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Abstract

Complex rheological properties of yield-stress materials may lead to the generation of an intensive mixing zone near a rotating impeller. From the practical point of view, the zone should cover most of the stirred liquid. According to the literature review, several parameters may affect the size of the mixing zone, in particular forces exerted on the liquid. This paper presents both experimental and numerical investigation of axial and tangential forces generated during mechanical mixing of yield-stress fluids in a stirred tank. The tested fluids were aqueous solutions of Carbopol Ultrez 30 of concentration either 0.2 or 0.6 wt% and pH = 5:0. The study was performed for three types of impeller, pitched blade turbine, Prochem Maxflo T and Rushton turbine, in a broad range of their rotational speed, N = 60 - 900 rpm. The axial and tangential forces were calculated from the apparent mass of the stirred tank and torque, respectively. The experimental results were compared with CFD predictions, revealing their good agreement. Analysis of the generated forces showed that they are dependent on the rheological characteristic of liquid and the impeller type. It was also found that although axial force was smaller than tangential force, it significantly increased the resultant force.
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Authors and Affiliations

Anna Story
1
Grzegorz Story
1
Zdzisław Jaworski
1

  1. West Pomeranian University of Technology in Szczecin, Faculty of Chemical Technology and Engineering, Department of Chemical and Process Engineering, al. Piastów 42,71-065 Szczecin, Poland
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Abstract

The article presents an experimental investigation of the rheological properties of carbomer microgels. All of the tested fluids were made up from commercial polyacrylic acid, Carbopol Ultrez 30. In total, eighteen microgels were prepared, differing in concentration; 0.2, 0.4 and 0.6 wt%, with six levels of neutralisation for pH from 4.0 to 9.0. Based on the experimental flow curves it was found that all tested microgels are yield stress shear-thinning fluids. Therefore, the Herschel–Bulkley model was used and its rheological parameters were determined. It was found that both the concentration and the pH value significantly affected the yield stress. As the Carbopol concentration increased, the yield point also increased. With the increasing value of pH, the yield stress first increased until a certain maximum level and then decreased. The maximum values of yield stress were obtained for pH = 6 to 7, depending on polymer concentration. It was also found that flow curves of the tested microgels could be described using one universal master curve, thus they have common rheological behaviour.

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Authors and Affiliations

Anna Story
Grzegorz Story
Zdzisław Jaworski
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Abstract

In this study, the effects of grain refinement and production methods on the corrosion, corrosive wear and mechanical properties of the as-cast and as-rolled Mg-2 wt.% Zn (ZM20) and Mg-2 wt.% Zn-0,51 wt.% Mn (ZM21) alloys were examined by using OM, XRD, SEM, hardness and uniaxial tensile test. Additionally, the potentiodynamic polarization, immersion corrosion test and corrosive wear properties of the ZM20 and ZM21 alloys were compared. According to the XRD results, MgZn and MgZn2 phases were found in the alloys and also MnZn3 phase occurred in the ZM21 alloy with the addition of manganese. Both during solidification forming nucleation points with the added manganese and during rolling the broken secondary phase particles distributed into the matrix prevented grain growth and led to the formation of a more refined structure. The tensile test results showed that the strength of the as-cast ZM21 alloys were better than that of the as-cast ZM20 alloys and further improvement in mechanical properties occurred with the rolling of the both alloys. The most superior hardness was found in the as-rolled ZM21 alloy. In the total 400-m reciprocal corrosive wear test in the 3.5% NaCl solution, the lowest mass loss was in the as-rolled ZM21 alloys. In the potentiodynamic corrosion test, the highest corrosion resistance was occurred by the as-cast ZM20 alloy.
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Authors and Affiliations

Halil Ahmet Gören
1
ORCID: ORCID
Mehmet Ünal
2
ORCID: ORCID
Yunus Türen
3
ORCID: ORCID
Hayrettin Ahlatçı
3
ORCID: ORCID
Yavuz Sun
3
ORCID: ORCID

  1. Sinop University, The Vocational School, Mechatronic Department, Sinop, Turkey
  2. Karabuk University, Manufacturing Engineering, Turkey
  3. Karabuk University, Metallurgy and Materials Engineering, Turkey
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Abstract

The paper deals with the variability of mechanical properties of EPSTAL steel rods produced in Polish steelworks, i.e. yield stress Re, tensile strength Rm, and elongation Agt. Our study is based on fundamental engineering static room-temperature tensile tests for large series specimens which have been made by manufacturers as the part of a factory quality control. Statistical analysis of these results shows that the stressstrain relationship of steel tensile tests should be described by a one-dimensional stochastic process, and three the most important mechanical parameters, i.e. the yield stress, tensile strength, and elongation by random variables. Based on the statistical elaboration of experimental data, it was found that the yield stress and tensile strength of steel rods produced in the years 2016-2017 had the coefficients of variation of less than 3%, and there is a reasonable basis for the manufacturer to increase the characteristic value of EPSTAL steel rods yield stress by a few percentages.

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Authors and Affiliations

T. Chmielewski
M. Piotrowska

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