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Number of results: 7
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Abstract

Besides centrifugal pumps, centrifugal fans are the most common turbomachines used in technical applications. They are commonly used in power engineering systems, such as heat engines and chillers, heating, ventilation, and air conditioning systems, supply and exhaust air systems. They are also used as machines consuming final energy (electricity). Therefore, any improvement in their efficiency affects the efficiency of energy generation and the level of electricity consumption. Many efforts have been made so far to find the most efficient numerical method of modelling flows in fans. However, only a few publications focus on the unsteadiness that may have an impact on device efficiency and noise generation. This paper presents an attempt to identify unsteadiness in the flow through a centrifugal fan by means of computational fluid dynamics and computational aeroacoustics methods. The works were performed using the Ansys CFX commercial software and the results of numerical studies are compared with experimental data.
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Bibliography

[1] Dykas S., Wróblewski W., Rulik S., Chmielniak T.: Numerical method for modelling of acoustic waves propagation. Arch. Acoust. 35(2010), 1, 35–48.
[2] Fortuna S., Sobczak K.: Numerical and experimental investigations of the flow in radial fan. Mechanics 27(2008), 4, 138–143
[3] Moon Y.J., Cho Y., Nam H.S.: Computation of unsteady viscous flow and aeroacoustic noise of the cross flow fan. Comput. Fluids 32(2003), 7, 995–1015.
[4] Rulik S., Dykas S., Wroblewski W.: Modelling of aerodynamic noise using hybrid SAS and DES methods. In: Proc. ASME Turbo Expo 2010: Power for Land, Sea and Air, Glasgow, June 14–18, 2010, 7(2010), 2835–2844., GT2010-2269.
[5] Stasko T., Dykas S., Majkut M., Smolka K.: An attempt to evaluate the cycloidal rotor fan performance. Open J. Fluid Dynam. 9(2019), 4.
[6] Benedek T., Vad J.: Beamforming based extension of semi-empirical noise modelling for low-speed axial flow fans. Appl. Acoust. 178(2021), 108018.
[7] Jiang H., Wang Q., Zheng T.F., Tu C.X., Zhang K.: PIV measurement of internal flow field in a range hood. In: Energy and Mechanical Engineering (S.Y. Liang, Ed.), 2015 Int. Conf. on Energy and Mechanical Engineering, Wuhan, 17-18 Oct. 2015, World Scientific, 2016, 570–575.
[8] Probst M., Pritz B.: Quantitative validation of CFD-simulation against PIV data for a centrifugal fan. In: Proc. 14th Int. Symp. on Experimental Computational Aerothermodynamics of Internal Flows, Gdansk 8-11 July 2019.
[9] Neise W., Michel U.: Aerodynamic Noise of Turbomachines. DLR-Interner Bericht, Berlin 1994.
[10] Jeon W.H., Lee D.J., Rhee H.: An application of the acoustic similarity law to the numerical analysis of centrifugal fan noise. JSME Int. J. C-mech Sy. 47(2004), 3, 845–851.
[11] Kissner C., Guerin S.: Comparison of predicted fan broadband noise using a twoversus a three-dimensional synthetic turbulence method. J. Sound Vib. 508(2021), 116221.
[12] Jaron R., Herthum H., Franke M., Moreau A., Guerin S.: Impact of turbulence models on RANS-informed prediction of fan broadband interaction noise. In: Proc. 12th Eur. Turbomachinery Conference (ETC), Stockholm, 3-7 April, 2017.
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[14] Blazquez-Navarro R., Corral R.: Prediction of fan acoustic blockage on fan/outlet guide vane broadband interaction noise using frequency domain linearized Navier–Stokes solvers. J. Sound Vib. 508(2021), 116033.
[15] Ffowcs-Williams J.E., Hawkings D.L.: Sound generation by turbulence and surfaces in arbitrary motion. Philos. T.R. Soc. Lond. S-A, 264(1969), 1151, 321–342.
[16] Lighthill M.J.: On sound generated aerodynamically. I. General theory. Proc. R. Soc. Lon. Ser.-A 211(1952) 1107, 564–587
[17] Menter F.R., Egorov Y.: A scale-adaptive simulation model using two-equation models. In: Proc. 43th AIAA Aerospace Sciences Meeting and Exhibit, Reno, 10-13 Jan. 2005, AIAA 2005-1095.
[18] Ansys Fluent Theory Guide, 2021R1. https://www.ansys.com (acessed 1 July 12021).
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Authors and Affiliations

Balazs Pritz
1
Matthias Probst
1
Piotr Wiśniewski
2
Sławomir Dykas
2
Mirosław Majkut
2
Krystian Smołka
2

  1. Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology, Kaiserstraße 12 D-76131 Karlsruhe, Germany
  2. Department of Power Engineering and Turbomachinery, Silesian University of Technology, Poland
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Abstract

Pathways of PCDTs and PCTAs in the environment are discussed. Data on levels of these compounds in various pan of the environment and their possible sources are presented. Finally, the data on biological effects of PCDTs and PCT As based on some preliminary toxicological investigations are given.
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Authors and Affiliations

Jacek Czerwiński
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Abstract

A contactless laser hygrometer based on light absorption by H2O molecules at 1392.5 nm is described. However, measurement results can be affected by optical noise when applied to an atmospheric tunnel or glass cuvette. The noises (occurring in the form of periodic fringes in the recorded spectrum) come from unexpected interference of the light beams reflected from surfaces of the windows or other optical elements. The method of their suppression is described in this article. It is based on wavelength modulation and signal averaging over the fringes period. Also, an experiment confirming the usefulness of this method is described here.
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Authors and Affiliations

Tadeusz Stacewicz
1
Mateusz Winkowski
1
Natalia Kuk
1

  1. Institute of Experimental Physics, Faculty of Physics, University of Warsaw, 02-093 Warsaw, Pasteura 5, Poland
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Abstract

This article presents test results of cement paste and binders with admixture of hydrophilic or hydrophobic nanosilica. The aim of the study was to determine the influence of nanosilica type and mixing method on compressive strength, porosity, and bulk density of cement paste, also on hydration heat of cement binders. The binder compounds were mixed in high speed mixer in order to provide the highest possible dispersion of nanoparticles in the binder before adding it to mixing water. Two mixing methods were studied. The admixtures increased the reactivity of cement binders. Both nanosilica types increased early compressive strength by 25% in comparison with control series. The increase in 28-day compressive strength was observed with the admixture of hydrophilic nanosilica. The differences in dynamics of binders rate of hydration and development of cement pastes compressive strength denote different reaction mechanisms of both types of nanosilica. Application of higher rotation speeds does not guarantee satisfactory mixing of the binder components. For compressive strength enhancement of cement paste prolonged mixing time occurred to be more important.

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Authors and Affiliations

J. Popławski
M. Lelusz
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Abstract

The main aim of this paper is to examine the variability of some dynamic properties of concrete composite panels to in-plane eccentric compression loads via static and dynamic impact testing. First, experimental tests were performed in order to obtain the dynamic and static properties of concrete composite panels. In-plane eccentric loads were statically applied to a couple of panels in ten uniform steps. For each step, dynamic impact testing was performed and the modal damping, peak amplitude and natural frequencies obtained. Second, a ‘hybrid’ model, based on the concepts of modal analysis and the Finite Element Method, was developed in order to obtain the natural frequencies and corresponding normal modes of the composite panels within the frequency range 0–200 Hz. For this model, an initial warp of the panel middle surface was incorporated into the formulation in order to represent the applied flexural moment provoked by the eccentric in-plane loads. The accuracy of the ‘hybrid’ model was verified by comparison with the experimental results. Third, comparison is made between predictions (using on the ‘hybrid’ model) and experimental results.
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Authors and Affiliations

Max de Castro Magalhaes
Roberto M. da Silva
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Abstract

The Author presents philosophical commentaries to the Polish translation of Wilhelm Dilthey's Formation ofthe Historical World in the Humanities.
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Authors and Affiliations

Izabela Szyroka

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