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Experimental Study on Heat Storage Properties Comparison of Paraffin/Metal Foams Phase Change Material Composites

Journal of Thermal Science 2024年第2期33卷 469-478页

作者： waqar AHMED Abid HUSSAIN Hanzla SHAHID Imran ALI Hafiz Muhammad ALI Department of Mechanical Engineering University of Engineering and TechnologyTaxila47080Pakistan Department of Mechanical Engineering Institute of Space TechnologyIslamabadPakistan Department of Mechanical Mechatronics and Manufacturing EngineeringUniversity of Engineering and Technology LahoreFaisalabad CampusPunjabPakistan Mechanical Engineering Department King Fahd University of Petroleum and MineralsDhahran31261Saudi Arabia Interdisciplinary Research Center for Renewable Energy and Power Systems(IRC-REPS) King Fahd University of Petroleum and MineralsDhahran31261Saudi Arabia

Heat storage properties of phase change materials(PCMs) are essential characteristics that perform a key role in thermal heat energy storage systems.The thermal properties of PCMs can be improved by developing metal foam/PCM composites.The addition of metal foam in PCMs has a significant effect on the thermal characteristics of PCMs.In this paper,the heat storage properties of two different metal foam/PCM composites were experimentally examined.The behavior of paraffin in metal foam(copper and iron-nickel)/paraffin composites concerning pure paraffin at a constant heat flux of 1000 W/m^(2) in three directions simultaneously(x,y,and z) was studied.Paraffin was infiltrated into copper and iron-nickel foams to develop composite materials which resulted in enhancing the thermal conductivity of the paraffin.A comparative analysis is made on the heat storage properties of paraffin in copper and iron-nickel foams/paraffin composites.Inner temperature distribution during the phase transition process is experimentally evaluated.This comparison indicates that temperature uniformity in copper foam/paraffin composite is better than in iron-nickel foam/paraffin composite and pure paraffin at the same heat flux.Experimental results show that at heat flux of 1000 W/m^(2),the heat storage time for copper foam/paraffin composite is 20.63% of that of iron-nickel foam/paraffin composite.

关键词： heat storage capacity paraffin/metal foam composite temperature uniformity heat storage rate phase transition process

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Dimethoxymethane production via CO_(2)hydrogenation in methanol over novel Ru based hierarchical BEA

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Journal of Energy Chemistry 2022年第3期31卷 181-189,I0006页

作者： waqar ahmad Fan Liang Chan Abhijit Shrotri Yayati Naresh Palai Huanting Wang Akshat Tanksale Department of Chemical Engineering Monash UniversityClayton 3800Australia Institute for Catalysis Hokkaido UniversitySapporo 001-0021Japan

Dimethoxymethane(DMM),a diesel blend fuel,is being researched with high interest recently due to its unique fuel properties.It is commercially produced via a two step-process of methanol oxidation to make formaldehyde,followed by its condensation with methanol.This study presents a one-pot method of DMM synthesis from methanol mediated carbon dioxide hydrogenation over novel heterogeneous catalysts.The effect of catalyst pore structure was investigated by synthesizing 3 wt%Ru over novel hierarchical zeolite beta(HBEASX)and comparing against Ru doped commercial zeolite beta(CBEA)and desilicated hierarchical zeolite beta(HBZDS).The results showed that 3%Ru/HBEASX provided the best activity for DMM production due to its large average pore size.It also showed the decisive role of SiO_(2)/Al_(2)O_(3)molar ratio,with SiO_(2)/Al_(2)O_(3)=75 providing the highest DMM yield of 13.2 mmol/gcat.LMeOH with ca.100%selectivity.The activity of 3%Ru/HBEAS3 after 5 recycle steps demonstrated the reusability of this catalyst.

关键词： Dimethoxymethane Methanol solvent CO_(2)hydrogenation Hierarchical BEA SiO_(2)/Al_(2)O_(3)molar ratio Ru catalysts

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Co-Adsorption of CO in NO-CO Reaction on a Metal Catalytic Surface Studied by Computer Simulation

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Chinese Physics Letters 2009年第3期26卷 189-192页

作者： waqar ahmad Pakistan Institute of Nuclear Science and Technology P.O. Nilore Islamabad Pakistan

The effect of co-adsorption of CO molecules in the NO-CO reaction on a metal catalytic surface like Pt（001） is studied by applying the Langmuir-Hinshelwood mechanism using the Monte Carlo simulations. The system is investigated by two approaches of NO adsorption; dissociatively at two empty surface sites and molecularly at a single vacant site. The elementary steps are the same as those in the conventional Ziff-Gulari-Barshad model. With the additional reaction step of co-adsorption, the sustained production of CO2 is obtained, which has never been seen on a square lattice without introducing additional parameters. The most interesting result is the elimination of continuous second order phase transition, i.e. the production of CO2 starts as soon as the partial pressure of CO departs from zero, which is in accordance with the experimental observations. The effect of co-adsorption probability on the phase diagrams has also been studied.

关键词： No English Keywords

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NO-CO-O2 Reaction on a Metal Catalytic Surface using Eley-Rideal Mechanism

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Chinese Physics Letters 2008年第10期25卷 3728-3731页

作者： waqar ahmad Physics Division PINSTECH P.O. Nilore Islamabad Pakistan

Interactions among the reacting species NO, CO and O2 on metal catalytic surfaces are studied by means of Monte Carlo simulation using the Eley-Rideal （ER） mechanism. The study of this three-component system is important for understanding of the reaction kinetics by varying the relative ratios of the reactants. It is found that contrary to the conventional Langmuir-Hinshelwood （LFI） thermal mechanism in which two irreversible phase transitions are obtained between active states and poisoned states, a single phase transition is observed when the ER mechanism is combined with the LH mechanism. The phase diagrams of the surface coverage and the steady state production of CO2, N2 and N2O are evaluated as a function of the partial pressures of the reactants in the gas phase. The continuous production of CO2 starts as soon as the CO pressure is switched on and the second order phase transition at the first critical point is eliminated, which is in agreement with the experimental findings.

关键词： the power-law exponents precipitation durative abrupt precipitation change

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Finite element model updating for structural damage detection using transmissibility data

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Earthquake Engineering and Engineering Vibration 2024年第1期23卷 87-101页

作者： ahmad Izadi Akbar Esfandiari Department of Maritime Engineering Amirkabir University of TechnologyTehran 15875-4413Iran

This paper presents a new finite element model updating method for estimating structural parameters and detecting structural damage location and severity based on the structural responses(output-only data).The method uses the sensitivity relation of transmissibility data through a least-squares algorithm and appropriate normalization of the extracted equations.The proposed transmissibility-based sensitivity equation produces a more significant number of equations than the sensitivity equations based on the frequency response function(FRF),which can estimate the structural parameters with higher accuracy.The abilities of the proposed method are assessed by using numerical data of a two-story two-bay frame model and a plate structure model.In evaluating different damage cases,the number,location,and stiffness reduction of the damaged elements and the severity of the simulated damage have been accurately identified.The reliability and stability of the presented method against measurement and modeling errors are examined using error-contaminated data.The parameter estimation results prove the method’s capabilities as an accurate model updating algorithm.

关键词： damage detection model updating output-only transmissibility sensitivity equation

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Flexible pavement longitudinal joint quality evaluation using non-destructive testing

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Journal of Road Engineering 2024年第2期4卷 189-202页

作者： Hamad Bin Muslim Syed waqar Haider Lev Khazanovich Department of Civil and Environmental Engineering Michigan State UniversityEast LansingMI 48824USA Department of Civil and Environmental Engineering University of PittsburghPittsburghPA 15261USA

Longitudinal joint construction quality is critical to the life of flexible pavements.Maintaining deteriorated longitudinal joints has become a challenge for many highway agencies.Improving the joint's quality through better compaction during construction can help achieve flexible pavements with longer service lives and less maintenance.Current quality control(QC)and quality assurance(QA)plans provide limited coverage.Consequently,the risk of missing areas with poor joint compaction is significant.A density profiling system(DPS)is a non-destructive alternative to conventional destructive evaluation methods.It can provide quick and continuous real-time coverage of the compaction during construction in dielectrics.The paper presents several case studies comparing various types of longitudinal joints and demonstrating the use of DPS to evaluate the joint's compaction quality.The paper shows that dielectric measurements can provide valuable insight into the ability of various construction techniques to achieve adequate levels of compaction at the longitudinal joint.The paper proposes a dielectric-based longitudinal joint quality index(LJQI)to evaluate the relative compaction of the joint during construction.It also shows that adopting DPS for assessing the compaction of longitudinal joints can minimize the risk of agencies accepting poorly constructed joints,identify locations of poor quality during construction,and achieve better-performing flexible pavements.

关键词： Sustainable pavements Dielectric/density profiling system Quality assurance Non-destructive testing Asphalt longitudinal joint

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Correlation between structural phase transition and physical properties of Co2+/Gd3+ co-substituted copper ferrite

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Journal of Rare Earths 2024年第7期42卷 1344-1353页

作者： Mohsen Choupani ahmad Gholizadeh School of Physics Damghan University

The doping of the spinel ferrites with selective cations usually improves the properties of the parent ferrite.The effect of Co2+/Gd3+co-substitution on the microstructure,optical,and magnetic properties of Cu1-xCoxFe2-xGdxO4prepared by the citrate-nitrate auto-combustion synthesis was investigated.Characterization of the samples was performed with powder X-ray diffraction（XRD）,Raman and Fouriertransform infrared（FTIR） spectroscopy,field-emission scanning electron microscopy,X-ray energydispersive spectroscopy,UV-Vis spectroscopy,and a vibrating sample magnetometer.The results of XRD,Raman,and FTIR analysis show a gradual structural phase transition from a tetragonal（I41/amd）structure to a cubic（Fd 3 m） structure.The bandgap energy of the studied samples is in a range of1.57-1.75 eV with a minimum in sample x=0,06 and then increases.Magnetic investigations show that the presence of Co2+/Gd3+cations in an octahedral site of the copper ferrite structure could increase saturation magnetization and coercive field from 567.9 Oe and 23.62 emu/g to 929.4 Oe and 28.27 emu/g,respectively.

关键词： Citrate-nitrate method Magnetic properties Microstructure properties Rare earths Spinel copper ferrite Structure phase transition

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Federated Learning Security and Privacy-Preserving Algorithm and Experiments Research Under Internet of Things Critical Infrastructure

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Tsinghua Science and Technology 2024年第2期29卷 400-414页

作者： Nasir ahmad Jalali Hongsong Chen Department of Computer Science University of Science and Technology Beijing(USTB)Beijing 100083China

The widespread use of the Internet of Things(IoTs)and the rapid development of artificial intelligence technologies have enabled applications to cross commercial and industrial band settings.Within such systems,all participants related to commercial and industrial systems must communicate and generate data.However,due to the small storage capacities of IoT devices,they are required to store and transfer the generated data to third-party entity called“cloud”,which creates one single point to store their data.However,as the number of participants increases,the size of generated data also increases.Therefore,such a centralized mechanism for data collection and exchange between participants is likely to face numerous challenges in terms of security,privacy,and performance.To address these challenges,Federated Learning(FL)has been proposed as a reasonable decentralizing approach,in which clients no longer need to transfer and store real data in the central server.Instead,they only share updated training models that are trained over their private datasets.At the same time,FL enables clients in distributed systems to share their machine learning models collaboratively without their training data,thus reducing data privacy and security challeges.However,slow model training and the execution of additional unnecessary communication rounds may hinder FL applications from operating properly in a distributed system.Furthermore,these unnecessary communication rounds make the system vulnerable to security and privacy issues,because irrelevant model updates are sent between clients and servers.Thus,in this work,we propose an algorithm for fully homomorphic encryption called Cheon-Kim-Kim-Song(CKKS)to encrypt model parameters for their local information privacy-preserving function.The proposed solution uses the impetus term to speed up model convergence during the model training process.Furthermore,it establishes a secure communication channel between IoT devices and the server.We also use a lightweight secure transport protocol

关键词： Federated Learning(FL) Internet of Things(IoTs) lightweight Transport Layer Security(iTLS) Cheon-Kim-Kim-Song(CKKS)

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Facies Analysis, Sequence Stratigraphy and Diagenetic Studies of the Jurassic Carbonates of the Kohat Basin, Northwest Pakistan: Reservoir Implications

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Acta Geologica Sinica(English Edition) 2022年第5期96卷 1673-1692页

作者： Emadullah KHAN Abbas Ali NASEEM Suleman KHAN Bilal WADOOD Faisal REHMAN Maryam SALEEM Mubashir MEHMOOD waqar ahmad Zubair AHMED Tahir AZEEM Department of Earth Sciences Quaid-e-Azam UniversityIslamabad 45320Pakistan Department of Geology Abdul Wali Khan UniversityMardan 23200Pakistan Department of Geology University of PeshawarPeshawar 24420Pakistan State Key Laboratory of Continental Dynamics Department of GeologyNorthwest UniversityXi’an 71006China Department of Geology University of SwabiSwabi 23561Pakistan Department of Earth&Environmental Sciences Bahria UniversityIslamabad 44000Pakistan Department of Earth&Atmospheric Sciences University of AlbertaEdmonton T6G 2R3Canada

The present study deals with the depositional facies, diagenetic processes and sequence stratigraphy of the shallow marine carbonates of the Samana Suk Formation, Kohat Basin, in order to elucidate its reservoir quality. The Samana Suk Formation consists of thin to thick-bedded, oolitic, bioclastic, dolomitic and fractured limestone. Based on the integration of outcrop, petrographic and biofacies analyses, the unit is thought to have been deposited on a gentle homoclinal ramp in peritidal, lagoonal and carbonate shoal settings. Frequent variations in microfacies based sea-level curve have revealed seven Transgressive Systems Tracts(TSTs) and six Regressive Systems Tracts(RSTs). The unit has undergone various stages of diagenetic processes, including mechanical and chemical compaction, cementation,micritization, dissolution and dolomitization. The petrographic analyses show the evolution of porosity in various depositional and diagenetic phases. The fenestral porosity was mainly developed in peritidal carbonates during deposition,while the burial dissolution and diagenetic dolomitization have greatly enhanced the reservoir potential of the rock unit, as is further confirmed by the plug porosity and permeability analyses. The porosities and permeabilities were higher in shoal facies deposited in TSTs, as compared to lagoonal and peritidal facies, except for the dolomite in mudstone, deposited during RSTs. Hence good, moderate and poor reservoir potential is suggested for shoal, lagoonal and peritidal facies,respectively.

关键词： porosity diagenesis reservoir Samana Suk Formation Kohat Basin

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Monte Carlo Study of CO-NO Catalytic Surface Reaction Including CO-CO Repulsion

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Chinese Physics Letters 2006年第4期23卷 1034-1037页

作者： waqar ahmad Musa Kaleem Baloach Physics Research Division Pakistan Institute of Nuclear Science and Technology PO Nilore Islamabad Pakista Department of Chemistry Gomal University D.I. Khan Pakistan

The CO-NO reaction on a catalytic surface is studied by using Langmuir-Hinshclwood thermal mechanism with Monte Carlo computer simulation. In this model, a novel concept of CO CO repulsion is introduced, which has experimental evidence due to the formation of dipoles when these molecules are chemisorbed on the surface. The system is investigated by applying two approaches of NO dissociation. In the first ca.se, NO always decomposes into N and O before adsorption on the surface, In the second case, NO adsorbs on the surface molecularly and then dissociates into N and O if a vacancy is present in its adjacent neighbourhood. The steady state reactive window （i.e. the continuous production of CO2 and N2） is obtained only with the diffusion of N-atoms on the surface, which extends with CO-CO repulsion in the first, case. Itowever, in the second case, reactive window is obtained with CO-CO repulsion alone, The reactive window width in this case is reasonably large. The first-order phase transition is eliminated in both the cases with CO-CO repulsion.

关键词： KINETIC PHASE-TRANSITIONS SQUARE LATTICE HEXAGONAL SURFACES REACTIONMODEL NITRIC-OXIDE SIMULATION MECHANISM

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