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Impact of Si on the high-temperature oxidation of AlCr(Si)N coatings

Journal of Materials Science & Technology 2022年第5期100卷 91-100页

作者： Nikolaus Jager Michael Meindlhumer Michal Zitek Stefan Spor Hynek Hruby Farwah Nahif jaakko julin Martin Rosenthal Jozef Keckes Christian Mitterer Rostislav Daniel Christian Doppler Laboratory for Advanced Synthesis of Novel Multifunctional Coatings at the Department of Materials Science Montanuniversität LeobenAustria voestalpine eifeler Vacotec GmbH DüsseldorfGermany Institute of Ion Beam Physics and Materials Research Helmholtz-Zentrum Dresden-RossendorfDresdenGermany Department of Physics University of JyvaskylaFinland European Synchrotron Radiation Facility GrenobleFrance Erich Schmid Institute for Materials Science Austrian Academy of SciencesAustria Department of Materials Science Montanuniversität LeobenAustria

The resistance of wear protective coatings against oxidation is crucial for their use at high ***,three nanocomposite AlCr(Si)N coatings with a fixed Al/Cr atomic ratio of 70/30 and a varying Si-content of 0 at.%,2.5 at.% and 5 at.% were analyzed by differential scanning calorimetry,thermogravimetric analysis and X-ray in order to understand the oxidation behavior depending on their ***,a partially oxidized AlCrSiN coating with 5 at.%Si on a sapphire substrate was studied across the coating thickness by depth-resolved cross-sectional X-ray nanodiffraction and scanning trans-mission electron microscopy to investigate the elemental composition,morphology,phases and residual stress evolution of the oxide scale and the non-oxidized coating *** results reveal enhanced oxidation properties of the AlCr(Si)N coatings with increasing Si-content,as demonstrated by a retarded onset of oxidation to higher temperatures from 1100℃ for AlCrN to 1260℃ for the Si-containing coatings and a simultaneous deceleration of the oxidation *** annealing of the AlCrSiN sample with5 at.%Si at an extraordinary high temperature of 1400℃ for 60 min in ambient air,three zones developed throughout the coating strongly differing in their composition and structure:(i)a dense oxide layer comprising an Al-rich and a Cr-rich zone formed at the very top,followed by(ii)a fine-grained transition zone with incomplete oxidation and(iii)a non-oxidized zone with a porous *** varying elemental composition of these zones is furthermore accompanied by micro-structural variations and a complex residual stress development revealed by cross-sectional X-ray *** results provide a deeper understanding of the oxidation behavior of AlCr(Si)N coatings depending on their Si-content and the associated elemental,microstructural and residual stress evolution during high-temperature oxidation.

关键词： AlCrSiN Nanocomposite Cathodic arc Oxidation behaviour Cross-sectional X-ray nanodiffraction

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Radial Forces in a Centrifugal Compressor; Experimental Investigation by Using Magnetic Bearings and Static Pressure Distribution

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Journal of Thermal Science 2005年第1期14卷 1-8页

作者： Arttu REUNANEN jaakko LARJOLA Department of Energy and Environmental Technology Lappeenranta University of Technology LappeenrantaFinlandDepartment of Energy and Environmental Technology Lappeenranta University of TechnologyLappeenrantaFinland

The volute of a centrifugal compressor causes a non-uniform pressure distribution which leads to a radial force on the impeller. This force was measured using magnetic bearings. In addition, the radial force was estimated using the static pressure distribution measured at the impeller outlet. The impeller force was found to be the highest at choke, the lowest at the design flow and moderate at stall. The radial force determined from the pressure measurements was only slightly different from the force obtained from the bearing measurements. The rotational speed was seen to affect the force to some extent.

关键词： centrifugal compressor aerodynamic force radial force volute.

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Unsteady Pressure Field in a Vaneless Diffuser of a Centrifugal Compressor: An Experimental and Computational Analysis

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Journal of Thermal Science 2004年第4期13卷 302-309页

作者： Teemu TURUNEN-SAARESTI jaakko LARJOLA Lappeenranta University of Technology Laboratory of Fluid Dynamics P.O. Box 20 53851 Lappeenranta FinlandLappeenranta University of Technology Laboratory of Fluid Dynamics P.O. Box 20 53851 Lappeenranta Finland

Unsteady static pressure was measured and time-accurate numerical simulations were conducted in order to analyze unsteady behaviour of the centrifugal compressor diffuser. The unsteady static pressure was measured at the diffuser inlet and outlet at three different circumferential positions. Operation points near the surge, the design operation point and operation point near the choke were used in measurements. The time-accurate simulations were conducted at the design operation point and operation point near the choke. The whole compressor was modelled and the low Reynolds number k-εturbulence model was utilized in numerical simulations. The gathered numerical and experimental unsteady pressures were compared with each other.

关键词： centrifugal compressor vaneless diffuser unsteady pressure.

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Numerical and Experimental Modelling of Gas Flow and Heat Transfer in the Air Gap of an Electric Machine

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Journal of Thermal Science 2004年第3期13卷 264-278页

作者： Maunu KUOSA Petri SALLINEN jaakko LARJOLA Lappeenranta University of Technology (LUT) Department of Energy and Environmental Technology P.O. Box 20 53851 Lappeenranta FinlandLappeenranta University of Technology (LUT) Department of Energy and Environmental Technology P.O. Box 20 53851 Lappeenranta FinlandLappeenranta University of Technology (LUT) Department of Energy and Environmental Technology P.O. Box 20 53851 Lappeenranta Finland

This work deals with the cooling of high-speed electric machines, such as motors and generators, through an air gap. It consists of numerical and experimental modeling of gas flow and heat transfer in an annular channel. Velocity and temperature profiles are modeled in the air gap of a high-speed test machine. Friction and heat transfer coefficients are presented in a large velocity range. The goals are reached acceptably using numerical and experimental research. The velocity field by the numerical method does not match in every respect the estimated flow mode. The absence of secondary Taylor vortices is evident when using time averaged numerical simulation.

关键词： heat transfer electric machine air gap friction coefficient CFD.

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THE EFFECT OF WORKER LEARNING ON SCHEDULING JOBS IN A HYBRID FLOW SHOP： A BI-OBJECTIVE APPROACH

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Journal of Systems Science and Systems Engineering 2018年第3期27卷 265-291页

作者： Farzad Pargar Mostafa Zandieh Osmo Kauppila jaakko Kujala Industrial Engineering and Management Faculty of Technology University ofOulu Oulu Finland Department of Industrial Management Management and Accounting Faculty Shahid Beheshti University G.C.Tehran Iran

This paper studies learning effect as a resource utilization technique that can model improvement in worker＇s ability as a result of repeating similar tasks. By considering learning of workers while performing setup times, a schedule can be determined to place jobs that share similar tools and fixtures next to each other. The purpose of this paper is to schedule a set of jobs in a hybrid flow shop （HFS） environment with learning effect while minimizing two objectives that are in conflict： namely maximum completion time （makespan） and total tardiness. Minimizing makespan is desirable from an internal efficiency viewpoint, but may result in individual jobs being scheduled past their due date, causing customer dissatisfaction and penalty costs. A bi-objective mixed integer programming model is developed, and the complexity of the developed bi-objective model is compared against the bi-criteria one through numerical examples. The effect of worker learning on the structure of assigned jobs to machines and their sequences is analyzed. Two solution methods based on the hybrid water flow like algorithm and non-dominated sorting and ranking concepts are proposed to solve the problem. The quality of the approximated sets of Pareto solutions is evaluated using several performance criteria. The results show that the proposed algorithms with learning effect perform well in reducing setup times and eliminate the need for setups itself through proper scheduling.

关键词： Bi-objective scheduling hybrid flow shop learning effect meta-heuristic

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Fluid dynamic modeling of a free piston engine with labyrinth seals

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Journal of Thermal Science 2010年第2期19卷 141-147页

作者： jaakko Larjola Juha Honkatukia Petri Sallinen Jari Backman Lappeenranta University of Technology P.O.Box 2053851 Lappeenranta

Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this *** properties,particularly the properties of gas seals of the engine are simulated using a simulation program developed for this case,and the results are utilized in preliminary main design parameter *** engine simulation program was developed by combining and modifying the source codes of the simulation and calculation programs obtained from Helsinki University of Technology,Tampere University of Technology,and Lappeenranta University of *** of the contact-free labyrinth seal used in the piston,the efficiency of the motor is lower than the efficiency of a conventional motor with oil lubricated piston *** the other hand,the lack of bearing losses,and the lack of losses associated with a crankshaft system and a gearbox,as well as the lack of lubrication oil expenses,compensates this *** a net result,this new motor would perform slightly better than the conventional *** completely oil-free,it is very environmentally friendly,and its exhaust gases are completely free of oil residuals which are causing problems in normal gas motors.

关键词： free piston engine distributed energy systems simulation labyrinth seal

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Philosophical Research and General Education

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Frontiers of Philosophy in China 2013年第2期8卷 240-246页

作者： jaakko Hintikka Department of Philosophy Boston University Boston MA 02215 USA

What can philosophical research do today to improve the lot of contemporary societies globally？ What can anyone do for the purpose？ To take the most urgent international problems as an example, what kind of person should the Secretary-General of the UN send to disarm a conflict situation？ Perhaps a religious leader, a priest, an imam or a guru？ But a leader of which religion？ Perhaps a lawyer？ But a lawyer is by definition some particular client＇s advocate. I submit that the best background of such a negotiator would be that of a labor arbitrator. Such a professional is trained to take into account the interest of different and conflicting parties. The success of a persuasive arbitrator presupposes a capacity to analyze objectively and realistically not only the professed goals of different parties, but the actual consequences of the realization of those goals. It presupposes objective knowledge of the consequences of different courses of action and the ability to explain them to the different parties. Above all, it presupposes a skill in finding possibilities of synthesizing apparently conflicting points of view.

关键词： Deductive reasoning Critical thinking Mathematical logic Thinking skills Epistemology Inference Mathematics Educational philosophies

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Optimization of the Mean Radius Flow Path of a Multi-Stage Steam Turbine with Evolution Algorithms

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Journal of Thermal Science 2011年第4期20卷 318-323页

作者： Jukka Huttunen jaakko Larjola Teemu Turunen-Saaresti Jari Backman Savonia Power ljytie 678710 VarkausFinlandjukka Lappeenranta University of Technology P.O.Box 2053851 LappeenrantaFinland

A prototype model of the mean radius flow path of a four-stage, high speed 1 MWe axial steam turbine was optimized by using evolution algorithms, DE （differential evolution） algorithm in this case. Also the cost-benefits of the optimization were inspected. The optimization was successfully performed but the accuracy of the optimization was slightly less than hoped when compared to the control modeling executed with the CFD （computational fluid dynamics）. The mentioned inaccuracy could have been hardly avoided because of problems with an initial presumption involving semi-empiric calculations and of the uncertainty concerning the absolute areas of qualification of the functions. This kind of algebraic modeling was essential for the success of the optimization because e.g. CFD-calculation could not have been done on each step of the optimization. During the optimization some problems occurred with the adequacy of the computer capacity and with finding a suitable solution that would keep the algorithms within mathematically allowable boundaries but would not restrict the progress of the opti- mization too much. The rest of the problems were due to the novelty of the application and problems with pre- ciseness when handling the areas of qualification of the functions. Although the accuracy of the optimization re- suits was not exactly in accordance with the objective, they did have a favorable effect on the designing of the turbine. The optimization executed with the help of the DE-algorithm got at least about 3.5 % more power out of the turbine which means about 150 000 ε cost-benefit per turbine in the form of additional electricity capacity.

关键词： steam turbine evolution algorithm optimization mean radius flow path semi-empirical loss correlations

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Feasibility of Pulse Combustion in Micro Gas Turbines

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Journal of Thermal Science 2012年第5期21卷 466-473页

作者： Juha Honkatukia Esa Saari Timo Knuuttila jaakko Larjola Jari Backman Lappeenranta University of Technology P.O. Box 2053851 Lappeenranta Finland T-Turbine Oy Rakentajainkuja 4 B02330 Espoo Finland

In gas turbines, a fast decrease of efficiency appears when the output decreases; the efficiency of a large gas tur-bine （20...30 MW） is in the order of 40 %, the efficiency of a 30 kW gas turbine with a recuperator is in the order of 25 %, but the efficiency of a very small gas turbine （2...6 kW） in the order of 4...6 % （or 8... 12 % with an op- timal recuperator）. This is mainly a result of the efficiency decrease in kinetic compressors, due to the Reynolds number effect. Losses in decelerating flow in a flow passage are sensitive to the Reynolds number effects. In con- trary to the compression, the efficiency of expansion in turbines is not so sensitive to the Reynolds number; very small turbines are made with rather good efficiency because the flow acceleration stabilizes the boundary layer. This study presents a system where the kinetic compressor of a gas turbine is replaced with a pulse combustor. The combustor is filled with a combustible gas mixture, ignited, and the generated high pressure gas is expanded in the turbine. The process is repeated frequently, thus producing a pulsating flow to the turbine; or almost a uni- form flow, if several parallel combustors are used and triggered a/ternately in a proper way. Almost all the com- pression work is made by the temperature increase from the combustion. This gas turbine type is investigated theoretically and its combustor also experimentally with the conclusion that in a 2 kW power size, the pulse flow gas turbine is not as attractive as expected due to the big size and weight of parallel combustors and due to the ef- ficiency being in the order of 8 % to 10 %. However, in special applications having a very low power demand, below 1000 W, this solution has better properties when compared to the conventional gas turbine and it could be worth of a more detailed investigation.

关键词： Gas turbine pulse combustion micro size low Reynolds number

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Indicators and tools for assessing sustainability impacts of the forest bioeconomy

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Forest Ecosystems 2017年第2期4卷 103-122页

作者： jaakko Karvonen Pradipta Halder Jyrki Kangas Pekka Leskinen Finnish Environment Institute Yliopistokatu 780100 JoensuuFinland Full list of author information is available at the end of the article University of Eastern Finland Faculty of Science and ForestrySchool of Forest SciencesP.O.Box 11180101 JoensuuFinland

The sustainable use of renewable resources has become an important issue worldwide in the move towards a less fossil-fuel-intensive *** method for fulfilling this aim is to increase the share of renewable energy and materials to substitute fossil fuels and to become fully independent from fossil fuels over the ***, the environmental sustainability of this endeavor has been *** addition,economic and social sustainability issues are also much debated topics in this particular *** resources are often thought to contribute partially to achieving a so-called ＂carbon-neutral society＂.In this review, we discuss sustainability issues of using forest *** present several sustainability indicators for ecological,economic and social dimensions and discuss the issues in applying them in sustainability impact assessments（SIAs）.We also present a number of tools and methods previously used in conducting *** approach our study from the perspective of the Finnish forestry; in addition, various aspects regarding the application of SIAs in a broader context are also *** of the key conclusions of the study is that although sufficient data are available to measure many indicators accurately, the impacts may be very difficult to assess（*** of greenhouse gases on biodiversity） for conducting a holistic ***, some indicators, such as ＂biodiversity＂, are difficult to quantify in the first ***, a mix of different methods, such as Multi-criteria Assessment, Life-cycle Assessment or Cost-Benefit Analysis, as well as different approaches（*** and strong/weak sustainability） are needed in aggregating the results of the *** are important in supporting and improving the acceptability of decision-making, but a certain degree of uncertainty will always have to be tolerated.

关键词： Forest bioeconomy Sustainability Indicators Impact assessment Decision support

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