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.

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.

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.

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.

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

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.

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.

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.

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.

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 (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.

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.

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.

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.

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.

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

The 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.

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.

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.

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

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.

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.

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

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.

The heat transfer efficiency of a thermal energy storage unit (TESU) can be improved by the addition of novel longitudinal fins. A series of TESUs are analyzed using the finite volume method (FVM) to determine the effect of fin angle on the heat transfer performance. As the fin angle increases, the TES rate first increases, then decreases, reaching a maximum rate at 60°, where the melting time is less by 30.9%, 28.58%, 21.99%, 9.02%, and 18.1% than at 0°, 15°, 30°, 45°, and 80°, respectively. In addition, it is found that the melting time of the phase change material is significantly greater at the bottom of the TESU. The time percentage of this stage decreases as the fin angle increases through these percentages by 7%, 14%, 23%, 33%, and 20%, respectively. Further, the response surface methodology (RSM) is applied to optimize the longitudinal fin by minimizing the total melting time. The analysis concludes that a fin angle of 58.68° reduces the complete melting time of the stearic acid by 44% below the time at 0°. These findings fill a gap in knowledge of the effect on melting performance of the design angle of longitudinal fins and provide a reference for the design of horizontally placed longitudinal finned thermal energy storage units.

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.

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.

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.

Molten salt and supercritical carbon dioxide (sCO₂) are considered to be one of the most promising combined heat transfer refrigerants for third-generation solar thermal power generation. To evaluate the potential of chloride salts and carbonates in third-generation solar thermal power generation, this paper uses molten salts and sCO₂ as the working media of printed circuit board heat exchangers (PCHE), and uses numerical simulation to study the heat transfer and friction of PCHE channels with different molten salts and sCO₂, and establishes predictive correlations respectively. A local heat transfer and friction study was conducted on the sCO₂ side of the airfoil channel, and it was found that the inlet mass flow rate has a significant impact on it, while the inlet temperature has a relatively small impact. A comprehensive comparison was made between the heat transfer and friction of two molten salts, and the comprehensive performance of chloride salts was 70%–80% higher than that of carbonates. The results indicate that the potential of chloride salts in third-generation solar thermal power generation is much greater than that of carbonates.

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.

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.

Achieving efficient thermal management urges to exploit high-thermal-conductivity materials to satisfy the boosted demand of heat dissipation. It is critical to adopt standardized characterization protocols to evaluate the intrinsic thermal conductivity of thermal management materials. However, for the most representative laser flash method, the lack of standard measurement methodology and systematic description on the thermal diffusivity and influencing factors has led to significant deviations and confusion of the thermal conduction performance in the emerging thermal management application. Here, the measurement error factors of thermal diffusivity by the common laser flash analyzer (LFA) are discussed. Taking high-thermal-conductivity graphitic film (GF) as a typical case, the key factors are analyzed to guide the measurement protocol of related carbon-based thermal management materials. The basic principle of the LFA measurement, actual pre-processing conditions, instrument parameters setting, and data analysis are elaborated for accurate measurements. Furthermore, the graphene thick films and common isotropic materials are also extended to meet various thermal measurement requirements. Based on the existing practical problems, we propose a feasible test flow to achieve a unified and standardized thermal conductivity measurement, which is beneficial to the rapid development of carbon-based thermal management materials.

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.

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.

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.

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.

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

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

The 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 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.