Ash powdery layer, arising from self-growing particle deposition in coal/biomass-fired boilers, seriously reduce the heat transfer efficiency. The lack of an analytical continuum mechanics solution, due to the layer's porosity, necessitates the use of discrete element method (DEM), while the high computational cost of DEM hinders its use at large scales. In this work, we propose a high-efficient fractal-based linear continuum model that addresses the mechanics of compressive non-continuous powdery layer. Initially, the mapping from fractal to continuum spaces is conceptualized using the bridging of fractal coordinates. Then a simplified fractal bar is used to construct the powdery layer, yielding the fractal-based continuum mechanics with three parameters: the fractal co-dimension zeta, cross-sectional dimension D s and the harmonic index p. Finally, utilizing quasi-static powdery layer DEM simulations, the parameter regularities are revealed, and the fractal-based continuum mechanics validated. Results show cross-sectional dimension D s , which quantifies microstructural complexity, exhibits an increase from 1.6 to 1.9 during layer growth before stabilizing, and co-dimension zeta, reflecting directional continuity, which declines from 0.9 to 0.7. Harmonic index p is calibrated to a constant value of 25 via least-squares optimization, confirming its universality across varying particle sizes and layer heights. Validation against DEM data corroborates the model's accuracy in capturing force-deformation behavior, with slight deviations attributable to linear elasticity assumptions. Furthermore, this framework provides both theoretical foundations and practical methodologies for efficient macro-scale analysis. It enables seamless integration into boundary element methods, achieving significant computational economies while preserving mechanical fidelity for industrial fouling evaluation.

Xylene is a widely used solvent in the coating and chemical industries and a major volatile organic compound with neurotoxic and pathogenic effects. It is also a key precursor of ozone depletion and fine particulate matter, posing serious environmental and occupational risks. This study experimentally investigates lean premixed xylene-air combustion in a porous-medium burner, focusing on how the equivalence ratio affects flame stability, heat feedback, and extinction. A dual-layer reactor comprising ceramic foam and alumina beads is operated at Phi = 0.25-0.8, and axial thermocouples record temperature profiles to analyze flame propagation and conduction-radiation coupling. As Phi increases from 0.5 to 0.8, the flame front shifts upstream and stabilizes more rapidly. Within the Phi = 0.6-0.8 range, the exhaust removal efficiency exceeds 90%, indicating effective oxidation of xylene under these conditions. At Phi = 0.5, a super-adiabatic peak of about 1265 K appears due to coupled thermal cracking and secondary oxidation of xylene, and steady combustion is reached after roughly 40-50 min. Under leaner conditions (Phi <= 0.45), insufficient heat feedback causes upstream-to-downstream extinction, yielding a stability limit of Phi approximate to 0.45. These results clarify heat-feedback kinetics and guide the design of low-emission, high-efficiency porous-medium burners.

Liquefied natural gas (LNG)-powered ships possess available utilizable energy resources, including LNG vaporization cold energy and main engine flue gas waste heat. To improve the ship energy utilization efficiency, this paper takes a 215,000-ton Very Large Crude Carrier (VLCC) as the research object, and couples the organic Rankine cycle (ORC) and transcritical carbon dioxide (TCO2) Rankine cycle to achieve the combined recovery of ship cold energy and waste heat. To systematically investigate the thermal performance of the integrated system, a simulation model is established by using Aspen HYSYS to acquire basic thermal parameters. Advanced exergy analysis is adopted as the core research method for the first time to evaluate the thermal performance of the system, and the obtained results are compared with those of the conventional exergy analysis. Conventional exergy analysis reveals that Heat Exchanger 1 is the core component restricting the performance optimization of the whole system. Further results from advanced exergy analysis show that the proportions of avoidable exergy destruction and endogenous exergy destruction of the overall system are 40.46% and 58.72%, respectively. Key optimization links are further identified based on the advanced exergy analysis results, and the genetic algorithm (GA) is applied for targeted system optimization. After optimization, the system output power reaches 1772.06 kW and the exergy efficiency is 48.32%, which are increased by 5.56% and 15.54% correspondingly. Economic evaluation indicates the annual net profit reaches 3.8336 million CNY, with a static payback period of 5.49 years.

To address the urgent need for low-carbon transformation in the marine sector, a novel hybrid propulsion system has been proposed and developed for a 3000 DWT ammonia-fuelled general cargo vessel. This system employs an external ammonia reforming-based solid oxide fuel cell and gas turbine as the upper cycle, coupled with a transcritical carbon dioxide Brayton cycle as the lower cycle. it also integrates subsystems for domestic heating and nitrogen-reclaimed water recovery to achieve deep cascading utilization of low-temperature waste heat. This study uses Aspen Plus to construct a steady-state simulation model for a comprehensive assessment of the system's energy efficiency, exergy efficiency, and economy from thermodynamic and economic perspectives. Subsequently, through the integration of MATLAB and Aspen Plus, multi-objective genetic algorithms is used to globally optimize critical operational parameters. Optimization results show that thermal performance and economy of hybrid system are significantly improved: the net power output reaches 5767 kW, energy efficiency and exergy efficiency attain 60.4% and 64%, respectively, while the unit cost of electricity generation is reduced to 0.1135 $/kWh.

Regenerative thermal oxidizer (RTO) is a widely used device for reducing volatile organic compounds (VOCs) generated in the industry. As an essential component of VOCs, o-xylene undergoes a complex multistep combustion process in RTO. A simplified combustion mechanism (SCM) containing 62 species and 296 elementary reactions is derived from the detailed combustion mechanism (DCM) of o-xylene. A comprehensive validation of the SCM is performed by comparing its predictions with experimental measurements of ignition delay times, laminar flame speeds, and species concentration distributions. Subsequently, an integrated RTO-SCM coupled combustion model is formulated and rigorously verified against experimental date. Simulation results reveal distinct distribution regions for o-xylene combustion intermediates within the RTO. The primary reaction zone is localized at the junction area connecting the regenerator and the combustion chamber. However, low concentrations of o-xylene cannot be completely oxidized to the final products in the RTO. During the initial operating cycle of the RTO, VOC emission peaks with o-xylene, C6H6, and C6H5CH3 as the dominant components. As combustion chamber temperature increases in subsequent cycles, the o-xylene concentration at the outlet gradually decreases to below 40% of the total emissions, with overall VOC levels maintained below 10 mg/m3.

Hydrophobic graphene nanosheets were successfully modified with TiO2 to create a pure and stable nanoparticle. The resulting material exhibited improved heat transfer efficiency when used as nanofluid in pool boiling. We prepared graphene nanofluid, TiO2 nanofluid, and graphene-TiO2 hybrid nanofluid with varying concentrations to investigate their heat transfer characteristics. The heat transfer coefficient of graphene-TiO2 hybrid nanofluid is higher than that of water at the same heat flow density, especially in the low heat flow density region( below q = 4 & sdot;105 W/m2). Additionally, by employing a high speed camera, we observed that the hybrid nanofluid displayed shorter bubble generation periods and smaller bubble separation diameters. These findings highlight the exceptional heat transfer performance of the covalently modified and hybridized nanofluid. Overall, our comprehensive testing program confirms the enhanced heat transfer capabilities of this modified nanofluid, positioning it as a promising choice for various heat transfer applications.

This paper presents an advanced numerical simulation method that overcomes the limitations of previous models in accurately predicting the behavior of nanoparticles in electrostatic precipitators. Building on the Fuchs diffusion charging theory, a correction factor is introduced, enhancing the prediction accuracy by approximately 30 % compared to earlier simulations. Moreover, the model incorporates the effects of non-uniform flow fields, electric fields, and space charge density distributions on nanoparticle behavior. The results demonstrate that, in comparison with experimental data, the deviation is less than 16.5 % for particle diameters ranging from 16 nm to 100 nm, and less than 5.5 % for diameters below 16 nm. Furthermore, the paper investigates the cause of the "U"-shaped penetration curve of nanoparticles (i.e., the penetration rate initially decreases and then increases with increasing particle size). For particles smaller than 16 nm, the decrease in penetration rate is primarily due to partial charging effects, where smaller particles are less likely to acquire a charge and, therefore, are less efficiently captured. In the 16 nm to 100 nm range, the increase in penetration rate is mainly attributed to the reduction in particle electric mobility as their size increases, leading to a decrease in their lateral velocity. This causes the particles to be carried out by the airflow before reaching the collection plates. The two-dimensional numerical simulation method proposed in this study provides a novel theoretical framework for accurately predicting the behavior of nanoparticles in electrostatic precipitators, offering valuable insights for the optimization of precipitator design.

The present study aimed to address the limitations of existing kinetic mechanisms for dimethyl methylphosphonate (DMMP) by experimental measurements and kinetic optimization. Some new experimental data on laminar flame speeds of CH4/air and C3H8/air mixtures doped with DMMP are obtained through the heat flux method, particularly in the rich combustion region where data are previously scarce. The results verify that, as the equivalence ratio increases, the inhibitory efficiency of DMMP decreases for methane and propane flames, but gradually increases for hydrogen flames. Subsequently, a new optimized DMMP mechanism is proposed utilizing the particle swarm algorithm to adjust the pre-exponential factors of 26 P-containing reactions within their uncertainty domains. The results demonstrate that the optimized mechanism not only improves the laminar flame speed of the DMMP-doped hydrocarbon flames (H2, CH4, and C3H8) in the stoichiometric and rich regions, but also improves the description of ignition delay time for the lean H2/DMMP and the rich CH4/DMMP mixtures. In addition, the updated model shows moderate to significant improvements in species concentration predictions, particularly in reproducing the CO yield during DMMP oxidation in Shock Tube, the HOPO of DMMP pyrolysis in Jet-Stirred Reactor, and the H-radicals of doped premixed flame in Flat Burner. In summary, the updated model offers a more comprehensive and accurate portrayal of the existing measurements including the laminar flame speed, ignition delay time, and species concentration.

The application of "biphilic surfaces" in boiling heat transfer has attracted widespread attention, and scholars have conducted numerous experimental studies in this field. Unfortunately, the relevant theoretical research is almost blank, especially in predicting essential parameters such as HTC. Therefore, it is necessary to develop a new correlation for the HTC of biphilic surfaces in boiling heat transfer. Firstly, in this study, biphilic surfaces composed of pure copper and Ag(S(CH2)17CH3) were prepared using standard photolithography and chemical etching techniques. All of the surfaces feature 1000 mu m square patterns, but there are variations in the contact angles (120.4 degrees, 124.5 degrees, 130.3 degrees, 135 degrees, 140 degrees) of the hydrophobic surfaces. The maximum critical heat flux was 1203.5 kW/m2, and the maximum heat transfer coefficient was 77.8 kW/m2K. Secondly, this study proposed the characteristic contact angle theta char, which solves the issue of representing the wettability of biphilic surfaces with two contact angles. Next, the paper verified reliability of normalization process by combining the theory of homogeneous surfaces. Finally, this paper analyzed the undetermined coefficients in Rohsenow's correlation by theta char, enabling the prediction of HTC for biphilic surfaces. Compared with experimental data, the maximum prediction error does not exceed 24.13 %.

This study demonstrated that combination hydrophilic copper and hydrophobic nano-silver surfaces simultaneously enhanced the critical heat flux (CHF) and heat transfer coefficient (HTC) in pool boiling heat transfer (BHT) with deionized water as the employed working fluid. To further investigate the influence of geometric factors on heat transfer, this study designed three patterns denoted as squares/stripes/networks, ranging from 50 mu m to 3000 mu m. The effects of pattern size d, spacing p, and pitch ratio p/d on heat transfer results were obtained. Based on bubble visualization, the study further analyzed the reasons for inflection points in the boiling curve and the mechanisms caused by porous hydrophobic coating. Finally, the study proposed a numerical model suitable for predicting CHF of biphilic surfaces based on Helmholtz instability and Taylor instability. The model began with vapor columns escaping toward far-field and the fluid supplied to the heating surface. Concrete model derivation and adjustments are categorized according to the relationship between pattern size and bubble detachment diameter. For surfaces where the bubble detachment diameter exceeds the pattern size, this study originated from the perspective of Helmholtz instability on the vapor column surface. The resulting model is anticipated to quantitatively solve for the former and modulate the wavelength of Taylor instability on biphilic surfaces. Regarding surfaces with bubble detachment diameters smaller than the pattern size, this research begins with the existence time of the micro-liquid layer. The derived model validates the predominant role of p/d in the CHF values on micron-scale biphilic surfaces.

Ethylene plays a crucial role as an intermediate component in the cracking and combustion processes of large molecular alkane and olefins. In this article, the laminar flame speed of ethylene-air mixtures was measured using the heat flux method. The mechanism of ethylene was simplified by utilizing the error propagation directed relationship graph (DRGEP) and sensitivity analysis (SA), and the Arrhenius pre-exponential factors for 20 selected reactions in the skeletal mechanism were optimized using the particle swarm optimization (PSO) algorithm. Finally, an ethylene optimization mechanism including 39 species and 85 reactions was obtained. The prediction results for flame speed, ignition delay time, and species concentration were compared with experimental data and other mechanisms, covering a wide range of temperatures (298-1725 K), pressures (1-22.8 atm), and equivalence ratios (0.5-2.0). The findings demonstrate that the optimization mechanism not only improves the prediction results of laminar flame speed in the rich combustion zone and low oxygen environment but also enhances the prediction accuracy of the ignition delay time at high pressure and in the lean combustion zone, as well as the prediction accuracy of C2H4 and H2O radicals. In conclusion, the optimized mechanism exhibits higher accuracy and broader applicability.

In the present work, the laminar burning velocities of NH3 + hydrous C2H5OH + air flames were measured using the heat flux method at 1 atm with varied equivalence ratios and mixing ratios (with hydrous ethanol molar fractions of 45%-75%). The measurements were carried out at unburned temperatures of 358 and 378 K. The results show that the laminar burning velocities increase with the increase of hydrous ethanol mixing ratio and temperature, indicating that hydrous ethanol contributes to the combustion of NH3 flames. Based on Wang et al.'s CEU-NH3 mechanism, sensitivity, reaction pathways, and product formation rate analyses were conducted. The results show that the addition of water reduces the laminar burning velocities of mixed fuel. Intermediate radicals such as NH and HNO are crucial for the formation of NO. After adding water, in the preheating zone, the total production rates of key species such as NH3, H, O, and OH radicals and intermediate species like NH2, NH, HNO, and N decrease, leading to a reduction in the total NO generation rate and the peak mole fraction of NO in the reaction zone.

In recent years, studies on patterned surfaces with different local wettabilities have emerged and developed. A number of peculiar structures are the most promising topographic ones in simultaneously enhancing CHF and HTC due to their high efficiency, and compatibility with other strengthening methods. Many studies have attempted to explore the optimal expression of wettability patterned surfaces for preparation of a boiling surface, pattern design, wettability, and diverse combination. There are hundreds of relevant literature works, and a comprehensive analysis and summary is required. This article first provides a detailed introduction to the manufacturing processes of these engineering surfaces, which are technically divided into wettability acquisition and pattern combination methods. It continues with different factors affecting surface boiling and the unique bubbling attributes which led to these differences. A review of visualization studies aims at providing an analytical basis for these effects. Finally, this article summarizes the prediction models and proposes challenges which confront future research works. This work provides a comprehensive introduction to the most recent research on wettability patterned surfaces.

This study investigates the boiling characteristics of graphene (GNP) nanofluids, graphene-copper (GNP-Cu) composite nanofluids, and graphene-iron (GNP-Fe) composite nanofluids with mass fractions of 0.001%, 0.002%, and 0.003%. The results indicate that GNP-Cu and GNP-Fe nanofluids can simultaneously enhance the critical heat flux (CHF) and heat transfer coefficient (HTC). Among different mass fractions, GNP-Cu nanofluids with a mass fraction of 0.003% exhibited the highest CHF and HTC. Through the observation of bubbles, the research elucidated that the presence of copper and iron elements is crucial in enhancing heat transfer. Based on the experimental results, this study modified the boiling curve equation of Rohsenow into a linear function. The modified model can predict the boiling curves of GNP-Cu, GNP-Fe, and GNP-Ag nanofluids at various concentrations. Furthermore, the experimental findings indicated a quadratic relationship between the boiling heat transfer coefficient and the heat flux in GNP, GNP-Cu, GNP-Fe, and GNP-Ag nanofluids. As a result, this study investigates the differences in heat transfer and bubble dynamics among GNP nanofluids modified with various metallic elements during boiling. It explores the underlying heat transfer mechanisms and proposes boiling curve equations that are applicable to a range of nanofluids. The findings suggest that acid-mixing treatment and metal-functionalization play a facilitating role in heat transfer of GNP nanofluids. Furthermore, nanofluids loaded with different metallic elements exhibit similar trends in their boiling curve equations.

The deposition characteristics of weld fume particles in an electrostatic precipitator were investigated by means of numerical simulations. In the calculations, the particle characteristics of the weld fume particles and the effect of ionic wind are considered. The effects of applied voltage, flow velocity, collecting plate spacing, particle concentration, electric field strength, and ionic wind on the collection efficiency of weld fume particles in the ESP are discussed. The velocity distribution of weld fume particles in the Electrostatic precipitator (ESP) was also investigated. The results show that the smaller the collection plate spacing, the higher the collection efficiency of particles. The particle concentration has a small effect on the collection efficiency of weld fume particles. The higher the applied voltage, the more obvious the difference of ESP on the collection efficiency of different particles.

Welding fume is hazardous to the environment and human health and is purified using an electrostatic precipitator (ESP). Electrostatic precipitators are widely used in waste gas treatment processes in thermal power plants, cement plants and other factories. The use of electrostatic precipitators to treat welding fumes requires further research. Corona discharge occurs at the electrostatic precipitator, the primary condition for particle charging. The components and physical parameters of the treated particles should be considered in the numerical simulation. This paper investigates the effects of polygonal electrode form, deflection angle, and spacing on the electric field distribution and collection efficiency. The physical quantities in the vicinity of the electrodes vary greatly. Therefore, the focus is on the vicinity of the electrode, and curves describing the trend. It is shown that the maximum velocity did not vary monotonically with increasing the number of tips and that the highest collection efficiency is obtained with a triangle electrode. Furthermore, it is shown that the variation of interelectrode distance leads to variations in the inter-electrode shielding effect.

As an important gas-solid two-phase separation equipment in industrial production, cyclone separator is widely used in shipbuilding, petrochemical, coal-fired power, resource development. According to the theory of turbulent mixing laminar flow separation, regarding the actual physical parameters of particles in dusty air and the structure size of cyclone dust collector as the variable, the corresponding mathematical model of collecting efficiency was established, which based on the semi-empirical design method of cyclone dust collector proposed by classical Leith-Licht theory. According to mathematical model, the optimization objective function was proposed, which was used to optimize the size of cyclone separator by self code. Finally, combined computational fluid dynamics（CFD）method, the dust removal efficiency of the optimized model was verified. The simulation results show that the theoretical calculation of the mathematical model is in great agreement with the simulation results, the error is only 1.41%. This method overcomes some shortcomings such as long period of experimental verification and poor economy, which also has important engineering application value to the optimum design of cyclone separator.

Graphene nanoplatelets (GNP) have natural hydrophobicity and are not easy to disperse in deionized (DI) water. In this study, Ag modified functionalized GNP (f-GNP) was used to prepare novel hybrid nanoparticles. Through phase and structural analysis, it is found that the material has high purity, and is dispersed in DI water to produce the nanofluids that are stable. The boiling heat transfer properties of GNP nanofluids, GNP/Ag mixed nanofluids and GNP-Ag hybrid nanofluids of three weight concentrations (wt% = 0.001, 0.002, 0.003) were investigated. Among the nine samples, the GNP-Ag hybrid nanofluids with weight concentration of 0.001% has the best heat transfer property, with a critical heat flux (CHF) of 170.74 W/cm(2), which is 52.31% more than the one of DI water. After the boiling experiment, the heating surface was analyzed by scanning electron microscope (SEM) to observe the deposition structure of nanoparticles. It is found that the self-assembled structure of the hybrid nanoparticle deposition is more complex. Under the combined action of the oxygen-containing functional groups of the nanoparticles, the lateral heat transfer of the working medium is strengthened, and the separation of the vapor bubbles is promoted. In the wettability analysis, the contact angle of the nanofluids were measured, and it was found that the hybrid nanofluids was hydrophilic, which improved the liquid supply mechanism on the heating surface and was beneficial to increase the CHF. The bubble formation characteristics of nanofluids were observed by high-speed camera, and it was found that the bubble formation period of hybrid nanofluids was short and the bubble separation diameter was small. Results from tests and experiments indicate that covalent modified hybrid nanofluids have good heat transfer performances.(c) 2022 Elsevier B.V. All rights reserved.