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

CFD Analysis of the Influence of Centrifugal Separator Geometry Modification on the Pulverized Coal Distribution at the Burners

This paper presents the results of 3D numerical flow simulation in the ventilation mill (VM) and air mixture channel (AMC) of Kostolac B power plant, where a centrifugal separator with adjustable blade angle is used. Numerical simulations of multiphase flow were performed using the Euler-Euler and the Euler-Lagrange approach of the ANSYS FLUENT software package. The geometry of the numerical model was almost identical to the VM and AMC of Kostolac B, except for the smallest details. An unstructured tetrahedral grid, consisted of almost three million cells, was generated. The main contribution of this paper is the original analysis of the influence of centrifugal separator (CFS) geometry modification on the coal powder distribution at the horizontal burners. The modification of the blade angle, blade shape, and vertical position of the separator and its effect on the coal powder distribution at the burners were analyzed and are published for the first time. Results of the numerical simulations were compared with the measurements and can be used in modifying the separator geometry and position to obtain optimal distribution of the pulverized coal at the burners. Application of these results, obtained by numerical methods, ensures significant savings in time and money, in the process of finding the optimal geometry of CFS

CFD Analysis of the Influence of Centrifugal Separator Geometry Modification on the Pulverized Coal Distribution at the Burners

This paper presents the results of 3D numerical flow simulation in the ventilation mill (VM) and air mixture channel (AMC) of Kostolac B power plant, where a centrifugal separator with adjustable blade angle is used. Numerical simulations of multiphase flow were performed using the Euler-Euler and the Euler-Lagrange approach of the ANSYS FLUENT software package. The geometry of the numerical model was almost identical to the VM and AMC of Kostolac B, except for the smallest details. An unstructured tetrahedral grid, consisted of almost three million cells, was generated. The main contribution of this paper is the original analysis of the influence of centrifugal separator (CFS) geometry modification on the coal powder distribution at the horizontal burners. The modification of the blade angle, blade shape, and vertical position of the separator and its effect on the coal powder distribution at the burners were analyzed and are published for the first time. Results of the numerical simulations were compared with the measurements and can be used in modifying the separator geometry and position to obtain optimal distribution of the pulverized coal at the burners. Application of these results, obtained by numerical methods, ensures significant savings in time and money, in the process of finding the optimal geometry of CFS

Surface modification on iron induced by Nd:YAG pulsed laser treatment

The modern military industry demands the most innovative and high-quality metals and alloys, as well as processing technologies. Iron and its alloys are a common material used for different types of weapons and military equipment. Lasers have been widely used in the metal surface processing, but the changes that occur on laser treated metal surfaces have not yet been sufficiently investigated. A study of morphological and chemical changes on the metal surface induced by Nd:YAG laser treatment in ambient air is presented. A pulsed Nd:YAG laser (1064 nm, Gaussian spatial profile, FWHM 8 ns, energy up to 525 mJ, beam diameter of 1-10 mm and fluence up to 3.5 J/cm 2 ) was used. Micro-morphological analyses of sample surfaces before and after laser treatment process were performed by optical and SEM microscopies. EDX method was used for chemical analyses and Spectra colorimeter for investigation of induced color changes. The laser irradiation effects were studied as a function of two laser parameters, number of laser pulses and laser fluencies, around and over the damage threshold. The results show that there are significant differences depending on these laser parameters

Experimental and numerical study of super-critical flow around the rough sphere

Rad predstavlja eksperimentalno i numeričko istraživanje modela sfere sa ciljem predviđanja ponašanja strujanja u prisustvu hrapavosti površina. Rezultati ukazuju na probleme i predlažu rešenje za inžinjersku primenu. Sličnost između strujnih slika dobijenih numeričkim putem i u aerotunelu je postignuta kombinovanim uvođenjem turbulencije u numeričkoj slobodnoj struji hrapavosti površine, zbog ograničavajućih zahteva turbulentnih modela.This paper presents the experimental and numerical research on the sphere model with the goal of prediction of a flow behaviour in a presence of the surface roughness. Results indicate the problems and suggest the solution for engineering practice. The similarity of the numerical and wind tunnel flows was reached by an application of a combination of the intentionally introduced turbulence intensity in a numerical flow as well the artificial roughness of the model, for a reason of restricted requirements of the turbulence modelling

Determination of braking force on the aerodynamic brake by numerical simulations

Ovaj rad predstavlja rezultate istraživanja uticaja aerodinamičkih kočnica, postavljenih na krov brzog voza, na strujno polje i ukupnu silu kočenja. Voz se sastoji od dve lokomotive, na svakom kraju, i četiri putnička vagona., ukupne dužine 121m. Aerodinamičke kočnice stvaraju silu kočenja povećavanjem aerodinamičkog otpora pomoću izvučenih panela na krovu voza. Simulacije strujanja su urađene softverom Fluent 12.1, za voz bez, sa jednom, dve i tri aerodinamičke kočnice, pri brzinama od 30, 50 i 70m/s. Sila otpora po jedinici površine panela je određena kao funkcija brzine voza i položaja aerodinamičke kočnice. Doprinosi ukupnoj sili kočenja svake od kočnica, određeni simulacijama su: za prvu 24%, za drugu 15% i za treću 14.8% i pokazali su , zajedno sa raspodelama pritisaka po panelima, dobro slaganje sa proračunima aerodinamičkog otpora za ravnu ploču upravno postavljenu prema strujanju.This work presents the research results of the aerodynamic brake influence, mounted on the high-speed train's roof, on the flow field and overall braking force. The train consists of two locomotives at each end and four passenger cars between, with 121m of overall length. Aerodynamic brakes are designed to generate braking force by means of increasing the aerodynamic drag by opened panels over the train. Flow simulations were made by Fluent 12.1 software, for the train without and with one, two and three aerodynamic brakes, and velocities of 30, 50 and 70m/s. Drag force per unit panel area was determined as a function of train's velocity and the brake position. Contributions to train's gross braking force of each brake, obtained by simulations were: for first 24%, for second 15% and third 14.8%, and showed, also with panels' pressure distribution, good correlation with the aerodynamic drag calculations for flat plate orthogonally disposed to flow stream

Experimental and numerical study of super-critical flow around the rough sphere

Rad predstavlja eksperimentalno i numeričko istraživanje modela sfere sa ciljem predviđanja ponašanja strujanja u prisustvu hrapavosti površina. Rezultati ukazuju na probleme i predlažu rešenje za inžinjersku primenu. Sličnost između strujnih slika dobijenih numeričkim putem i u aerotunelu je postignuta kombinovanim uvođenjem turbulencije u numeričkoj slobodnoj struji hrapavosti površine, zbog ograničavajućih zahteva turbulentnih modela.This paper presents the experimental and numerical research on the sphere model with the goal of prediction of a flow behaviour in a presence of the surface roughness. Results indicate the problems and suggest the solution for engineering practice. The similarity of the numerical and wind tunnel flows was reached by an application of a combination of the intentionally introduced turbulence intensity in a numerical flow as well the artificial roughness of the model, for a reason of restricted requirements of the turbulence modelling

Determination of braking force on the aerodynamic brake by numerical simulations

Ovaj rad predstavlja rezultate istraživanja uticaja aerodinamičkih kočnica, postavljenih na krov brzog voza, na strujno polje i ukupnu silu kočenja. Voz se sastoji od dve lokomotive, na svakom kraju, i četiri putnička vagona., ukupne dužine 121m. Aerodinamičke kočnice stvaraju silu kočenja povećavanjem aerodinamičkog otpora pomoću izvučenih panela na krovu voza. Simulacije strujanja su urađene softverom Fluent 12.1, za voz bez, sa jednom, dve i tri aerodinamičke kočnice, pri brzinama od 30, 50 i 70m/s. Sila otpora po jedinici površine panela je određena kao funkcija brzine voza i položaja aerodinamičke kočnice. Doprinosi ukupnoj sili kočenja svake od kočnica, određeni simulacijama su: za prvu 24%, za drugu 15% i za treću 14.8% i pokazali su , zajedno sa raspodelama pritisaka po panelima, dobro slaganje sa proračunima aerodinamičkog otpora za ravnu ploču upravno postavljenu prema strujanju.This work presents the research results of the aerodynamic brake influence, mounted on the high-speed train's roof, on the flow field and overall braking force. The train consists of two locomotives at each end and four passenger cars between, with 121m of overall length. Aerodynamic brakes are designed to generate braking force by means of increasing the aerodynamic drag by opened panels over the train. Flow simulations were made by Fluent 12.1 software, for the train without and with one, two and three aerodynamic brakes, and velocities of 30, 50 and 70m/s. Drag force per unit panel area was determined as a function of train's velocity and the brake position. Contributions to train's gross braking force of each brake, obtained by simulations were: for first 24%, for second 15% and third 14.8%, and showed, also with panels' pressure distribution, good correlation with the aerodynamic drag calculations for flat plate orthogonally disposed to flow stream

Laser cleaning of varnish from bog oak surface

The removal of varnish is a very challenging task in the conservation of wooden artifacts. The results of experiments performed to investigate the suitability of lasers for cleaning aged varnish from bog oak wood (ebony) are presented in this paper. Optimal laser parameters for safe and efficient varnish ablation were determined in order to preserve the integrity of the original wooden substrate during the cleaning process. The ablation threshold for varnish and wood damage threshold was examined using Nd:YAG laser (1064, 532 and 355 nm) emitting pulses of nanosecond (8 ns) duration. Results of induced varnish removal and other morphological alterations to the wood surface were investigated by optical microscopy and colorimetry

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%