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Efekt odparowania fazy ciekłej na fali uderzeniowej w przepływach okołodźwiękowych powietrza wilgotnego z kondensacją pary wodnej

Szymański A., Dykas S., Majkut M.

Modelowanie Inżynierskie

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2015

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T. 26, nr 57

54--62

PL

W pracy przeprowadzono analizę numeryczną przepływu transonicznego powietrza atmosferycznego, które ze swojej natury zawsze zawiera pewną ilość pary wodnej, w dyszach de Lavala. Do obliczeń wybrano dyszę de Lavala o dużej prędkości ekspansji i połówkową dyszę zbieżno-rozbieżną o znacznie mniejszej prędkości ekspansji. Obliczenia przeprowadzono za pomocą własnego kodu CFD, w którym zamodelowano powstawanie fazy ciekłej w wyniku kondesacji spontanicznej pary wodnej zawartej w powietrzu wilgotnym. W obliczeniach przepływu okołodźwiękowego uwzględniono również obecność prostopadłej fali uderzeniowej w części naddźwiękowej dyszy w celu analizy efektu odparowani fazy ciekłej.

EN

This paper presents a numerical analysis of the atmospheric air transonic flow through de Laval nozzles. By nature, atmospheric air always contains a certain amount of water vapour. The calculations were made using a Laval nozzle with a high expansion rate and a convergent-divergent (CD) “half-nozzle”, referred to as a transonic diffuser, with a much slower expansion rate. The calculations were performed using an in-house CFD code. The computational model made it possible to simulate the formation of the liquid phase due to spontaneous condensation of water vapour contained in moist air. The transonic flow calculations also take account of the presence of a normal shock wave in the nozzle supersonic part to analyse the effect of the liquid phase evaporation.

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Numerical simulations of a conceptual blade cooling with a working medium

Rogoziński K., Nowak G.

Computer Assisted Methods in Engineering and Science

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2015

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Vol. 22, no. 3

267--278

EN

The development of steam power units aims to increase the working steam parameters as they are the main factors that determine the efficiency of energy conversion. Most state of the art units are designed for supercritical steam parameters. However, the temperature level of steam feeding the turbine is limited by thermal strength of the material used to make the machine components. In this situation, using nickel alloys or cooling the elements exposed to the impact of high temperatures could be the appropriate solution. The former is rather expensive and the latter – technically difficult. The cooling option would require that the cooled element should be fed by a steam with a very high pressure and with a lower temperature than the temperature in the machine flow system. This paper presents the concept of using working steam as the cooling medium after it is expanded in a convergent-divergent nozzle. In such a case, the cooling system is very simple and the performed simulations indicate, for example, that the turbine blades may be cooled in this way.

3

Modeling of pneumatic melt drawing of polypropylene super-thin fibers in the Laval nozzle

Blim A., Jarecki L., Blonski S.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2014

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Vol. 62, nr 1

43--54

EN

Melt spinning of the fibers by supersonic air jet in the Laval nozzle is a novel, efficient and energy saving method of formation of super-thin fibers. In the process, polymer melt is extruded from a row of orifices and fast drawn by the pneumatic forces. In the modelling, air velocity, temperature and pressure distributions are computed from the k-! aerodynamic model. Computations of the polymer air-drawing dynamics are based on the mathematical model of melt spinning in a single-, thin-filament approximation and Phan-Thien/Tanner non-linear viscoelasticity of the polymer melt. Axial profiles of the polymer velocity, temperature, tensile stress and rheological extra-pressure are computed. Influence of the Laval nozzle geometry, initial air compression, an initial melt temperature, a polymer mass output and the diameter of the melt extrusion die is discussed. The role of the polymer molecular weight, melt viscosity and relaxation time is considered. Example computations show the influence of important processing and material parameters. In the supersonic process, a high negative internal extra-pressure is predicted in the polymer melt under high elongation rates which may lead to cavitation and longitudinal burst splitting of the filament into a high number of sub-filaments. A hypothetical number of sub-filaments at the splitting is estimated from an energetic criterion. The diameter of the sub-filaments may reach the range of nano-fibers. A substantial influence of the Laval nozzle geometry is also predicted.

4

Models for water steam condensing flows

Wróblewski W., Dykas S., Chmielniak T.

Archives of Thermodynamics

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2012

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Vol. 33, no. 1

67-86

EN

Abstract The paper presents a description of selected models dedicated to steam condensing flow modelling. The models are implemented into an in-house computational fluid dynamics code that has been successfully applied to wet steam flow calculation for many years now. All models use the same condensation model that has been validated against the majority of available experimental data. The state equations for vapour and liquid water, the physical model as well as the numerical techniques of solution to flow governing equations have been presented. For the single-fluid model, the Reynolds-averaged Navier-Stokes equations for vapour/liquid mixture are solved, whereas the two-fluid model solves separate flow governing equations for the compressible, viscous and turbulent vapour phase and for the compressible and inviscid liquid phase. All described models have been compared with relation to the flow through the Laval nozzle.