Extending the Role of Computational Fluid Dynamics in Screw Machines

Previous publications show that computational fluid dynamics (CFD) can be readily used for the flow prediction and analysis of screw compressors. Several case studies are presented in this article to show the scope and applicability of such methods. These include solid–fluid interaction in screw compressors, prediction of flow generated noise in screw machines, cavitation modelling in gear pumps, and flow in multiphase pumps for oil and gas industry. Numerical grids for all these cases were generated by the authors using an in-house grid generator, while the CFD calculations were performed with a variety of commercially available CFD codes. In order to validate the accuracy of the CFD calculations, an extended test programme was carried out using laser Doppler velocimetry to measure the mean and fluctuating velocity distribution in screw compressor flow domains. The measurement results are then compared with the CFD simulations. The results confirm the viability of the developed techniques. It is shown in this publication that the flexibility of the developed method creates further opportunities for a broader use of CFD for analysis of twin screw machines in a range of new applications

Some Studies on the Reaction of B-(N,N-Heptamethylenimino) ethanol with Arylsulphonyl Chlorides

In a series of reactions of ~-(N,N-heptamethylenimino) ethanol with arylsulphonyl chlorides, four groups of compounds having different structures are described. The reaction in benzene in the presence of anhydrous sodium carbonate led to the formation of N,N-bis (heptamethylene)piperazinium salt of the arylsulphonic acid. When ~-(N,N-heptamethylenimino) ethanol and arylsulphonyl chloride were reacted in pyridine at o0 the hydrochloride of W-(N,N-heptamethylenimino) ethyl]-pyridinium-arylsulphonate was isolated. The same reaction in boiling pyridine gave the hydrochloride of [~-(N,N-heptamethylenimino) ethyl]-pyridinium chloride. The p-toluenesulphonic ester of ~-(N,N-heptamethylenimino) ethanol was prepared by reacting the sodium salt of ~-(N,N- heptamethylenimino)ethanol ,and p-toluenesulphonyl chloride. All compounds containing the pyridinium moiety showed strong hypotensive effect

Some Studies on the Reaction of B-(N,N-Heptamethylenimino) ethanol with Arylsulphonyl Chlorides

In a series of reactions of ~-(N,N-heptamethylenimino) ethanol with arylsulphonyl chlorides, four groups of compounds having different structures are described. The reaction in benzene in the presence of anhydrous sodium carbonate led to the formation of N,N-bis (heptamethylene)piperazinium salt of the arylsulphonic acid. When ~-(N,N-heptamethylenimino) ethanol and arylsulphonyl chloride were reacted in pyridine at o0 the hydrochloride of W-(N,N-heptamethylenimino) ethyl]-pyridinium-arylsulphonate was isolated. The same reaction in boiling pyridine gave the hydrochloride of [~-(N,N-heptamethylenimino) ethyl]-pyridinium chloride. The p-toluenesulphonic ester of ~-(N,N-heptamethylenimino) ethanol was prepared by reacting the sodium salt of ~-(N,N- heptamethylenimino)ethanol ,and p-toluenesulphonyl chloride. All compounds containing the pyridinium moiety showed strong hypotensive effect

Application of numerical grid generation for improved CFD analysis of multiphase screw machines

Algebraic grid generation is widely used for discretization of the working domain of twin screw machines. Algebraic grid generation is fast and has good control over the placement of grid nodes. However, the desired qualities of grid which should be able to handle multiphase flows such as oil injection, may be difficult to achieve at times. In order to obtain fast solution of multiphase screw machines, it is important to further improve the quality and robustness of the computational grid. In this paper, a deforming grid of a twin screw machine is generated using algebraic transfinite interpolation to produce initial mesh upon which an elliptic partial differential equations (PDE) of the Poisson's form is solved numerically to produce smooth final computational mesh. The quality of numerical cells and their distribution obtained by the differential method is greatly improved. In addition, a similar procedure was introduced to fully smoothen the transition of the partitioning rack curve between the rotors thus improving continuous movement of grid nodes and in turn improve robustness and speed of the Computational Fluid Dynamic (CFD) solver. Analysis of an oil injected twin screw compressor is presented to compare the improvements in grid quality factors in the regions of importance such as interlobe space, radial tip and the core of the rotor. The proposed method that combines algebraic and differential grid generation offer significant improvement in grid quality and robustness of numerical solution

Measurement of 60CO gamma radiation induced attenuation in multimode step-index POF at 530 nm

As optical fibres are used ever more extensively in space applications, nuclear industry, medicine and high-energy physics experiments, it has become essential to investigate the influence of ionizing radiation on their characteristics. In this work, the radiation-induced attenuation at 530 nm is investigated experimentally in step-index multimode polymethyl-methacrylate plastic optical fibres exposed to low dose-rate gamma radiation. Cumulative doses ranged from 50 Gy to 500 Gy. The radiation induced attenuation has been empirically found to obey the power law RIA= aDb, where D is the total radiation dose and a and b are the constants determined by fitting

Analytical Grid Generation for accurate representation of clearances in CFD for Screw Machines

One of the major factors affecting the performance prediction of twin screw compressors by use of computational fluid dynamics (CFD) is the accuracy with which the leakage gaps are captured by the discretization methods. The accuracy of mapping leakage flows can be improved by increasing the number of grid points on the profile. However, this method faces limitations when it comes to the complex deforming domains of a twin screw compressor because the computational time increases tremendously. In order to address this problem, an analytical grid distribution procedure is formulated that can independently refine the region of high importance for leakage flows in the interlobe space. This paper describes the procedure of analytical grid generation with the refined mesh in the interlobe area and presents a test case to show the influence of the mesh refinement in that area on the performance prediction. It is shown that by using this method, the flow domains in the vicinity of the interlobe gap and the blowhole area are refined which improves accuracy of leakage flow predictions

Znakovni jezici - nekad i sad

A way of communication on an equal footing with oral and written speech is sign language. Oral speech is a common way of communication, written speech has, with the development of information technologies, been taking up more and more space. In a parallel with them, communication can also take place through sign language, which is, to deaf people, as well as to all those who use it, a natural, simple and easy way to communicate. Relationship towards sign language has changed significantly throughout history from acceptance and isolated use, to complete rejection, and then to encouraging its adoption and emphasizing its importance for the cognitive, emotional, educational, social, and general development of deaf children. Serbian Sign Language (SSL) serves deaf people in Serbia as a means for everyday communication, for expressing desires, willingness, for learning, for intellectual discussions, for expressing personal style. Although the standardization of the Serbian Sign Language was completed in 2015, even nowadays we may still find certain gestures of expression varying in different regions. Different countries have different sign languages that are not reciprocally understood in use. They are distinguished by their own grammar (semantics, morphology, and syntax), different from the grammar of spoken languages. The distinguishing and recognition of sign languages in the world has led to changes in the field of education of deaf children. In bilingual schools, children acquire both sign and spoken languages, and teachers know both of the mentioned languages. The importance of sign language in the education of deaf children is emphasized.Ravnopravan način komunikacije sa usmenim i pisanim govorom jeste znakovni jezik. Usmeni govor je uobičajeni način komunikacije, a pisani govor razvojem informacionih tehnologija zauzima sve više prostora. Paralelno sa njima može se odvijati i komunikacija putem znakovnog jezika, koji je prirodan, jednostavan i lak način komunikacije gluvim ljudima, ali i svima onima koji ga koriste. Odnos prema znakovnom jeziku se kroz istoriju značajno menjao. Od prihvatanja i izolovane upotrebe do potpunog odbacivanja, zatim i do podsticanja njegovog usvajanja i isticanja značaja za kognitivni, emocionalni, edukativni, socijalni i opšti razvoj gluve dece. Srpski znakovni jezik (SZJ) gluvim osobama u Srbiji služi kao sredstvo za svakodnevnu komunikaciju, za iskazivanje želja, volje, za učenje, intelektualne rasprave, izražavanje ličnog stila. Standardizacija srpskog znakovnog jezika završena je 2015. godine i danas imamo mogućnost regionalnih varijacija pojedinih gestova i načina izražavanja. U različitim delovima sveta koriste se različiti znakovni jezici koji nisu međusobno razumljivi. Odlikuju se sopstvenom gramatikom (semantikom, morfologijom i sintaksom) različitom od gramatike govornih jezika. Prepoznavanje i priznavanje znakovnih jezika u svetu dovelo je do promena u sferi vaspitanja i obrazovanja gluve dece. U dvojezičnim školama deca uče oba jezika, i znakovni i govorni, a nastavnici istovremeno vladaju i jednim i drugim oblikom izražavanja. U radu se ističe značaj znakovnog jezika za obrazovanje gluve dece

Probabilistic analysis of voltage divider ratios

Tolerancija modernih otpornika obično varira od 0.1% do 1 %. Sa probabilističke tačke gledišta to znači da se odgovarajući otpor može posmatrati kao slučajna promenljiva sa odgovarajućom funkcijom gustine raspodele verovatnoće (PDF). Dobijen je izraz za PDF za odnos prenosa dvo-otporničkog razdelničkog napona, kada je otporima u razdelniku dodeljena uniformna raspodela. Grafikoni dobijeni analitičkim izrazima, za različite kombinacije nominalnih otpora i tolerancije dvaju otpornika, upoređeni su sa onima dobijenim numeričkim simulacijama. Asimetrični karakter dobijenog rezultantnog PDF-a, uzrokovan nelinearnošću funkcije razdelničkog kola, implicira da se nominalna, srednja i najverovatnija vrednost razdelničkog odnosa mogu razlikovati. Za normalnu raspodelu otpora u dvootporničkom razdelniku, analitički pristup postaje složen, dok Monte Karlo simulacije lako daju grafikone naponskih odnosa PDF-a i izračunavaju vrednosti njihovih parametara.Tolerance of modern resistors typically ranges from 0.1% to 1%. From the probabilistic viewpoint, this is taken to mean that the corresponding resistance can be treated as a random variable, with an appropriate probability density function (PDF). We derive an expression for the PDF of a two-resistor voltage divider's transfer ratio, when the resistances in the divider are assigned uniform distributions. Plots of the obtained analytical expression, for various combinations of nominal resistances and tolerances of the two resistors, are compared to those produced by numerical (Monte Carlo) simulations. The asymmetrical character of the obtained resultant PDF, caused by non-linearity of the divider's circuit function, implies that the nominal, the mean and the most probable value of the divider's ratio can all differ. For normally distributed resistances in the two-resistor divider, analytical approach becomes complex, while Monte Carlo simulations readily provide the plots of voltage ratio PDFs and calculate the values of their parameters

Algorithm for calculating influence of power transformer oil temperature change on the accuracy of allacoustic non-iterative partial discharge localization

Ovaj rad razmatra čisto akustičku metodu za lokalizaciju parcijalnog pražnjenja u energetskom transformatoru. Ova metoda se zasniva na matematičkom modelu koji koristi multilateraciju, princip vremenske razlike kašnjenja signala i neiterativni matematički algoritam. U ovom modelu pretpostavlja se da akustički signal prolazi jedino kroz transformatorsko ulje i da je brzina akustičkog signala konstantna. Brzina akustičkog signala u velikoj meri zavisi od temperature transformatorskog ulja što znači da se i temperatura transformatorskog ulja smatra konstantnom. U realnim uslovima, sa aspekta fizike, termodinamike fluida, konstrukcije transformatora itd., ova pretpostavka je najblaže rečeno velika. Upravo zato se u ovom radu istražuje uticaj promene temperature transformatorskog ulja (promene brzine akustičkog signala) na preciznost razmatrane metode. Za tu namenu, dizajniran je algoritam i implementiran u programskom jeziku Visual C#. Na osnovu sprovedenih simulacija stečena su nova saznanja o interakciji između temperature transformatorskog ulja i položaja akustičkih senzora. Ova interakcija dovela je do značajne razlike u preciznosti neiterativnog matematičkog algoritma za različite položaje akustičkih senzora pri promeni temperature transformatorskog ulja. Kako bi se uočena interakcija maksimalno iskoristila za unapređenje preciznosti razmatrane metode, predloženi su određeni koraci za dalje istraživanje i razvoj.This article investigates the all-acoustic method for partial discharge localization in a power transformer. This method is based on mathematical model that uses multilateration with Time Difference of Arrival (TDOA) principle and non-itterative mathematical algorithm. In this model, it is assumed that acoustic signal propagates only through transformer oil and that the velocity of acoustic signal is constant. Acoustic signal velocity is largely dependent on transformer oil temperature meaning that oil temperature is also considered to be constant. In reality if we look from the perspective of physics, thermo dynamics of fluids, transformer construction etc. this approximation is enormous. Therefore, influence of power transformer oil temperature change (velocity of acoustic signal change) on the accuracy of this method is investigated. For that purpose special algorithm is designed and implemented in Visual C# programming language. Based on conducted simulations, further knowledge is gained about interaction between transformer oil temperature and placement of acoustic sensors. This interaction produced significant disparity in noniterative algorithm's accuracy for different sensor positions with oil temperature change. In order to fully take advantage of noticed interaction, certain steps for further research and development are proposed

Probabilistic analysis of voltage divider ratios

Tolerancija modernih otpornika obično varira od 0.1% do 1 %. Sa probabilističke tačke gledišta to znači da se odgovarajući otpor može posmatrati kao slučajna promenljiva sa odgovarajućom funkcijom gustine raspodele verovatnoće (PDF). Dobijen je izraz za PDF za odnos prenosa dvo-otporničkog razdelničkog napona, kada je otporima u razdelniku dodeljena uniformna raspodela. Grafikoni dobijeni analitičkim izrazima, za različite kombinacije nominalnih otpora i tolerancije dvaju otpornika, upoređeni su sa onima dobijenim numeričkim simulacijama. Asimetrični karakter dobijenog rezultantnog PDF-a, uzrokovan nelinearnošću funkcije razdelničkog kola, implicira da se nominalna, srednja i najverovatnija vrednost razdelničkog odnosa mogu razlikovati. Za normalnu raspodelu otpora u dvootporničkom razdelniku, analitički pristup postaje složen, dok Monte Karlo simulacije lako daju grafikone naponskih odnosa PDF-a i izračunavaju vrednosti njihovih parametara.Tolerance of modern resistors typically ranges from 0.1% to 1%. From the probabilistic viewpoint, this is taken to mean that the corresponding resistance can be treated as a random variable, with an appropriate probability density function (PDF). We derive an expression for the PDF of a two-resistor voltage divider's transfer ratio, when the resistances in the divider are assigned uniform distributions. Plots of the obtained analytical expression, for various combinations of nominal resistances and tolerances of the two resistors, are compared to those produced by numerical (Monte Carlo) simulations. The asymmetrical character of the obtained resultant PDF, caused by non-linearity of the divider's circuit function, implies that the nominal, the mean and the most probable value of the divider's ratio can all differ. For normally distributed resistances in the two-resistor divider, analytical approach becomes complex, while Monte Carlo simulations readily provide the plots of voltage ratio PDFs and calculate the values of their parameters