Browsing by Author "Kracík Jan"

Now showing 1 - 8 of 8
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    CFD simulation of ejector: is it worth to use real gas models?
    (EDP Sciences, 2018-01-01) Nguyen Van Vu; Kracík Jan
    This paper presents progress of evaluation existing ejector of previous work with different gases, included real gas. This work was done by the Ansys simulation tool. The paper also discussed about the two solvers used for simulating real gas difluoromethane (R32). The results showed that entrainment ratios are almost not influenced by different gases but by the working conditions. Secondly, the solver pressure-based can obtain comparable results with the density-based one, while it is much more stable and solution converges faster than the density-based.
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    Contract research of steam ejectors
    (2017-01-01) Dvořák Václav; Kracík Jan
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    Contractual research of flow in the compressor
    (2017-01-01) Dvořák Václav; Kracík Jan
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    Experimental and numerical investigation of an air to air supersonic ejector for propulsion of a small supersonic wind tunnel
    (E D P SCIENCES, 17 AVE DU HOGGAR PARC D ACTIVITES COUTABOEUF BP 112, F-91944 CEDEX A, FRANCE, 2015-01-01) Kracík Jan; Dvořák Václav
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    Experimental and Numerical Study on Supersonic Ejectors Working with R-1234ze(E)
    (EDP Sciences, 2018-01-01) Kracík Jan; Dvořák Václav; Nguyen Van Vu; Smierciew Kamil
    These days, much effort is being put into lowering the consumption of electric energy and involving renewable energy sources. Many engineers and designers are trying to develop environment-friendly technologies worldwide. It is related to incorporating appropriate devices into such technologies. The object of this paper is to investigate these devices in connection with refrigeration systems. Ejectors can be considered such as these devices. The primary interest of this paper is to investigate the suitability of a numerical model for an ejector, which is incorporated into a refrigeration system. In the present paper, there have been investigated seven different test runs of working of the ejector with a working fluid R-1234ze(E). Some of the investigated cases seem to have a good agreement and there are no significant discrepancies between them, however, there are also cases that do not correspond to the experimental data at all. The ejector has been investigated in both on-design and off-design working modes. A comparison between the experimental and numerical data (CFD) performed by Ansys Fluent software is presented and discussed for both an ideal and a real gas model. In addition, an enhanced analytical model has been introduced for all runs of the ejector.
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    Introductory Numerical Study on Supersonic Ejector Working with R32
    (EDP Sciences, 2019-01-01) Vojta Lukáš; Kracík Jan; Dvořák Václav
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    Preliminary study of the primary nozzle position of a supersonic air ejector with a constant-area mixing chamber
    (2017-01-01) Kracík Jan; Dvořák Václav
    This work aims at investigating the primary nozzle position in a proposed supersonic air ejector device. The ejector is primarily made up of a supersonic primary nozzle, which is located in the axis of the ejector, a suction chamber or secondary stream inlet, a mixing chamber and a diffuser. The ejector design allows to translate the primary nozzle in the axis direction and fix it in a chosen distance from the beginning of the mixing chamber and hence influence the secondary mass flow rate. In a limit case, it is possible to set the nozzle to such a position where no secondary flow occurs. If we ignore the case where no secondary flow occurs, five different nozzle distances have been investigated in this paper. Some cases seem to be alike and there are no significant dissimilarities between them. Courses of relative back-pressure ratio are carried out against the entrainment ratio and transition between on-design and off-design regimes is determined. Measurements of the mixed flow based on the standard ISO 5167 are performed by means of orifice plate method. In addition, a comparison between experiments and simulations performed by Ansys Fluent software is presented in order to indicate further improvements to the numerical model.