Scale Water Model Research Articles

Concentration Measurements in a Water Model Tundish using the Combined DPIV/PLIF Technique

The mixing process in a 1:3 scaled water model of a single‐strand tundish for the production of stainless steel is investigated using the combined DPIV/PLIF (Digital Particle Image Velocimetry/Planar Laser Induced Fluorescence) technique. The velocities in the water model are measured in different light sheet planes up to a size of 300 mm · 1100 mm by the conventional DPIV method. The variation of the time‐dependent concentration field is measured in the same plane by the PLIF method. The tracers are polyamide particles for DPIV and a rhodamine 6G solution as fluorescent dye for PLIF. Due to the special calibration procedure of the DPIV/PLIF system, the optical, geometrical and physical parameters do not have to be determined analytically, thus leading to reliable results. The experiments are carried out with a turbulent Reynolds number of Re = 5000 and show that the mixing process correlates with the quasi steady‐state flow pattern. The residence time of some water region in the tundish model is significantly longer than the mean residence time (θ < 5). Such information is important for the steel production because the number of mixed slabs produced during sequence casting with a grade change is closely related to the mixing of the tundish melt. The presented laser‐optical investigations have been used to establish the combination of DPIV and PLIF technique. The results of combined DPIV/PLIF measurements will be used to validate numerical simulations of the mixing processes in water models of metallurgical reactors.

An investigation into the interaction of closely-spaced starting jets

The transient, three-dimensional scavenging flow inside a novel two-stroke engine has been investigated both experimentally in a scaled water model as well as numerically using a commercial CFD code incorporating an unsteady Reynolds averaged Navier–Stokes (URANS) formulation. The scavenging flow consists of 16 round jets in close proximity of each other and the cylinder wall, developing from the top of the combustion chamber down towards the exhaust ports located along the wall at the bottom of the cylinder. Flow visualization of the scavenging flow was performed using a scaled fixed-piston water model and was used as a means of validating the URANS simulations themselves. The flow visualization experiments provided insight into the complex jet–jet and jet–wall interactions within the engine cylinder. These interactions were not as well predicted by the CFD simulations. In fact, the CFD simulations were found to significantly under-predict the turbulent mixing between the jets. This suggests that unsteady-RANS formulations are incapable of reproducing the large-scale and unsteady mixing structures associated with the vortex shedding between the closely-spaced jets.

Large-Eddy Simulations and Particle-Image Velocimetry Measurements of Tundish Flow

Large-eddy simulations (LES) and digital particle-image velocimetry (DPIV) of a tundish flow are performed to investigate the turbulent flow structures and vortex dynamics. The LES is carried out using an implicit approach. In implicitly filtered LES, the computational grid and the discretization operators are considered as the filtering tools of the governing equations. The numerical computations are performed by solving the viscous conservation equations for compressible fluids. An implicit dual-time stepping scheme combined with low Mach number pre-conditioning and a multigrid accelerating technique is implemented for LES computations. The impact of jet spreading, jet impingement on the wall, and wall jets on the flow field and steel quality is investigated. The characteristics of the flow field in a one-strand tundish such as the time-dependent turbulent flow structure and vortex dynamics are analysed and compared with experimental results. To validate the numerical results, DPIV measurements are performed in a reduced 1:1.7 scaled water model. The investigations focus on steady-state casting conditions for the flow in a tundish. The results evidence a good agreement between the LES and experimental data. The LES solutions provide an extremely detailed insight into the highly intricate turbulent flow structure. Even phenomena like funnel-shaped vortices downward the shroud jet are well captured.

Mathematical simulation of fluid dynamics during steel draining operations from a ladle

Fluid flow dynamics during ladle drainage operations of steel under isothermal and nonisothermal conditions has been studied using the turbulence shear stress transport k-e model (SST k-ω) and the multiphase volume of fluid (VOF) model. At high bath levels, the angular velocity of the melt, close to the ladle nozzle, is small rotating anticlockwise and intense vertical-recirculating flows are developed in most of the liquid volume due to descending steel streams along the ladle vertical wall. These streams ascend further downstream driven by buoyancy forces. At low bath levels, the melt, which is close to the nozzle, rotates clockwise with higher velocities whose magnitudes are higher for shorter ladle standstill times. These velocities are responsible for the formation and development of a vortex on the bath free surface, which entrains slag into the nozzle by shear-stress mechanisms at the metal-slag interface. The critical bath level or bath height for this phenomenon is 0.35 m (in this particular ladle design) for a ladle standstill time of 15 minutes and decreases with longer ladle standstill times. At these steps, the vertical-recirculating flows are substituted by complex horizontal-rotating flows in most of the liquid volume. Under isothermal conditions, the critical bath level for vortex formation on the melt free surface is 0.20 m, which agrees very well with that determined with a 1/3 scale water model of 0.073 m. It is concluded that buoyancy forces, originated by thermal gradients, as the ladle cools, are responsible for increasing the critical bath level for vortex formation. Understanding vortex mechanisms will be useful to design simple and efficient devices to break down the vortex flow during steel draining even at very low metal residues in the ladle.

Experimental validation of flow and tracer-dispersion models in a four-strand billet-casting tundish

An exhaustive literature search indicates that, despite a large number of physical and mathematical model studies, very little efforts have been made to assess predicted flow and turbulence parameters in the tundish directly against equivalent experimental measurements until recently. Consequently, experimental measurements on the instantaneous velocity and residence-time distribution (RTD) were carried out in a scaled water model of a four-strand billet-casting tundish. While particle-image velocimetry (PIV) was applied to measure instantaneous flow, the electrical-conductivity measurement technique was applied to determine the RTD. Through PIV, the mean and the fluctuating components were derived along the central vertical plane of the tundish at two different liquid inflow rates: 1.55×10−4 m3/s and 3.10×10−4 m3/s, respectively. Similarly, RTD curves were obtained for tundish operations without and with a dam+turbulence inhibitor device (TID). Parallel to these operations, the flow and tracer dispersion were numerically predicted by FLUENT®. It is shown that the predicted time-average velocity components within the bath bear excellent correspondence with PIV measurements. On the assumption of isotropic fluctuations, turbulent kinetic energy was derived from experimental measurements, which agreed moderately with predictions. Furthermore, the experimentally derived fluctuating velocity components were compared with those obtained from the Reynolds stress model. This indicated very reasonable agreement between measurement and predictions (within ±20 pct). Despite such a difference, however, the extent of agreement between the measured and computed C curves was found to be excellent.

Inertial and buoyancy driven water flows under gas bubbling and thermal stratification conditions in a tundish model

Steel flow dominated by inertial and buoyancy flows under gas bubbling and thermal stratification conditions, in a one-strand tundish, was studied using a 2/5 scale water model. The use of a turbulence inhibitor yields plug flow volume fractions well above 40 pct for a casting rate of 3.12 tons/min under isothermal conditions. Small flow rates of gas injection (246 cm3/min), through a gas curtain, improved the fluid flow by enhancing the plug flow volume fraction. Higher flow rates originated an increase of back-mixing flow, thus forming recirculating flows in both sides of this curtain. Step inputs of hot water drove streams of this fluid toward the bath surface due to buoyancy forces. A rise in gas flow rate led to a thermal homogenization in two separated cells of flow located at each side of the gas curtain. Step inputs of cold water drove streams of fluid along the tundish bottom. Use of the gas curtain homogenized the lower part of the tundish as well as the upper part of the bath at the left side of the curtain. However, temperature at the top corner of the tundish, in the outlet box, remained very different than the rest of the temperatures inside this tundish. High gas flow rates (912 cm3/min) were required to homogenize the bath after times as long as twice the mean residence time of the fluid. Particle image velocimetry (PIV) measurements corroborated the formation of recirculating flows at both sides of the gas curtain.

A DPIV Study of Liquid Steel Flow in a Wide Thin Slab Caster Using Four Ports Submerged Entry Nozzles

Influence of SEN design and its depth below the meniscus on liquid steel flow inside a large width thin slab mold was studied using a 1:1 scale water model. Fluid flow characterization was performed through Digital Particle Image Velocimetry techniques, measurements of bath oscillations and tracer dispersion experiments. Two designs of SEN with four ports (two lateral ports with two bottom ports) were investigated. SEN-1 has a wider bottom base and SEN-2 has a narrow one. Both SEN's provide fluid flows in the mold with upper and lower recirculating flows. Jets emerging from the lateral and bottom ports do not overlap although the surface area of the lateral jet of SEN-1 works inefficiently as compared with that of SEN-2. SEN-1 promotes higher bath oscillations than SEN-2 because the lateral jets travel almost horizontally toward the narrow face. This enhances fluid velocities along the narrow wall until the bath surface. A recirculating flow is formed close to the SEN-1 in the upper bath surface that provokes also high bath oscillations. Design of SEN-2 avoids these flow defects yielding more stable fluid flows. Rising the SEN depths alters negatively the flow characteristics, although SEN-2 is better than SEN-1. Generally speaking both designs yield complex turbulent and unsteady flows and a better SEN design is suggested.

Mixing and solid-liquid mass-transfer rates in a creusot-loire uddeholm vessel: A water model case study

The process of mixing and solid-liquid mass transfer in a one-fifth scale water model of a 100-ton Creusot-Loire Uddeholm (CLU) converter was investigated. The modified Froude number was used to relate gas flow rates between the model and its protoype. The influences of gas flow rate between 0.010 and 0.018 m3/s and bath height from 0.50 to 0.70 m on mixing time were examined. The results indicated that mixing time decreased with increasing gas flow rate and increased with increasing bath height. The mixing time results were evaluated in terms of specific energy input and the following correlation was proposed for estimating mixing times in the model CLU converter: Tmix=1.08Q−1.05W0.35, where Q (m3/s) is the gas flow rate and W (tons) is the model bath weight. Solid-liquid mass-transfer rates from benzoic acid specimens immersed in the gas-agitated liquid phase were assessed by a weight loss measurement technique. The calculated mass-transfer coefficients were highest at the bath surface reaching a value of 6.40 × 10−5 m/s in the sprout region. Mass-transfer coefficients and turbulence parameters decreased with depth, reaching minimum values at the bottom of the vessel.

An Experimental Study of the Velocity Field during Filling of an Ingot Mould

In the present study the velocity field in a 1:3 scale water model of a 4.2-tonne ingot mould was determined using Laser Doppler Anemometry (LDA). The velocity was measured in the horizontal and vertical directions at several different locations along the centre plane of the model. The effect of different volumetric flow rates and water temperatures was also investigated. The reproducibility of the measurements was found to be satisfactory, since the mean velocity at any measurement location had an average difference of around 10% between two fillings. The effect of different volumetric flow rates showed that while decreasing the flow rate, the mean velocity at the bottom turned from an upward direction to a downward direction. At the top of the model the difference between the mean velocities for the different flow rates was less pronounced. An influence of the temperature on the mean velocity could be observed. However, further studies are required to verify this result.

The Application of Two Phase Flow Simulation to the Development of Direct Iron Ore Smelting Reduction Process

The purpose of this research is to numerically simulate the fluid flow phenomena and the corresponding stirring efficiency in the iron bath induced by bottom blowing for the direct iron ore smelting reduction process. The processing conditions under consideration include gas flow rate, tuyere number, tuyere diameter. To verify the accuracy of the simulation model, the calculated results are also compared with the existing experimental observation from a water model.The numerical simulation tools employed in this study are a commercial package named PHOENICS and several generically developed modules to incorporate with PHOENICS for the specific needs of this study. For PHOENICS, the Scalar Equation Method (SEM) model is chosen to handle the two phase flow problems. For SEM model, it employs a function; h, to represent the extent of mixing between gas and liquid. A post-processing module to show the front-view of h distribution is developed to compare with the photograph taken from a 0.6 scale water model. Another post-processing module is also developed to calculate the mixing time, which is a direct index of stirring efficiency, based on the velocity profile simulated by PHOENICS. A shorter mixing time represents a better stirring efficiency. With the calculated mixing times under various processing conditions, the effects of individual processing condition on the stirring efficiency can be evaluated.

Study on flow and mixing characteristics of molten steel in RH and RH-KTB refining processes

The flow and mixing characteristics of molten steel during the vacuum circulation refining, including RH(Ruhrstahl-Heraeus) and RH-KTB(Ruhrstahl-Heraeus-Kawasaki top blowing) processes, were investigated on a 1/5 linear scale water model of a 90 t multifunction RH degasser. The circulation rate was directly and more accurately determined, using a new method by which the more reliable results can be obtained. The fluid flow pattern and flow field in the ladle were demonstrated, observed and analyzed. The mixing time of liquid in the ladle was measured using electrical conductivity method. The residence time distribution in the RH model was obtained by tracer response technique. The influence of the main technological and geometric factors, including the gas top blowing (KTB) operation, was examined. The results indicated that the circulation rate of molten steel in the RH degasser can be fairly precisely calculated by the formula: Q lp=0.0333Q g 0.26 D u 0.69 D d 0.80 (t/min), where Q g - the lifting gas flow rate (NL/min); D u and D d - the inner diameters of the up and down-snorkels (cm), respectively. The maximum value of circulation rate of molten steel in the case of the 30 cm diameters either of the up-and down-snorkels for the RH degasser (the “saturated” rate) is approximately 31 t/min. The corresponding gas flow rate is 900 NL/min. Blowing gas into the vacuum chamber through the top lance like KTB operation does not markedly influence the circulatory flow and mixing characteristics of the RH process under the conditions of the present work. There exist a major loop and a large number of small vortices and eddies in the ladle during the RH refining process. A liquid-liquid two-phase flow is formed between the descending stream from the down-snorkel and the liquid around the stream. All of these flow situation and pattern will strongly influence and determine the mixing and mass transfer in the ladle during the refining. The correlation between the mixing time and the stirring energy density is τ m∞e −0.50 for the RH degasser. The mixing time rapidly shortens with an increase in the lifting gas flowrate. At a same gas flow rate, the mixing times with the up-and down-snorkel diameters either of 6 and 7 cm are essentially same. The 30 cm diameters either of the up-and down-snorkels for the RH degasser would be reasonable. The concentration-time curve showed that three circulation cycles are at least needed for complete mixing of the liquid steel in the RH degasser.

Oscillatory Flow in a Physical Model of a Thin Slab Casting Mould With a Bifurcated Submerged Entry Nozzle

Laser Doppler anemometry (LDA) measurements are presented of the oscillatory flow in a 33% scale water model of thin slab casting mould when the flow enters as two lateral jets through a bifurcated nozzle. The submerged entry nozzle (SEN) and the mould were geometrically scaled to be representative of industrial thin slab casters. Mean and RMS LDA velocity measurements were taken at three selected points in the region surrounding the SEN, at 500 points in the central plane parallel to the broad face of the mould, and at points in selected transverse sections, for casting rates up to 1.53 m/min. Flow visualization was also taken at two selected planes in the mould. The LDA results showed each jet to form an upper and lower recirculation zone with the lower zones adjacent to one another bounded by the jets and the mould walls and the upper zones bounded by the jet, the SEN, the mould walls and the free surface. Both jets were found to have most oscillatory energy at frequencies below 5 Hz with high energy low frequency modes occurring at frequencies below 0.2 Hz. However, no single dominant frequency occurred in the spectrum and flow visualization revealed an apparently chaotic flow pattern in the oscillation. Midpoint jet deflection was restricted to 6–8 mm RMS, and no coherence was observed between jet (and free surface) movements on either side of the mould. The time averaged flow pattern was found to be almost symmetric across the wide face of the mould. It is concluded that both shear layer instability in the impinging jets, and deflection of the jets due to cross-flow at the SEN-mould wall, contribute to the flow oscillation.

Combined blowing with three ‐ hole lance in a sidewall blowing converter

Traditionally, in stainless steelmaking converters, oxygen has been blown by a one‐hole lance (1 HL) and sidewall tuyères. In order to reduce the tap‐to‐tap time, the multi‐hole lance has been used for oxygen blowing. The aim of this work was to develop blowing practise for a multi‐hole lance to reduce the tap‐to‐tap time and minimise metal splashing and spitting in the sidewall blowing converter (chromium converter). In the chromium converter the chemical energy of liquid ferrochrome (which contains 4 % silicon and 7 % carbon) is utilised for scrap melting by oxidising the silicon and the part of carbon.The research has been made by a dynamically scaled water model and full‐scale converter. Used parameters were the gas flowrate from sidewall tuyères and lance, lance height, charge weight and position of multi‐hole lance. Splashing has been measured during blowing from walls (splashing) and mouth of the converter model (spitting). The model tests indicated less splashing and spitting by the three‐hole lance (3 HL) than traditional 1 HL. The 1 HL caused strong skulling of the converter cone. By 3 HL blowing the position of the lance has a remarkable effect on the direction and the amount of splashing and lance life. Because of hot metal‐slag splashes, the life time of the 3 HL was halved by position 1 (compared to 1 HL). With the lance position 2 the splashing decreased by approx. 50% in model tests and lance life time increased by ~ 50% (compared to 1 HL) in the full‐scale converter. The model agreed well with the full‐scale converter. According to the process tests, the nominal productivity of the chromium converter has increased 15 % and depending on the refining practise and the silicon content of ferrochromium the lining life has increased 20 ‐ 30 %. In the future the multi‐hole lance will be tested in the AOD vessel.

Mass transfer characteristics between molten steel and particles in RH–PTB refining

The mass transfer characteristics between powder particles and liquid steel in RH–PTB (powder top blowing) refining have been investigated on a ⅕ scale water model of a 90 t RH degasser. Sodium chloride powder of analytical purity has been used as the flux for blowing, and the mass transfer coefficient of solute (NaCl) in the liquid has been determined under the conditions of the RH–PTB process. The influence of the main technological and structural parameters on the mass transfer rate has been examined. The results have shown that, under the conditions of the present work, the mass transfer coefficient in the liquid increases with increasing lifting gas flowrate, with increasing inner diameter of the upsnorkel, with increasing circulation rate of the liquid, and with increasing particle size of powdered flux. On the other hand, mass transfer in the liquid decreases with an increase in the inner diameter of the downsnorkel. Its value is in the range (1·36–7·30) × 10−4 m s−1. The following dimensionless relationships, correspondingly, have been obtained for the mass transfer coefficient in the range:Sh = 2 + 0·073Re0·777s Sc1/3Sh = 2 + 0·073(ϵ1sd4p/ν3l)0·259 Sc1/3When the mass transfer is treated as that between rigid bubbles and molten steel, it may be characterised bySh = 2 + 0·026[Re0·48s Sc0·339(g1/3dp/D2/3p)0·072]1·455

Mathematical Modeling of Iron and Steel Making Processes. Comparison of Four Methods to Evaluate Fluid Velocities in a Continuous Slab Casting Mold.

Four different methods are compared for evaluating fluid flow velocities in the liquid pool in the mold region of a continuous caster of steel slabs. First, the instantaneous and time-averaged flow pattern in a 0.4scale water model with single-phase flow is quantified using particle image velocimetry (PIV). Next, three-dimensional computations are performed to calculate the time-average flow pattern in the same system using a conventional finite-difference program, CFX, with the conventional K‐e model for handling turbulence. Transient computations are then performed using a 1.5-million node grid to resolve the turbulent eddies, both without a turbulence model (direct numerical simulation: DNS) and with a subgrid scale model (large eddy simulation: LES). Finally, measurements are obtained using electromagnetic sensors embedded in the mold walls of an operating steel slab casting machine. The comparisons reveal remarkable quantitative agreement between all four methods for the overall time-averaged flow pattern and surface velocities for these conditions. The time-averaged K‐e model is capable of accurate quantitative calculations of the steady flow field with the least effort, but has difficulty with transient behavior. The LES model predicts both steady and transient phenomena, but has severe computational cost. Water models with PIV are useful and practical tools, but are difficult to extend beyond the flow pattern to practical phenomena, such as heat transfer, solidification, surface slag entrainment, two-phase flow, and particle motion. The electromagnetic sensor has the advantage of measuring the real process, but is computed to be accurate only where the flow is roughly uniform and directly horizontally between the two probes, so is limited to measuring average speed at just a few points. Thus, each method has its own merits and disadvantages relative to the others, and can be a useful tool for investigating flow phenomena in processes with molten metal. Together, these methods reveal new insights into steady and transient flow in the continuous slab-casting mold, which are discussed in this work.

Numerical simulation of the flow and the solid transport when tilting a holding furnace

This study deals with the flows and the transport of solid inclusions in an aluminum holding furnace. A numerical model was developed that solved the governing equations for both the velocity and temperature fields and computed particle trajectories. This numerical model was used to simulate two flow situations: a holding flow and a pouring flow. In the first flow situation, the thermal conductivity was kept constant and special attention was paid to the thermal boundary conditions. The computed flow was strongly stratified and produced two contrarotating vortices. The second flow situation was a pouring flow in a 1/10 scaled water model of a real aluminum furnace. The calculation was done in a reference frame tilting with the vessel. Calculated velocities at the free surface of this pouring flow compared satisfactorily with experimental results. Finally, the trajectory of a solid particle in this transient pouring flow was calculated. This calculation was performed several times for various particle sizes and initial positions to determine the potential areas for inclusion settling or draining.

Velocity Field Measurements of Flow inside Snout of Continuous Hot-Dip Galvanizing Process Using a Single-frame PIV Technique.

In the continuous hot-dip galvanizing process of steel strips, the snout has been installed at the entering region of feeding strip into the molten zinc (Zn) pot. However, evaporated Zn particles in the snout cause ash imperfection on the galvanized steel strip surface. In order to resolve this problem, the flow field inside the snout, both on the deoxidization gas flow above the free surface and the molten Zn flow in the Zn pot. has been investigated experientially. For a 1/10 scale water model, flow visualization and PIV (Particle Image Velocimetry) velocity field measurements were carried out at the strip speed V s =1.5 m/s Aluminum flakes (1 μm) and atomized olive oil (3 μm) were used as seeding particles to simulate the molten Zn flow and the deoxidization gas flow, respectively. As a result, the liquid flow in the Zn pot is dominantly influenced by the up-rising flow in diagonal direction caused by the rotating sink roll. For gas flow in front of the strip inside the snout, the large-scale vortex formed by the downward moving strip is dominant. In the rear side of the strip, a counter-clockwise vortex is formed and some of the flow following by the moving strip impinges on the free surface of molten Zn. The liquid flow in front of the strip is governed by the up-rising flow entering the snout, caused by the rotating sink roll. The moving strip affects dominantly the liquid flow behind the strip inside the snout and large amounts of liquid are entrained and followed the moving strip toward the sink roll. A thin boundary layer is formed on the front side due to the up-rising flow, however, a relatively thick boundary layer is formed in the rear side of the strip. Inside the snout, the deoxidization gas flow above the free surface is much faster than the liquid flow in the Zn pot. More ash imperfections are anticipated on the rear surface of the strip where larger influx flow moves toward the strip in the region near the free surface.

Numerical Calculation of Circulation Flow Rate in the Degassing Rheinstahl-Heraeus Process.

The circulation flow rate of a steel melt, which is one of the important factors which determine decarburization rate of RH system, was calculated by using a 3-dimensional numerical simulation technique. A new model for evaluating the shape and volume of the plume zone, formed by Ar gas blown through multiple nozzles on the wall of the snorkel, was proposed to determine the driving force of melt circulation. Circulation flow rates were measured in the 1/10 scale water model and in a real RH system to verify the calculation results with good agreement with the calculated circulation flow rates. Because the computer program can calculate the circulation flow rates at various operating conditions and dimensions of the RH system, it may be useful in determining the optimum operating conditions and designing new RH systems.

Crossflow Characteristics of an Oscillating Jet in a Thin Slab Casting Mould

The application of LDA to a transient 1/3 scale (500 mm wide) water model of a mould, typical of steel thin slab casting, is presented. The characteristics of a crossflow, associated with the oscillating jet emerging from a submerged nozzle (internal diameter 33 mm), were analyzed for a range of casting rates (0–2 m/min), nozzle submergences (20–120 mm) and nozzle-mould wall gap widths (0–21 mm). The frequency of oscillation was found to be primarily dependent on the casting rate of the system, independent of nozzle submergence or gap width, whereas the RMS crossflow velocity depended on all three parameters. Additional crossflow was also observed past the jet below the nozzle exit and this allowed the jet to oscillate even with zero gap width.

Modelling gas injection of a Peirce–Smith-converter

A commercial CFD-code PHOENICS was used to solve isothermal flow field of gas and liquid in a Peirce–Smith-converter. An Euler–Euler based algorithm was chosen for modelling fluid dynamics and evaluating controlling forces of a submerged gas injection. Predictions were made with a k– ε turbulence model in the body fitted coordinate system. The model has been verified with a 1/4 scale water model, and a parametric study with the mathematical model of submerged gas injection was made for the PS-process and the ladle injection processes. Limits of the modelling technique used were recognised, but calculated results indicate that the present model predicts the general flow field with reasonable accuracy. Predicted bubble distribution, pattern of the flow field and magnitude of flow velocities were used to evaluate scaling factors of physical models and general flow conditions of an industrial PS-converter.