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cfd modeling of Phase Change during the Flashing-Induced Instability in a Natural Circulation Circuit

PROCESSES 2023年第7期11卷 1974页

作者： Liao, Yixiang Lucas, Dirk Helmholtz Zentrum Dresden Rossendorf Inst Fluid Dynam Bautzner Landstr 400 D-01328 Dresden Germany

Flashing-induced instability (FII) has a significant impact on the safe operation of a natural circulation circuit, a phenomenon frequently encountered in the cooling systems of advanced light water reactors. While one-dimensional system codes are commonly used for the engineering design and safety analysis of FII, there is a strong academic interest in understanding the underlying physical mechanisms. To address this, high-resolution computational fluid dynamics (cfd) simulations serve as a valuable tool. However, the current state of cfd modeling for two-phase flows with phase change, which are particularly highly transient fluctuating flashing flows, is still in its early stages of development. In this study, we establish a cfd model that focuses on interphase heat transfer to analyze the phase change during FII. By incorporating experimental data from the literature, we investigate the transient flow field and thermodynamic behavior in the riser of the GENEVA test facility. The study provides valuable insights into the non-equilibrium and interfacial transfer phenomena during the phase change as well as the effect of high-frequency fluctuation. Additionally, we discuss in detail the challenges associated with FII modeling and the limitations of the current model. We also provide suggestions for potential improvements in future numerical studies. The results show that the thermal phase change and heat transfer coefficient model adopted for the simulation reasonably captures the evaporation and condensation process. However, it tends to under-predict the evaporation rate, which results in a larger pressure drop through the riser. The observation that the void fraction close to the wall is higher than that in the riser center evidences that the reliable modeling of bubble size distribution as well as the inclusion of non-drag forces are important for predicting the transverse void distribution. Furthermore, it reveals that both the temperature and pressure change i

关键词： flashing-induced instability thermal phase change model thermal and mechanical non-equilibrium cfd modeling

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cfd modeling of optimal airflow rates for safe production in isolated mining faces with high methane concentration and coal spontaneous combustion

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JOURNAL OF CLEANER PRODUCTION 2023年 423卷

作者： Chen, Dawei Xie, Jun Wang, Yi Sun, Xiangke Du, Haigang Li, Gang Shandong Univ Sci & Technol Coll Safety & Environm Engn Qingdao 266590 Peoples R China Shandong Univ Sci & Technol State Key Lab Min Disaster Prevent & Control Cofou Minist Sci & Technol Qingdao 266590 Peoples R China Liupanshui Normal Univ Dept Min Engn Liupanshui 553004 Peoples R China

From the perspective of airflow rate adjustment for disaster prevention, controlling methane concentration and reducing spontaneous combustion zone in the goaf naturally contradict. Generally, an increased airflow rate is beneficial in reducing methane concentration but also increases the risk of coal spontaneous combustion. Coal pillars on both sides of an isolated mining face are broken to form air leakage passages, which connect its goaf and the two sides of the goafs to form triple goafs. Especially for triple goafs of the isolated mining faces with high methane concentration and coal spontaneous combustion tendencies, the lack of air leakage law and knowledge of the distribution of methane and oxygen concentrations makes disaster prevention and control difficult. To solve the above problem, this study adopts a computational fluid dynamics (cfd) modeling method to construct a physical model containing triple goafs and investigate the optimal airflow rates for safe produc-tion, with an isolated mining face in a mine in Guizhou taken as an object. Results show that the air leakage paths in the triple goafs of the isolated mining face mainly consist of "U-shaped" and "semi-U-shaped". The optimal airflow rates to maintain methane concentration at safety limits and to minimize the spontaneous combustion zone in the triple goafs are 1800 m3/min to 2000 m3/min. In consideration of economic efficiency and workload, the optimal installation spacing of the dynamic barriers is determined as 15.0 m-20.0 m. The study results provide scientific concepts and practical guidance for the prevention and control of methane and coal sponta-neous combustion hazards in triple goafs of isolated working faces.

关键词： cfd modeling Methane hazard Coal spontaneous combustion Optimal airflow rates Isolated mining face Triple goafs

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cfd modeling of MEA-based CO2 spray scrubbing with computational-effective interphase mass transfer description

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CHEMICAL ENGINEERING RESEARCH & DESIGN 2023年 189卷 606-618页

作者： Xu, Yin Chang, Wenjie Chen, Xiaole Jin, Baosheng Yangzhou Univ Sch Elect Energy & Power Engn Yangzhou 225127 Jiangsu Peoples R China Southeast Univ Sch Energy & Environm Key Lab Energy Thermal Convers & Control Minist Educ Nanjing 210096 Jiangsu Peoples R China Nanjing Normal Univ Sch Energy & Mech Engn Nanjing 210042 Jiangsu Peoples R China

Great concerns for global warming and stringent regulations have spurred the development of feasible technologies to reduce CO2 emissions from the power generation sector. In thermal power plants, spray scrubbing is one of the most used methods for separating gaseous pollutants, which inspires the idea of applying spray scrubbing in CO2 capture. However, this new idea still necessitates investigation, particularly in developing a novel modeling tool. This motivates us to present the cfd modeling of CO2 spray scrubbing using MEA solution in this work. CO2 spray scrubbing is a complex process. Herein, the established model combines the multiphase flow with interphase transfer and chemical reactions in the Euler-Lagrange framework. To efficiently describe the interphase mass transfer, we proposed a new method based on the thermodynamic consistency between the CO2 equilibrium pressure and the enthalpy of CO2 absorption. Validated by the experimental data, this method can achieve an acceptable balance between accuracy and computational cost. The zwitterion mechanism was employed to describe the chemical reactions. Kinetic analysis shows that E = (1 +Ha2)0.5 can reasonably evaluate the enhancement factor value in a wide range of MEA concentrations. Additionally, the effects of operating parameters on CO2 removal were numerically studied, focusing on mass transfer characteristics. Therefore, the proposed numerical model will be beneficial for facilitating the deployment of CO2 spray scrubbing in the power sector, and the numerical results provide helpful information for design and optimization.(c) 2022 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

关键词： cfd modeling CO2 capture Mass transfer Chemical scrubbing

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Multi-step kinetic mechanism coupled with cfd modeling of slow pyrolysis of biomass at different heating rates

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CHEMICAL ENGINEERING JOURNAL 2024年 479卷

作者： Sangare, Diakaridia Moscosa-Santillan, Mario Bostyn, Stephane Belandria, Veronica Martinez, Alejandro De la Cruz Van De Steene, Laurent CIRAD UPR BioWooEB 73 rue Jean Francois Breton F-34398 Montpellier France Univ Autonoma San Luis Potosi Fac Ciencias Quim Ave Dr Nova 6 San Luis Potosi 78210 Mexico CNRS UPR3021 1C Ave Rech Sci F-45071 Orleans 2 France Univ Orleans Inst Univ Technol 16 rue Issoudun BP16724 F-45067 Orleans 2 France

This study employed numerical modeling to investigate the reactivity and kinetics involved in the slow pyrolysis of lignocellulosic biomass. The model integrates a biomass multi-step kinetics scheme with heat, momentum, and mass transfer, and it was based on the transport of species and flow in a porous medium approach. To develop the multi-step kinetics model, two samples of biomass, avocado stone (AS) with a high hemicellulose content and alpha-cellulose (CEL), were subjected to TGA experiments in an inert atmosphere. Furthermore, several experimental data in the literature on the evolution of slow pyrolysis products and data obtained by TGA experiments were considered to refine and validate the proposed kinetic mechanism. The temperature range, from 25 to 700 degrees C, was explored using different heating rates (10, 20, and 40 degrees C/min). Experimental results showed that CO and CO2 are the predominant gases during primary devolatilization, whereas H2 and CH4 result from secondary reactions at temperatures above 400 degrees C. The proposed mechanism involves computational fluid dynamic (cfd) simulations of laboratory-scale biomass pyrolysis, comparing temperature and species concentrations with experimental data. The predicted results for individual non-condensable gas mass yields showed an average relative error of below 6.90 % and 11.59 % for CEL and AS, respectively. In the case of biochar, the error was 6.41 % and 9.74 % for AS and CEL, respectively. The developed kinetic model can be applied to simulate the slow pyrolytic degradation of biomass based on its chemical composition.

关键词： Biomass Pyrolysis Multi-step kinetic mechanism Finite element method cfd modeling Porous media

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Comparative Analysis of cfd modeling and Process Simulation for Pyro-Gasification of Biomass

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BIORESOURCES 2025年第2期20卷 2844-2870页

作者： Sangare, Diakaridia Belandria, Veronica Bostyn, Stephane Moscosa-Santillan, Mario UPR BioWooEB CIRAD 73 Rue Jean Francois Breton F-34398 Montpellier France Zona Univ San Luis Potosi SLP Fac Ciencias Quim Univ Autonoma San Luis Potosi Ave Dr Nava 6 Mexico City 78210 DF Mexico ICARE Inst Combust Aerotherm Reactivite & Environm CNRS UPR3021 1C Ave Rech Scientifique F-45071 Orleans 2 France Univ Orleans Inst Univ Technol 16 Rue Issoudun BP16724 F-45067 Orleans 2 France

A comparative analysis of Computational Fluid Dynamics (cfd) modeling and process simulation (SIM) was carried out to evaluate biomass pyro-gasification, using experimental data from agave bagasse (AB) as a case study. Experimental data were obtained via thermogravimetric analysis (TGA) under varying conditions, including non-isothermal (700 to 1000 degrees C) and isothermal (900 degrees C and 950 degrees C) gasification at different air-to-biomass ratios (ABR). cfd modeling in COMSOL Multiphysics focused on micro-scale mass and heat transfer phenomena, while Aspen Plus simulations provided macro-scale process insights. Results showed that SIM closely matched experimental product yields under isothermal conditions (maximum deviation: 4.23 wt.%), while cfd excelled in predicting gas composition under non-isothermal conditions (e.g., H-2 deviation: 3.29 vol.%). Sensitivity analysis showed how temperature and ABR are critical factors that influence the product yield and gas composition, highlighting the strengths of each modeling approach. These findings underline the potential of integrating cfd and SIM approaches for improving the accuracy of biomass conversion modeling, paving the way for optimized process designs and scalable industrial applications.

关键词： Biomass Pyrolysis Gasification cfd modeling Process simulation Sensitivity analysis

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Improving the performance of photovoltaic panels integrated with ultrasound and phase change materials: experimental study and cfd modeling

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JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY 2024年第15期149卷 8193-8213页

作者： Azimi, Neda Sharifzadeh, Esmail Rahimi, Masoud Nouira, Meriem Razi Univ Adv Chem Engn Res Ctr CFD Res Div Kermanshah Iran Razi Univ Fac Petr & Chem Engn Dept Chem Engn Kermanshah Iran Razi Univ Adv Chem Engn Res Ctr Polymer Res Div Kermanshah Iran Univ Sousse ESSTH Sousse Lab Energy & Mat LabEM LR11ES34 Abbassi Lamine St Hammam Sousse 4011 Tunisia

New phase change materials (PCMs) and ultrasound energy are used to enhance the performance of a photovoltaic (PV) panel. Design of experiment (DOE) method is applied to optimize the surface temperature and output power of the PV panel. In response surface methodology (RSM), volume fraction of glycerol in the mixture of oleic acid and beeswax (0-50%), mass fraction of CuO nanoparticles (0-5%) and solar intensity (500-1000Wm-2) is investigated as three key parameters. At first, an experimental work is conducted in which a U-shape tube is installed inside the enclosure containing PCM with cold water flow. Secondly, cfd modeling is applied to propose a new method for the heat removal from the PCM integrated with the PV panel. A cold water jacket equipped with 1.7 MHz ultrasound waves is inserted instead of the U-shape tube and surrounds the PCM enclosure. Experimental data showed that the PCM with 22.52% glycerol shows the highest PV power. Adding 5%CuO nanoparticles to PCMs caused minimum temperature and the maximum power of the PV panel. Using U-shape tube at optimum condition led to electrical efficiency about 14.33%. cfd data proved that propagation of 1.7 MHz ultrasonic into water jacket led to remarkable reduction in the PV temperature compared to applying the U-shape tube. cfd results demonstrated a good agreement with experimental data with maximum error of 0.97%.

关键词： cfd modeling Photovoltaic Ultrasound Phase change materials Solar energy

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cfd modeling of a multichannel Fischer-Tropsch reactor module with microscale cooling channels: Effects of mirrored structure cooling layers

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KOREAN JOURNAL OF CHEMICAL ENGINEERING 2023年第10期40卷 2572-2580页

作者： Woo, Yesol Oh, Da Bin Park, Jae Eun Han, Seung Ju Lee, Yun-Jo Park, Myung-June Ajou Univ Dept Energy Syst Res Suwon 16499 South Korea Ajou Univ Dept Chem Engn Suwon 16499 South Korea Korea Res Inst Chem Technol KRICT C1 Gas & Carbon Convergent Res Ctr Daejeon 34114 South Korea

Computational fluid dynamics (cfd) modeling of a multichannel Fischer-Tropsch reactor with microscale cooling channels is addressed in this study, wherein detailed mass, momentum, and energy balances were solved to retrieve detailed distributions of the conversion and temperature of both catalytic and cooling layers. A comparison between experimental data and simulation results showed relative errors of 6.73% and 1.22% for conversion and C5+ selectivity, respectively, which proves the validity of the proposed model. The novel structure of the reactor composed of mirrored structure cooling layers is suggested to prevent the thermal instability of a large-scale reactor module. The simulation showed that the symmetric distribution of the dense cooling channel area in the early part of the reactor decreased peak temperatures (& UDelta;T-max=28.6 & DEG;C), whereas the nonmirrored case resulted in hot spots caused by the limited heat transfer capacity (& UDelta;T-max=39.2 & DEG;C). The effects of the feed/coolant temperature, space velocity, and pressure were evaluated, and high temperatures and pressures resulted in a steep temperature increase in the early part of the reactor, whereas the high space velocity showed an increase in the area of peak temperature. Further, the analysis showed trade-offs of operating conditions between the conversion and selectivity of desired products.

关键词： Fischer-Tropsch Multichannel Reactor Microscale Cooling Channels Mirrored Cooling Layer cfd modeling

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cfd modeling of Sustainable Aviation Fuel Sensitivity on Aero-Engine Combustor 1

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Asia-Pacific International Symposium on Aerospace Technology (APISAT)

作者： Li, Songyang Wang, Ruixin Tao, Wenjie AECC Commercial Aircraft Engine Co Ltd Dept Adv Technol Res Shanghai 200241 Peoples R China

ISBN: (数字)9789819739981

ISBN: (纸本)9789819740000;9789819739981;9789819739974

Sustainable aviation fuels (SAFs), which is produced from alternative sources, such as bio-derived feedstocks, provide essentially identical performance to that from petroleum-derived jet fuels. SAFs are identified as the best near- to mid-term solution for reducing carbon emissions, with carbon offsetting being the other major carbon mitigation strategy. The primary objective of the research in the paper is to determine if state-of-the-art computational fluid dynamics (cfd) models could predict the fuel effects in a realistic combustor as a pathway for original equipment manufactures (OEMs) to assess the risk of their combustor designs using SAFs. In order to develop a numerical simulation method of SAFs combustion, a simplified chemical reaction kinetic model has been developed to simulate the combustion of a SAF fuel, G + FT, selected for study. In this paper, Hybrid Chemistry (HyChem) method has been referred to reduce the kinetic models to small sets of species and reaction steps that enable cfd simulations. First, a surrogate fuel which contains 56% n-dodecane and 44% iso-octane in mole fraction has been proposed to mimic the G + FT fuel. Second, the HyChem method is applied to the surrogate fuel to establish the simplified mechanism which consists of 43 species and 293 steps, and the number of steps is only 10% of that in the detailed mechanism. Then, we have validated the accuracy of the simplified model with G + FT fuel's combustion testing data. For example, the average relative error of the predicted laminar flame speed is only 8.8%. Besides, the simplified mechanism has been successfully applied to the cfd modeling. In order to study the fuel sensitivity and verify the cfd modeling with the simplified mechanism, we have conducted a series of combustor rig tests with a conventional petroleum-derived fuel (RP-3) and a blend fuel (90% RP-3: 10% G+ FT). Relative difference in simulated values of combustion efficiency, NOx emission and pattern factor due to t

关键词： Sustainable aviation fuel Kinetic mechanism cfd modeling Combustor

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Effect of indoor temperature on the velocity fields and airborne transmission of sneeze droplets: An experimental study and transient cfd modeling

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SCIENCE OF THE TOTAL ENVIRONMENT 2023年第Part2期858卷 159444页

作者： Bahramian, Alireza Mohammadi, Maryam Ahmadi, Goodarz Hamedan Univ Technol Dept Chem Engn POB 65155 Hamadan Iran Islamic Azad Univ Dept Chem Engn Sci & Res Branch Tehran Iran Clarkson Univ Dept Mech & Aerosp Engn Potsdam NY 13699 USA

The spread of the COVID-19 pandemic through the airborne transmission of coronavirus-containing droplets emitted during coughing, sneezing, and speaking has now been well recognized. This study presented the effect of indoor tem-perature (T infinity) on the airflow dynamics, velocity fields, size distribution, and airborne transmission of sneeze droplets in a confined space through experimental investigation and computational fluid dynamic (cfd) modeling. The cfd simulations were performed using the renormalization group k-epsilon turbulence model. The experimental shadowgraph imaging and cfd simulations showed the time evolution of sneeze droplet concentrations into the turbulent expanded puff, droplet cloud, and fully-dispersed droplets. Also, the predicted mean velocity of droplets was compared with the obtained experimental data to assess the accuracy of the results. In addition, the validated computational model was used to study the sneeze complex airflow behavior and airborne transmission of small, medium, and large respiratory droplets in confined spaces at different temperatures. The warm room showed more than-14 % increase in airborne aerosols than the room with a mild temperature. The study provides information on the effect of room temperature on the evaporation of respiratory droplets during sneezing. The findings of this fundamental study may be used in devel-oping exposure guidelines by controlling the temperature level in indoor environments to reduce the exposure risk of COVID-19.

关键词： COVID-19 spread Airborne transmission Sneeze droplets cfd modeling Indoor temperature

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3D cfd modeling for the limits' identification of 2D flow pattern's effects on the aerodynamic performance of a reference H-Darrieus prototype

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INTERNATIONAL JOURNAL OF INTERACTIVE DESIGN AND MANUFACTURING - IJIDEM 2023年第6期17卷 3229-3278页

作者： Fertahi, Saif ed-Din Belhadad, Tarik Kanna, Anass Samaouali, A. Kadiri, I. Arid, A. Benini, E. Agounoun, R. El Rhafiki, T. Elyamani, Nacer Eddine El Kadri Mohammed V Univ Rabat Fac Sci Energy Res Ctr Phys DeptThermodynam & Energy ResTeam 4 Ave Ibn BatoutaBP 1014 Rabat Morocco Univ Pau & Pays Adour UPPA Energy Lab Sci lngenieur Appl Mecan & genie Elect SIAME Federat IPRA EA4581Environm Solut E2S F-64000 Pau France Sidi Mohamed Ben Abdellah Univ Fez USMBA Polydisciplinary Fac Taza Engn Sci Lab BP 1223 Taza Morocco Univ Moulay Ismail UMI Ecole Super Technol Meknes Lab Etud Mat Avances Applicat LEM2A Km 5Route Agouray N6 Meknes 50040 Morocco Moulay Ismail Univ Meknes UMI Ecole Natl Super Arts Metiers Meknes ENSAM M Marjane 2 BP 15290 Meknes Morocco Univ Padua Dept Ind Engn Via Venezia 1 I-35131 Padua Italy

The comparative assessment carried out in this paper aims to investigate the results driven from our 2D and 3D cfd modeling of H-Darrieus, based on the URANS approach. It describes the aerodynamic operation of H-Darrieus that has been used for several numerical investigations since 2010. The k-omega SST has been used to reproduce the flowstructures developing in thewake. Themaximal 2Dand 3D power coefficients that have been achieved are Cp = 0.4016 and Cp = 0.5734, respectively for lambda = 3.0976. The maximal 2D and 3D absolute error, which is corresponding to the power coefficient assessment were equal respectively to 14.9714% and 29.1582%. They were calculated at lambda = 2.5183 and lambda = 3.0976. Our parametric study showed that the increase range of the power coefficient, while taking into account the 3D aerodynamic effects becomes larger than that obtained by 2D calculations. This range is defined in 3D modeling between lambda = 1.85 and lambda = 3.10, while it is defined in 2D modeling by the interval having the bounds lambda = 2.05 and lambda = 3.10. The necessary contours to conduct our confrontation between the 2D and 3D approach and to describe the flow structures developing around H-Darrieus were constructed and discussed.

关键词： H-Darrieus Power coefficient cfd modeling Comparative assessment Complex turbulent flow structures Wake zone

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