To improve the NO modelling in turbulent flames, the flamelet/progress variable (FPV) model is extended by introducing NO mass fraction into the progress variable and incorporating an additional NO transport equation. Two sets of flamelet databases are tabulated with progress variables based on major species and NO mass fraction, respectively. The former is used for the acquisition of the main thermochemical variables, while the latter is employed for NO modelling. Moreover, an additional transport equation is solved to obtain the NO mass fraction, with the source term corrected using the scale similarity method. Model assessments are first conducted on laminar counterflow diffusion flames to identify lookup-related errors and assess the suitability of progress variable definitions. The results show that the progress variables based on major species and NO could correctly describe the main thermochemical quantities and NO-related variables, respectively. Subsequently, the model is applied to the large eddy simulation (LES) of Sandia flames. The results indicate that the extended FPV model improves the NO prediction, with a mean error for NO prediction at 55%, significantly lower than those of existing FPV models (130% and 385%). The LES with the extended FPV model quantitatively captures NO suppression in the mid-range of Reynolds numbers from 22 400 (Flame D) to 33 600 (Flame E), but underestimates the NO suppression at higher Reynolds numbers from 33 600 to 44 800 (Flame F). This underprediction is primarily attributed to the underestimation of local extinction levels in flames with high Reynolds numbers.

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

This paper reports the results of an experimental study on the liquid phase characteristics of the biodiesel and diesel discharged from an equilateral triangular orifice and a circular orifice under different injection conditions by Mie-scattering imaging. The results revealed that the biodiesel liquid penetration length was longer than that of diesel under the same injection conditions. In addition, the increase of the chamber pressure was expected to enhance the interaction between air and fuel, resulting in the acceleration of the liquid phase breakup process. Moreover, with increasing chamber temperature, the liquid penetration of biodiesel was reduced less than that of diesel. This was due to the high surface tension and viscosity of biodiesel which inhibited the chamber air entrainment and suppressed the liquid breakup process. Accordingly, the higher probability of shorter diesel liquid penetration length indicated better air-fuel mixing than that of biodiesel. Besides, the triangular orifice liquid length was shorter than that of the circular orifice. And the stabilized liquid cone angle from the circular orifice was larger than that from the triangular orifice, indicating that using an equilateral triangular orifice has the potential to improve the air-fuel mixing process.

In line with achieving the outlook of Sustainable Energy Development (SED), Iran intends to increase the share of clean power to at least 8% of the country’s capacity by the end of 2026. This research aims to investigate the role and share of Bushehr Nuclear Power Plants (BNPP-1, 2, 3) in achieving the SED perspective of Iran, which has never been examined so far. In this connection, the comparative analyses of various power plants (PPs) of Iran including nuclear, fossil fuel, biomass, wind, solar thermal, photovoltaic, geothermal, and hydro PPs are carried out and discussed. The main indicators of SED such as Levelized Cost of Electricity (LCOE) metric, grid-level system cost, investment cost, external cost, average CO2 equivalent emission, ecosystem impact, required land area, required water, preservation of natural resources, human health, created jobs, international cooperation, social acceptance and Corporate Social Responsibility (CSR), and energy-water hub are thoroughly investigated. The statistical data used in the present study are extracted based on the authors’ experiences gained during the construction, operation and maintenance (O&M) of BNPP-1, the energy-environment balance sheets of Iran, as well as the design documents of BNPPs. Moreover, the gathered data are evaluated using MatLab programing language and analyzed in terms of comparative diagrams. The evaluations of BNPP-1 performance within the framework of SED indicate that BNPP-1 has little effect on ecosystems and is among the lowest greenhouse gases emitters compared to other Iran’s PPs so that it annually prevent the release of 0.7 million tonnes of carbon, SOx, and NOx compared to a gas-fired PP. Also, the cost analysis shows that the external cost of BNPP-1 is nearly zero and the grid-level cost is approximately 3 USD/(MW∙h) which is much lower than that for renewable powers. As per the LCOE metric and the cost of fuel supply, BNPP-1 is cost-competitive with other Iran’s PPs. The nuclear fuel cost of BNPP-1 is nearly 49 million USD per year which is at least 666 million USD per year less than Iran’s fossil fuel power plants (FFPPs). As per the nuclear and radiation safety of BNPP-1, the results illustrate that the average dose received by the residents living around the BNPP-1 is 2×10–4 mSv/year that is 10 000 times smaller than the average natural background radiation. Within the past ten years of BNPP-1 operation, no increase in cancers or death of skilled workers and residents living around the BNPP-1 has been reported. In addition to the production of clean power and freshwater, BNPP-1 has been developing excellent international relations and has been creating high-paying jobs, in particular for the local societies. Consequently, BNPP-1 could minimize the socio-economic and environmental concerns compared to the other Iran’s PPs, and therefore, BNPPs may play a vital and key role towards achieving the SED outlook of Iran through producing clean, reasonably-priced, environmentally friendly, reliable, and sustainable power and freshwater. Accordingly, Iran is to substitute nuclear power with more portions of the FFPPs in line with the sustainable development goals.

Ice accretion on surfaces of the aircraft and engine is a serious threat to the flight safety. In this paper, a novel hot air anti-icing method is proposed based on the porous foam. Taking the NACA0012 airfoil as an example, the traditional thermal protection structure is proved to exist the deficiency in balancing the heat exchange caused by route loss of the heat. By dividing the hot chamber into multiple regions to fill with various foam metal, flow resistance characteristics and heat transfer characteristics for this protection mode are analyzed in order to derive the maximized benefit in anti-icing process. The calculation results reveal that, under the same condition, the region filled with foamed copper not only improves the temperature uniformity on the anti-icing area, but also achieves a better protection effect for enhancing heat transfer between the tube and the hot gas, averagely above 20°C higher than it without porous foam filling in surface temperature. Additionally, the minimum mass flow rate of the protection hot air is reduced by 16.7%. The gratifying efficiency of the porous filler in fortifying heat transfer confirms the potential of replacing the efficient but complex heat transfer design with simple structure filled with foam metal.

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

In conventional parabolic trough collectors (PTCs), sunlight is concentrated at the bottom of the absorber tube, resulting in a significant circumferential temperature gradient across the absorber tube, heat loss and thermal deformation, which affects the safety and thermal performance of PTCs. In this study, a new receiver with homogenizer and spiral (RHS) is proposed, achieving the optical and thermal synergy to ameliorate the thermal deformation of the absorber tube and enhance thermal efficiency. A plane structure homogenizer is designed to improve uniformity of the concentrated solar flux of absorber tube through second reflection. In combination with the spiral, it improves the optical-thermal efficiency of the PTC by enhancing heat exchange between the fluid and the backlight side of the absorber tube. The performance of the collector is numerically studied by building a three-dimensional coupled light-thermal-structure model. The results show that the thermal deformation of the RHS is reduced by more than 96% and the optical-thermal efficiency is improved by 1.2%–0.63% compared with conventional receivers (CRs) under the same inlet temperature conditions. The proposed receiver is validated to be effective in reducing thermal deformation and improving optical-thermal efficiency.

Dodecyl alcohol (DDA) is a promising solid-liquid phase change material (PCM) due to its favorable latent heat storage (LHS) characteristics. However, the leakage issue of PCM in a melted state during the heating period and low thermal conductivity restricts its utilization potential in thermal energy storage (TES) practices. Within the same context, the present work aims to overcome the leakage issue and improve the thermal conductivity of the DDA. With this in mind, a novel leak-proof layered double hydroxide (LDH)/DDA composite PCM is proposed through a solution-based impregnation method. The leak-proof impregnation ratio of the DDA impregnated within the cavities of the synthesized Al/Fe-LDH was determined to be 60%. Detailed morphological, physicochemical, and thermal properties of the fabricated composite were studied by scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, differential scanning calorimetry (DSC), thermalgravimetric analysis (TGA), and thermal cycling study. The results show that the LDH/DDA composite has a suitable phase change temperature (about 20°C) for passive solar thermal management of building envelopes. This composite PCM showed high LHS enthalpy (about 136 J/g), good thermal stability, and cycling LHS reliability. It also showed nearly 152% higher thermal conductivity compared to that of pure DDA, ultimately reducing the melting and solidification time of the pure DDA by 44.9% and 45.5%, respectively.

The present study focuses on the influence of the swirling flows on flow behaviors and performance of a radial-flow turbocharger turbine under pulsating inflow condition. To characterize the effects of swirling flow, three sets of simulations of the turbine were carried out, which are an unsteady simulation under pulsating swirling inflow, an unsteady simulation under equivalent pulsating uniform inflow, and quasi-steady simulations under uniform inflow. Results proved that swirling flow has a considerable negative influence on turbine instantaneous performance and lead to 2.5% cycle-averaged efficiency reduction under pulsating flow condition. Swirling inflow would lead to significant losses in both the volute and the rotor, while the pulsating inflow leads to higher losses in the rotor and shows little influence on the losses in the volute. The instantaneous efficiency reduction of the turbine could be correlated with the time-varying inlet swirl strength. Under the influence of unsteady inlet swirls, the volute flow field is highly distorted and the free vortex relation is no longer valid. The swirling flow has strong interactions with the wake flow of the volute tongue, leading to additional losses. Relative flow angle at rotor inlet is remarkably reduced and its distribution is significantly distorted. Strong separation flows and passage vortices would appear in the rotor because of the swirling inflow, leading to inferior rotor performance.

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.

In terms of developing supercritical CO₂ (sCO₂) coal-fired power plants, enhancing cooling wall performance is one of significant factors to improve system performance. In this paper, a new cooling wall tube structure is proposed to match the non-uniform heat flux (NUH) with the thermal resistance by changing the cooling wall tube eccentricity. A three-dimensional multi-physical coupling model of cooling wall is constructed to compare the novel structure to the conventional structures. The properties of fluid dynamics, thermal stress, coupled heat transfer and cooling wall deformation are analyzed. In contrast to the traditional structure, the maximum temperature and circumferential temperature difference (CTD) of the proposed structure can be reduced by 2% and 27.4%, respectively. The essential working parameters related to the performances of the cooling wall tube are discussed. The maximum temperature of the new structure is reduced by 8–13 K and the maximum thermal stress is reduced by about 10%–15% under all the simulated working conditions when the eccentricity changes from 0 to 0.2. The proposed structure can effectively reduce the maximum temperature and circumferential temperature gradient under NUH. Consequently, a novel insight is put out for the design and optimization of the cooling wall tube in coal-fired power plants.

Swirl combustion serves as a helpful flame stabilization method, which also affects the combustion and emission characteristics. This article experimentally investigated the effects of CO₂ microjets on combustion instability and NO_x emissions in lean premixed flames with different swirl numbers. The microjets’ control feasibility was examined from three variables of CO₂ jet flow rate, thermal power, and swirl angles. Results indicate that microjets can mitigate the combustion instability and NO_x emissions in lean premixed burners with different swirl numbers and thermal power. Still, the damping effect of microjets in low swirl intensity is better than that in high swirl intensity. The damping ratio of pressure amplitude can reach the maximum of 98%, and NO_x emissions can realize the maximum reduction of 10.1×10^–6 at the swirl angle of 30°. Besides, the flame macrostructure switches from an inverted cone shape to a petal shape, and the flame length reduction at low swirl intensity is higher than that of high swirl intensity. This research clarified the control differences of mitigation of combustion instability and NO_x emissions by microjets in lean premixed flames with different swirl numbers, contributing to the optimization of microjets control and the construction of high-performance burners.

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.

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.

Water is a recyclable resource and the largest energy carrier on Earth. New hydropower generation technologies hold great promise for the future. However, there is a lack of evaluation standards for power generation performance. And, the mechanism of hydrovoltaic power generation lacks systematic clarity. In this study, a thermodynamic analysis method about hot and humid air energy conversion based on the principle of hydropower generation is established. To author’s knowledge, it is the first time that the maximum available energy of hydropower generation is analyzed by exergy and parametric calculations. The greater the difference, the higher the available energy. Also, a series of experiments were conducted to explore the power generation device materials, structural composition, and structural parameters, further clarifying the principle of electricity generation. And, the influence of temperature and relative humidity on the power generation performance was also studied. The increase in temperature can effectively increase the output electrical performance of the power generation. The open-circuit voltage and short-circuit current of water evaporation power generation with Al₂O₃ nanoparticles are higher than 2.5 V and 150 nA respectively. Through analysis, we propose relevant application strategies to provide theoretical and practical support for the development of green energy.

Methane has a narrow range of flammable limits, low flame speed and poor ignition characteristics, which limit its utilization in internal combustion engines. However, this issue can be remedied through the use of CH₄/DME blends, because DME has better ignition and combustion characteristics. In this study, the effects of pressure and blending ratio on the combustion characteristics of CH₄/DME blended fuels were investigated by using a high-pressure diffusion counterflow system, a constant volume combustion bomb, and CHEMKIN software. The reaction pressures are 0.1 MPa, 0.2 MPa, 0.3 MPa, and the blending ratios are 100% DME, 75% DME+25% CH₄, 50% DME+50% CH₄ and 25% DME+75% CH₄ (mol%). The results show that the laminar flame speed, flame temperature, and extinction limit of CH₄/DME blended fuel decrease as the CH₄ blending ratio or pressure increases. CH₄ addition and increasing pressure both lead to the competition for OH and H radicals between CH₄ and DME. However, the increase of CH4 mole fraction can also increase the path flux of CH₄+H= CH₃+H₂, while the increase of pressure can decrease this path flux. Moreover, increasing pressure can promote all reaction processes and reaction rates.

Recently, natural draft dry cooling system with the main-auxiliary integrated air-cooled heat exchangers in the up and lower layers, has drawn attention to the electric power industry. This research firstly develops two physical models for the integrated cooling system, namely Case A and Case B. In Case A, the main air-cooled heat exchanger is arranged in the upper layer and the auxiliary air-cooled heat exchanger arranged in the lower layer, while in Case B, the two heat exchanger systems are arranged in the opposite way. And then, directing at the engineering TMCR and TRL 1 working conditions, the unit-local-overall thermo-flow characteristics of Case A and Case B are obtained and compared by numerical simulation. The findings show that, for the auxiliary air-cooled exchanger, Case A has obviously higher cooling performances than Case B, with the difference varying from 5.46% to 7.55%. Whereas, for the main air-cooled exchanger, Case B shows the recovered cooling performances, with the difference changing from 1.15% to 2.99%. Case A is preferably recommended to the engineering application in consideration of more strict cooling demand of the auxiliary cooling system. Conclusively, this research will provide some theoretical guidelines for the design and construction of the main-auxiliary integrated natural draft dry cooling system.

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.

An extensive numerical investigation is conducted to characterize the flow separation control in a transonic compressor cascade with a porous bleed. The bleed holes are arranged on the suction surface in a single row, two staggered rows and three staggered rows. For each bleed scheme, five bleed pressure ratios are examined at an inlet Mach number of 1.0. The results indicate that the aerodynamic performance of the cascade is significantly improved by the porous bleed. For the single-row scheme, the maximum reduction in total pressure losses is 57%. For the two-staggered-row and three-staggered-row schemes, there is an optimal bleed pressure ratio of 1.0, and the maximum reductions in total pressure loss are 68% and 75%, respectively. The low loss in the cascade is due to the well-controlled boundary layer. The new local supersonic region created by the bleed hole is the key reason for the improved boundary layer. The vortex induced by side bleeding provides another mechanism for delaying flow separation. Increasing the bleed holes could create multiple local supersonic regions, which reduce the range of the adverse pressure gradient that the boundary layer needs to withstand. This is the reason why cascades with more bleed holes perform better.

To control the transition process in a laminar separation bubble (LSB) over an ultra-high load compressor blade at a Re of 1.5×10⁵, the effects of wall heat transfer were considered and numerically investigated by large eddy simulations (LES). Compared with the adiabatic wall condition, the local kinematic viscosity of airflow was reduced by wall cooling; thus the effects of turbulent dissipation on the growth of fluctuations were weakened. As such, the transition occurred much earlier, and the size of LSB became smaller. On the cooled surface, the spanwise vortices deformed much more rapidly and the size of hairpin vortex structures was decreased. Furthermore, the rolling-up of 3D hairpin vortices and the ejection and sweeping process very close to the blade surface was weakened. Correspondingly, the aerodynamic losses of the compressor blade were reduced by 18.2% and 38.4% for the two cooled wall conditions. The results demonstrated the feasibility of wall cooling in controlling the transition within an LSB and reducing the aerodynamic loss of an ultra-highly loaded compressor blade.

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.

Based on the actual operation parameters and temperature-dependent material properties of a gas turbine unit, composite cooling blade model and corresponding reliable boundary conditions were established. Transient thermal-fluid-solid coupling simulations were then comprehensively conducted to analyze the transient flow and the temperature field of the blade under startup, shutdown, and variable loads condition. Combined with the obtained transient temperature data, the non-linear finite element method was exploited to examine the effect of these transient operations on the turbine blade thermal stress characteristics. Results show that the temperature and pressure on the blade surface increase with the load level and vice versa. As the startup process progresses, the film cooling effectiveness and the heat convection of airflows inside the blade continuously grow; high-temperature areas on the pressure surface and along the trailing edge of the blade tip gradually disappear. Locally high-temperature zones with the maximum of 1280 K are generated at the air inlet and outlet of the blade platform and the leading edge of the blade tip. The high thermal stresses detected on the higher temperature side of the temperature gradient are commonly generated in places with large temperature gradients and significant geometry variations. For the startup/shutdown process, the rate of increase/decrease of the thermal stress is positively correlated with the load variation rate. A slight variation rate of the load (1.52%/min) can lead to an apparent alteration (41%) to the thermal stress. In operations under action of the variable load, although thermal stress is less sensitive to the load variation, the rising or falling rate of the exerted load still needs to be carefully controlled due to the highly leveled thermal stresses.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Syngas fuel generated by solar energy integrating with fuel cell technology is one of the promising methods for future green energy solutions to carbon neutrality. This paper designs a novel solar-driven solid oxide electrolyzer system integrated with waste heat for syngas production. Solar photovoltaic and parabolic trough collecter together drive the solid oxide electrolysis cell to improve system efficiency. The thermodynamic models of components are established, and the energy, exergy, and exergoeconomic analysis are conducted to evaluate the system’s performance. Under the design work conditions, the solar photovoltaic accounts for 88.46% of total exergy destruction caused by its less conversion efficiency. The exergoeconomic analysis indicates that the fuel cell component has a high exergoeconomic factor of 89.56% due to the large capital investment cost. The impacts of key parameters such as current density, operating temperature, pressure and mole fraction on system performances are discussed. The results demonstrate that the optimal energy and exergy efficiencies are achieved at 19.04% and 19.90% when the temperature, pressure, and molar fraction of H2O are 1223.15 K, 0.1 MPa, and 50%, respectively.

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.

Since the transition from rotating stall to surge in a transonic compressor at high speed is very quick, quite often there is no time to take measures to prevent the surge. Therefore, it is desired to find any rotating stall precursors, of which the occurrence can offer sufficient time for stall or surge prevention. In this study, a series of unsteady flow analyses were performed on a transonic compressor under operating conditions before rotating stall with unsteady results scrutinized to find rotating stall precursors. Particular attention is paid to the spatial modes and time modes of static pressure near the casing and around the blade leading and trailing edges. The results show that the characteristics of the precursor in both spatial and time domains can be used as rotating stall warnings.

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.

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.