The National Technical University of Ukraine “Kyiv Polytechnic Institute” is a major university in Kyiv, Ukraine. In January 2012 Webometrics Ranking KPI made it into top 1,000 – taking 957th place out of 20,300 universities, 510th . Wikipedia.
News Article | December 17, 2015
Did you know that ultrasonic cleaning is connected with early studies at the Kiev Institute of Cinema? Lazar Davidovich Rozenberg (1908-1968) was a researcher in acoustic cavitation and has been credited with laying the scientific foundation for the development of ultrasonic cleaning. He founded the Department of Acoustics and Acoustoelectronics, originally as part of the Kiev Institute of Cinema; it is now part of the National Technical University of Ukraine.1 Ultrasonic cleaning — cleaning with high frequency sound waves — has become a staple of the laboratory and of the manufacturing facility for generations. For years, we have understood and “taught” the impact of temperature on cavitation based on studies by Rozenberg published in 1960.2 Specifically, the “Rozenberg graph” (see Fig. 1) shows the impact of temperature on cavitation for a number of solvents; there is a peak at which cavitation is most effective for each solvent. Components and product have evolved, and so have ultrasonic cleaning systems. Ultrasonic cleaning is used with new materials of construction and of engineered coatings, and the miniaturization of components. Ultrasonics may have value to exploit the promise and to meet the challenges of additive manufacturing. In the “olden days,” there was ultrasonic cleaning with 18KHz. Now, ultrasonic cleaning equipment with many options such as ever-higher frequencies and controllable power level, has been developed. In Controlled Environments columns that appeared a decade ago, we emphasized that independent studies are a must to determine optimal approaches to ultrasonic cleaning.3, 4 Therefore, we have been evaluating the impact of ultrasonic variables on cleaning performance. Some of these variables include the shape and materials of construction of the substrate, the soils, the chemical or chemical blend used for cleaning, the ultrasonic frequency, power density, temperature, and time. Our experiments included revisiting the Rozenberg study. Attention: we do not intend to revisit the study using low flashpoint solvents, and we strongly recommend that you not play with fire either. The potential for fire posed by heat and ignitions sources is real. We evaluated the impact of temperature on cavitation in 40 KHz systems with sweep operated at about 18 watts/L (80 percent of maximum power). We tested water and two commercially-available aqueous chemistries.5 The chemistries were tested at the manufacturer’s recommended dilution, ranging from 1 to 10 percent, for 3 minutes at ambient temperature. To monitor cavitation, commercially-available 0.015 mm thick aluminum foil was immersed in the chemistry being testing. The effectiveness of ultrasonic cavitation was judged visually by the characteristic orange peel deformation pattern of the foil. While ultrasonic monitors have been developed, the aluminum foil test remains the most widely-used test for cavitation, perhaps because it is readily accessible, simple to perform, and cost-effective. Be aware that at higher frequencies, commercial aluminum foil becomes a less effective indicator of cavitation. Our results are summarized in Fig. 2, and they are somewhat different than the Rozenberg results. While we considered calling this the “Kanegsberg, Kanegsberg, Norris graph,” in the interest of not inflicting polysyllabic torture we will mercifully refer it to as the KN graph. In both the KN and the Rozenberg results, as the temperature of the cleaning agent approaches the boiling point, cavitation decreases. The most likely explanation is that cavitation involves implosion of vacuum voids (“bubbles”) that result from tears in the liquid. As liquids approach the boiling point, the voids in the liquid become filled with vapor; the more vapor, the less forceful the implosion. Manufacturers involved in critical cleaning of high-value product may increase the temperature of an ultrasonic system to near the boiling point. Cleaning effectiveness may actually decrease due to decreased cavitation. If cleaning effectiveness is effective primarily near the boiling point, it may be due to melting and solubilization of the soil; you have very likely lost the benefit of ultrasonics. However, in contrast with Rozenberg, the KN results show a sort of cavitation “tail” at ambient temperature, with a valley as the temperature increases before then increasing to a maximum. However, those involved in cleaning heat-sensitive product might consider testing ultrasonics cavitation at ambient temperature versus at somewhat elevated temperature. We do not know if this phenomenon occurs in 40 KHz ultrasonic systems from other suppliers. Further, initial studies at 132 KHz indicate that yet a different pattern of cavitation versus temperature may emerge. Many people take ultrasonic cleaning systems for granted.6 Manufacturers may use default settings and practices based on historical experience. Or they may rely solely on recommendations from equipment suppliers. We all probably make assumptions that are logical but may not be correct. It is impractical to test all the variables, particularly in a busy manufacturing environment. However, investing in some initial effort to test and optimize the ultrasonic system is likely to yield benefits in terms of cleanliness, surface quality, and contamination control. The authors wish to convey thanks and appreciation to Plasma Technology Inc. of Torrance, Calif., for providing test facilities. They also wish to thank Crest Ultrasonics for providing ultrasonic cleaning equipment, and The Brulin Co., Crest Ultrasonics, e-Chem, and Mirachem for supplying aqueous chemistries. References 1. Department of Acoustics and Acoustoelectronics, National Technical University of Ukraine, http://kpi.ua/en/node/203. 2. Rozenberg, L.D. “On the Physics of Ultrasonic Cleaning,” Ultrasonic News, 4, p. 16 (1960). 3-4. Kanegsberg, B. and E. Kanegsberg, “Ultrasonics Cleaning: Parts 1 and 2,” Controlled Environments Magazine, and . 5. Kanegsberg, B. and E. Kanegsberg, “New Studies: Improve Your Ultrasonic Cleaning Process,” presented at SUR/FIN, Rosemont, Ill., June 10, 2015. 6. Kanegsberg, B, E. Kanegsberg, and Steve Norris, “Ferris and Ultrasonics,” Spraytime Magazine, Third Quarter, 2014. Barbara Kanegsberg and Ed Kanegsberg (the Cleaning Lady and the Rocket Scientist) are experienced consultants and educators in critical and precision cleaning, surface preparation, and contamination control. Their diverse projects include medical device manufacturing, microelectronics, optics, and aerospace. They can be reached at email@example.com. Steve Norris is New Project Director at Plasma Technology Inc. with locations in Torrance, Calif. and Hartford, Conn. He has had 13 years of experience in studying the effect of ultrasonic cleaning on metal surfaces to be used with engineered coatings. He can be reached at firstname.lastname@example.org. This article appeared in the November/December 2015 issue of Controlled Environments.
Bodson M.,University of Utah |
Kiselychnyk O.,National Technical University of Ukraine
IEEE Transactions on Automatic Control | Year: 2013
Spontaneous self-excitation in induction generators is a fascinating phenomenon triggered by the instability of a zero equilibrium state. Prediction of this condition for various values of free parameters requires many computations of the eigenvalues of a 6$\,\times\,$ 6 matrix over a large space. The technical note uses a novel approach to stability using a transformation of the state-space system and an extension of the Hurwitz test to polynomials with complex coefficients. The analytic formulas that are obtained give the values of the minimum load resistance, the range of capacitor values, and the range of speeds for which spontaneous self-excitation appears. The technical note concludes with an illustration of the results on an example. © 2012 IEEE.
Bodson M.,University of Utah |
Kiselychnyk O.,National Technical University of Ukraine
IEEE Transactions on Energy Conversion | Year: 2012
In self-excited induction machines, a power generating mode of operation can often be attained only by precharging at least one of the capacitors connected to the windings. The paper shows how a carefully derived state-space model with nonlinear magnetic characteristics enables the assessment of all possible operating regimes including their stability properties. In particular, the analysis reveals the possible existence of an unstable operating regime, which creates a barrier that must be overcome through precharged capacitors. In such case, the analytical results of the paper yield a simple formula that predicts the voltage needed to trigger self-excitation. Close to the boundary, voltages can be generated for extended periods of time before growing to a stable operating regime, or collapsing to zero. Experimental results validate the results of the paper on the transient properties of self-excited induction generators. © 2012 IEEE.
Pis'mennyi E.N.,National Technical University of Ukraine
International Journal of Heat and Mass Transfer | Year: 2012
A great number of experimental investigations allowing one to reveal the physical mechanism of processes responsible for their thermal and hydraulic performance are carried out in attempt to solve problems of updating constructions and methods of thermal design of heating surfaces of transversely finned tubes widespread in power engineering. Results of flow visualization and investigation of pressure fields and local heat transfer at the fin surface over the Reynolds number range Re = (1.0 ⋯ 6.6)·10 4 are presented for the case of a wide variation of geometric characteristics of finned tubes and parameters of their arrangement in a bundle. Regularities substantially changing the existing concept of transfer processes in the interfin space and in the wake behind a finned tube are revealed. It is found that the flow behavior and the distribution of local heat transfer coefficients over the fin surface change significantly at the fin height-to-finned tube diameter h/d approximately equal to 0.4. The results obtained are generalized in the form of the patterns of flow and heat transfer at the finned tube surface, including seven characteristic regions and four types of flow separation. © 2012 Elsevier Ltd. All rights reserved.
Pis'Mennyi E.N.,National Technical University of Ukraine
Applied Thermal Engineering | Year: 2016
A new type of extended heat transfer surfaces in the form of incompletely finned flat-oval tubes is proposed. They are easily manufactured, have a high surface extension degree, high convective heat transfer intensity and a low aerodynamic drag. The experimental results of research of thermal and aerodynamic characteristics of such surfaces, their analysis and comparison with the data for the existing round finned tubes are presented. Given are the examples of application of incompletely finned flat-oval tubes in the waste-gas heat utilizers of power plants. © 2016 Elsevier Ltd. All rights reserved.
Fokin A.A.,National Technical University of Ukraine |
Gerbig D.,Justus Liebig University |
Schreiner P.R.,Justus Liebig University
Journal of the American Chemical Society | Year: 2011
The properties of single-sheet [n]graphanes, their double-layered forms (diamondoids), and their van der Waals (vdW) complexes (multilayered [n]graphanes) were studied for n = 10-97 at the dispersion-corrected density functional theory (DFT) level utilizing B97D with a 6-31G(d,p) basis set; for comparison, we also computed a series of structures at M06-2X/6-31G(d,p) as well as B3LYP-D3/6-31G(d,p) and evaluated SCS-MP2/cc-pVDZ single-point energies. The association energies for the vdW complexes reach 120 kcal mol -1 already at 2 nm particle size (graphane dimer), and graphanes adopt layered structures similar to that of graphenes. The association energies of multilayered graphanes per carbon atom are rather similar and independent of the number of layers (ca. 1.2 kcal mol -1). Graphanes show quantum confinement effects as the HOMO-LUMO gaps decrease from 8.2 eV for graphane to 5.7 eV for graphane, asymptotically approaching 5.4 eV previously obtained for bulk graphane. Similar trends were found for layered graphanes, where the differences in the electronic properties of double-sheet CH/σ vdW and double-layered CC/σ diamondoids vanish at particles sizes of 1 nm. For comparison, we studied the parent CC/π systems, i.e., the single- and double-sheet [n]graphenes (n = 10-130) for which the association energies demonstrate the same trends as in the case of [n]graphanes; in both cases the band gaps decrease with an increase in system size. The graphene dimer (HOMO-LUMO gap = 0.5 eV) already approaches the 2D metallic properties of graphite. © 2011 American Chemical Society.
Kasyanov P.O.,National Technical University of Ukraine
Cybernetics and Systems Analysis | Year: 2011
This article considers a nonlinear autonomous differential-operator inclusion with a pseudomonotone dependence between determinative problem parameters. The dynamics of all weak solutions defined on the positive semi-axis of time is studied. The existence of trajectory and global attractors is proved and their structure is investigated. A class of high-order nonlinear parabolic equations is considered to be a possible application. © 2011 Springer Science+Business Media, Inc.
Borovytsky V.,National Technical University of Ukraine
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012
The paper presents the mathematical description of an optical microscope with a digital camera and an image processing as an analog-digital-analog imaging system. This description considers a channel of the microscope as a sequence of the linear spatial filters of two dimensional signals. The channel contains an optical system as a low frequency analog filter, a digital camera as a low frequency analog filter with spatial and amplitude discretization and noise generation, a digital linear filter which has to amplify the high frequency harmonics and a restoration unit that plays a role of a two dimensional interpolator. This mathematical apparatus is useful for proper selection of a digital camera which guarantees the maximal field of view with absence of image distortions. The terms like optimal, nonsufficient and non-useful (void) linear magnification of a microscope optical system are expanded from a visual microscopy to a digital one. This mathematical description is also applied for selection of a digital filter for focusing and digital focus extension. The modulation transfer function of this filter should match for the spatial spectrum of observed objects in the zone of spatial harmonics that is most sensitive to defocusing. In this case the maximal sensitivity to defocusing with minimization of influence of noise can be reached. © 2012 SPIE.
Shcherba M.A.,National Technical University of Ukraine
2014 IEEE International Conference on Intelligent Energy and Power Systems, IEPS 2014 - Conference Proceedings | Year: 2014
The mathematical modeling of the electric field amplification in a solid dielectric medium with varying degrees of water tree branching in it was made. The dependences governing this field amplification subject to the degree of tree branching were established. The dependences of maximal field strength and quantity of dielectric tensed volume depending on the number of tree branches, their length and location relative to the tree channel were found. The most dangerous situations in terms of deterministic and stochastic processes of solid dielectric degradation in a strong electric field were identified. © 2014 IEEE.
Pis'mennyi E.N.,National Technical University of Ukraine
International Journal of Heat and Mass Transfer | Year: 2011
Based on the analysis of experimental data the universal methods of calculating convective heat transfer of smooth and finned tube bundles in the crossflow have been developed over the ranges of geometric characteristics covering all practical needs at the Reynolds number Re = 3 × 10 3...1 × 105. The distinctive feature of the methods proposed is that the generalized similarity equation of convective heat transfer takes into account the dependence of the Reynolds number exponent on tube pitch characteristics in a bundle. This has allowed the mechanism of heat transfer and hydraulic performance in tube bundles to be taken into utmost consideration and the asymptotic character to be given to the generalized dependence. In turn, this has permitted one to show the presence of maximum of heat transfer intensity and also to cover limiting combinations of pitches, at which differences in staggered and in-line arrangements of tubes are leveled, i.e., practically the restrictions on the ranges of tube pitch characteristics of bundles can be removed. © 2011 Elsevier Ltd. All rights reserved.