling design based on a large-pitch highly loaded cascade is studied by numerical simulation. The partitioned profile is mainly composed of a pressure-side convex structure near the leading edge and a suction-side convex structure at the midstream and downstream sides of the passage. The influence of the change in the vertex axial position and peak value of the B-line on the secondary flow control is analyzed. In this paper, air (ideal gas) is selected as the flow media. The average static pressure at the outlet and the average total temperature at the inlet are kept constant. SST γ-θ is used as the turbulence model. The results show that the pressure-side convex structure suppresses the spanwise and pitchwise migration of the inlet flow by adjusting the static pressure distribution of the flow field, so the development of the pressure-side leg of the horseshoe vortex is effectively limited. The suction-side convex structure adjusts the static pressure distribution of the flow field and increases the included angle between the cross-flow and suction surface, so the accumulation of low-momentum fluid, the development of a corner vortex and the flow separation at the trailing edge of the suction-side surface are all suppressed near the endwall-suction corner. Consequently, the energy loss coefficient of the large-pitch highly loaded cascade is decreased from 0.0564 to 0.0485, representing a 25% reduction in secondary flow losses.

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.

During data center operation, it generates a significant volume of low-grade waste heat. To recover waste heat, a coupled system including solar collector, double effect absorption refrigeration and organic Rankine cycle is proposed. The system performance is analyzed in detail. For the organic Rankine cycle, five organic working fluids (R245fa, R245ca, R123, R11, and R113) are selected. R245fa, R113 and R245ca obtain the maximum net power output, thermal efficiency and exergy efficiency, respectively. In the double effect absorption refrigeration system, the evaporation temperature, condensation temperature, and generation pressure affect the COP and exergy efficiency. When the generator pressure is unchanged, the COP increases with increasing evaporation temperature and decreasing condensation temperature. When the COP reaches 1.3, the COP slightly decreases as the evaporation temperature or condensation temperature changes. Similarly, the exergy efficiency of refrigeration systems exhibits the same trend as the COP, and the exergy efficiency maximum value appears at approximately 0.32. A new performance indicator, rPUE, was defined to evaluate the data center power utilization efficiency. The flow distribution ratio and heat source temperature were optimized with multi-objective optimization. When the mass flow distribution rate is 0.6 and the heat source temperature is 441.5 K, rPUE and the total unit production costs of the system obtain the optimal solution.

The asymmetry of the multi-orifice spray will cause uneven heat load of the marine diesel engine, thereby affecting its working performance and service life. Therefore, an in-depth understanding of the spray and flame characteristics of multi-orifice nozzles will guide the optimization of the nozzle structure, needle design and diesel atomization and combustion process. For this reason, four groups of dual-orifice nozzles with different hole diameters (0.1–0.55 mm) and mass flow rates covering the typical marine medium-speed diesel injections are designed and customized, and the constant volume chamber (CVC) with high temperature and pressure is used to simulate the actual in-cylinder working conditions of the diesel engine for the spray visualization experiment. To study the asymmetry of the fuel sprays discharged from a diesel injector, the multi-orifice nozzle is simplified as a dual-orifice nozzle in this study. Combined with X-ray Computed Tomography (CT) imaging technology, the influences of the nozzle internal structure on the spray and flame asymmetry are studied in the constructed supercritical environment. It is found that the asymmetry of the inlet angle and the equivalent length-diameter ratio is positively correlated with the inconsistency of the dual sprays. With an increase in the injection pressure and nozzle diameter, the asymmetry of the dual spray becomes more pronounced, resulting in greater disparities in the ignition delay times and ignition positions of the two sprays. Moreover, the increase in nozzle diameter also leads to combustion instability, resulting in a flame with a serrated appearance. With the increase of ambient temperature, the proportion of liquid phase in the jet decreases and the relative density of spray front decreases.

The paper utilizes a combination of entropy production theory and numerical simulation to analyze the energy dissipation of Francis turbines. The distribution law of local entropy production rate (LEPR) in various components of hydraulic turbines is explored under different operating conditions. A detailed examination of hydraulic losses within the Francis turbine reveals that the primary contributors are the runner and draft tube, with comparatively smaller losses occurring in the spiral casing and guide vane areas. The study further explores the formation reasons behind these losses. Within the runner area, the LEPR mainly concentrates in the inlet area of the blade channel, as well as the pressure and suction surfaces of the runner blades. The main reason for hydraulic losses in the runner area is the movement of vortex structures in the blade channel. Within the draft tube area, the hydraulic losses mainly occur on the walls of the straight cone section and the elbow section. There is a backflow phenomenon in the draft tube, which is the main reason for hydraulic losses in the draft tube area. This article can provide a certain theoretical reference for exploring the influencing factors of hydraulic losses in hydraulic turbines.

The present work aims to provide preliminary support and research foundation for developing integrated technology of CO₂ utilization and tar-rich coal pyrolysis to produce high-value chemicals and fuels. The chemical properties of tar produced by tar-rich coal pyrolysis under traditional N₂ and N₂/CO₂ atmospheres were investigated in a fixed-bed reactor at different temperatures (600°C–800°C) and atmospheric pressures. The results showed that tar-rich coal pyrolysis under CO₂ atmosphere can promote tar production (mass fraction 8.42% increased) compared with that of traditional pyrolysis (under N₂), with the maximum value up to 21.26% (in weight). It should be noted that the generation of coal tar and CO small molecule gas can be promoted by increasing the concentrations of CO₂ in pyrolysis atmosphere gases. GC-MS and simulated distillation results showed that the CO₂ atmosphere can promote the production of light oil components such as phenols, alcohols, and olefins, while inhibiting the production of heavy components such as asphalt simultaneously. Elemental analysis results showed the H/C ratio of coal tar increased under CO₂ atmosphere indicating that the high quality of coal tar is improved, which is consistent with that of simulated distillation and GC-MS test. Finally, a possible reaction pathway of tar-rich coal under CO₂ atmosphere pyrolysis is also proposed.

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.

Traditional salt solutions, due to their susceptibility to crystallization and corrosion, can be replaced by ionic liquids (ILs) to enhance the effectiveness of liquid desiccant dehumidification systems. This study proposes integrating a transcritical-carbon-dioxide heat pump (TCHP) with an IL dehumidification cycle, thereby providing both cooling and heating for IL under large temperature differentials. Thermodynamic analysis is conducted to investigate the influence of key design parameters. The findings reveal that the TCHP is capable of handling the significant temperature rise during IL regeneration. The evaporation temperature is the key factor for matching the supply and demand of cooling and heating in the system. The self-circulation ratio of the solution is limited by the regeneration temperature. When the initial air humidity ratio is 8.0 g/kg and the supply air humidity ratio is 1.0 g/kg, the proposed system’s total heat COP is 31.9% higher than that of the reference systems.