Darina Jasikova

Thermodynamics of aerogel-treated nonwoven fabrics at subzero temperatures

Nonwoven fabrics and aerogel have complementary properties required for good thermal insulation. In this work, the polyester/polyethylene nonwoven thermal wraps treated with amorphous silica aerogel are studied and characterized with regard to thermodynamical properties at subzero temperatures. The characterization of physical structure was done by scanning electron microscope. C-Therm TCi thermal conductivity analyzer was used to measure thermal properties like conductivity, resistance, and effusivity at subzero temperatures. Heat transfer caused by convection through the thermal wraps was measured by particle image velocimetry technique, which allows obtaining information about the current distribution of velocities in two-dimensional array in a flowing fluid. Vector and scalar maps of the fluid flow were caused by thermal convection. The samples were studied for different temperature gradients. On scientific evaluation of results, thermal conductivity and thermal effusivity were found to be differing with respect to different temperatures and fabric density. Thermal resistance showed an increase as the fabric thickness increases. It was observed that fabric density and the aerogel present in the structures have a significant effect on thermal properties of aerogel-treated nonwoven fabrics. The findings in this study are significant and can be used for further research in aerogel-treated nonwoven fabrics.

The methodic for study of smart surfaces using PIV technique

This article introduces the methodic for the study of smart surfaces using PIV method. The problem of investigation of super- and ultrahydrophobic- surfaces deals with the quantifying description of the fluid flow behavior in the near-wall region. The objective is to realize comparative study of commercial smart surfaces and their interaction of fluid flow according to the assessment of contact angle. The article interprets the results of measurement of fluid behavior over the whole testing chamber and the synchronized near-wall measurement with optimized dynamic range. The results are shown in the correlation of measured contact angle before and after testing and there are explained changes in the flow behavior.

Experimental setup for laser-induced breakdown in aqueous media

This article presents the visualization of the cavitation bubble generated with laser-induced breakdown. The cavitation bubble is generated with 532nm Nd: YAG laser beam, 10ns short with two different optical setups. Here, we use direct optical way focusing the laser beam, and reverse way base on the focusing mirror. We are using different laser light power and visualize the laser probe in correlation of bubble characteristics. The visualization is set on long-distance microscopy and shadowgraph lightening method. The main goal of the research is to set the optical setup for the laserinduced breakdown and to create the calibration relation curve for the bubble size dependence on the input energy of the laser beam. This calibration curve is related to the lifespan of each bubble, or the group of bubbles.

Time resolved PIV measurement of fluid dynamics in agitated vessels

Here we present the results obtained by TR PIV measurements focused on detailed flow analysis in the selected region. The investigated area was placed 3mm above the blades axis and 5mm far from the blade edge. The captured images were firstly analysed on the mean velocity distribution and the intensity of turbulence {UV} statistics. Here we used the time resolved technique for the experimental study of the flow field in the agitated vessel. The results of the application POD and ODP algorithm on the captured datasets uncovered the existence of unsteady structures in the area that was assumed to be stable. The existence of these structures is bringing a novel view on the mixing process.

Local Turbulent Energy Dissipation Rate in an Agitated Vessel: Experimental and Turbulence Scaling

The hydrodynamics and the flow field in an agitated vessel were measured using 2-D time resolved particle image velocimetry (2-D TR PIV). The experiments were carried out in fully baffled cylindrical flat bottom vessels 300 and 400 mm in inner diameter. The 300 mm inner diameter tank was agitated by a Rushton turbine 100 mm in diameter, and the 400 mm inner diameter tank was agitated by a Rushton turbine 133 mm in diameter. Three liquids of different viscosities were used as the agitated liquid: (i) distilled water (ν = 9.35 × 10–7 m2/s), (ii) a 28 vol % aqueous solution of glycol (ν = 2 × 10–6 m2/s), and (iii) a 43 vol % aqueous solution of glycol (ν = 3 × 10–6 m2/s). The velocity fields were measured at an impeller rotation speed in the range from 300 to 850 rpm, which covers the Reynolds number range from 50000 to 189000. This means that fullydeveloped turbulent flow was reached. The experiments were performed to investigate the applicability of the following relations: ε* = ε/(u4/ν) = const, vK/u = const, Λ/ηK = const, τΛ/τK = const, ε* = ε/((Nd)4/ν) = const, Λ/d ∝ Re–1, ηK/d ∝ Re–1, vK/(Nd) = const, NτΛ ∝ R–1, NτK ∝ Re–1, and ε/(Nq) ∝ Re. These formulas were theoretically derived in our previous work, using turbulence theory, in particular, using turbulence spectrum analysis. The correctness of the proposed relations is investigated by statistical hypothesis testing.

Flow of Newtonian and non-Newtonian fluid through pipe with flexible wall

This paper solves fluid-structure interaction between flexible wall and two types of fluid. Wall was considered as aorta and was described as hyperelastic material by 5-parameters Mooney-Rivlin model. Fluids and structure were set as incompressible. First fluid was Newtonian and has dynamic viscosity of the blood. Second was non-Newtonian and its viscosity was defined with Carreau rheology model. The aim of this paper is to show a comparison between Newtonian and non-Newtonian fluid flow in pliable vessel.This paper solves fluid-structure interaction between flexible wall and two types of fluid. Wall was considered as aorta and was described as hyperelastic material by 5-parameters Mooney-Rivlin model. Fluids and structure were set as incompressible. First fluid was Newtonian and has dynamic viscosity of the blood. Second was non-Newtonian and its viscosity was defined with Carreau rheology model. The aim of this paper is to show a comparison between Newtonian and non-Newtonian fluid flow in pliable vessel.

Local velocity scaling in an impeller discharge flow in T400 vessel agitated by tooth impeller in a fully turbulent region

Hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter. The velocity fields were measured in the impeller discharge flow for impeller rotation speeds from 300 rpm to 700 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 68 000 < Re < 221 000. This Re range secures the fully-developed turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The radial turbulence intensity was found to be in the majority in the range from 0.3 to 0.9, which corresponds to the high level of this quantity.

The interaction between fluid flow and ultra-hydrophobic surface in mini channel

Interaction of liquid with ultra-hydrophobic surface is accompanied by creation of layer of air. The effect of the air film has a potential of use in industry in many applications. The quality of the surface is influenced by matrix roughness, the character of physical or chemical cover. There was developed a method for analysis of the liquid flow and the air film using the lighting in volume, visualization with CCD camera and long distance microscope, and optical filters. There were prepared four stainless steel samples of inner channel of dimensions (80 × 8 × 8) mm and initial surface roughness Ra 0.33, Ra 1.0, Ra 2.0, and Ra 2.2. The inner channel was treated with plasma and commercial hydrophobic coating Greblon (WEILBURGER Coatings GmbH). There was realized study focused on the liquid flow velocity profile close to the air film. There are present results for laminar, transient and turbulent flows. The study also estimated the air film thickness depending on the Re number. The knowledge of the air film behaviour helps applied suitable degree of processing and cover for the target application.

An effect of entrance length on development of velocity profile in channel of millimeter dimensions

Here we used modified PIV technique completed with long distance microscope probe for experimental investigation of the flow velocity profile in a rectangular duct. We came from the analytical and numerical prediction of the entrance length for fully developed velocity profile. The results of measurement completed knowledge about the flow stability and velocity profile shape in the channel of 0.00375 hydraulic diameters. There was marked a range of entrance length constant for the transient flow area. The presents of the fluctuating velocities in the transition flow is explained with POD snapshot and modes projection. The minimal entrance length for the laminar, transition, and turbulent flow is set.

Visualization and measurement of the air film close ultra-hydrophobic surfaces

The ultra-hydrophobic surfaces have the prospect of great importance in industry, both in applications demanding easy cleaning, and they are presumed to reduce loss when the active parts of hydraulic machines are treated. Interaction of fluids with ultra-hydrophobic surface is accompanied by creation of layer of air, so called air film, which depends on the quality of the surface. The quality of the surface is influenced by the matrix roughness, the character of physical or chemical cover. This properties lead to monolithic air layer presented as air film, or lead to plurality of bubbles of various sizes seated upon the surface. The air film can be observed visually at sufficient magnification and the dynamic interaction between fluid flow and air film can be studied with Global Imaging methods, particularly Particle Image Velocimetry (PIV). There is the velocity profile in the vicinity of the air film in the main interest of the research. Here we present the visualization of air film depending on Reynolds number of flowing liquid.