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

The supercritical CO₂ Brayton cycle has potential to be used in electricity generation occasions with its advantages of high efficiency and compact structure. Focusing on a so-called self-condensing CO₂ transcritical power cycle, a model was established and four different layouts of heat recuperation process were analyzed, a without-recuperation cycle, a post-recuperation cycle, a pre-recuperation cycle and a re-recuperation cycle. The results showed that the internal normal cycle’s share of the whole cycle increases with increasing the cooling pressure and decreasing the final cooled temperature. Heat load in the supercritical heater decreases with increasing the cooling pressure. From perspective of performance, the re-recuperation cycle and the pre-recuperation cycle have similar thermal efficiency which is much higher than other two layouts. Both thermal efficiency and net power output have a maximum value with the cooling pressure, except in the condition with the final cooled temperature of 31°C. Considering both the complexity and the economy, the pre-recuperation cycle is more applicable than the other options. Under 35°C of the final cooled temperature, the thermal efficiency of the pre-recuperation cycle reaches the peak 0.34 with the cooling pressure of 8.4 MPa and the maximum net power output is 2355.24 kW at 8.2 MPa of the cooling pressure.

Hybrid deflagration/auto-ignition flame structures coexist in the combustion of advanced engines. Decoupling exergy destruction caused by different irreversible processes under varied flame regimes is thus important for understanding engine thermodynamics. In this study, the flame propagation modes for the premixed DME/air mixtures are numerically investigated under engine-relevant conditions. Local entropy generation and exergy destruction characteristics are compared under different flame structures. Results reveal that as the typical premixed flame transition towards auto-ignition front, the exergy destruction from heat conduction and species mass diffusion gradually vanish and are dominated by chemical reaction. The distributions of temperature and species mole fraction in the flame domain are analyzed to clarify the exergy destruction behaviors caused by heat conduction and mass diffusion. Furthermore, by dividing the DME oxidation process into four stages, the main reaction channels that contribute to the increase in exergy destruction from chemical reaction have been identified. It is found that the production and consumption of CH₂O and HȮ₂ radical dominate the exergy destruction behavior during DME oxidation. On this basis, the kinetic mechanism of low-temperature chemistry causing greater exergy destruction is elucidated. Specifically, low-temperature chemistry leads to significant exergy destruction due to (a) the large irreversibility of itself and (b) (mainly) the enhancement of H₂O₂ loop reactions by low-temperature reaction intermediates. Thus the reduction of combustion irreversibility is promising to be achieved by reasonably regulating the fuel oxidation path.

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

To achieve high-performance compressor cascades at low Reynolds number (Re), it is important to organize the boundary layer transition and separation processes efficiently and reasonably. In this study, the airfoil is focused on at a 5% blade height at the root of the orthogonal blade in the downflow passage of the high-load booster stage. The bionics modeling design is carried out for the leading edge of the original blade cascade; the response characteristics of laminar transition and separation to blades with different leading edge shapes at low Reynolds numbers are studied by using large eddy simulations combined with Omega vortex identification. The findings of this study demonstrate that bionic leading edge modeling can significantly improve the aerodynamic performance of blades at low Reynolds numbers. The blades effectively suppress the formation of separation bubbles at low Reynolds numbers and weaken or even eliminate large-scale flow separation at the trailing edge. In addition, the blades can weaken the vortex intensity on the blade surface, reduce the areas of high-velocity fluctuations, and minimize aerodynamic losses caused by turbulence dissipation. These results should serve as a valuable reference for the aerodynamic design and flow control of the high-load booster stage blade at low Re.

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.

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.

In this paper, a novel NH₃/CO₂ ejector-cascade refrigeration system with regenerator is proposed, which can recycle the waste heat at the outlet of the compressor. After establishing the mathematical model of the system, the theoretical energy and exergy analysis are carried out and compared with the conventional cascade refrigeration system. It is concluded that compared with the conventional cascade refrigeration system, the novel ejector-cascade refrigeration system with regenerator has the advantages of less power consumption of the compressor, less component exergy destruction, high system performance, and is more suitable for working at a lower temperature. Under the working conditions studied in this paper, compared with the conventional cascade refrigeration system, the COP of the novel ejector-cascade refrigeration system with regenerator is increased by 9.58%; the exergy efficiency is increased by 9.50%, and the optimal evaporation temperature is about –45°C.

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.

Coal-fired power plant is a major contributor to greenhouse gas emissions. The post-combustion capture is a promising method for CO₂ emission reduction but the high thermal demand is unbearable. To address this issue, solar thermal energy and CO₂ capture are jointly integrated into the coal-fired power plant in this study. The solar thermal energy is employed to meet the heat requirement of the CO₂ capture process, thereby avoiding the electricity loss caused by self-driven CO₂ capture. Furthermore, the heat released from the carbonation reaction of MgO adsorbent is integrated into the steam Rankine cycle. By partially substituting the extracted steam for feedwater heating, the electricity output of the power plant is further increased. According to the results from the developed model, the system could achieve a CO₂ capture rate of 86.5% and an electricity output enhancement of 9.8% compared to the reference system, which consists of a self-driven CO₂ capture coal-fired power plant and PV generation unit. The operational strategy is also optimized and the amount of CO₂ emission reduction on a typical day is increased by 11.06%. This work shows a way to combine fossil fuels and renewable energy for low carbon emissions and efficient power generation.

To address the pressing need for intelligent and efficient control of circulating fluidized bed (CFB) units, it is crucial to develop a dynamic model for the key operating parameters of supercritical circulating fluidized bed (SCFB) units. Therefore, data-knowledge-driven dynamic model of bed temperature, load, and main steam pressure of the SCFB unit has been proposed. Firstly, a knowledge-driven method is employed to develop a dynamic model for key operating parameters of SCFB units. The model parameters are determined based on the operating data of the unit and continuously optimized in real time. Then, Bidirectional Long Short-Term Memory combined with Convolutional Neural Network and Attention Mechanism is utilized to build the dynamic model of bed temperature, load, and main steam pressure. Finally, a collaboration and integration method based on the critic weight method and the variation coefficient method is proposed to establish data-knowledge-driven model of key operating parameters for SCFB units. The model displays great accuracy and fitting ability compared with other methods and effectively captures the dynamic characteristics, which can provide a research basis for the design of intelligent flexible control mode of SCFB unit.

With the development of detection and identification technology, infrared stealth is of great value to realize anti-reconnaissance detection of military targets. At present, infrared stealth materials generally have deficiency, such as complex structure, inconvenient radiation regulation and cumbersome preparation steps, which greatly limit the practical application of infrared stealth materials. In view of the above deficiency of infrared stealth materials, we proposed a kind of multilayer film for infrared stealth using VO₂ thermochromism based on the temperature response mechanism of tuna to adjust its color, and through the intelligent reversible radiation regulation mechanism to meet the infrared stealth requirements of tanks in different actual scenes. The results show that when the temperature increases from 300 K to 373 K, the peak emissivity of the film decreases from 94% to 20% in the 8–14 μm band after structural optimization, which can realize the infrared stealth of the high temperature target in the 8–14 μm band. The average emissivity of the multilayer film for infrared stealth at 3–5 μm and 8–14 μm band can be reduced to 34% and 27% at 373 K, and the peak emissivity at 5–8 μm band can reach 65%, realizing dual-band infrared stealth in the 3–5 μm and 8–14 μm bands and heat dissipation in the 5–8 μm band. The multilayer film for infrared stealth based on VO₂ thermochromism designed by the authors can meet the characteristics of simple film structure, convenient radiation regulation and simple preparation.

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

For complex flows in compressors containing flow separations and adverse pressure gradients, the numerical simulation results based on Reynolds-averaged Navier-Stokes (RANS) models often deviate from experimental measurements more or less. To improve the prediction accuracy and reduce the difference between the RANS prediction results and experimental measurements, an experimental data-driven flow field prediction method based on deep learning and ℓ₁ regularization is proposed and applied to a compressor cascade flow field. The inlet boundary conditions and turbulence model parameters are calibrated to obtain the high-fidelity flow fields. The Saplart-Allmaras and SST turbulence models are used independently for mutual validation. The contributions of key modified parameters are also analyzed via sensitivity analysis. The results show that the prediction error can be reduced by nearly 70% based on the proposed algorithm. The flow fields predicted by the two calibrated turbulence models are almost the same and nearly independent of the turbulence models. The corrections of the inlet boundary conditions reduce the error in the first half of the chord. The turbulence model calibrations fix the overprediction of flow separation on the suction surface near the tail edge.

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.

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.

Lithium-ion batteries (LIBs) undergo various degradation phenomena such as material decomposition, structural change and uneven lithium ion distribution during long-term cycles, which would affect their performance and safety. In order to improve the performance of the LIBs during their life cycle, preload force is preset when the batteries are assembled. Different preload forces will in turn affect the cycle life and heat generation of the battery. In order to address this issue, this work carries out charge/discharge cycle tests on a NCM811 battery under different preload forces. Isothermal calorimetry tests are performed to investigate the battery heat generation under different states of health (SOHs) and preload forces. Based on the test results, an empirical prediction model for heat generation power as a function of SOH is established. Results show that when the preload force is 5 N·m, the battery capacity decreases in the slowest rate and the average heat generation power is the lowest. Changes in peaks of the incremental capacity curve can be used to characterize the loss of lithium at the electrode, which in turn characterizes the change of heat generation power of the battery. The average heat generation power is mainly affected by the SOH, going through a period of trough with the decrease of the SOH and continuing to increase after crossing the critical point. In general, these findings emphasize the relationship between preload force, SOH and heat generation power, which is helpful for the judgment of optimal preload to improve the efficiency of LIBs.

The introduction of fresh air into the indoor space leads to a significant increase in cooling or heating loads. Solid desiccant heat pump fresh air unit which can handle the latent and sensible load of fresh air efficiently have been proposed recently. To improve the performance of the solid desiccant heat pump fresh air unit in the fresh air handling process, in this paper, the application of composite silica gel in a heat pump fresh air unit was investigated. The comparison between silica gel coating (SGC) and composite silica gel coating (CSGC) shows that the adsorption rate and water uptake capacity of CSGC are more than two times higher than those of SGC. An experimental setup for the solid desiccant heat pump fresh air unit was established. The performance of SGC and CSGC was tested in the setup successively. Results show that under summer conditions, compared with the solid desiccant heat pump fresh air unit using silica gel (SGFU), the average moisture removal and COP of the one using composite silica gel (CSGFU) increased by 15% and 30%, respectively. Under winter conditions, compared with SGFU, the average humidification and COP of CSGFU increased by 42% and 17%. With optimal operation conditions of 3 min switchover time and 40 r/s compressor frequency, the COP of CSGFU under summer conditions can reach 7.6. Results also show that the CSGFU and SGFU have higher COP and dehumidification rate under higher outdoor temperature and humidity ratio.

The external surface heat transfer coefficient of building envelope is one of the important parameters necessary for building energy saving design, but the basic data in high-altitude area are scarce. Therefore, the authors propose a modified measurement method based on the heat balance of a model building, and use the same model building to measure its external surface heat transfer coefficient under outdoor conditions in Chengdu city, China at an altitude of 520 m and Daocheng city at an altitude of 3750 m respectively. The results show that the total heat transfer coefficient (h_t) of building surface in high-altitude area is reduced by 34.48%. The influence of outdoor wind speed on the convective heat transfer coefficient (h_c) in high-altitude area is not as significant as that in low-altitude area. The fitting relation between convection heat transfer coefficient and outdoor wind speed is also obtained. Under the same heating power, the average temperature rise of indoor and outdoor air at high- altitude is 41.9% higher than that at low altitude, and the average temperature rise of inner wall is 25.8% higher than that at low altitude. It shows that high-altitude area can create a more comfortable indoor thermal environment than low-altitude area under the same energy consumption condition. It is not appropriate to use the heat transfer characteristics of the exterior surface of buildings in low-altitude area for building energy saving design and related heating equipment selection and system terminal matching design in high-altitude area.

The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct. Multiple shock waves are formed inside the duct at a shock Mach number of 1.75. The duct has an exit height of H, and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H, 50H, and 150H. The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves. The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure, shock train leading-edge location, shock train length, and the size of the separation bubble. The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition. The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted. The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations. The RMS amplitude of the normalized shock train length (ζ_ST) increases with an increase in the exit duct length for the self-excited oscillation condition. When the downstream perturbation frequency is increased, ζ_ST is decreased for exit duct configurations. For all exit duct designs and downstream forcing frequencies, the size of the separation bubble grows and shrinks during the shock oscillations, demonstrating the dependence on duct resonance and forced oscillations.

Multi-fidelity simulations incorporate computational fluid dynamics (CFD) models into a thermodynamic model, enabling the simulation of the overall performance of an entire gas turbine with high-fidelity components. Traditional iterative coupled methods rely on characteristic maps, while fully coupled methods directly incorporate high-fidelity simulations. However, fully coupled methods face challenges in simulating rotating components, including weak convergence and complex implementation. To address these challenges, a fully coupled method with logarithmic transformations was developed to directly integrate high-fidelity CFD models of multiple rotating components. The developed fully coupled method was then applied to evaluate the overall performance of a KJ66 micro gas turbine across various off-design simulations. The developed fully coupled method was also compared with the traditional iterative coupled method. Furthermore, experimental data from ground tests were conducted to verify its effectiveness. The convergence history indicated that the proposed fully coupled method exhibited stable convergence, even under far-off-design simulations. The experimental verification demonstrated that the multi-fidelity simulation with the fully coupled method achieved high accuracy in off-design conditions. Further analysis revealed inherent differences in the coupling methods of CFD models between the developed fully coupled and traditional iterative coupled methods. These inherent differences provide valuable insights for reducing errors between the component-level model and CFD models in different coupling methods. The developed fully coupled method, introducing logarithmic transformations, offers more realistic support for the detailed and optimal design of high-fidelity rotating components within the overall performance platform of gas turbines.

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.

Combined cooling and power (CCP) system driven by low-grade heat is promising for improving energy efficiency. This work proposes a CCP system that integrates a regenerative organic Rankine cycle (RORC) and an absorption chiller on both driving and cooling fluid sides. The system is modeled by using the heat current method to fully consider nonlinear heat transfer and heat-work conversion constraints and resolve its behavior accurately. The off-design system simulation is performed next, showing that the fluid inlet temperatures and flow rates of cooling water as well as RORC working fluid strongly affect system performance. The off-design operation even becomes infeasible when parameters deviate from nominal values largely due to limited heat transfer capability of components, highlighting the importance of considering heat transfer constraints via heat current method. Design optimization aiming to minimize the total thermal conductance is also conducted. RORC efficiency increases by 7.9% and decreases by 12.4% after optimization, with the hot fluid inlet temperature increase from 373.15 to 403.15 K and mass flow rate ranges from 10 to 30 kg/s, emphasizing the necessity of balancing system cost and performance.

Efficient thermal management of lithium-ion battery, working under extremely rapid charging-discharging, is of widespread interest to avoid the battery degradation due to temperature rise, resulting in the enhanced lifespan. Herein, thermal management of lithium-ion battery has been performed via a liquid cooling theoretical model integrated with thermoelectric model of battery packs and single-phase heat transfer. Aiming to alleviate the battery temperature fluctuation by automatically manipulating the flow rate of working fluid, a nominal model-free controller, i.e., fuzzy logic controller is designed. An optimized on-off controller based on pump speed optimization is introduced to serve as the comparative controller. Thermal control simulations are conducted under regular operating and extreme operating conditions, and two controllers are applied to control battery temperature with proper intervals which is conducive to enhance the battery charge-discharge efficiency. The results indicate that, for any operating condition, the fuzzy logic controller shows excellence in terms of the tracking accuracy of set-point of battery temperature. Thanks to the establishment of fuzzy set and fuzzy behavioral rules, the battery temperature has been throughout maintained near the set point, and the temperature fluctuation amplitude is highly reduced, with better temperature control accuracy of ~0.2°C (regular condition) and ~0.5°C (extreme condition) compared with ~1.1°C (regular condition) and ~1.6°C (extreme condition) of optimized on-off controller. While in the case of extreme operating condition, the proposed optimized on-off controller manifests the hysteresis in temperature fluctuation, which is ascribed to the set of dead-band for the feedback temperature. The simulation results cast new light on the utilization and development of model-free temperature controller for the thermal management of lithium-ion battery.

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

Humid air turbine cycle (HAT) has potential of electrical efficiencies comparable to combined cycle, with lower investment cost and NOx emission. The typical heat exchanger network of HAT consists of intercooler (if there is), aftercooler, recuperator, economizer and humidifier, which brings higher efficiency but makes the system more complex. To simplify HAT layout, a novel humidifier concept is proposed by integrating the aftercooler into traditional counter-current humidifier. Based on this concept, a one-dimensional model including pressure drop and exergy calculation is established to distinguish the thermodynamic and hydrodynamic characteristics, and then the structural parameters, such as the number of rows and columns, tube diameter, pitch and type for a micro HAT are identified. The results show that the aftercool-humidifier plays the same role as original aftercooler and humidifier, and can match the in-tube air, out-tube air and water stream well with lower volume. In the case of micro HAT cycle, the volume of heat and mass transfer area can be reduced by 47% compared with traditional design. The major thermal resistance occurred in the convection heat transfer process inside the tube; however, using enhanced tube cannot effectively improve the compactness of device.

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

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.

In this paper, a numerical simulation method is used to calculate a 1.5-stage axial transonic compressor to explore its unsteady flow mechanism. The performance curve is compared with the experimental data to verify the calculation method with a high numerical accuracy, which shows that the unsteady calculation has good reliability. According to the analysis of the data from the monitoring points under the near-stall condition, the unsteady disturbances originate from the tip region of blade and perform the strongest at the blade pressure surface with a broadband characteristic. Further analysis is conducted by combining with the characteristics of the transient flow field at the tip of blade. The results show that the unsteady pressure fluctuations are caused by the migration of the new vortex cores. These new vortex cores are generated by the breakdown of leakage vortex in the downstream, which is induced by the leakage vortex and shock wave interference. Moreover, the relationship between the unsteady flow characteristics and the working conditions is also studied. The leakage vortex intensity and the shock wave strength gradually increase with the decrease of flow rate. When the combination of the leakage vortex intensity and shock wave strength reaches the first threshold, a single frequency of unsteady disturbances appears at the blade tip. When the combination of the leakage vortex intensity and shock wave strength reaches the second threshold, the frequency of unsteady disturbances changes to a broadband.

In order to reduce the environmental impact of conventional sludge treatment methods and to utilize the energy in sludge more effectively, a coupled system based on sewage sludge gasifier (SSG), solid oxide fuel cells (SOFC), supercritical CO₂ cycle (S-CO₂), and organic Rankine cycle (ORC) is proposed. The clean syngas obtained from sludge gasification is mixed with CH₄ and then first utilized by the fuel cell. The exhaust gas from the fuel cell is fully combusted in the afterburning chamber and then enters the bottom cycle system consisting of S-CO₂ & ORC to generate electricity. To understand the performance of the system, thermodynamic and economic analyses were conducted to examine the project’s performance. The thermodynamics as well as the economics of the coupled system were analyzed to arrive at the following conclusions, the power production of the system is 37.34 MW; the exergy efficiency is 55.62%, and the net electrical efficiency is 61.48%. The main exergy destruction is the gasifier and SOFC, accounting for 62.45% of the total exergy destruction. It takes only 6.13 years to repay the construction investment in the novel system, and the project obtains a NPV of 17 723 820 USD during 20 years lifetime. The above findings indicate that the new coupled system has a better performance in terms of energy utilization and economy.

Thermal energy conversion and also storage system is to advance knowledge and develop practical solutions at the intersection of micro and nano-scale engineering, energy conversion, and sustainability. This research addresses the challenge of enhancing these critical aspects to ensure prolonged system performance and durability in the context of evolving energy technologies. This research analyses the anti-oxidation and filtration behaviours of micro and nano-scale structures in the context of electro- and photo-thermal energy conversion and also storage systems. A micro multiscale hierarchical structure strategy is presented to fabricate multi-scale double-layer porous wick evaporators with the electrospun nanofibers made of gelatin-polyamide 6 (GPA6) and Ti₃C₂T_x MXene/silver nanowire with Cellulose Micro/NanoFibers (CMNF) cryogens by using spark plasma sintering (SPS) based high-pressure hydrothermal treatment model. An excellent anti-oxidation effect was offered by coating the film in thermal conditions and the anti-oxidation properties were further examined from 500°C to 850°C. The results are analysed using Matlab software to improve the efficiency of energy conversion processes by integrating nanostructures into thermal systems, to increase energy output while minimizing losses. The silver nanowire is with a heat transfer coefficient of 78%, a mass remaining rate of 98.7%, and an energy storage efficiency of 23.8%. This study enhances energy density and duration by integrating nanostructures into thermal systems while minimizing energy losses, and it not only exhibits excellent anti-oxidation properties but also possesses superior filtration capabilities for designing and engineering multifunctional nanomaterials.

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

A pair of unidirectional turbines (UT) can operate in oscillatory airflow without additional units. However, this arrangement suffers from poor flow rectification. A fluidic diode (FD) offers variable hydrodynamic resistance based on the flow direction, and this can be coupled with UT to improve flow rectification. In this work, a numerical investigation on the effect of FD with UT is presented using the commercial fluid dynamics software ANSYS Fluent 16.1 with k-ω SST turbulence closure model. Periodic domains of UT and FD are numerically validated individually with experimental results. Later, both are coupled to obtain the combined effect, and these results are compared with the analytical approach. It was observed that coupling FD with UT improved the unit’s performance at the lower flow coefficient (<1), but its performance decreased as the flow coefficient increased. Due to the diode’s presence, fluid leaving the turbine experiences higher resistance at a higher flow coefficient, which decreases the overall performance of the combined unit.

Flow around a pair of flat plates is a basic hydrodynamics problem. In this paper, the flow and heat transfer characteristics of two parallel plates with different edge shapes are numerically calculated. Under different inclined angles, the influence of chamfered and rounded structures with different sizes at the end-edge on unsteady flow and heat transfer characteristics of two parallel plates are analyzed. It is found that the instability and unsteadiness of flow decrease with the increase of end-edge size, and the non-uniformity of wake velocity of both rounded and chamfered plates decreases gradually. The non-uniformity of wake temperature increases firstly and then decreases at a small inclined angle, and the amplitude becomes the largest when S_rou(S_cha)=3, while it basically keeps monotonically increasing at a large inclined angle. Moreover, the global heat transfer performance of the flat plate is obviously affected by the end-edge modification, especially the chamfered structure. With the increase of chamfered size, the global Nusselt number basically shows the decreasing trend. This study provides a theoretical basis for the application of plate-shape structure in engineering fields.

This paper aims to conduct a comprehensive exergoeconomic analysis of a novel zero-carbon-emission multi-generation system and propose a fast optimization method combined with machine learning. The detailed exergoeconomic analysis of a novel combined power, freshwater and cooling multi-generation system is performed in this study. The exergoeconomic analysis model is established by exergy flow theory. A comprehensive exergy, exergoeconomic and environmental analysis is carried out. Five critical decision variables are researched to bring out effects on the multi-generation system exergoeconomic performance. A novel fast optimization method combining genetic algorithm and Bagging neural network is proposed. The advanced nature comparison is made between the proposed system and four similar cases. Results display that increasing the turbine inlet temperature can improve exergy efficiency and decrease the total product unit cost. The multi-generation system exergy destruction directly determines exergy efficiency and total exergy destruction cost rate. The total product unit cost in the cost optimal design case is reduced by 7.7% and 25%, respectively, compared with exergy efficiency optimal design case and basic design case. Compared with four similar cases, the proposed multi-generation system has great advantages in thermodynamic performance and exergoeconomic performance. This paper can provide research methods and ideas for performance analysis and fast optimization of multi-generation system.

Natural gas is a promising alternative fuel for the internal combustion engine, and natural gas engine has become an efficient and feasible measure to deal with the energy shortage and climate change. Since the laminar flame characteristics are the foundation of the turbulent flame, the laminar flame characteristics of natural gas have a significant impact on the combustion status and efficiency of the engine. A visual constant volume bomb was used to study the influence of the gas components, different excess air coefficient (λ), and initial conditions on the laminar combustion characteristics of natural gas. The experimental results showed that when the initial pressure and temperature were 0.1 MPa and 300 K respectively, compared to propane, ethane had a remarkable influence on the equivalent-combustion laminar-combustion-speed, with an average increase of approximately 5.1% for every 2.5% increase in the ethane proportion. The laminar combustion velocity of the natural gas under different excess air coefficients had a maximum value at about λ=1.0, and the Markstein length of the flame decreased with the increase of the λ. The increase in the initial pressure of the mixture resulted in a decrease in the equivalent-combustion laminar-combustion-speed of the flame, a significant decrease in the Markstein length. The increase of the initial temperature of the mixture led to a rapid increase of the equivalent-combustion laminar-combustion-speed, but the effect on the flame Markstein length was not dominant.

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

The ignition tendency of diesel fuels is highly sensitive to ambient conditions and fuel properties. In this study, the ignition characteristics of different diesel surrogate fuels with the same derived cetane numbers (DCN) were measured and compared in varied thermodynamic and oxidizing environments. The combustion pressures, heat release rates, ignition delays, and combustion delays of the test fuels were compared. The experimental results showed that the diesel surrogate fuels with the same DCNs exhibit similar ignition propensity at standard DCN test conditions. Further, for the test conditions of high cetane fuels, high ambient temperatures, and sufficient oxygen concentrations, surrogate fuels with the same DCN have similar ignition behaviors, and using the DCN to evaluate fuel ignition tendency is appropriate. However, for the test conditions of low cetane fuels, low ambient temperatures, and reduced oxygen concentrations, different ignition behaviors are observed for the surrogate fuels with the same DCN, so at these conditions using DCN as the evaluation index for fuel ignition tendency may lead to higher uncertainty.

Rectangular microchannel heat sinks (MCHS) are widely used to cool high-heat-flux electronic devices. However, previous studies focused mainly on MCHS with uniform channels (UCs). This study considers a microchannel heat sink with non-uniform channels (NUCs). A mathematical model is developed based on energy equations and the Darcy flow principle. Explicit expressions for total thermal resistance and coolant pressure drop are derived using the thermoelectric analogy. Experiments and numerical simulations are performed to verify the mathematical model. As non-uniformity increases, total coolant pressure drop decreases but at the cost of higher thermal resistance. The overall performance of NUCs is better than that of UCs because of their lower ratio of pumping power to cooling power. Heat transfer performance of NUCs changes little for more than 120 channels and depends mainly on channel arrangement. A multi-objective optimization is conducted to minimize the thermal resistance and pumping power of an NUC. An optimal NUC saves 64% pumping power compared with a conventional UC for the total thermal resistance of 0.1°C/W, indicating that the use of non-uniform channels could be very helpful to reduce the flow resistance of MCHS.