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Comparative Evaluation and Performance Analysis of Heat Exchangers Featured with Peened Surface

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Journal of Thermal Science 2025年第1期 50-61页

作者： DINESHBABU Chinnadurai SHIVA SANKARAN Nallasamy VENKATESH raja Krishnan VENKATESH Rathinavelu Department of Mechanical Engineering Kongunadu College of Engineering and Technology Department of Mechanical Engineering Selvam College of Technology Department of Mechanical Engineering Sona College of Technology Department of Mechanical Engineering Saveetha School of EngineeringSaveetha Institute of Medical and Technical Sciences (SIMATS)Saveetha University

Heat exchangers have the potential for various engineering applications,and their performance is enriched by surface *** proposed system enriches the heat exchanger's performance by adapting a peened stainless steel（SS） surface blasted with copper,grinding,sand,and *** influences peened SS surface modified with a copper blast,grinding,sandblast,and iron blast on the surface morphology of shell and tube heat exchanger surface（STHE） is analyzed via tungsten heated cathode electron gun featured scanning electron microscope and observed coarse grain *** SS surface featured STHE performance is experimentally evaluated by different flow rates（30,60,90,and 120 L/min） underwater fluid medium functioned by the temperature ranges of 25-75℃ and its results are compared with computational fluid dynamic（CFD）/heat transfer research（HTRI） analyzed *** 60 L/min flow rate was spotted as an optimum value for both shell and tube side *** STHE is operated with a 60 L/min flow rate under the different peened surfaces and evaluated its Stanton number,Nusselt number,logarithmic mean temperature difference（LMTD）,overall heat transfer coefficient,number of transfer units（NTU）,effectiveness,and exergy *** iron blasted SS peened surface was observed to have better SHTE performance like Stanton number（0.0012）,Nusselt number（2180）,reduced LMTD of 31℃,improved overall heat transfer co-efficient of 2400 W/（m2·K）,better NTU of 0.5532,good effectiveness value of 0.451 62,and hiked exergy efficiency of 10% respectively.

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AN UNCONDITIONALLY STABLE HYBRID FE-FD SCHEME FOR SOLVING A 3-D HEAT TRANSPORT EQUATION IN A CYLINDRICAL THIN FILM WITH SUB-MICROSCALE THICKNESS

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Journal of Computational Mathematics 2003年第5期21卷 555-568页

作者： raja Nassar Mathematics and Statistics College of Engineering and Science Louisiana Tech University Ruston LA 71272 USA

Heat transport at the microscale is of vital importance in microtechnology applications. The heat transport equation is different from the traditional heat transport equation since a second order derivative of temperature with respect to time and a third-order mixed derivative of temperature with respect to space and time are introduced. In this study, we develop a hybrid finite element-finite difference (FE-FD) scheme with two levels in time for the three dimensional heat transport equation in a cylindrical thin film with sub-microscale thickness. It is shown that the scheme is unconditionally stable. The scheme is then employed to obtain the temperature rise in a sub-microscale cylindrical gold film. The method can be applied to obtain the temperature rise in any thin films with sub-microscale thickness, where the geometry in the planar direction is arbitrary.

关键词： Finite element Finite difference Stability Heat transport equation Thin film Microscale

Magnetic properties of gadolinium and/or dysprosium substituted Sm-Co nanocomposite ribbons

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Journal of Rare Earths 2024年第6期42卷 1093-1100,I0004页

作者： Akila raja Shampa Aich Department of Metallurgical A Materials EngineeringIndian Institute of Technology(IIT) Kharagpur721302India

The present study reported the influence of heavy rare-earth elements(Gd and/or Dy)on Sm-Co-based melt-spun *** and magnetic properties of Sm-Co-based(Sm_(1-x)RE_(x)Co_(5))ternary and quaternary systems were *** X-ray diffraction,Auger spectroscopy,scanning electron microscopy(SEM)and transmission electron microscopy(TEM)analyses reveal the presence of the 1:5H and 2:17R phases in the as-spun ribbons.A high-temperature magnetic measurement reports a Curie temperature(Tc)at~825 and~869 K in Sm0.6Gd0.4Co5(ribbon A)and Sm_(0.6)Gd_(0.3)Dy_(0.1)Co_(5)(ribbon B),respectively.A low-temperature magnetic measurement on Sm0.6Gd0.3Dy0.1Co5 ribbons exhibits a type-2 SR(spin reorientation)behaviour at~72 K,which arises due to the presence of the DyCo5 *** temperature magnetic measurements reveal that overall magnetic measurement(OMP)is about 24 and 29.9 for ribbons A and B,***,the comparative investigations profess that ribbon B shows better magnetic performance due to Dy addition with reduced grain *** observation indicates that the Gd and Dy substituted Sm-Co magnet can be a potential magnet for high-temperature applications.

关键词： Permanent magnets Melt-spinning Heavy rare-earth Curie temperature Rare earths

Frequency Analysis of Multiple Layered Cylindrical Shells under Lateral Pressure with Asymmetric Boundary Conditions

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Chinese Journal of Mechanical Engineering 2014年第1期27卷 23-31页

作者： ISVANDZIBAEI Mohammad Reza JAMALUDDIN Hishamuddin raja HAMZAH raja Ishak Faculty of Mechanical Engineering Universiti Teknologi Malaysia

Natural frequency characteristics of a thin-walled multiple layered cylindrical shell under lateral pressure are studied. The multiple layered cylindrical shell configuration is formed by three layers of isotropic material where the inner and outer layers are stainless steel and the middle layer is aluminum. The multiple layered shell equations with lateral pressure are established based on Love＇s shell theory. The governing equations of motion with lateral pressure are employed by using energy functional and applying the Ritz method. The boundary conditions represented by end conditions of the multiple layered cylindrical shell are simply supported-clamped（SS-C）, free-clamped（F-C） and simply supported-free（SS-F）. The influence of different lateral pressures, different thickness to radius ratios, different length to radius ratios and effect of the asymmetric boundary conditions on natural frequency characteristics are studied. It is shown that the lateral pressure has effect on the natural frequency of multiple layered cylindrical shell and causes the natural frequency to increase. The natural frequency of the developed multilayered cylindrical shell is validated by comparing with those in the literature. The proposed research provides an effective approach for vibration analysis shell structures subjected to lateral pressure with an energy method.

关键词： multiple layered ritz method lateral pressure shell boundary conditions

Biphasic reduction model for predicting the impacts of dye-bath constituents on the reduction of tris-azo dye Direct Green-1 by zero valent iron(Fe^0)

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Journal of Environmental Sciences 2017年第2期29卷 160-169页

作者： raja Kumar Alok Sinha Department of Environmental Science&Engineering Indian School of MinesDhanbad 826004JharkhandIndia

Influence of common dye-bath additives, namely sodium chloride, ammonium sulphate,urea, acetic acid and citric acid, on the reductive decolouration of Direct Green 1 dye in the presence of Fe0 was investigated. Organic acids improved dye reduction by augmenting Fe0 corrosion, with acetic acid performing better than citric acid. Na Cl enhanced the reduction rate by its ‘salting out’ effect on the bulk solution and by Cl-anion-mediated pitting corrosion of iron surface.（NH4）2SO4induced ‘salting out’ effect accompanied by enhanced iron corrosion by SO42-anion and buffering effect of NH4＋ improved the reduction ***, at 2 g/L（NH4）2SO4concentration, complexating of SO42-with iron oxides decreased Fe0 reactivity. Urea severely compromised the reduction reaction, onus to its chaotropic and‘salting in’ effect in solution, and due to it masking the Fe0 surface. Decolouration obeyed biphasic reduction kinetics（R2〉 0.993 in all the cases） exhibiting an initial rapid phase,when more than 95% dye reduction was observed, preceding a tedious phase. Maximum rapid phase reduction rate of 0.955/min was observed at p H 2 in the co-presence of all dye-bath constituents. The developed biphasic model reckoned the influence of each dye-bath additive on decolouration and simulated well with the experimental data obtained at pH 2.

关键词： Biphasic kinetics/model Direct Green 1 Dye-bath additives Fe0

Unsupervised neural networks for solving Troesch＇s problem

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Chinese Physics B 2014年第1期23卷 546-556页

作者： Muhammad Asif Zahoor raja Muhammad.asif@ciit-attock.edu.pk rasifzahoor@*** []Department of Electrical Engineering COMSATS Institute of Information Technology Attock Campus Attock Pakistan

In this study, stochastic computational intelligence techniques are presented for the solution of Troesch's boundary value problem. The proposed stochastic solvers use the competency of a feed-forward artificial neural network for mathematical modeling of the problem in an unsupervised manner, whereas the learning of unknown parameters is made with local and global optimization methods as well as their combinations. Genetic algorithm (GA) and pattern search (PS) techniques are used as the global search methods and the interior point method (IPM) is used for an efficient local search. The combination of techniques like GA hybridized with IPM (GA-IPM) and PS hybridized with IPM (PS-IPM) are also applied to solve different forms of the equation. A comparison of the proposed results obtained from GA, PS, IPM, PS-IPM and GA-IPM has been made with the standard solutions including well known analytic techniques of the Adomian decomposition method, the variational iterational method and the homotopy perturbation method. The reliability and effectiveness of the proposed schemes, in term of accuracy and convergence, are evaluated from the results of statistical analysis based on sufficiently large independent runs. [ABSTRACT FROM AUTHOR]

关键词： GENETIC algorithms COMBINATORIAL optimization EVOLUTIONARY algorithms EVOLUTIONARY computation PHYSICS

Machine Learning Accelerated Real-Time Model Predictive Control for Power Systems

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IEEE/CAA Journal of Automatica Sinica 2023年第4期10卷 916-930页

作者： Ramij raja Hossain Ratnesh Kumar Department of Electrical and Computer Engineering Iowa State UniversityAmesIA 50011 USA

This paper presents a machine-learning-based speedup strategy for real-time implementation of model-predictive-control(MPC)in emergency voltage stabilization of power *** success in various applications,real-time implementation of MPC in power systems has not been successful due to the online control computation time required for large-sized complex systems,and in power systems,the computation time exceeds the available decision time used in practice by a large *** long-standing problem is addressed here by developing a novel MPC-based framework that i)computes an optimal strategy for nominal loads in an offline setting and adapts it for real-time scenarios by successive online control corrections at each control instant utilizing the latest measurements,and ii)employs a machine-learning based approach for the prediction of voltage trajectory and its sensitivity to control inputs,thereby accelerating the overall control computation by multiple ***,a realistic control coordination scheme among static var compensators(SVC),load-shedding(LS),and load tap-changers(LTC)is presented that incorporates the practical delayed actions of the *** performance of the proposed scheme is validated for IEEE 9-bus and 39-bus systems,with±20%variations in nominal loading conditions together with *** show that our proposed methodology speeds up the online computation by 20-fold,bringing it down to a practically feasible value(fraction of a second),making the MPC real-time and feasible for power system control for the first time.

关键词： Machine learning model predictive control(MPC) neural network perturbation control voltage stabilization

Curve25519 based lightweight end-to-end encryption in resource constrained autonomous 8-bit IoT devices

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Cybersecurity 2021年第1期4卷 147-159页

作者： Shafi Ullah raja Zahilah School of Computing Faculty of EngineeringUniversiti Teknologi Malaysia81310 Johor BahruJohorMalaysia

Robust encryption techniques require heavy computational capability and consume large amount of memory which are unaffordable for resource constrained IoT devices and Cyber-Physical Systems with an inclusion of general-purpose data manipulation *** encryption techniques have been introduced to address the inability of such devices,lacking in robust security provision at low *** article presents an encryption technique,implemented on a resource constrained IoT device(AVR ATmega2560)through utilizing fast execution and less memory consumption properties of curve25519 in a novel and efficient lightweight hash *** hash function utilizes GMP library for multi-precision arithmetic calculations and pre-calculated curve points to devise a good cipher block using ECDH based key exchange protocols and large random prime number generator function.

关键词： Cyber-physical systems IoT Resource constrained IoT devices Lightweight encryption End-to-end encryption Elliptic curve cryptography Curve25519

Natural frequency characteristics of thin-walled homogeneous and manifold layered cylindrical shells under pressure using energy method

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Journal of Central South University 2014年第2期21卷 521-532页

作者： M.R.Isvandzibaei Hishamuddin Jamaluddin raja Ishak raja Hamzah Faculty of Mechanical Engineering Universiti Teknologi Malaysia

Energy method for the vibration of two types of cylindrical shells,namely thin-walled homogeneous isotropic and manifold layered isotropic cylindrical shells under uniform external lateral pressure is *** study is carried out based on strain-displacement relationship from Love's shell theory with beam functions as axial modal function.A manifold layered cylindrical shell configuration is formed by three layers of isotropic material where the inner and outer layers are stainless steel and the middle layer is *** homogeneous cylindrical shell is made-up of isotropic one layer with stainless *** governing equations with uniform external lateral pressure for homogeneous isotropic and manifold layered isotropic cylindrical shells are obtained using energy functional by the Lagrangian function with Rayleigh-Ritz *** boundary conditions that are presented at the end conditions of the cylindrical shell are simply supported-simply supported,clamped-clamped and *** influences of uniform external lateral pressure and symmetrical boundary conditions on the natural frequency characteristics for both homogeneous and manifold layered isotropic cylindrical shells are *** all boundary conditions considered,the natural frequency of both cylindrical shells with symmetric uniform lateral pressure increases as h/R ratio increases and those considering natural frequency of the both cylindrical shells with symmetric uniform lateral pressure decrease as L/R ratio increases.

关键词： cylindrical shell manifold layered pressure energy method