摘要：
The installation of functional materials, including thermal insulation materials (TIMs) and phase change materials (PCMs), in concrete masonry unit (CMU) block (brick) walls is expected to obtain high thermal performance. However, since the apparent thermal capacity of PCMs is affected by a variety of factors, how to use PCMs rationally becomes a complex and systematic issue. At the same time, how to combine PCMs with TIMs in building envelope to achieve high stationary and transient thermal performances simultaneously is also an important issue that arises with the application of PCMs. The quantitative impact of the key factors, including the underlying patterns of the functional materials themselves, as well as others such as wall pattern, the location, quantity, and handling of the functional materials, is still not clear. In this study, a wall pattern analysis is experimentally performed for the integration of TIM and PCM in CMU-block walls. Walls equipped with various volumes of the two functional materials in eight placement modes under three representative thermal conditions are measured and discussed. The performance associated with the wall modes is completely analyzed. Thermal bridging is found to be a key factor in weakening the effect of the functional materials filled in wall cavities. In addition, the optimal locations and volumes of the functional materials are obtained. This study thermally reveals and gathers effect laws and applied principles, and provides data reference for the proper use of TIM and PCM outfitted building envelopes.
摘要：
Nano zero-valent iron (NZVI) technology has shown good potential for the treatment of selenium in wastewater. In this study, NZVI was loaded on activated carbon (AC) by carbothermal reduction method to synthesize highefficiency adsorbent (NZVI@AC). The agglomeration of NZVI was suppressed and its reactivity was improved. The optimum preparation temperature of NZVI@AC (600 degrees C) was determined by comparing its purity. Moreover, the synergistic effect between the active component (NZVI) and the support (AC) was investigated on the basis of the density functional theory method. The smaller HOMO-LUMO gap (0.87 eV) and charge distribution of NZVI@AC indicated favorable electron transfer and enhanced chemical reactivity. The adsorption and reduction to Se(0)/Se(-II) were elucidated as the underlying mechanisms for the removal of selenite by comparative analysis of the morphological transformation of iron and selenium species. Furthermore, the selenite removal performance of NZVI@AC was investigated on account of the impact of dissolved oxygen and pH values, and the interaction mechanism of these factors was revealed. The decrease of solution pH and dissolved oxygen concentration are effective ways to improve the removal efficiency of selenite.
摘要：
An imidazolium‐based 1‐B‐3‐MIMPF6 ionic liquid containing benzene ring with its large size, π‐π conjugation bond, and asymmetric charge distribution effect was utilized as the interface modifier for CsPbI2Br PSCs. The imidazole ring, benzene ring, and fluorine atoms of 1‐B‐3‐MIMPF6 have played a pivotal role in the synergistic effect of defect passivation, carrier transfer enhancement, large steric hindrance, and hydrophobicity. Abstract In recent years, hole transport layer‐free all‐inorganic CsPbI2Br carbon‐electroded perovskite solar cells (C‐PSCs) have garnered significant attention due to a trade‐off between stability and photovoltaic performance. However, there are inevitably many defects generated at the surfaces or grain boundaries of CsPbI2Br perovskite films, which will serve as carrier non‐radiative recombination centers, and CsPbI2Br perovskite films are sensitive to water molecules to degrade, together with energy level mismatch between CsPbI2Br perovskite and carbon electrodes. Herein, 1‐benzyl‐3‐methylimidazolium hexafluorophosphate (1‐B‐3‐MIMPF6), an imidazolium‐based ionic liquid simultaneously containing benzene ring and fluorine atoms, was introduced for the modification of the perovskite/carbon interface. The results showed that it could effectively reduce defects, enhance carrier transfer, mitigate carrier non‐radiative recombination, facilitate energy alignment, and block moisture intrusion. Therefore, the photovoltaic performance of the modified PSCs with ITO/SnO2/CsPbI2Br/1‐B‐3‐MIMPF6/carbon architecture has been boosted with a champion power conversion efficiency (PCE) of 13.47 %, open circuit voltage of 1.20 V, short circuit current density of 14.69 mA/cm2, and fill factor of 76 %. Moreover, the unencapsulated modified devices exhibited an improved stability and the PCE maintained 78 % of their initial PCE after 24 h storage at room temperature in a 30 %–35 % humidity environment, whereas that of the pristine devices dropped to almost zero.
关键词：
Quasi -zero -stiffness;Dynamic vibration absorber;Double frequency;Low frequency;Vibration suppression
摘要：
Generally, a dynamic vibration absorber (DVA) is effective in suppressing single-frequency vibration, which would be unworkable for double-frequency vibration. This study introduces a dual quasi-zero-stiffness dynamic vibration absorber (DQZS-DVA) as a solution to this problem. Firstly, the DQZS-DVA with a pair of mutually exclusive permanent magnets as the negative stiffness mechanism (NSM) is designed, and its static characteristics are theoretically analyzed. Next, the Harmonic Balance Method (HBM) is used to derive an approximate analytical solution, and the effect of system parameters on the dynamic characteristics of the primary oscillator is discussed. In addition, the dynamic behavior of the primary oscillator under a random or impulse excitation is numerically analyzed. The results demonstrate that the DQZS-DVA exhibits excellent vibration suppression under double-low-frequency harmonic, random, and impulse excitations. The anti-resonance frequency of the system with the DQZS-DVA can be reduced by 50 % compared to the linear DVA. Furthermore, the system parameters of the DQZS-DVA are optimized using the fixed-points theory to further improve the vibration suppression performance. Finally, a prototype of the DQZS-DVA is manufactured, and verification experiments are conducted. The experimental results confirm that the DQZS-DVA can suppress vibrations with double low frequencies of 3.5 Hz and 7.0 Hz. More importantly, the design procedure of the DQZS-DVA should be a valuable guide for dealing with the scenario when the primary oscillator suffers from an excitation with three or more frequencies.
摘要：
The usage of Mg-Al-Zn alloys for lithium-ion battery shell is able to achieve further lightweight of electric vehicles, and their corrosion resistance would highly determine the service life. In this work, therefore, a Ymodified AZ91 magnesium alloy (AZ91-0.5Y) was first prepared by conventional casting and following hot extrusion, and the influence of solution treatment (ST) and subsequent pre-deformation (SP) treatments on its electrochemical corrosion and stress corrosion cracking (SCC) resistance in 1 mol/L LiPF6 electrolyte were then investigated. The results indicated that the presence of large lamellar or rod-like beta-Mg17Al12 phase in as-extruded AZ91-0.5Y alloy would lead to serious micro-galvanic corrosion and SCC. After solution treatment, the beta-Mg17Al12 phase almost completely dissolved into Mg matrix, weakening the micro-galvanic corrosion and anodic dissolution (AD) and hydrogen embrittlement (HE) effect. Further, the subsequent pre-deformation treatment could introduce dislocation, more precipitation of Al2Y phase, massive twins and optimized texture, leading to the improved corrosion resistance and mechanical strength as well as the formation of well-integrated protective corrosion product film MgF2 with low porosity. As a result, the corrosion and SCC resistance of asextruded, ST and SP specimens is ordered from low to high.
摘要：
Ice on the surface of wind turbine blades may result in power production losses and unsafe operations. An effective technological solution to the ice issue is coating de-icing. This study first constructed SiO2 aerogel/CNTs (carbon nanotube) coating with photothermal de-icing by incorporating photothermal nanoparticles into the created nanoporous structure. The coating structure examined by SEM and EDS analysis demonstrates that CNT particles can be well captured by the three-dimensional nanostructure of SiO2 aerogel and form a stable symbiotic skeleton. After that, we examined how the quantity of CNT doping affected the coating's surface morphology and photothermal properties. The findings demonstrated that the C-6 coating made from 0.6% CNTs performed best. Utilizing the photothermal effect of CNTs, it exhibited a steady rate of temperature increase and reached the target temperature of 153.4 degrees C in 561 s upon near-infrared light (808 nm) irradiation. According to the results of experiments testing the photothermal performance, mechanical/chemical stability, and applicability of the coating, the coating has the advantages of being lightweight, provides quick de-icing, high stability, and simple production. This study not only increases the viability of using coating de-icing technology on wind turbine blades but also offers creative solutions to scientific investigation in the area of coating de-icing.
关键词：
Spectral beam splitter coating;Photothermal synergetic catalysis;Hydrogen production from biomass;Performance analysis
摘要：
Solar-energy-driven hydrogen production from biomass is a key technology for green hydrogen production. Photothermal synergistic catalysis is an effective means to enhance biological hydrogen production. In this study, a spectral beam splitter coating (SBSC) adapted for photothermal synergetic catalysis is designed and developed based on cesium tungsten bronze (CWO) and silicon dioxide (SiO2) in a sol-gel system. The CWO/SiO2 SBSC exhibits short-wavelength transmittance up to 85.7 % and absorption of near-infrared (NIR) light up to 91.3 % by adjusting the lifting speed, filling factor, and curing temperature. Evaluation model calculations reveal that the CWO/SiO2 SBSC can significantly improve the hydrogen production rate when the reaction solution temperature is 80 degrees C and that the integrated solar energy conversion efficiency is 3.7 times that without the SBSC. The results demonstrate the high durability of the CWO/SiO2 SBSC as well as its promising application scope in the pho-tothermal synergetic catalysis of biomass hydrogen.
作者机构：
[Zhang, Wei; Yang, Rufan; Liu, Liang; Qing, Mengxia; Ye, Yuchun; Yin, Yanshan] Changsha Univ Sci & Technol, Sch Energy & Power Engn, Changsha 410114, Peoples R China.;[Wu, Zhiliang; Wu, ZL] Curtin Univ, Western Australian Sch Mines Minerals Energy & Che, Discipline Chem Engn, GPO Box U1987, Perth, WA 6845, Australia.;[Chen, Houtao] State Grid Hunan Elect Power Co Ltd, Res Inst, Changsha 410003, Peoples R China.;[Xu, Yin] Yangzhou Univ, Sch Elect Energy & Power Engn, Yangzhou 225127, Peoples R China.
通讯机构：
[Zhang, W ; Wu, ZL ] C;Changsha Univ Sci & Technol, Sch Energy & Power Engn, Changsha 410114, Peoples R China.;Curtin Univ, Western Australian Sch Mines Minerals Energy & Che, Discipline Chem Engn, GPO Box U1987, Perth, WA 6845, Australia.
关键词：
Zigzag char;Defective char;Oxygen-containing functional groups;Density functional theory
摘要：
This work aims to investigate the effect of oxygen-containing functional groups (OFGs) on nitrous oxide (N2O) adsorption on char based on density-functional theory (DFT) at M06-2X/6-311G(d) level using pristine and defective zigzag char models. The char model configurations were geometrically optimized and single -point energy was calculated. The adsorption energy, bond length, Mayer bond order (MBO), atomic dipole moment corrected Hirshfeld (ADCH) charges, electrostatic potential (ESP), partial density of states (PDOS) and interaction region indicator (IRI) were analyzed. Results show that the presence of OFGs has little influence on the structure of char model but increases its activity. In addition, it was found that the effect of OFGs on N2O adsorption on char surface is related to char model and adsorption configurations. Further char configurations analysis after adsorbing N2O molecules suggests that the OFGs addition can significantly affect adsorption energies by changing chemical bond length and MBO. Moreover, the ESP analysis indicates that the OFGs addition increases the overall level of ESP on char surface, leading to the formation of orbital hybridization and electrons transfer and further promoting N2O adsorption on char surface. ADCH analysis indicates that OFGs affect the active site charge and facilitate N2O adsorption. IRI analysis reveals a variety of weak interactions in the structure after the incorporation of OFGs. Therefore, this study provides a theoretical foundation for a better understanding of the heterogenous adsorption of N2O on char.
摘要：
Pyrolysis technology is an effective way to realize the reduction and recycling of food waste (FW), but the generation of N-containing substances has a great impact on the quality of pyrolysis products and the environment. The present study mainly focused on the effect of typical component interaction on nitrogen conversion during the pyrolysis of FW, which was investigated by TG-FTIR, GC-MS, and DFT calculation. The experimental results show that during pyrolysis at 500 celcius, compared with soybean protein pyrolysis, co-pyrolysis of soybean protein with rice starch reduces the production of NH3 and HCN in the pyrolysis gas and reduces the production of nitriles in the pyrolysis oil, while the production of N-containing heterocycles and amides in the pyrolysis oil increases. Soybean protein and rice starch promote the immobilization of N in pyrolysis oil through Maillard reaction and produce Maillard reaction products (MRPs). MRPs can be converted to nitrogenous heterocycles by ring formation reactions, and to amides by continued cleavage, which results in the increased yields of N-containing heterocycles and amides in the pyrolysis oil.
摘要：
In this study, the condensation, as the fundamental step of polymerization, and decomposition mechanisms of levoglucosan in the condensed phase during cellulose pyrolysis were investigated using density functional theory (DFT) calculations to investigate non-specific solvent effects. The condensed phase was simulated using an im-plicit solvent model, while the dielectric constants of levoglucosan at different temperatures were determined by theoretical calculations. This study considered levoglucosan condensation reactions to form anhydro-disaccharides with various alpha and beta linkages (including 1,2-, 1,3-and 1,4-glycosidic bonds) and levoglucosan decomposition reactions including 1,2-dehydration, 1,3-dehydration, and ring-opening reactions. Our results show that the formation of beta-anhydro-disaccharides prefers the direct condensation mechanism of two levo-glucosan molecules through a four-member ring transition state, while kinetically more disadvantageous alpha-anhydro-disaccharides are generally formed by the condensation of levoglucosan molecule and alpha-d-glucose from levoglucosan hydrolysis. However, levoglucosan condensation without catalysis is unlikely to take place at typical temperatures of cellulose pyrolysis, due to the low reaction rate at low temperatures. At high tempera-tures above 625 K, levoglucosan condensation is also inhibited due to the higher Delta G theta and lower reaction rates, compared to those of levoglucosan decomposition. A high temperature above 800 K is needed for the obvious decomposition of levoglucosan, mainly through the ring-opening reaction to form 5-keto-6-deoxy-glucose, which is further promoted by the dielectric environment of the condensed phase during cellulose pyrolysis. Further calculations on acetic acid-catalyzed levoglucosan condensation and decomposition suggest that the consump-tion of levoglucosan at low temperatures is mainly due to catalysis of acetic acid on polymerization and further decomposition of polymers.
期刊：
Journal of Energy Storage,2024年78:110108 ISSN：2352-152X
通讯作者：
Sun, XQ
作者机构：
[Peng, Zian; Sun, Xiaoqin; Li, Jie; Yang, Huiting; Zhang, Hang; Sun, XQ] Changsha Univ Sci & Technol, Sch Energy & Power Engn, Changsha 410004, Hunan, Peoples R China.;[Liao, Shuguang] Changsha Maxxom High tech Co Ltd, Changsha 410000, Hunan, Peoples R China.;[Al-Saadi, Saleh Nasser] Sultan Qaboos Univ, Dept Civil & Architectural Engn, POB 33, Seeb 123, Oman.
通讯机构：
[Sun, XQ ] C;Changsha Univ Sci & Technol, Sch Energy & Power Engn, Changsha 410004, Hunan, Peoples R China.
关键词：
Composite PCM;Nanoparticle;Cold harvest;Multiwalled carbon nanotube;Heat transfer rate
摘要：
This paper investigates the cold energy storage of a horizontal shell-tube latent heat thermal energy storage (LHTES) unit for the cold harvest during night time. An experimental apparatus containing a horizontal circular tube with circumferential heating/cooling was designed and developed. Paraffin based phase change material (PCM) with a melting temperature of 27 degrees C was adopted as the cold harvest media. To improve the heat transfer rate, multi-walled carbon nanotubes (MWCNTs) were mixed with the paraffin to form a composite PCM with high thermal conductivity. A corresponding model of the composite PCM was developed and verified against the experimental data. Numerical simulations were performed for different boundary temperatures and concentrations of MWCNTs. The results show that when the heat transfer temperature difference is 20 degrees C, 0.05 wt% nanoparticles increase the melting rate of PCMs. When the heat transfer temperature difference was 40 degrees C, 0.10 wt% nanoparticles significantly affect the PCM melting rate. For low or high temperature (heat transfer temperature difference of 10 degrees C and 80 degrees C), the addition of nanoparticles is not conducive to improving the melting rate.
作者：
Chen, Xiangmin;Yao, Peng;Shu, Guoqiang;Zhang, Kang
期刊：
Journal of Mechanical Science and Technology,2024年38(3):1027-1037 ISSN：1738-494X
通讯作者：
Chen, XM
作者机构：
[Chen, XM; Chen, Xiangmin; Zhang, Kang; Yao, Peng; Shu, Guoqiang] Changsha Univ Sci & Technol, Sch Energy & Power Engn, Changsha 410114, Peoples R China.
通讯机构：
[Chen, XM ] C;Changsha Univ Sci & Technol, Sch Energy & Power Engn, Changsha 410114, Peoples R China.
关键词：
Multivariate variational mode decomposition;Improved dynamic time warping;Cross-correlation;Gear;Incipient fault
摘要：
The fault characteristics of incipient fault gears are relatively weak and easily buried by background noise. Moreover, the characteristics of fault gears exhibit similarities to those of normal gears, which may easily lead to misdiagnosis or missed diagnosis. To address these problems, an improved dynamic time warping (IDTW) method is proposed, and a methodology that combines IDTW and multivariate variational mode decomposition (MVMD) is also developed to extract the fault characteristics of incipient fault gears. In the developed methodology, MVMD is utilized to decompose the vibration signals of incipient fault and normal gears simultaneously to ensure the consistency of component frequency. Then, IDTW is employed to align the signal components that exhibit gear meshing frequency in normal and fault statuses to obtain the residual signal. Simulation and experimental results show that the developed method can effectively extract the incipient fault features of gears.
摘要：
Utilization of high-quality biomass resources such as Miscanthus is considered an effective way to alleviate energy shortages and develop a low-carbon energy economy. In this work, the economic benefits and environmental impacts of producing hydrocarbon biofuel by fast pyrolysis and catalytic hydrotreatment from Miscanthus were investigated, along with the differences in the utilization of biochar: combustion for heat supply (HS), soil amendment (SA) and upgrading to activated carbon (AC). The hydrocarbon biofuel mass yields of up to 23.3 % for all scenarios. The SA scenario had the lowest selling price of 6.89 Chinese Yuan (CNY) per liter. The HS scenario had the lowest total GHG emissions and fossil energy requirement (FED) of 19.2 gCO2e/MJ and 0.615 MJ/MJ, respectively. The AC scenario had the best net GHG emissions of -46.2 gCO2/MJ due to the replacement of the coal-based activated carbon pathway, but the higher energy consumption and capital investment limit its economic performance. Sensitivity analysis showed that fuel output had the most significant economic and environmental impacts. Optimizing the financing cost and system energy supply was a feasible and effective way to improve the economic and environmental sustainability of the bio-energy plant.
摘要：
Understanding and quantifying uncertainty factors are crucial for accurately predicting thermomagnetic convection phenomena. This study presented a mathematical model and algorithm framework for uncertainty analysis of thermomagnetic convection in porous media with random porosity. The proposed method combined Karhunen-Loe`ve expansion and intrusive polynomial chaos expansion to represent the input random parameters and output response, respectively. The Galerkin projection method was employed to decouple the stochastic governing equations of thermomagnetic convection into deterministic governing equations that can be efficiently solved using the finite volume method. By solving the polynomial chaos expansion of the output response and employing the stochastic projection method to solve the associated decoupled governing equations, the temporal evolution and statistical characteristics of the output response were obtained. The study revealed that porosity uncertainty in the porous medium affects the thermomagnetic convection of paramagnetic fluid, exhibiting significant chaos effects. Monte Carlo simulations were performed to validate the accuracy of the proposed approach and demonstrate its computational efficiency compared to traditional Monte Carlo methods. This research provides valuable insights into the uncertainty analysis of thermomagnetic convection and offers a promising methodology for analyzing heat transfer in various porous media applications.
摘要：
The dynamic response description of materials in high-speed impact fields is of practical significance to structural design and practical engineering application. In this paper, an electromagnetic impact (EI) loading process was proposed to acquire dynamic stress-strain relationships of 2A10 aluminum alloys. A modified Johnson-Cook (J-C) material model was obtained by combining with Quasi-static experiments and verified by numerical simulations. Comparing the J-C model obtained by a Split Hopkinson pressure bar, the simulative results about maximum deformation displacements showed the modified J-C model was more in line with actual experimental results. The accuracy under the discharge energy of 4 and 5 kJ was improved by 50% and 11%, respectively. In addition, electromagnetic impact loading characteristics and microstructure evolution of materials were studied. The discharge current with an attenuated sine wave caused that electromagnetic impact forces demonstrated a bimodal trend. The maximum impact velocities reached up to 4.7 m/s and 6.7 m/s under the discharge energy of 4 and 5 kJ, respectively (the maximum strain rates are 655.0 and 932.3 s-1, respectively). The high-speed impact effect led to the emergence of adiabatic shear bands (ASBs) during deformation microstructure evolution. Due to higher impact speed, the deformation concentration degree was more remarkable under the energy of 5 kJ.
摘要：
A mixture of polyethylene glycol and stearic acid is developed to extend the working temperature range and improve the heat utilization efficiency, and composited with carbonized loofah sponge fragments using melt impregnation method to improve the thermal conductivity of solid-liquid phase change material and find a solution for its leakage issue. The combination of different components, thermal stability, phase change behavior, thermal conductivity, shape stability, temperature response time and application cost are investigated. The results reveal that the mixture has two phase change temperature peaks including 59.81 degrees C and 68.01 degrees C, latent heat of melting is 215.20 J & sdot;g 1 and latent heat of crystallization is 193.40 J & sdot;g 1. The composites of polyethylene glycol, stearic acid and carbonized loofah sponge fragments is in a physical. Compared to the mixture, the latent heat of the composites gradually decreases, with a maximum decrease of latent heat of melting approximately 12.69 %, a maximum decrease of latent heat of crystallization approximately 10.24 %. For the same content of additives, the latent heat of the proposed composites in this work is greater than that of polyethylene glycolbased and stearic acid -based composites. The thermal conductivity of the composites gradually increases, in a range from 4.47 % to 10.91 %. The thermal conductivity of polyethylene glycol -based and stearic acid -based composites is lower than that of the proposed composites in this work in the case of the same content of additives. The cost of the composites with 2.5 wt% carbonized loofah sponge fragments is with a maximum 33.59 times cheaper than that of the composites with graphene nanoplatelets. Thus, from the perspective of cost, the combination of mixture and carbonized loofah sponge fragments has good economic benefit for thermal energy storage. The proposed composites demonstrate good shape stability, temperature response behavior and good economic benefit, indicating their good application prospects for thermal energy storage.
摘要：
The global energy consumption in the building sector is enormous annually, and the energy consumed in the building part is mainly used for heating, ventilation, and air conditioning. Smart windows can effectively reduce the energy consumed for heating, ventilation, and air conditioning. Vanadium dioxide (VO2) has been widely used in the preparation of thermochromic smart window films due to its excellent properties, but the low luminous transmittance of VO2-based smart films has been one of the main issues limiting their application. In this paper, we utilized the electrospinning technology to prepare VO2/PAN nanocomposite films with polyacrylonitrile (PAN) as the matrix and VO2 as the filler. Then, the VO2/PAN nanocomposite films were heattreated by the hot pressing technique. The VO2/PAN nanocomposite films with excellent performance were finally obtained. VO2/PAN nanocomposite films had stable morphology, uniform VO2 distribution, and high thermal stability. Besides, the hot-pressing process could significantly improve the mechanical properties of the films, and the maximum tensile strength of VO2/PAN nanocomposite film was 24.15 MPa. Moreover, according to UV-vis spectra, when the loading of VO2 was 20 %, the luminous transmittance (Tlum) of VO2/PAN nanocomposite film was 68.66 % and the solar modulating ability (Delta Tsol) was 0.28 %. Hence, this research offered a new option for the preparation of energy-saving materials that could replace smart glass.
期刊：
Environmental Science and Pollution Research,2024年31(3):3828-3852 ISSN：0944-1344
通讯作者：
Wang, JJ
作者机构：
[Li, Xinzhuo; Sun, Liutao; Tian, Hong; Kuang, Shengyu; Li, Weilin] Changsha Univ Sci & Technol, Sch Energy & Power Engn, Changsha 410114, Hunan, Peoples R China.;[Zhu, Lingkun; Wang, Jingjie; Xu, Yanhui] Harbin Elect Corp Harbin, Harbin Boiler Co Ltd, State Key Lab Efficient & Clean Coal Fired Util Bo, Harbin 150046, Peoples R China.;[Sun, Rui] Harbin Inst Technol, Sch Energy Sci & Engn, Harbin 150001, Peoples R China.;[Wang, Dengke] Henan Polytech Univ, Sch Safety Sci & Engn, Jiaozuo 454000, Peoples R China.
通讯机构：
[Wang, JJ ] H;Harbin Elect Corp Harbin, Harbin Boiler Co Ltd, State Key Lab Efficient & Clean Coal Fired Util Bo, Harbin 150046, Peoples R China.
关键词：
Burnout;Damköhler number;Inner recirculation zone;NOx emission;Swirl number
摘要：
To enhance the combustion efficiency and reduce NOx emissions in large-scale semicoke and bituminous coal blends, an extensive numerical study was conducted. The focus of this study was to optimize the quaternary air vane angle (α(v)) through detailed analysis of the temperature and flow fields, turbulence-chemistry interactions, char burnout, and NOx formation in a carefully scaled 1:5 dual-swirl burner. The results showed that with increasing α(v), the high-temperature flame region was narrowed and the peak temperature was reduced along with the broadened inner recirculation zone and the shrunken external recirculation zone due to better pulverized fuel-oxidant blending and reinforced convective heat transfer. The peak turbulent Damköhler number Da(t) evidently increased from 197.5 to 496 with increasing α(v), which implied a strengthened homogeneous combustion. Additionally, the corresponding mixing time scales increased while the chemical kinetics time scales decreased, which denoted that an intense diffusing flame was generated with a strong turbulent intensity. The peak heterogeneous Damköhler number Da(s-O2) showed a reduction from 2.54 to 2.27, while the peak values of Da(s-CO2) and Da(s-H2O) decreased from 0.1 to 0.077 and from 0.02 to 0.015, respectively. The char-O(2) reaction was controlled by diffusion/kinetics; both char-CO(2) and char-H(2)O reactions were determined by kinetics, and all gas‒solid reactions showed a kinetically controlled regime. With increasing α(v), the enlarged inner recirculation region increased the residence time, and a higher dilution level lessened the peak temperature, which led to reductions in fuel-NOx and the thermal-NOx. The α(v) range of 30-45° (or swirl number S(n) = 0.55-0.95) was suggested by taking the high burnout and low-NOx formation into account.
摘要：
Uncertainty propagation analysis plays a crucial role in understanding the impact of variations in initial condition, boundary condition, and fluid physical properties on simulation results for thermomagnetic convection heat transfer problems. To effectively analyze the uncertainty problem of thermomagnetic convection caused by random temperature fluctuations, a novel and comprehensive computational framework based on intrusive polynomial chaos approach was proposed in this paper. Our proposed approach aims to represent random temperature boundaries using Karhunen-Loe`ve expansion (KLE) and stochastic output response using polynomial chaos expansion (PCE). In addition, we use spectral projection method to transform the stochastic control equation into a group of deterministic control equations. We obtained the uncertainty characteristics of the stochastic output response by solving each polynomial chaos basis. Compared with Monte Carlo simulation (MCS), our approach accurately and efficiently predicts the uncertainty characteristics of thermomagnetic convection problems under stochastic temperature boundary conditions while significantly reducing computational resources.
