Fast fluid transport on graphene has attracted a growing body of research due to a wide range of potential applications including thermal management, water desalination, energy harvesting, and lab-on-a-chip. Here, we critically review the theoretical, simulational, and experimental progress regarding the fluid slippage on graphene. Based on the summary of the past studies, we give perspectives on future research directions towards complete understanding and practical applications of slip flow on graphene.

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

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.

The complex flow phenomenon of rotating instability (RI) and its induced non-synchronous vibration (NSV) have become a significant challenge as they continuously increase aerodynamic load. This study aims to provide an understanding of the non-synchronous blade vibration phenomenon caused by the rotating instability of a transonic axial compressor rotor. In this case, blade vibrations and non-synchronous excitation are captured by strain gauges and unsteady wall pressure transducer sensors. Unsteady numerical simulations for a full-annulus configuration are used to obtain the non-synchronous flow excitation. The results show that the first-stage rotor blade exhibits an NSV close to the first bending mode; NSV is accompanied by a sharp increase in pressure pulsation; amplitude can reach 20%, and unsteady aerodynamic frequency will lock in a structural mode frequency when the blade vibrates in a large-amplitude motion. The predicted NSV frequency aligns well with the experimental results. The dominant mode of circumferential instability flow structure is approximately 47% of the number blades, and the cell size occupies 2–3 pitches in the circumferential direction. The full-annulus unsteady simulations demonstrate that the streamwise oscillation of the shedding and reattachment vortex structure is the main cause of NSV owing to the strong interaction between the tip leakage and separation vortices near the suction surface.

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.

In order to solve the conflict between indoor lighting and PV cells in building-integrated photovoltaic/thermal (BIPV/T) systems, a glass curtain wall system based on a tiny transmissive concentrator is proposed. This glass curtain wall has a direct influence on the heat transfer between indoor and outdoor, and the operating parameters of air and water inlet temperature, indoor and outdoor temperature, and radiation intensity have a significant influence on the heat transfer characteristics of the glass curtain wall. The 3D model is established by SoildWorks software, and the thermal characteristics of the new glass curtain wall system are simulated through computational fluid dynamics (CFD) method. Thermal performance was tested under actual weather for the winter working conditions. The CFD simulation results are verified by the test results under actual weather. The results show that thermal efficiency simulation results are in good agreement with the experimental results of the new glass curtain wall system. The simulation conditions were designed by using the orthogonal method, and the significance analysis of the influencing factors of the indoor wall surface heat gain was carried out. With the increase of the bottom heat flux and the air velocity, the heat absorption of the inner wall surface increases. When the wind speed is 0.1 m/s, the heat flow on the bottom surface rises from 500 W/m² to 2500 W/m², and the heat flow intensity on the interior wall changes from 10.31 W/m² to –29.12 W/m². Under typical working conditions, the new glass curtain wall system can reduce the indoor heat load by 47.5% than ordinary glass curtain wall.

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.

Stall in compressors can cause performance degradation and even lead to disasters. These unacceptable consequences can be avoided by timely monitoring stall inception and taking effective measures. This paper focused on the rotating stall warning in a low-speed axial contra-rotating compressor. Firstly, the stall disturbance characteristics under different speed configurations were analyzed. The results showed that as the speed ratio (RR) increased, the stall disturbance propagation speed based on the rear rotor speed gradually decreased. Subsequently, the standard deviation (SD) method, the cross-correlation (CC) method, and the discrete wavelet transform (DWT) method were employed to obtain the stall initiation moments of three different speed configurations. It was found that the SD and CC methods did not achieve significant stall warning results in all three speed configurations. Besides, the stall initiation moment obtained by the DWT method at RR=1.125 was one period after the stall had fully developed, which was unacceptable. Therefore, a stall warning method was developed in the present work based on the long short-term memory (LSTM) regression model. By applying the LSTM model, the predicted stall initiation moments of three speed configurations were at the 557th, 518th, and 333rd revolution, which were 44, 2, and 74 revolutions ahead of stall onset moments, respectively. Furthermore, in scenarios where a minor disturbance preceded the stall, the stall warning effect of the LSTM was greatly improved in comparison with the aforementioned three methods. In contrast, when the pressure fluctuation before the stall was relatively small, the differences between the stall initiation moments predicted by these four methods were not significant.

To enhance the understanding of design characters, which have prominent influences during the fan blade out event, a simplified geometrical and dynamic analysis method was derived, and a typical 2-shaft high bypass ratio turbofan engine was selected and modeled. Based on analytical deriving and engineering experience learned from the real engine failure case, three determinative impact actions were recognized from the fan blade out process. The transient trajectories of these impact actions were researched in analytical method, and then thickness of acoustic lining, quantity of fan blades and threshold load of structural fuse were analyzed as key design characters. 36 serialized fan blade out transient dynamic simulations were conducted by using the 2-shaft high bypass ratio turbofan engine model within different combinations of the three key design factors. The results from geometrical and dynamic analysis matched mainly well with the results from simulations. Characteristic phenomenon in simulation can be explained theoretically. Five conclusions can be summarized from these results. (1) If thickness fan acoustic lining was thinner, the deviation between simplified analytical calculation and simulation were not outstanding to predict Blade-Casing the first impact time and angular position. (2) An appropriate thickness of acoustic lining could make a lower impact stress of fan casing at the first impact. (3) Different thickness of acoustic linings leaded to two impact modes for blade 2, which were tip impact and root impact. (4) Different impact conditions between blade 1 and blade 2 caused remarkable speed components distinction of blade 1, and leaded to a wide range of transient trajectory of blade 1 during FBO event. (5) Thicker acoustic lining in this research can usually find the porper threshold loads setting, which can give a satisfactory outbound vibration. Two details were raised for further research, which were impact behavior of composite material fan blade and honeycomb and influences of wider FBO threshold load ranges in design cases with thinner acoustic lining.

Coal gasification technology is a prominent technology in the coal chemical industry and serves as the fundamental basis for various process industries, including coal-based chemicals, coal-based liquid fuels, Integrated Gasification Combined Cycle (IGCC) power generation, multi-generation systems, hydrogen production, and fuel cells. The gasification process generates significant quantities of ash residue, with annual emissions exceeding tens of millions of tons and accumulation reaching hundreds of millions of tons. Accordingly, there is an urgent need to investigate methods for its disposal. The combustion of gasified fine ash (GFA) was conducted in a tube furnace, and the conventional shrinking core model was modified to accurately predict the combustion behaviors at different temperatures (900°C–1500°C). We divided the reaction temperatures into three ranges, which is defined as unmelted combustion (T<DT), melted combustion (T>FT) and mixed combustion (DT<T<FT) (DT: deformation temperature; FT: flow temperature). There is a large difference between the reaction rates of unmelted and melted combustion of GFA. In the range of DT<T<FT, the ash in the grains existed as a liquid-solid state, and had high viscosity and low fluidity, but still adhered to the grain surface, which prolonged the grain burnout time. At T>FT, the surface ash of GFA grains fell off, and the residual carbon and gas-phase reactants were nearly no longer affected by the diffusion resistance, thus significantly accelerated the reaction of internal residual carbon. In order to predict the melt combustion process more accurately, the time term of the shrinkage core model (SCM) is modified, and the effective diffusion coefficient of T>FT is defined.

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.

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

Present work investigates the heat transfer and melting behaviour of phase change material (PCM) in six enclosures (enclosure-1 to 6) filled with paraffin wax. Proposed enclosures are equipped with distinct arrangements of the fins while keeping the fin’s surface area equal in each case. Comparative analysis has been presented to recognize the suitable fin arrangements that facilitate improved heat transfer and melting rate of the PCM. Left wall of the enclosure is maintained isothermal for the temperature values 335 K, 350 K and 365 K. Dimensionless length of the enclosure including fins is ranging between 0 and 1. Results have been illustrated through the estimation of important performance parameters such as energy absorbing capacity, melting rate, enhancement ratio, and Nusselt number. It has been found that melting time (to melt 100% of the PCM) is 60.5% less in enclosure-2 (with two fins of equal length) as compared to the enclosure-1, having no fins. Keeping the fin surface area equal, if the longer fin is placed below the shorter fin (enclosure-3), melting time is further decreased by 14.1% as compared to enclosure-2. However, among all the configurations, enclosure-6 with wire-mesh fin structure exhibits minimum melting time which is 68.4% less as compared to the enclosure-1. Based on the findings, it may be concluded that fins are the main driving agent in the enclosure to transfer the heat from heated wall to the PCM. Proper design and positioning of the fins improve the heat transfer rate followed by melting of the PCM in the entire area of the enclosure. Evolution of the favourable vortices and natural convection current in the enclosure accelerate the melting phenomenon and help to reduce charging time.

As a solution for solar heating, the low-cost and long-life vanadium-titanium black ceramic solar absorbers have been used in rural construction. However, in contrast to its high absorptance (0.93–0.97), ceramic also has high emissivity (approximately 90%) and low thermal conductivity (1.3 W/(m∙K)). Without a glaze covering, ceramic absorbers cannot meet the industrial standard. This paper assumes that glaze covering can be substituted by insulation film in a solar greenhouse. To verify this assumption, field experiments were conducted. First, a traditional greenhouse in the Tacheng Basin, a severely cold area in China, was renovated to improve its passive thermal performance. Then, 90 m² of ceramic absorbers and floor coils as well as a water tank were installed inside the greenhouse, which made the entire construction act as an integrated solar collector. This heat collection and release system moderately increased the indoor air temperature (0.9°C–22.4°C) and substantially increased the soil temperature (15.5°C–31.2°C). The average daily useful heat gain under a daily solar insolation value of 17 MJ/m² was 13.8 MJ, and the mean value of the collection efficiency was 0.81. Furthermore, the payback time of the project (7 years) is short, which is principally due to the low cost of ceramic materials and the financial savings of the shared construction components (e.g., transparent cover, metal frame and extra insulation). In conclusion, the main contribution of this study is the verification that it is feasible to replace glaze covering with insulation film in a novel greenhouse-integrated vanadium-titanium black ceramic solar system.

Based on a small perturbation stability model for periodic flow, the effects of inlet total temperature ramp distortion on the axial compressor are investigated and the compressor stability is quantitatively evaluated. In the beginning, a small perturbation stability model for the periodic flow in compressors is proposed, referring to the governing equations of the Harmonic Balance Method. This stability model is validated on a single-stage low-speed compressor TA36 with uniform inlet flow. Then, the unsteady flow of TA36 with different inlet total temperature ramps and constant back pressure is simulated based on the Harmonic Balance Method. Based on these simulations, the compressor stability is analyzed using the proposed small perturbation model.Further, the Dynamic Mode Decomposition method is employed to accurately extract pressure oscillations. The two parameters of the temperature ramp, ramp rate and Strouhal number, are discussed in this paper. The results indicate the occurrence and extension of hysteresis loops in the rows, and a decrease in compressor stability with increasing ramp rate. Compressor performance is divided into two phases, stable and limit, based on the ramp rate. Furthermore, the model predictions suggest that a decrease in period length and an increase in Strouhal number lead to improved compressor stability. The DMD results imply that for compressors with inlet temperature ramp distortion, the increase of high-order modes and oscillations at the rotor tip is always the signal of decreasing stability.

The two-stage transcritical CO₂ refrigeration cycle with dedicated dual-subcooling and mechanical recooling is proposed. The inter-stage pressure is critical for such cycle performances; however, it has not been studied exactly. Therefore, the research aim is to disclose the effect of inter-stage pressure on performances of the proposed cycle. The main work consists of four aspects. Firstly, the comparative study is performed to display advantages of the proposed cycle. Secondly, the key temperatures, heat and power consumptions as well as performance indicators for different inter-stage pressures are analyzed in detail, based on the parametric model. Thirdly, the optimal inter-stage pressure for different conditions is obtained by the nonlinear direct search method. Finally, the economic performance is assessed. It is found that the compressor power of the proposed cycle drops by 12%, and the working temperature lower limit is reduced by 11°C. Furthermore, it is considered that the optimal inter-stage pressure is insensitive to the heat source temperature. The novelty lies in illustrating the effect of inter-stage pressure, obtaining trends of the optimal value, and pointing out the system feasibility. The paper is favorable for design and operation optimization of the proposed system.

This paper studied the thermal physical properties of foundation materials in the molten salt tank of thermal energy storage system after molten salt leakage by Transient plane source experiment and X-ray computed microtomography simulation methods. The microstructure, thermal properties and pressure resistance with different particle diameters were addressed. The measured heat conductivities from Transient plane source experiment for three cases are 0.49 W/(m∙K), 0.48 W/(m∙K), and 0.51 W/(m∙K), and the porosity is 30.1%, 30.7%, and 31.2% respectively. The heat conductivity simulating results of three cases are 0.471 W/(m∙K), 0.482 W/(m∙K), and 0.513 W/(m∙K). The ratio of difference between the results of simulation and Transient plane source measurement is as low as 1.2%, verifying the reliability of experimental and simulation results to a certain degree. Compared with the heat conductivity of 0.097–0.129 W/(m∙K) and porosity of 71.6%–78.9% without leaking salt, the porosity is reduced by more than 50% while the heat conductivity increased by 4 to 5 times after molten salt leakage. This significant increase in heat conductivity has a great impact on security operation, structure design, and modeling of the tank foundation for solar power plants.

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.

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

Accurately and directly characterizing the thermal properties of graphene and thin-graphite films (GFs) is of fundamental importance for understanding the heat transport mechanism and of practical interest in possible applications of thermal management. However, due to the lack of experiment data, the mechanism of the thickness dependence of GFs thermal properties has not been fully understood yet. In this study, a 90-nm-thick GF is characterized by the time-domain thermoreflectance method, and the obtained GFs in-plane thermal conductivity and interfacial thermal conductance between GFs and gold are (1354±297) W/(m·K) and (38±6) MW/(m2·K), respectively. Two theoretical models are also applied for comparison and discussion, and we conclude that the influence from the surface perturbation by supporting materials on the phonon transport of graphite nano-films will beyond the near surface layers to the more inner ones. This work not only provides a better understanding of the fundamental mechanisms of the thermal transport size effect in GFs, but also facilitates the possible applications of GFs as heat spreaders in the future.

Previous studies in literatures adequately emphasized that inserting fins into phase change material is among the most promising techniques to augment thermal performance of shell-and-tube latent heat thermal energy storage unit. In this study, the novel unequal-length fins are designed from the perspective of synergistic benefits of heat transfer and energy storage performance, and the effects of arrangement, number and total length of unequal-length fins are numerically investigated. Results show that utilization of fins with ascending length, when short and long fins are located in the inlet and outlet of heat transfer fluid respectively, can further promote the heat transfer and energy storage performance compared with equal length fins, and a maximum 6.17% and 0.43% increment of heat transfer performance and stored energy is achieved in full melting time, respectively. The number of unequal-length fins plays a major role in the energy storage, and 18.95% and 0.91% improvement of heat transfer performance and stored energy is realized when equipped with 2 unequal-length fins. A 21.17% improvement of the heat transfer performance is obtained when the total length of unequal-length fins is 18 mm. The present study is helpful to make further efforts to enhance heat transfer and energy storage of shell-and-tube latent heat thermal energy storage unit with unequal-length fins.

Microwave-assisted ignition (MAI) is a promising technology to improve the ignition stability in internal combustion engines under lean conditions. To investigate the interplay between the microwave pulses and the electrical characteristics of ignition plasma, the high-time-resolved electrical characteristics of MAI are measured based on the discharge voltage and current profiles with microwave power varying from 0 to 1000 W. The effects of microwave pulse on the electrical characteristics in the breakdown and glow discharge phases are discussed respectively. The results show that the microwave-induced-voltage-decline (MIVD) occurs during the glow discharge phase, which originates from the increment of free electrons and the additional microwave field. However, this voltage decline is insignificant in the breakdown phase. Moreover, as the free electron number reaches a critical value, a shining plasma can be observed between the gap of electrodes and the voltage decline is stabilized to a “saturated voltage curve”. Ultimately, the effect of microwave plasma on the enhancement of ignition kernel area is explored. The result indicates that the enhancement effect increases with plasma duration rising. Those enhancements of earlier-generated plasmas are more significant than those of subsequent plasmas due to the distance limit of the plasma propulsive effect.

The constrained multi-objective multi-variable optimization of fans usually needs a great deal of computational fluid dynamics (CFD) calculations and is time-consuming. In this study, a new multi-model ensemble optimization algorithm is proposed to tackle such an expensive optimization problem. The multi-variable and multi-objective optimization are conducted with a new flexible multi-objective infill criterion. In addition, the search direction is determined by the multi-model ensemble assisted evolutionary algorithm and the feature extraction by the principal component analysis is used to reduce the dimension of optimization variables. First, the proposed algorithm and other two optimization algorithms which prevail in fan optimizations were compared by using test functions. With the same number of objective function evaluations, the proposed algorithm shows a fast convergency rate on finding the optimal objective function values. Then, this algorithm was used to optimize the rotor and stator blades of a large axial fan, with the efficiencies as the objectives at three flow rates, the high, the design and the low flow rate. Forty-two variables were included in the optimization process. The results show that compared with the prototype fan, the total pressure efficiencies of the optimized fan at the high, the design and the low flow rate were increased by 3.35%, 3.07% and 2.89%, respectively, after CFD simulations for 500 fan candidates with the constraint for the design pressure. The optimization results validate the effectiveness and feasibility of the proposed algorithm.

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.

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

Superheated droplets vaporized in a vacuum or vapor chamber was studied using smoothed particle hydrodynamics method. The two-phase fluids of vapor and liquid with a diffused interface were modeled by Navier-Stokes-Korteweg equations, with the van der Waals equation of state. The liquid-vapor separation was processed with different initial temperature and density. Simulation was firstly validated by the proper equilibrium states with analytical data from the binodal line of Maxwell construction, as well as the droplet surface tension compared with experimental and other groups’ numerical data in a good agreement. Droplet morphology, density, temperature and entropy increment were then carefully examined during the dynamic process from evaporation to boiling. Four phase transitions patterns were concluded, namely from surface evaporation, internal bubble, fragment and explosion, to flash boiling with increasing equivalent superheat degree that is defined by the non-dimensional superheat temperature over surface tension. Results showed that droplet temperature and density decreased slightly at surface evaporation when equivalent superheat degree was lower than 1/3. Above this criterion, the internal bubble could be sustained. Growth of new liquid nucleates and connected secondary liquid ring were calculated by domain growth theory. We found that droplet continuous to expand at high superheat but withdrawn at equivalent superheat degree equal to or lower than 0.52. At equivalent superheat degree higher than 1, the growth and expansion of droplet resulted in liquid fragment and explosion to many small secondary droplets. Mean mass and diameter of these droplets were found to have power-law dependency on the expansion rate. Finally, fast flash boiling occurred at equivalent superheat degree higher than 3. The vapor pressure in the chamber showed a negative linear correlation between the overpressure and the atmospheric pressure. We also found out that comparing to increase the pressure value, dense gas had better efficiency on retarding the propagation of shock wave.

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

The 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 seemingly useless reeds are prepared as thermal insulation materials, which not only meet the requirements of environmental sustainability but also enhance the added value of reeds, creating new economic benefits. The hydrophobicity of raw biomass surfaces leads to problems such as weak bonding strength and non-dense structure in the formed materials, as well as issues related to the residual insect infestations on the surface. In this study, reed straw was used as the raw material, and foamed geopolymer was used as the binder to prepare building insulation materials based reed. To improve the interfacial adhesion performance between reed straw and foamed geopolymer, a thermochemical modification method-thermal carbonization, was proposed. In this study, the mechanical properties and hydraulic properties of the studied materials with different degrees of surface thermal modification were tested, especially the fire resistance performance, and weathering resistance performance rarely found in published literature. When the surface thermal modification condition of reed straw was 250°C (30 min), the comprehensive performance of reed-based building insulation materials was the best, when the studied material density was 321.3 kg/m³; the compressive strength was 0.59 MPa; the thermal conductivity was 0.101 W/(m∙K); the pH was 11.27; the moisture absorption rate was 25.1%, and the compressive strength loss rate in wet-dry cycles was 18.5%. In addition, it had excellent fire resistance performance and weathering resistance performance. This new material can be widely used to improve the thermal insulation of traditional buildings and as sandwich filler in prefabricated buildings, such as preparing insulating walls.

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.

Phase change materials (PCMs) designate materials able to store latent heat. PCMs change state from solid to liquid over a defined temperature range. This process is reversible and can be used for thermo-technical purposes. The present paper aims to study the thermal performance of an inorganic eutectic PCM integrated into the rooftop slab of a test room and analyze its potential for building thermal management. The experiment is conducted in two test rooms in Antofagasta (Chile) during summer, fall, and winter. The PCM is integrated into the rooftop of the first test room, while the roof panel of the second room is a sealed air cavity. The work introduces a numerical model, which is built using the finite difference method and used to simulate the rooms’ thermal behavior. Several thermal simulations of the PCM room are performed for other Chilean locations to evaluate and compare the capability of the PCM panel to store latent heat thermal energy in different climates. Results show that the indoor temperature of the PCM room in Antofagasta varies only 21.1°C±10.6°C, while the one of the air-panel room varies 28.3°C±18.5°C. Under the experiment’s conditions, the PCM room’s indoor temperature observes smoother diurnal fluctuations, with lower maximum and higher minimum indoor temperatures than that of the air-panel room. Thermal simulations in other cities show that the PCM panel has a better thermal performance during winter, as it helps to maintain or increase the room temperature by some degrees to reach comfort temperatures. This demonstrates that the implementation of such PCM in the building envelope can effectively reduce space heating and cooling needs, and improve indoor thermal comfort in different climates of Chile.

Due to the wide application of floor heating systems, the radiant floor cooling systems has developed rapidly in recent years. In this paper, TRNSYS numerical simulation methods are used to study the influence of chilled water supply temperature and flow rate on the cold storage characteristics of a standard floor structure for office buildings in northern China. The results are verified by experimental measurements. The functional relationship between the saturated cold storage time and the chilled water flow rate is quadratic polynomial, while the changes of supply-water temperature have no effect on the saturation time; the supply-water temperature has a linear relationship with the saturated cold storage volume, while the chilled water flow rate has almost no effect on the saturation cold storage volume. The accumulated cold volume of floor changes with time in an exponential distribution with four coefficients, and the floor has the characteristics of rapid cold storage. This paper is instructive for the design, application and promotion of radiant floor cooling systems.

The temperature-dependent absorption coefficient and thermal conductivity of a quartz window are obtained through experimental tests at a wide range of temperatures. A Fourier transform infrared spectrometer with a heated cavity is used for performing the transmittance measurements. The spectral absorption coefficient of the quartz window is inverted by the transmittance information at different temperatures using a genetic algorithm. Then, a quartz window-graphite plate-quartz window multilayer structure is designed, and the transient response of the structure subjected to high-temperature heating is recorded by a self-designed setup. Cooperating with the above absorption coefficient, a non-gray radiative-conductive heat transfer model is built for the multilayer structure, and the intrinsic thermal conductivity of the quartz window is identified. Finally, the effects of the temperature-dependent absorption coefficient and spectral selective features of the medium on the heat transfer characteristics are discussed. The results show that the absorption coefficient gradually increases with temperature. The intrinsic thermal conductivity of the quartz window varies from 1.35 to 2.52 W/(m·K) as the temperature rises, while the effective thermal conductivity is higher than the intrinsic thermal conductivity due to thermal radiation, specifically 26.4% higher at 1100 K. In addition, it is found that the influence of the temperature-dependent absorption coefficient on temperature of unheated side shows a trend of first increasing and then decreasing. When the absorption coefficient varies greatly with wavelength, a non-gray radiative-conductive heat transfer model should be built for the semitransparent materials.

The characteristics of wind turbine wakes are influenced by multiple factors, including the atmospheric boundary layer (ABL) wind and wind turbine operating conditions (e.g., tip speed ratio and yaw angle). In this study, two types of ABL winds with different velocity gradients and turbulence intensities are generated in a wind tunnel through configurations of spires, baffles, and various numbers of roughness elements. A wind turbine with a rotor diameter of 0.8 m and a hub height of 0.6 m is tested under varying tip speed ratios, yaw angles, and ABL wind conditions. The results indicate that the streamwise velocity deficit in the near-wake region becomes more pronounced with an increase in the tip speed ratio, while the far-wake velocity deficit remains largely unaffected by changes in the tip speed ratio. As the yaw angle increases, the wake deflection becomes more prominent and the wake narrows; the offset of the wake center at various downstream positions grows linearly, reaching a maximum value of approximately half the rotor diameter. Furthermore, the turbulence level and influence range in the wake region are reduced when the turbine is yawed. Under ABL wind conditions, high turbulence intensity in the incoming flow accelerates wake recovery, and the Reynolds stress at different lateral positions tends to become consistent with increasing longitudinal distance. Additionally, turbulence has a significant impact on the meandering characteristics of the wind turbine wake, with greater fluctuations in the wake center observed under higher turbulence intensities. Overall, this study provides insights that could inform the optimal operation of wind farms.

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.

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.

Energy efficiency issues are being focused on the growing concern of global warming and environmental pollution. The high-temperature heat pipe (HTHP) is an effective and environmental-friendly heat transfer device employed in many industries, including solar power generation, high-temperature flue gas waste heat recovery, industrial furnaces, nuclear industries, and aviation. As a critical factor in HTHPs, thermal performance is mainly introduced in the entire paper. To date, most reviews have been published concerning one or several application scenarios. However, to the best of authors’ knowledge, it is hard to find a review discussing how to improve the thermal performance of HTHPs comprehensively. First, the impact on the performance of three main components of HTHPs over the past 30 years is introduced: the working fluid, the HTHP structure, and the wick structure. Herein, it is a considerable review of the optimal operating conditions for each direction, and we expect this paper contribute to improving the thermal performance of HTHPs. Then, current numerical simulations and theoretical research on the heat transfer limit of HTHPs are recommended. The significant hypotheses used in numerical simulations and the present theoretical studies are compiled here. Finally, some potential future directions and tentative suggestions for HTHP research are put forward.

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

Spray experiments of RP-3 jet fuel at non-evaporating and evaporating environments were studied on a constant volume spray chamber, and diffusive back-imaging technique was used to capture the transient spray development processes. Spray tip penetration, projected spray area and cone angle of RP-3 jet fuel were derived from the spray development images, and compared to those of diesel fuel. It is observed that non-evaporating sprays of RP-3 jet fuel and diesel fuel do not exhibit significant differences, as their spray penetration distances, projected spray areas and spray cone angles are consistent at most test conditions. The evaporating sprays of RP-3 jet fuel produce shorter liquid-phase penetration distances and lower projected spray areas than those of diesel fuel, and these differences are particularly pronounced at low ambient temperatures. However, fuel effects on the evaporating spray cone angle are insignificant. Further, increased ambient density or ambient temperature shortens the liquid-phase spray penetration distance and reduces the liquid-phase spray area, and these effects are more pronounced for diesel fuel than RP-3 jet fuel.