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Krella A.,Szewalski Institute of Fluid Flow Machinery
Wear | Year: 2013

TiN and CrN coatings with various thicknesses deposited on X6CrNiTi18-10 and X39Cr13 steel by means of the cathodic arc evaporation method were tested in a cavitation tunnel with a slot cavitator and tap water as the medium. Steels were subjected to thermal treatment in order to obtain substrates of different properties. Present investigation shows that the properties of the substrate, especially the thermal properties, influence the properties of the TiN coatings. Deposition of hard TiN and CrN coatings on the steel substrates has caused the improvement of the cavitation erosion resistance. The increase of coating thickness decreases the positive effect of the TiN and CrN coatings deposition. The 8 and 12μm thick TiN and CrN coatings undergo degradation mostly via spalling by removal of the thin flakes of the coating. The resistance parameter, RCAV=(kc/ks)/(αc/αs){dot operator}(Hc{dot operator}(1-vc2))/(Ec{dot operator}(1+vc2)){dot operator}(Es{dot operator}(1+vS2))/(Hs{dot operator}(1-vS2)){dot operator}(LC2/pc{dot operator}h), where k is thermal conductivity, α is the thermal expansion coefficient, H is the hardness in GPa, LC2 is the adhesion force in N obtained in the scratch tests, E is the Young's modulus in GPa, pc is the number of phases in the coating phase composition, h is the coating thickness in μm, subscript c applies for coating, s is for the substrate, has been positively verified by present investigations. This indicates that not only the mechanical properties of the coating and of the substrate influence the cavitation erosion resistance of the PVD coating-steel substrate system, but also their thermal properties. © 2012 Elsevier B.V.

Krella A.,Szewalski Institute of Fluid Flow Machinery
Wear | Year: 2011

A series of cavitation erosion tests were carried out to investigate the resistance of the TiN coatings against cavitation action. The TiN coatings were deposited at various deposition parameters on austenitic stainless steel, X6CrNiTi18-10, with various coating thicknesses by means of the cathodic arc evaporation method (CAVD). Investigations were performed in a cavitation tunnel with a slot cavitator. The estimation of cavitation resistance of the TiN coatings was performed on the basis of the incubation period and the mass loss. The investigations show that coating hardness, Young's modulus, adhesion and coating thickness have an influence on coating endurance to cavitation degradation. The parameter H·LC2/E·h1/2 shows very good fitting to data points (R2=0.9707). Along with the increase of the H·LC2/E·h1/2 parameter the mass loss decreases indicating a continuous improvement in the cavitation erosion resistance. © 2010 Elsevier B.V.

Mikielewicz D.,Technical University of Gdansk | Mikielewicz J.,Szewalski Institute of Fluid Flow Machinery
Applied Thermal Engineering | Year: 2010

A thermodynamic criterion for selection of a fluid both for subcritical and supercritical organic Rankine cycle has been proposed. Theoretical performances of few fluids have been comparatively assessed for use in low-temperature domestic organic Rankine cycle micro systems. Of the 20 fluids investigated, ethanol, R123 and R141b appear as the most suitable for small scale domestic CHP applications. © 2010 Elsevier Ltd. All rights reserved.

Pietraszkiewicz W.,Szewalski Institute of Fluid Flow Machinery
International Journal of Engineering Science | Year: 2011

The resultant two-dimensional (2D) balance laws of mass, linear and angular momentum, and energy as well as the entropy inequality for shells are derived by direct through-the-thickness integration of corresponding 3D laws of continuum thermomechanics. It is indicated that the resultant shell stress power cannot be expressed exactly through the 2D shell stress and strain measures alone. Hence, an additional stress power called an interstitial working is added to the resultant 2D balance of energy. The new, refined, resultant balance of energy and entropy inequality derived here are regarded to be exact implications of corresponding global 3D laws of rational thermodynamics. The kinematic structure of our shell theory is that of the Cosserat surface, while our refined resultant laws of thermomechanics contain three additional surface fields somewhat similar to those present in 3D extended thermodynamics. We briefly analyse the restrictions imposed by our refined resultant entropy inequality on the forms of 2D constitutive equations of viscous shells with heat conduction and of thermoelastic shells. It is shown, in particular, that in such shells the refined resultant entropy inequality allows one to account for some longer-range spatial interactions. We also present several novel forms of 2D kinetic constitutive equations compatible with the resultant shell equations. © 2011 Elsevier Ltd. All rights reserved.

Krella A.K.,Szewalski Institute of Fluid Flow Machinery
Engineering Failure Analysis | Year: 2011

Most machinery elements are coated with hard coatings to prolong their lifetime and to improve working efficiency. Cavitation test was used as a tool for studies of dynamic impact degradation. Ti- and Cr-based coatings were chosen for investigations. The TiN and Cr-N coatings with various thicknesses were deposited on stainless steel by means of the cathodic arc evaporation method at various deposition parameters. Tests were performed in the cavitation chamber with a system of barricades. Nearly all the TiN and Cr-N coatings have undergone micro-undulation. The first cohesive fractures have occurred on top of the micro-folding and at delamination spots. The analysis of degradation mechanism of thin hard coatings under repeated impact loading has resulted in deriving a new empirical parameter suitable for description of the hard coating cavitation resistance. The derived parameter is proportional to the plasticity index, H/E (defined as ratio of hardness, H, and Young's modulus, E), adhesion force, LC2, ratio of thermal conductivity of the coating to that of the substrate, and inversely proportional to the number of phases in the coating phase composition, the ratio of the thermal expansion of the coatings to that of the substrate and the square root of the coating thickness. The new endurance parameter shows good correlation with the mass loss of all the tested hard coatings indicating a continuous improvement in the erosion resistance with the increase of the new parameter. © 2010 Elsevier Ltd.

Kicinski J.,Szewalski Institute of Fluid Flow Machinery
Bulletin of the Polish Academy of Sciences: Technical Sciences | Year: 2013

This paper presents examples of technologies for distributed energy generation developed under the projects coordinated by the IFFM PAS in Gdańsk. These are CHP units (generating heat and electricity) for houses with a power from several to tens of kW and for municipalities in the form of the Municipal Energy Centers (with a capacity of several hundred kW up to several MW). A unique project, specializing in "energy-plus" technologies for residential houses and other buildings, which aims to build a Research Centre of PAS in Jabłonna is also presented,. These are key technologies for energy sector with respect to distributed generation. Additionally, the article discusses the conditions and opportunities for the development of energy generation or more broadly: civic energy generation in our country. Civic energy generation is a great vision in which the citizen becomes an entity and do not subject to the energy market, and additionally has its virtual advisor in the form of smart grid and data processing technologies in a "digital cloud".

Szwaba R.,Szewalski Institute of Fluid Flow Machinery
Journal of Thermal Science | Year: 2013

Control of shock wave and boundary layer interaction continues to attract a lot of attention. In recent decades several methods of interaction control have been investigated. The research has mostly concerned solid (vane type) vortex generators and transpiration methods of suction and blowing. This investigation concerns interaction control using air-jets to generate streamwise vortices. The effectiveness of air-jet vortex generators in controlling separation has been proved in a previous research. The present paper focuses on the influence of the vortex generator diameter on the separation region. It presents the results of experimental investigations and provides new guidelines for the design of air-jet vortex generators to obtain more effective separation control. © 2013 Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag Berlin Heidelberg.

Henry C.,Szewalski Institute of Fluid Flow Machinery | Minier J.-P.,Électricité de France
Progress in Energy and Combustion Science | Year: 2014

This article deals with the resuspension phenomenon whereby particles adhering on a wall surface can be re-entrained by a flowing fluid. This is an area where significant progress has been achieved over the last years from an experimental, theoretical and numerical point of view. A first purpose of the present work is to report on the advances that have clarified our understanding of the physics of particle resuspension. It will be seen that new pictures have emerged about the physical processes involved in particle resuspension and, correspondingly, that new models have been proposed. A second purpose of the review is to put forward a general framework that allows both experimental analysis and new modelling ideas to be developed in terms of the fundamental interactions at play. These interactions are made up by the particle-fluid, particle-surface and particle-particle forces which are, in turn, related to the three specific fields of fluid dynamics, interface chemistry and surface roughness. Such a separation is helpful to highlight the actual physical processes while emphasising their relative importance in different situations and to provide useful guidelines for the necessary modelling efforts. In particular, it is stressed that new models which capture particle motion along a wall and simulate the complete particle dynamics represent an improvement over more classical static approaches. It is proposed that these new approaches be pursued and brought to higher levels of maturity. In this paper, attention is first focussed on the case where only a single layer of particles is sticking on the surface and, thus, can be re-entrained. A detailed review of the experimental works brings out the essential mechanisms and particle resuspension is shown to result from a balance between particle-fluid interactions and particle-surface interactions influenced by surface heterogeneities (roughness). The numerical models which have been proposed are then thoroughly discussed with respect to a new hierarchy of modelling approaches which is introduced. The present paper also outlines the mechanisms of multilayer particle resuspension which is still an open subject and where our present understanding remains preliminary. In this situation, resuspension is shown to be also governed by particle-fluid and particle-surface interactions but with the addition of particle-particle interactions (through cohesion forces or impaction). Finally, suggestions about the areas that still need to be addressed as well as about the issues that remain to be improved are addressed. © 2014 Elsevier Ltd. All rights reserved.

Krella A.K.,Szewalski Institute of Fluid Flow Machinery
Surface and Coatings Technology | Year: 2013

The results of cavitation erosion tests of the Ti/TiN multilayer coatings protecting the X6CrNiTi18-10 steel are presented in this paper. The Ti/TiN multilayer coatings were deposited on the X6CrNiTi18-10 steel surface by means of the cathodic arc evaporation PVD method. The multilayer coatings were deposited as 4, 12 and 40-layer structures with the Ti layer at the bottom and the TiN layer on the top. All layers showed similar thickness; the total thickness of the Ti/TiN multilayer coatings was approximately 4 μm. The coated specimens showed better cavitation erosion resistance than the uncoated stainless steel. With an increase of the number of coating layers the cavitation erosion resistance of the Ti/TiN multilayer coating was lower. It was shown experimentally that the Ti/TiN-4 coating provided the best protection against cavitation erosion. The degree of cavitation erosion was estimated by mass measurements and surface roughness measurement tests. The value of surface roughness of the Ti/TiN-4 coating was closest to that of the uncoated steel. The surface profiles of the Ti/TiN-12 and Ti/TiN-40 coatings showed little undulation, not visible in the profiles of the Ti/TiN-4 coating and the uncoated X6CrNiTi18-10 steel. The microscopic observation showed that deformation of the multilayer coatings developed via cracking, which further propagated by simultaneous fracture of numerous coating layers. © 2013 Elsevier B.V.

Rybczyski J.,Szewalski Institute of Fluid Flow Machinery
Mechanical Systems and Signal Processing | Year: 2011

This paper presents the results of computer simulation of bearing misalignment defects in a power turbogenerator. This malfunction is typical for great multi-rotor and multi-bearing rotating machines and very common in power turbo-sets. Necessary calculations were carried out by the computer code system MESWIR, developed and used at the IFFM in Gdansk for calculating dynamics of rotors supported on oil bearings. The results are presented in the form of a set of journal and bush trajectories of all turbo-set bearings. Our analysis focuses on the vibrational effects of displacing the two most vulnerable machine bearings in horizontal and vertical directions by the maximum acceptable range calculated with regard to bearing vibration criterion. This assumption required preliminary assessment of the maximum values for the permissible bearing dislocations. We show the relations between the attributes of the particular bearing trajectories and the bearing displacements in relation to their base design position. The shape and dimensions of bearing trajectories are interpreted based on the theory of hydrodynamic lubrication of oil bearings. It was shown that the relative journal trajectories and absolute bush trajectories carry much important information about the dynamic state of the machine, indicating also the way in which bearings are loaded. Therefore, trajectories can be a source of information about the position and direction of bearing misalignments. This article indicates the potential of using trajectory patterns for diagnosing misalignment defects in rotating machines and suggests including sets of trajectory patterns to the knowledge base of a machine diagnostic system. © 2010 Elsevier Ltd.All rights reserved.

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