Laser doppler velocimetry and confined flows

Finding the mode, in which two component laser Doppler velocimetry can be applied to flows confined in cylindrical tubes or vessels, was the aim of this study. We have identified principle issues that influence the propagation of laser beams in laser Doppler velocimetry system, applied to flow confined in cylindrical tube. Among them, the most important are influences of fluid and wall refractive indices, wall thickness and internal radius ratio and beam intersection angle. In analysis of the degrees of these influences, we have applied mathematical model, based on geometrical optics. The separation of measurement volumes, that measure different velocity components, has been recognized as the main drawback. To overcome this, we propose a lens with dual focal length primary focal length for the measurement of one velocity component and secondary focal length for the measurement of the other velocity component. We present here the procedure for calculating the optimal value of secondary focal length, depending on experimental set-up parameters. The mathematical simulation of the application of the dual focal length lens, for chosen cases presented here, confirmed the accuracy of the proposed procedure

Estimation of laser-Doppler anemometry measuring volume displacement in cylindrical pipe flow

Laser-Doppler anemometry application in measurements of the 3-D swirl turbulent flow velocity in the cylindrical pipe, behind the axial fan, have been analysed. This paper presents a brief overview of uncertainty sources in the laser-Doppler anemometry measurements. Special attention is paid to estimation of laser-Doppler anemometry measuring volume positioning in cylindrical pipe flow due to optical aberrations, caused by the pipe wall curvature. The hypothesis, that in the central part of the pipe (r/R < 0.6) exists a small, or negligible pipe wall influence on laser- -Doppler anemometry measuring position, is investigate. The required corrections, for measurements of axial, tangential, and radial velocity components such: shift of measuring volume and its orientation are analyzed and determined for used test rig and for some other pipe geometries. [Projekat Ministarstva nauke Republike Srbije, br. TR 35046

The comparison of air flow LDA measurement in simple cylindrical and cylindrical tube with flat external wall

Primena 2D laser Dopler anemometarskih sistema je razmatrana za slučaj zatvorenog toka fluida u običnoj cilindričnoj i u cilindričnoj cevi sa ravnim spoljašnjim zidom. Zakoni geometrijske optike su primenjeni na centralne linije laserskih snopova. Izvedeni su izrazi za dislokacije mernih zapremina, uglove kalibracije i rastojanja centra merne zapremine od centra vidnog polja foto-detektora. Izrazi izvedeni u ovom radu su preimenjeni na određeni vrtložni tok u cevi. To je pokazalo nekoliko prednosti korišćenja obične cilindrične cevi u odnosu na danas omiljenije korišćenje cilindrične cevi sa ravnim spoljašnjim zidom. Ovi rezultati ukazuju na to da bi se sadašnje izbegavanje LDA merenja kod obične cilindrične cevi trebalo preispitati.The application of 2D laser Doppler anemometry systems is considered, in the case of fluid flow confined in simple cylindrical and in cylindrical tube with flat external surface of the wall. Geometric optics laws are applied to the central lines of laser beams. Measurement volume dislocations, calibration angles and distances of measurement volume centre from the photo-detector field of view centre are expressed. The expressions derived in this paper were applied to specific turbulent swirl flow in pipe. That revealed several advantages of use of a simple cylindrical tube over nowadays favored use of cylindrical tube with flat external surface. Those results suggest that current avoiding of laser Doppler anemometry measurements with simple cylindrical tubes should be reconsidered

Savremene metode laserskog čišćenja predmeta kulturnog nasledja

The monograph presents the results of perennial research of laser application in the cleaning of undesirable layers on cultural heritage objects. Keeping in mind the priceless value of the items that have to be cleaned, research has been carried out with the aim of provide a scientifically based contribution to the safe and efficient application of lasers in conservation laboratories. Laser cleaning is a complex phenomenon that is followed by thermal, mechanical, optical, and chemical effects. Investigation of the laser light interaction with different materials is the first step in the process of successful laser application in the protection of cultural heritage objects. These processes depend on the characteristics of laser irradiation and materials characteristics. The results presented in this monograph included four types of lasers: Nd:YAG, CO2, Er:Glass and ruby laser. Laser irradiation parameters such as beam energy density (fluence), pulse length, number of pulses per second, wavelength and energy distribution within the laser beam are changed. Archaeological objects, samples from museums study collections and samples of contemporary materials (modern ceramics, metals, metal alloys, glass, textiles and a combination of these materials) have been cleaned. Each sample from the cultural heritage collection represents a unique conservation challenge because it has the inherent values of the reflection and absorption coefficients, the chemical and physical properties of the surface, the specific topology at the micro and nano levels, the homogeneity, the thermal expansion coefficient, the melting temperature, and the boiling temperature. Cleaning each of the items requires a proper selection of operating parameters and process control. Morphological and chemical changes in the cleaned zones were examined by optical and SEM microscopy, EDX, XRF, XRD and LIBS analysis. The analysis of cleansing effects includes colorimetric tests, roughness and micro-hardness testing. Other modern methods for monitoring the interaction process (thermography) were also used, and experimental results were processed and verified by numerical methods. Over the past decade, a number of European projects, related to the development and application of new scientific methods and new technologies in the protection of cultural heritage, have been implemented. Our country, rich in cultural heritage, should follow this trend of using modern technology and so in the best way preserve archaeological and cultural heritage for its descendants.U monografiji su prikazani rezultati višegodišnjih istraživanja u oblasti primene lasera u čišćenju nepoželjnih slojeva na predmetima kulturne baštine. Imajući u vidu da baštini pripadaju i predmeti neprocenjive vrednosti, istraživanja su sprovedena s ciljem da se pruži naučno zasnovani doprinos bezbednoj i efikasnoj primeni lasera u konzervatorskim ateljeima. Lasersko čišćenje je kompleksna pojava koju prate toplotni, mehanički, optički i hemijski efekti. Ispitivanje interakcije laserske svetlosti sa različitim materijalima je prvi korak u procesu uspešne primene lasera u zaštiti objekata kulturne baštine. Ovi procesi zavise od karakteristike laserskog zračenja i materijala. Istraživanja, čiji su rezultati prikazani u ovoj monografiji, uključila su četiri tipa lasera: Nd:YAG, CO2, ER:Glass i rubinski laser. Varirani su parametri laserskog zračenja, kao što su gustina energije snopa (fluenca), dužina impulsa, broj impulsa u sekundi, talasna dužina i raspodela energije unutar laserskog snopa. Čišćeni su arheološki predmeti, uzorci iz muzejskih studijskih zbirki i uzorci savremenih materijala (keramika, metali, metalne legure, staklo, tekstil i kombinaciju ovih materijala) kakvi se koriste u savremenoj umetnosti. Svaki uzorak iz zbirke kulturne baštine predstavlja jedinstven konzervacijski problem, jer ima svojstvene vrednosti koeficijenta refleksije i apsorpcije, hemijske i fizičke osobine površine, specifičnu topologiju na mikro i nano nivou, homogenost, koeficijent širenja toplote, temperaturu topljenja i temperaturu ključanja. Čišćenje svakog predmeta zahteva pravilan izbor radnih parametara i kontrolu procesa. Morfološke i hemijske promene u zonama čišćenja, ispitivane su optičkom i SEM mikroskopijom, EDX, XRF i XRD analizom. Dijagnostika efekata čišćenja uključila je i kolorimetrijska ispitivanja, ispitivanja hrapavosti i mikrotvrdoće. Korišćene su i druge savremene metode za praćenje procesa interakcije (termografija), a eksperimentalni rezultati su obrađivani i verifikovani numeričkim metodama. U proteklih desetak godina realizovan je veliki broj evropskih projekata, koji se odnose na razvoj i primenu novih naučnih metoda i novih tehnologija u zaštiti kulturne baštine. Naša zemlja, bogata kulturnim nasleđem, treba da prati ovaj trend korišćenja savremenih tehnologija i tako na najbolji način sačuva arheološko i kulturno nasleđe za budućnost

Savremene metode laserskog čišćenja predmeta kulturnog nasledja

The monograph presents the results of perennial research of laser application in the cleaning of undesirable layers on cultural heritage objects. Keeping in mind the priceless value of the items that have to be cleaned, research has been carried out with the aim of provide a scientifically based contribution to the safe and efficient application of lasers in conservation laboratories. Laser cleaning is a complex phenomenon that is followed by thermal, mechanical, optical, and chemical effects. Investigation of the laser light interaction with different materials is the first step in the process of successful laser application in the protection of cultural heritage objects. These processes depend on the characteristics of laser irradiation and materials characteristics. The results presented in this monograph included four types of lasers: Nd:YAG, CO2, Er:Glass and ruby laser. Laser irradiation parameters such as beam energy density (fluence), pulse length, number of pulses per second, wavelength and energy distribution within the laser beam are changed. Archaeological objects, samples from museums study collections and samples of contemporary materials (modern ceramics, metals, metal alloys, glass, textiles and a combination of these materials) have been cleaned. Each sample from the cultural heritage collection represents a unique conservation challenge because it has the inherent values of the reflection and absorption coefficients, the chemical and physical properties of the surface, the specific topology at the micro and nano levels, the homogeneity, the thermal expansion coefficient, the melting temperature, and the boiling temperature. Cleaning each of the items requires a proper selection of operating parameters and process control. Morphological and chemical changes in the cleaned zones were examined by optical and SEM microscopy, EDX, XRF, XRD and LIBS analysis. The analysis of cleansing effects includes colorimetric tests, roughness and micro-hardness testing. Other modern methods for monitoring the interaction process (thermography) were also used, and experimental results were processed and verified by numerical methods. Over the past decade, a number of European projects, related to the development and application of new scientific methods and new technologies in the protection of cultural heritage, have been implemented. Our country, rich in cultural heritage, should follow this trend of using modern technology and so in the best way preserve archaeological and cultural heritage for its descendants.U monografiji su prikazani rezultati višegodišnjih istraživanja u oblasti primene lasera u čišćenju nepoželjnih slojeva na predmetima kulturne baštine. Imajući u vidu da baštini pripadaju i predmeti neprocenjive vrednosti, istraživanja su sprovedena s ciljem da se pruži naučno zasnovani doprinos bezbednoj i efikasnoj primeni lasera u konzervatorskim ateljeima. Lasersko čišćenje je kompleksna pojava koju prate toplotni, mehanički, optički i hemijski efekti. Ispitivanje interakcije laserske svetlosti sa različitim materijalima je prvi korak u procesu uspešne primene lasera u zaštiti objekata kulturne baštine. Ovi procesi zavise od karakteristike laserskog zračenja i materijala. Istraživanja, čiji su rezultati prikazani u ovoj monografiji, uključila su četiri tipa lasera: Nd:YAG, CO2, ER:Glass i rubinski laser. Varirani su parametri laserskog zračenja, kao što su gustina energije snopa (fluenca), dužina impulsa, broj impulsa u sekundi, talasna dužina i raspodela energije unutar laserskog snopa. Čišćeni su arheološki predmeti, uzorci iz muzejskih studijskih zbirki i uzorci savremenih materijala (keramika, metali, metalne legure, staklo, tekstil i kombinaciju ovih materijala) kakvi se koriste u savremenoj umetnosti. Svaki uzorak iz zbirke kulturne baštine predstavlja jedinstven konzervacijski problem, jer ima svojstvene vrednosti koeficijenta refleksije i apsorpcije, hemijske i fizičke osobine površine, specifičnu topologiju na mikro i nano nivou, homogenost, koeficijent širenja toplote, temperaturu topljenja i temperaturu ključanja. Čišćenje svakog predmeta zahteva pravilan izbor radnih parametara i kontrolu procesa. Morfološke i hemijske promene u zonama čišćenja, ispitivane su optičkom i SEM mikroskopijom, EDX, XRF i XRD analizom. Dijagnostika efekata čišćenja uključila je i kolorimetrijska ispitivanja, ispitivanja hrapavosti i mikrotvrdoće. Korišćene su i druge savremene metode za praćenje procesa interakcije (termografija), a eksperimentalni rezultati su obrađivani i verifikovani numeričkim metodama. U proteklih desetak godina realizovan je veliki broj evropskih projekata, koji se odnose na razvoj i primenu novih naučnih metoda i novih tehnologija u zaštiti kulturne baštine. Naša zemlja, bogata kulturnim nasleđem, treba da prati ovaj trend korišćenja savremenih tehnologija i tako na najbolji način sačuva arheološko i kulturno nasleđe za budućnost

Turbulence recognition in free convective flow by thermal-video post-processing in the case of a thermal power plant mill

This paper presents a study of a free convection flow around the walls of a ventilation mill of the Thermal Power Plant "Kostolac B", Kostolac, Serbia. A combined method consists of thermography and software post-processing, PATS. The PATS is specially developed for recognition of turbulence zones by the custom processing of large input data sets from thermal videos. The calculations determine maximum temperature fluctuation i.e. peak-to-peak fluctuation at every spot during the recording time. Three thermal videos of the walls were analyzed. Maximum temperature fluctuation occurred in the zones close to the obstacles, which are thus recognized as one of the main sources of turbulence. Besides, PATS has recognized fine camera oscillations and mechanical movements of a flexible material near the dozer wall. The detected zones of turbulence correspond to the previous studies and to the theory. The method shows good potential in the field of free convective flow research through the improvement of testing efficiency and cost savings. State-of-the-art thermograph cameras and updated software are recommended

Determination of air and hydrofoil pressure coefficient by laser doppler anemometry

Some results of experiments performed in water cavitation tunnel are presented. Pressure coefficient (Cp) was experimentally determined by Laser Doppler Anemometry (LDA) measurements. Two models were tested: model of airplane G4 (Super Galeb) and hydrofoil of high speed axial pump. These models are not prepared for conventional pressure measurements, so that LDA is applied for Cp determination. Numerical results were obtained using a code for average Navier-Stokes equations solutions. Comparisons between computational and experimental results prove the effectiveness of the LDA. The advantages and disadvantages of LDA application are discussed. Flow visualization was made by air bubbles

Wear resistance improvement of thermal plant fan mill impact plates based on numerical flow simulation

Numerical simulation of 3D multiphase flow is performed to determine the velocity field in the fan mill. The mixture model of the Euler-Euler approach is used. Recirculating gas is a primary phase that carries granular phases including the coal powder and sand. The latter causes heavy wear of mill impact plates. The optimal form of hardfacing geometry and technology has an impact both on velocity magnitude and direction of flow in such a way as to reduce plate wear. This paper presents results of surface modification (based on numerical simulation), implemented on impact plates of the fan mill in the Kostolac B power plant in Serbia. Fishbone hardfacing is made in order to increase the lifetime of impact plates and extend the period between overhauls of fan mills. The experimental tests of fishbone surfacing plates, in exploitation conditions, show that the applied modification, hardfacing technologies and coating materials, give expected results. The application of this hardfacing in the form of a fishbone is simpler, faster and more economical compared to complete overlaying and honeycomb impact plate surfacing. The relative weight loss of base plate after an 1440-hour period of exploitation is 8%, while the weight losses for the hard-faced plate is below 7%

Termografsko ispitivanje energetske efikasnosti zgrade Vojnog muzeja

Infrared (IR) thermography, as a diagnostic technique, is used to find anomalies in the thermal signature of the Military museum building in Belgrade, to identify irregularities or deficiencies, such as wet materials, voids, or missing insulation and to inspect energy efficiency of the museum building and microclimatic indoor conditions. It is very important to perform preventative maintenance and stop undesirable environment influences that induce structural damage, modification of materials and agglomeration of pollutants and microorganisms on the cultural heritage artifacts, stored in the museum depot or exhibited in the galleries. The main causes for corrosion in historical buildings and museum artifacts are moisture and changeable temperature conditions. This paper deals with the results obtained in the application of IR thermography in determination of these conditions in the Military museum building, where very important metal artifacts are exhibited and deposed. The results show poor thermal insulation, wet walls and, generally, low energy efficiency.Infracrvena termografija, kao dijagnostička tehnika, služi za ispitivanje energetske efikasnosti zgrada i unutrašnjih mikroklimatskih uslova. Korišćena je za otkrivanje nepravilnosti toplotnih karakteristika zgrade Vojnog muzeja u Beogradu, s ciljem da se pronađu nepravilnosti ili nedostaci, kao što su vlažni materijali, šupljine, oštećenja ili nedostatak toplotne izolacije. Ova ispitivanja su veoma važna za preventivno održavanje zgrade, kao i za sprečavanje nepovoljnih uticaja iz okruženja na objekte istorijskog i kulturnog nasleđa, koji izazivaju oštećenja na strukturi i materijalu i dovode do nagomilavanja štetnih zagađivača na objektima koji su smešteni u muzejskim depoima ili izloženi u galerijama. Na primer, vlaga i promenljivi temperaturni uslovi glavni su uzroci pojave i razvoja korozije u zgradama od istorijskog značaja i muzejskim eksponatima. Ovaj rad prikazuje rezultate termografskih ispitivanja zgrade Vojnog muzeja, gde se nalaze veoma značajni metalni eksponati. Rezultati pokazuju da postoji veoma loša toplotna izolacija, vlaga u zidovima i slaba energetska efikasnost

Corrosion resistance of metalized layers on steel parts in ventilation mill

Corrosion behavior of metalized layers, obtained by Plasma Transferred Arc (PTA) process and by High-Velocity Oxygen Fuel (HVOF) process with the purpose to improve the wear resistance of vital parts of ventilation mill in a thermal power plant, has been tested. The test is performed using three electrochemical techniques, in a solution containing chloride and sulfate ions. It is shown that the steel surface (base metal) dissolves uniformly, without pitting or other forms of local dissolution. Morphology of metalized layers surface indicates that dissolution is non-uniform, but it still can be considered as general corrosion. The corrosion rate of base metal and metalized layer obtained by PTA process is rather low, while the corrosion rate of the metalized layer obtained by HVOF process is much higher. Also, the difference in corrosion potentials between the base metal and the HVOF layer is pretty high but slightly less than maximum allowed difference (prescribed by the standard), to avoid excessive galvanic corrosion. The values of corrosion rate obtained by different electrochemical techniques are in excellent agreement