The article presents the infrared (IR) thermovision diagnostic method as one of the tools for mon... more The article presents the infrared (IR) thermovision diagnostic method as one of the tools for monitoring changes in an athletes' loading conditions during their training. The advantage of the method lies in its quantitative approach, fast analysis and the comparative studies involving the application of this method. All of the basic mechanisms of heat transfer to the skin's surface are presented, enabling a comprehension of the experimental results. In this article the results are presented as a temperature field distribution on a selected segment of skin and they change with time, depending on the integral parameters of an athlete's loading. Also examined were the characteristic changes in the temperature field which depend on an athlete's physical loading. In addition to a quality evaluation of the topological structures of the temperature field, time-related changes in locally averaged temperatures in a selected window were evaluated, as well as the pertinent time-dependent local temperature variations in individual training loading regimes. The results of the study indicate the rationality of applying the IR method for monitoring various types of loading on an athlete's muscle segments. This method may also be used as a comparative tool for establishing the efficiency of different means and methods in the training process.
The performance of secondary clarifiers is strongly related to density effects in the sedimentati... more The performance of secondary clarifiers is strongly related to density effects in the sedimentation vessel. The upper level of the clarifier's chamber-once considered to be inactive at the sedimentation processnow appears to play an important role in solids removal. A fully developed three-layer flow phenomenon that develops in some cases is proved to promote settling. Therefore, investigation of flow patterns at different operative conditions was carried out. Experiments were conducted in a model of a circular, centre-feed settling tank with continuous operation. Ground hazelnut shells served as the settling matter; in one set of experiments only dye was used. All laboratory runs were filmed and analysed, qualitatively and quantitatively, by means of computer-aided visualisation. The results of the study showed that a determining factor of the conditions favourable for formation of a fully developed three-layer flow is the theoretical densimetric Froude number. If the hydraulic and solid loadings are soundly chosen in accordance with these findings, the clarifier performance can be evidently improved.
A new, relatively simple method for determining the kinematic properties of jellyfish is presente... more A new, relatively simple method for determining the kinematic properties of jellyfish is presented. The bell movement of the scyphomedusa (Aurelia sp.) during its pulsation cycle was analysed using computer-aided visualization. Sequences of video images of individual Aurelia in a large aquarium were taken using a standard video camera. The images were then processed to obtain time series of the relative positions of selected points on the surface of the medusa's bell. The duration of the bell relaxation was longer than that of the bell contraction, thereby confirming published results. In addition, the area of the exumbrellar surface of Aurelia increased during bell relaxation by more than 1.3-times that of the exumbrellar surface area during the maximum contraction of the bell. The volume change during the bell pulsation cycle was also measured using the same visualization method. Significant changes, of up to 50%, in the subumbrellar cavity volume were revealed while, in contrast, the volume between the exumbrellar and subumbrellar surfaces generally remained unchanged during the entire pulsation cycle of the bell. Comparison of the time series of the exumbrellar surface area and of the subumbrellar cavity volume indicated that the change of volume takes place before the change of the surface area of the bell.
Journal of Fluids Engineering-transactions of The Asme, Apr 2, 2007
The goal of the study was to explain the relationship between different acoustic signals and visu... more The goal of the study was to explain the relationship between different acoustic signals and visual appearance of cavitation. Measurements of acoustic emission, vibration, and noise were performed on a Kaplan turbine model, with only two blades, in a cavitating condition. Since a model with only two blades was used, most of the side effects were eliminated, and it was concluded that the cavitation itself is the source of the recorded signal. Results showed an interesting relationship between the extent of the cavitation and the recorded data from sensors. At a decreasing cavitation number, the recorded amplitudes from all measurements first rose, experienced a local maximum, then fell to a local minimum, and finally rose again. The cavitation was also visually observed. It was concluded from the measurements that there are distinct correlations between acoustic emission, vibration, and noise on one side and the topology, extent, and type of cavitation structures on the other side. A physical explanation for the phenomenon was introduced and included in a semi-empirical model that links the visual appearance of cavitation on the blade of the turbine to the generated noise and vibration.
Cytostatic drug residues in the aqueous environment are of concern due to their possible adverse ... more Cytostatic drug residues in the aqueous environment are of concern due to their possible adverse effects on non-target organisms. Here we report the occurrence and removal efficiency of cyclophosphamide (CP) and ifosfamide (IF) by biological and abiotic treatments including advanced oxidation processes (AOPs). Cyclophosphamide was detected in hospital wastewaters (14-22,000ngL(-1)), wastewater treatment plant influents (19-27ngL(-1)) and effluent (17ngL(-1)), whereas IF was detected only in hospital wastewaters (48-6800ngL(-1)). The highest removal efficiency during biological treatment (attached growth biomass in a flow through bioreactor) was 59±15% and 35±9.3% for CP and IF, respectively. Also reported are the removal efficiencies of both compounds from wastewater using hydrodynamic cavitation (HC), ozonation (O3) and/or UV, either individually or in combination with hydrogen peroxide (H2O2). Hydrodynamic cavitation did not remove CP and IF to any significant degree. The highest removal efficiencies: 99±0.71% for CP and 94±2.4% for IF, were achieved using UV/O3/H2O2 at 5gL(-1) for 120min. When combined with biological treatment, removal efficiencies were >99% for both compounds. This is the first report of combined biological and AOP treatment of CP and IF from wastewater with a removal efficiency >99%.
To augment the removal of pharmaceuticals different conventional and alternative wastewater treat... more To augment the removal of pharmaceuticals different conventional and alternative wastewater treatment processes and their combinations were investigated. We tested the efficiency of (1) two distinct laboratory scale biological processes: suspended activated sludge and attached-growth biomass, (2) a combined hydrodynamic cavitation-hydrogen peroxide process and (3) UV treatment. Five pharmaceuticals were chosen including ibuprofen, naproxen, ketoprofen, carbamazepine and diclofenac, and an active metabolite of the lipid regulating agent clofibric acid. Biological treatment efficiency was evaluated using lab-scale suspended activated sludge and moving bed biofilm flow-through reactors, which were operated under identical conditions in respect to hydraulic retention time, working volume, concentration of added pharmaceuticals and synthetic wastewater composition. The suspended activated sludge process showed poor and inconsistent removal of clofibric acid, carbamazepine and diclofenac, while ibuprofen, naproxen and ketoprofen yielded over 74 % removal. Moving bed biofilm reactors were filled with two different types of carriers i.e. Kaldnes K1 and Mutag BioChip TM and resulted in higher removal efficiencies for ibuprofen and diclofenac. Augmentation and consistency in the removal of diclofenac were observed in reactors using Mutag BioChip TM carriers (85 % ± 10 %) compared to reactors using Kaldnes carriers and suspended activated sludge (74 % ± 22 % and 48 % ± 19 %, respectively). To enhance the removal of pharmaceuticals hydrodynamic cavitation with hydrogen peroxide, process was evaluated and optimal conditions for removal were established regarding the duration of cavitation, amount of added hydrogen peroxide and initial pressure, all of which influence the efficiency of the process. Optimal parameters resulted in removal efficiencies between 3-70 %. Coupling the attached-growth biomass biological treatment, hydrodynamic cavitation/hydrogen peroxide process and UV treatment resulted in removal efficiencies of > 90 % for clofibric acid and > 98 % for carbamazepine and diclofenac, while the remaining compounds were reduced to levels below the LOD. For ibuprofen, naproxen, ketoprofen and diclofenac the highest contribution to overall removal was attributed to biological treatment, for clofibric acid UV treatment was the most efficient, while for carbamazepine hydrodynamic cavitation/hydrogen peroxide process and UV treatment were equally efficient. Highlights Higher removal of ibuprofen and diclofenac in attached-growth biomass vs. suspended activated sludge process First study on removal of clofibric acid, ibuprofen, ketoprofen, naproxen, diclofenac using a hydrodynamic cavitation/H 2 O 2 Recalcitrant carbamazepine susceptible to hydrodynamic cavitation/hydrogen peroxide process 98 % removal for most pharmaceuticals by sequentially coupling biological, hydrodynamic cavitation and UV treatment
... of great importance. Present methods for cavitation detection in water turbines are based on ... more ... of great importance. Present methods for cavitation detection in water turbines are based on observation of pressure pulsations, acoustic emission and mechanical vibrations on the turbine casing. Changes of dynamic properties ...
The paper presents an experimental study of suspension flow patterns and velocity field inside a ... more The paper presents an experimental study of suspension flow patterns and velocity field inside a circular settling tank with continuous operation. Research was focused on the impact of a specific flow pattern on the sedimentation efficiency of the prototype settling tank. The latter ...
This study presents a newly developed approach to velocity measurements of moist air in a natural... more This study presents a newly developed approach to velocity measurements of moist air in a natural-draught cooling tower (CT). It is based on the cross-correlation of two signals acquired from infrared (IR) light-to-voltage optical sensors. The air flowing through the CT becomes supersaturated in CT packings and thus consists of small water droplets of size 4-12 µm. The same air
The paper presents an experimental study of suspension flow patterns and velocity field inside tw... more The paper presents an experimental study of suspension flow patterns and velocity field inside two types of circular settling tanks with continuous operation. The two tanks differ in inlet-and outlet configurations. Research was focused on the influence of flow field on the sedimentation efficiency of both settling tanks. Experiment was carried out on a settling tank sections made of plexi-glass that represented radial slices of prototype circular settling tanks. Kinematic flow properties inside settling tank sections were determined by computer-aided visualization in order to analyse the whole instantaneous flow field at once. Sedimentation efficiency was assessed by measurements of inlet-and effluent suspension concentrations. Pronounced density current evolved in both tanks, which under certain conditions enhanced sedimentation. Flow field showed qualitative changes during operation and proved to be significantly dependent on average suspension density in the inner chamber of the settling tank. Some important properties of the flow field could also be reconstructed from the spatial distribution of the remaining sludge. Centrally fed settling tank with peripheral effluent generally performed better in terms of sedimentation efficiency mainly due to insufficient height of the effluent baffle in the peripherally fed settling tank.
This paper presents a novel non-contact method for simultaneous analysis of pressure and velocity... more This paper presents a novel non-contact method for simultaneous analysis of pressure and velocity conditions in cavitating flows. The method (implemented in our software ADMflow) is based on high-speed camera flow visualization and was evaluated in an experiment with ultrasonically induced acoustic cavitation of different intensities. Attached cavitation with clearly visible cavitation structures occurred on the tip of an ultrasonic probe immersed in distilled water. Using the high-speed imaging data, pressure fluctuations were calculated by a computer-aided algorithm based on the Brennen's theory of cavitation cloud kinematics and a modified version of the Rayleigh-Plesset equation. Reference measurements of pressure pulsations were conducted by a hydrophone installed at the bottom of the liquid container. The analysis of cavitation structure dynamics was complemented by calculation of velocity fields from the imaging data, the algorithm for which is based on the advectiondiffusion equation. Calculated pressure fluctuations were analyzed in the spatial, temporal and spectral domain. Presented results indicate a strong correlation between the fields of velocity and pressure fluctuations during the growth and collapse of cavitation structures. A comparison of time series and power spectra demonstrates that our cavitation analysis method is in a reasonably good agreement with results of the reference measurement methods and can therefore be used for non-contact analysis of pressure and velocity conditions in cavitating flows.
Strojniski Vestnik-journal of Mechanical Engineering, 2010
This article describes a bladeless turbo machine impeller that transfers energy from rotor to flu... more This article describes a bladeless turbo machine impeller that transfers energy from rotor to fluid over a structure of porous material. Impeller construction is described and theoretical description of fluid flow through rotating porous material is given. Pressure drops for impellers made of different materials and with different design parameters in dependence on air volume flow rate were measured. Measurements of local air flow velocity field close to impeller circumference were performed on a stationary impeller with one component hot-wire anemometer. Air flow velocity dependence on local material structure and volume flow rate was analysed. Integral characteristics measurements for different impellers made of different materials and with different design parameters are presented. Local measurements of local radial and tangential velocities close to rotating impeller circumference are shown.
Prispevek obravnava numerièno in preizkusno tudijo kavitirajoèega toka okrog razliènih osamljeni... more Prispevek obravnava numerièno in preizkusno tudijo kavitirajoèega toka okrog razliènih osamljenih profilov. Za simulacijo neustaljenega toka je bil uporabljen programski paket Fluent. Dvofazni tok smo opisali z vpeljavo homogenega toka meanice. Za popis nastanka in kolapsa kavitacijskega oblaka je bil uporabljen kavitacijski model, utemeljen na poenostavljeni Rayleigh-Plessetovi enaèbi dinamike mehurèka. Narejene so bile trirazsene simulacije kavitirajoèega toka v razliènih razmerah za dva osamljena profila. Za dva profila smo posneli slike kavitacijskih struktur v razliènih razmerah. Za doloèitev hitrostnega polja zunaj in znotraj kavitacijskega oblaka smo uporabili metodo PIV-LIF. Izmerili smo frekvence trganja kavitacijskega oblaka. Numerièno napovedane porazdelitve delea pare in hitrostnega polja smo primerjali s preizkusnimi rezultati. Narejena je bila primerjava s preizkusi doloèenih in numerièno napovedanih povpreènih dolin kavitacijske strukture vzdol profila. Primerja...
The object of this work was to evaluate the capability of numerical simulation to predict differe... more The object of this work was to evaluate the capability of numerical simulation to predict different features of non-Newtonian fluid mixing process. A relatively simple impeller (six bladed vane rotor) was used for the mixing of carboxymethyl cellulose. A LDA method was used to measure the tangential velocity at two points inside the mixing vessel. Using visualization, a significant vortex above the impeller was observed. The shape of the free surface was determined by a geometrical reconstruction of the images of the illuminated section. Torque on the impeller shaft was measured to determine the characteristics of the fluid. Fluent program package was used for the simulation. The problem is challenging since the effects of nonNewtonian fluid, mixing process and free surface have to be included in the simulation. The comparison between the experimental and numerical results confirms the accuracy of the simulations.
The contribution deals with numerical simulation of conjugate heat transfer in air heater of the ... more The contribution deals with numerical simulation of conjugate heat transfer in air heater of the laundry dryer. The heat transfer consists of internal heat generation in the electrical heating coils, forced convection from the coils to the air and heat conduction through the metal walls of the heater. In order to simplify the computational mesh the porous media concept was used for discretization of electrical coils. A special attention was given to the selection of a turbulence model, capable of accurate solution of conjugate heat transfer. After extensive testings the SST model, used in the numerical code CFX5, was selected. The computational results were compared with results of velocity and temperature measurements on the device in the laundry dryer, and good agreement was observed.
Orchards and grapevines are currently sprayed overall. Most bush and tree crop sprayers use airfl... more Orchards and grapevines are currently sprayed overall. Most bush and tree crop sprayers use airflow assistance which generates movements in canopy exposing both sides of the leaves to the spray. Also, large coherent vortices are formed further contributing to improved spray coverage. A new close-range air-assisted spot-spraying method for the selective treatments of disease foci is evaluated here which is promising for reduction of pesticides. Targets structures are expected to have typical diameters around 150 mm and the size of the unit matches this. In contrast to conventional methods, this size of unit prevents the generation of large scale coherent turbulent structures in the airflow that could provide spray coverage of both sides of the target leaves. Therefore, to enhance the beneficial effects of local turbulence, and to induce leaf movement whilst retaining the small size of the spray unit, a rotating screen to generate airflow pulses with discrete peaks in velocity was added and tested. Experiments on the close-range spraying of young grapevine plants using the rotating airflow screen were performed. A high-speed camera, image analysis system and water sensitive papers were used for analysis of the spraying. Natural frequencies of individual leaves showed sharp fluctuations at discrete frequencies and single leaf fluctuations of root mean square velocity corresponded well to the pulsating airflow. Spraying was evaluated as percentage spray coverage and number of droplet impacts. Spray coverage of front side of leaves (facing the sprayer) was good, but coverage on the back of the leaves was limited.
The article presents the infrared (IR) thermovision diagnostic method as one of the tools for mon... more The article presents the infrared (IR) thermovision diagnostic method as one of the tools for monitoring changes in an athletes' loading conditions during their training. The advantage of the method lies in its quantitative approach, fast analysis and the comparative studies involving the application of this method. All of the basic mechanisms of heat transfer to the skin's surface are presented, enabling a comprehension of the experimental results. In this article the results are presented as a temperature field distribution on a selected segment of skin and they change with time, depending on the integral parameters of an athlete's loading. Also examined were the characteristic changes in the temperature field which depend on an athlete's physical loading. In addition to a quality evaluation of the topological structures of the temperature field, time-related changes in locally averaged temperatures in a selected window were evaluated, as well as the pertinent time-dependent local temperature variations in individual training loading regimes. The results of the study indicate the rationality of applying the IR method for monitoring various types of loading on an athlete's muscle segments. This method may also be used as a comparative tool for establishing the efficiency of different means and methods in the training process.
The performance of secondary clarifiers is strongly related to density effects in the sedimentati... more The performance of secondary clarifiers is strongly related to density effects in the sedimentation vessel. The upper level of the clarifier's chamber-once considered to be inactive at the sedimentation processnow appears to play an important role in solids removal. A fully developed three-layer flow phenomenon that develops in some cases is proved to promote settling. Therefore, investigation of flow patterns at different operative conditions was carried out. Experiments were conducted in a model of a circular, centre-feed settling tank with continuous operation. Ground hazelnut shells served as the settling matter; in one set of experiments only dye was used. All laboratory runs were filmed and analysed, qualitatively and quantitatively, by means of computer-aided visualisation. The results of the study showed that a determining factor of the conditions favourable for formation of a fully developed three-layer flow is the theoretical densimetric Froude number. If the hydraulic and solid loadings are soundly chosen in accordance with these findings, the clarifier performance can be evidently improved.
A new, relatively simple method for determining the kinematic properties of jellyfish is presente... more A new, relatively simple method for determining the kinematic properties of jellyfish is presented. The bell movement of the scyphomedusa (Aurelia sp.) during its pulsation cycle was analysed using computer-aided visualization. Sequences of video images of individual Aurelia in a large aquarium were taken using a standard video camera. The images were then processed to obtain time series of the relative positions of selected points on the surface of the medusa's bell. The duration of the bell relaxation was longer than that of the bell contraction, thereby confirming published results. In addition, the area of the exumbrellar surface of Aurelia increased during bell relaxation by more than 1.3-times that of the exumbrellar surface area during the maximum contraction of the bell. The volume change during the bell pulsation cycle was also measured using the same visualization method. Significant changes, of up to 50%, in the subumbrellar cavity volume were revealed while, in contrast, the volume between the exumbrellar and subumbrellar surfaces generally remained unchanged during the entire pulsation cycle of the bell. Comparison of the time series of the exumbrellar surface area and of the subumbrellar cavity volume indicated that the change of volume takes place before the change of the surface area of the bell.
Journal of Fluids Engineering-transactions of The Asme, Apr 2, 2007
The goal of the study was to explain the relationship between different acoustic signals and visu... more The goal of the study was to explain the relationship between different acoustic signals and visual appearance of cavitation. Measurements of acoustic emission, vibration, and noise were performed on a Kaplan turbine model, with only two blades, in a cavitating condition. Since a model with only two blades was used, most of the side effects were eliminated, and it was concluded that the cavitation itself is the source of the recorded signal. Results showed an interesting relationship between the extent of the cavitation and the recorded data from sensors. At a decreasing cavitation number, the recorded amplitudes from all measurements first rose, experienced a local maximum, then fell to a local minimum, and finally rose again. The cavitation was also visually observed. It was concluded from the measurements that there are distinct correlations between acoustic emission, vibration, and noise on one side and the topology, extent, and type of cavitation structures on the other side. A physical explanation for the phenomenon was introduced and included in a semi-empirical model that links the visual appearance of cavitation on the blade of the turbine to the generated noise and vibration.
Cytostatic drug residues in the aqueous environment are of concern due to their possible adverse ... more Cytostatic drug residues in the aqueous environment are of concern due to their possible adverse effects on non-target organisms. Here we report the occurrence and removal efficiency of cyclophosphamide (CP) and ifosfamide (IF) by biological and abiotic treatments including advanced oxidation processes (AOPs). Cyclophosphamide was detected in hospital wastewaters (14-22,000ngL(-1)), wastewater treatment plant influents (19-27ngL(-1)) and effluent (17ngL(-1)), whereas IF was detected only in hospital wastewaters (48-6800ngL(-1)). The highest removal efficiency during biological treatment (attached growth biomass in a flow through bioreactor) was 59±15% and 35±9.3% for CP and IF, respectively. Also reported are the removal efficiencies of both compounds from wastewater using hydrodynamic cavitation (HC), ozonation (O3) and/or UV, either individually or in combination with hydrogen peroxide (H2O2). Hydrodynamic cavitation did not remove CP and IF to any significant degree. The highest removal efficiencies: 99±0.71% for CP and 94±2.4% for IF, were achieved using UV/O3/H2O2 at 5gL(-1) for 120min. When combined with biological treatment, removal efficiencies were >99% for both compounds. This is the first report of combined biological and AOP treatment of CP and IF from wastewater with a removal efficiency >99%.
To augment the removal of pharmaceuticals different conventional and alternative wastewater treat... more To augment the removal of pharmaceuticals different conventional and alternative wastewater treatment processes and their combinations were investigated. We tested the efficiency of (1) two distinct laboratory scale biological processes: suspended activated sludge and attached-growth biomass, (2) a combined hydrodynamic cavitation-hydrogen peroxide process and (3) UV treatment. Five pharmaceuticals were chosen including ibuprofen, naproxen, ketoprofen, carbamazepine and diclofenac, and an active metabolite of the lipid regulating agent clofibric acid. Biological treatment efficiency was evaluated using lab-scale suspended activated sludge and moving bed biofilm flow-through reactors, which were operated under identical conditions in respect to hydraulic retention time, working volume, concentration of added pharmaceuticals and synthetic wastewater composition. The suspended activated sludge process showed poor and inconsistent removal of clofibric acid, carbamazepine and diclofenac, while ibuprofen, naproxen and ketoprofen yielded over 74 % removal. Moving bed biofilm reactors were filled with two different types of carriers i.e. Kaldnes K1 and Mutag BioChip TM and resulted in higher removal efficiencies for ibuprofen and diclofenac. Augmentation and consistency in the removal of diclofenac were observed in reactors using Mutag BioChip TM carriers (85 % ± 10 %) compared to reactors using Kaldnes carriers and suspended activated sludge (74 % ± 22 % and 48 % ± 19 %, respectively). To enhance the removal of pharmaceuticals hydrodynamic cavitation with hydrogen peroxide, process was evaluated and optimal conditions for removal were established regarding the duration of cavitation, amount of added hydrogen peroxide and initial pressure, all of which influence the efficiency of the process. Optimal parameters resulted in removal efficiencies between 3-70 %. Coupling the attached-growth biomass biological treatment, hydrodynamic cavitation/hydrogen peroxide process and UV treatment resulted in removal efficiencies of > 90 % for clofibric acid and > 98 % for carbamazepine and diclofenac, while the remaining compounds were reduced to levels below the LOD. For ibuprofen, naproxen, ketoprofen and diclofenac the highest contribution to overall removal was attributed to biological treatment, for clofibric acid UV treatment was the most efficient, while for carbamazepine hydrodynamic cavitation/hydrogen peroxide process and UV treatment were equally efficient. Highlights Higher removal of ibuprofen and diclofenac in attached-growth biomass vs. suspended activated sludge process First study on removal of clofibric acid, ibuprofen, ketoprofen, naproxen, diclofenac using a hydrodynamic cavitation/H 2 O 2 Recalcitrant carbamazepine susceptible to hydrodynamic cavitation/hydrogen peroxide process 98 % removal for most pharmaceuticals by sequentially coupling biological, hydrodynamic cavitation and UV treatment
... of great importance. Present methods for cavitation detection in water turbines are based on ... more ... of great importance. Present methods for cavitation detection in water turbines are based on observation of pressure pulsations, acoustic emission and mechanical vibrations on the turbine casing. Changes of dynamic properties ...
The paper presents an experimental study of suspension flow patterns and velocity field inside a ... more The paper presents an experimental study of suspension flow patterns and velocity field inside a circular settling tank with continuous operation. Research was focused on the impact of a specific flow pattern on the sedimentation efficiency of the prototype settling tank. The latter ...
This study presents a newly developed approach to velocity measurements of moist air in a natural... more This study presents a newly developed approach to velocity measurements of moist air in a natural-draught cooling tower (CT). It is based on the cross-correlation of two signals acquired from infrared (IR) light-to-voltage optical sensors. The air flowing through the CT becomes supersaturated in CT packings and thus consists of small water droplets of size 4-12 µm. The same air
The paper presents an experimental study of suspension flow patterns and velocity field inside tw... more The paper presents an experimental study of suspension flow patterns and velocity field inside two types of circular settling tanks with continuous operation. The two tanks differ in inlet-and outlet configurations. Research was focused on the influence of flow field on the sedimentation efficiency of both settling tanks. Experiment was carried out on a settling tank sections made of plexi-glass that represented radial slices of prototype circular settling tanks. Kinematic flow properties inside settling tank sections were determined by computer-aided visualization in order to analyse the whole instantaneous flow field at once. Sedimentation efficiency was assessed by measurements of inlet-and effluent suspension concentrations. Pronounced density current evolved in both tanks, which under certain conditions enhanced sedimentation. Flow field showed qualitative changes during operation and proved to be significantly dependent on average suspension density in the inner chamber of the settling tank. Some important properties of the flow field could also be reconstructed from the spatial distribution of the remaining sludge. Centrally fed settling tank with peripheral effluent generally performed better in terms of sedimentation efficiency mainly due to insufficient height of the effluent baffle in the peripherally fed settling tank.
This paper presents a novel non-contact method for simultaneous analysis of pressure and velocity... more This paper presents a novel non-contact method for simultaneous analysis of pressure and velocity conditions in cavitating flows. The method (implemented in our software ADMflow) is based on high-speed camera flow visualization and was evaluated in an experiment with ultrasonically induced acoustic cavitation of different intensities. Attached cavitation with clearly visible cavitation structures occurred on the tip of an ultrasonic probe immersed in distilled water. Using the high-speed imaging data, pressure fluctuations were calculated by a computer-aided algorithm based on the Brennen's theory of cavitation cloud kinematics and a modified version of the Rayleigh-Plesset equation. Reference measurements of pressure pulsations were conducted by a hydrophone installed at the bottom of the liquid container. The analysis of cavitation structure dynamics was complemented by calculation of velocity fields from the imaging data, the algorithm for which is based on the advectiondiffusion equation. Calculated pressure fluctuations were analyzed in the spatial, temporal and spectral domain. Presented results indicate a strong correlation between the fields of velocity and pressure fluctuations during the growth and collapse of cavitation structures. A comparison of time series and power spectra demonstrates that our cavitation analysis method is in a reasonably good agreement with results of the reference measurement methods and can therefore be used for non-contact analysis of pressure and velocity conditions in cavitating flows.
Strojniski Vestnik-journal of Mechanical Engineering, 2010
This article describes a bladeless turbo machine impeller that transfers energy from rotor to flu... more This article describes a bladeless turbo machine impeller that transfers energy from rotor to fluid over a structure of porous material. Impeller construction is described and theoretical description of fluid flow through rotating porous material is given. Pressure drops for impellers made of different materials and with different design parameters in dependence on air volume flow rate were measured. Measurements of local air flow velocity field close to impeller circumference were performed on a stationary impeller with one component hot-wire anemometer. Air flow velocity dependence on local material structure and volume flow rate was analysed. Integral characteristics measurements for different impellers made of different materials and with different design parameters are presented. Local measurements of local radial and tangential velocities close to rotating impeller circumference are shown.
Prispevek obravnava numerièno in preizkusno tudijo kavitirajoèega toka okrog razliènih osamljeni... more Prispevek obravnava numerièno in preizkusno tudijo kavitirajoèega toka okrog razliènih osamljenih profilov. Za simulacijo neustaljenega toka je bil uporabljen programski paket Fluent. Dvofazni tok smo opisali z vpeljavo homogenega toka meanice. Za popis nastanka in kolapsa kavitacijskega oblaka je bil uporabljen kavitacijski model, utemeljen na poenostavljeni Rayleigh-Plessetovi enaèbi dinamike mehurèka. Narejene so bile trirazsene simulacije kavitirajoèega toka v razliènih razmerah za dva osamljena profila. Za dva profila smo posneli slike kavitacijskih struktur v razliènih razmerah. Za doloèitev hitrostnega polja zunaj in znotraj kavitacijskega oblaka smo uporabili metodo PIV-LIF. Izmerili smo frekvence trganja kavitacijskega oblaka. Numerièno napovedane porazdelitve delea pare in hitrostnega polja smo primerjali s preizkusnimi rezultati. Narejena je bila primerjava s preizkusi doloèenih in numerièno napovedanih povpreènih dolin kavitacijske strukture vzdol profila. Primerja...
The object of this work was to evaluate the capability of numerical simulation to predict differe... more The object of this work was to evaluate the capability of numerical simulation to predict different features of non-Newtonian fluid mixing process. A relatively simple impeller (six bladed vane rotor) was used for the mixing of carboxymethyl cellulose. A LDA method was used to measure the tangential velocity at two points inside the mixing vessel. Using visualization, a significant vortex above the impeller was observed. The shape of the free surface was determined by a geometrical reconstruction of the images of the illuminated section. Torque on the impeller shaft was measured to determine the characteristics of the fluid. Fluent program package was used for the simulation. The problem is challenging since the effects of nonNewtonian fluid, mixing process and free surface have to be included in the simulation. The comparison between the experimental and numerical results confirms the accuracy of the simulations.
The contribution deals with numerical simulation of conjugate heat transfer in air heater of the ... more The contribution deals with numerical simulation of conjugate heat transfer in air heater of the laundry dryer. The heat transfer consists of internal heat generation in the electrical heating coils, forced convection from the coils to the air and heat conduction through the metal walls of the heater. In order to simplify the computational mesh the porous media concept was used for discretization of electrical coils. A special attention was given to the selection of a turbulence model, capable of accurate solution of conjugate heat transfer. After extensive testings the SST model, used in the numerical code CFX5, was selected. The computational results were compared with results of velocity and temperature measurements on the device in the laundry dryer, and good agreement was observed.
Orchards and grapevines are currently sprayed overall. Most bush and tree crop sprayers use airfl... more Orchards and grapevines are currently sprayed overall. Most bush and tree crop sprayers use airflow assistance which generates movements in canopy exposing both sides of the leaves to the spray. Also, large coherent vortices are formed further contributing to improved spray coverage. A new close-range air-assisted spot-spraying method for the selective treatments of disease foci is evaluated here which is promising for reduction of pesticides. Targets structures are expected to have typical diameters around 150 mm and the size of the unit matches this. In contrast to conventional methods, this size of unit prevents the generation of large scale coherent turbulent structures in the airflow that could provide spray coverage of both sides of the target leaves. Therefore, to enhance the beneficial effects of local turbulence, and to induce leaf movement whilst retaining the small size of the spray unit, a rotating screen to generate airflow pulses with discrete peaks in velocity was added and tested. Experiments on the close-range spraying of young grapevine plants using the rotating airflow screen were performed. A high-speed camera, image analysis system and water sensitive papers were used for analysis of the spraying. Natural frequencies of individual leaves showed sharp fluctuations at discrete frequencies and single leaf fluctuations of root mean square velocity corresponded well to the pulsating airflow. Spraying was evaluated as percentage spray coverage and number of droplet impacts. Spray coverage of front side of leaves (facing the sprayer) was good, but coverage on the back of the leaves was limited.
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Papers by Brane Širok