Analytical investigation of simultaneous effects of convergent section heating of Laval nozzle, steam inlet condition, and nozzle geometry on condensation shock

Progress in the development of the steam turbines brings about a renewal of interest in wetness associated problems. In turbine steam expansion, the vapour first supercools and then condenses spontaneously to become a two phase mixture. The flow initially is single phase but after Wilson point water droplets are developed and there is a non equilibrium two phase flow. The formation and behavior of the liquid create problems that lower the performance of the turbine wet stage and the mechanisms underlying this are insufficiently understood. This growing droplets release their latent heat to the flow and this heat addition to the supersonic flow cause a pressure rise called condensation shock. Because of irreversible heat transfer in this region the entropy will increase tremendously. Removal of condensates from wet steam flow in the last stage of steam turbines significantly promotes stage efficiency and prevents erosion of rotors. The following study investigates the spraying water droplets at inlet and at throat of mini Laval nozzle and their effects on nucleation rate and condensation shock. According to the results, the nucleation rate is considerably suppressed and therefore the condensation shock nearly disappeared. In other words the injecting droplets would decrease the thermodynamic losses or improve the turbine efficiency.

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Flow Simulation as a Support to Predict Shape of Plasma Beam Affected by the Nozzle Geometry

MATEC Web of Conferences ◽

10.1051/matecconf/202032802008 ◽

2020 ◽

Vol 328 ◽

pp. 02008

Author(s):

Miloslav Málek ◽

Miloš Mičian ◽

Augustín Sládek

Keyword(s):

Laval Nozzle ◽

Flow Simulation ◽

Simulation Software ◽

Nozzle Geometry ◽

Ansys Fluent ◽

Beam Shape ◽

Nozzle Orifice ◽

Flow Simulations ◽

Plasma Beam ◽

Made In

This paper deals with flow simulation of plasma beam shape affected by the different nozzle geometry. The flow simulations for different nozzles geometry were made in simulation software Ansys-Fluent. The evaluation of flow simulations was based on comparing shapes of the flow media out from the modified nozzle orifice against reference nozzle. There were investigated 8 different modification of nozzle orifice. Modified nozzle n. 7 (in the shape of a Laval nozzle) has achieved significant improvement from all simulated. There were observed 3 cores of plasma beam, which could help blow dross out from cutting gap. Investigated results serve for further research.

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

Bulletin of the Polish Academy of Sciences Technical Sciences ◽

10.2478/bpasts-2014-0005 ◽

2014 ◽

Vol 62 (1) ◽

pp. 43-54 ◽

Cited By ~ 2

Author(s):

A. Blim ◽

L. Jarecki ◽

S. Blonski

Keyword(s):

Melt Spinning ◽

Laval Nozzle ◽

Polymer Melt ◽

Nozzle Geometry ◽

Melt Temperature ◽

Pressure Distributions ◽

Aerodynamic Model ◽

Air Jet ◽

High Elongation ◽

Air Compression

Abstract 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.

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Viscous–inviscid interactions in transonic flows through slender nozzles

Journal of Fluid Mechanics ◽

10.1017/s0022112010006130 ◽

2011 ◽

Vol 672 ◽

pp. 487-520 ◽

Cited By ~ 8

Author(s):

A. KLUWICK ◽

G. MEYER

Keyword(s):

Boundary Layer ◽

Laval Nozzle ◽

Vapour Phase ◽

Ideal Gas ◽

Core Region ◽

Nozzle Geometry ◽

Sonic Point ◽

Transonic Flows ◽

Nozzle Geometries ◽

Bzt Fluids

Considering the miniaturization trend in technical applications, the need of a slender nozzle theory for such conventional, that is ideal-gas-like, fluids, which accounts for a strong boundary-layer interaction with the core region, arises in quite a natural way as the dimensions of the flow device are successively reduced. Moreover, a number of modern technological processes (e.g. organic Rankine cycles) involve fluids with high molecular complexity, some of which are expected to exhibit embedded regions with negative values of the fundamental derivative in the vapour phase commonly termed Bethe–Zel'dovich–Thompson (BZT) fluids. Linked to it, unconventional Laval nozzle geometries are needed to transform subsonic to supersonic internal flows. In the present paper, the transonic flows through nozzles of short length scales located in a channel of constant cross-section so slender that the flow in the inviscid core region is one-dimensional are considered. Rapid streamwise changes of the flow field caused by the nozzle then lead to a local breakdown of the classical hierarchical boundary-layer approach, which is overcome by the triple-deck concept. Consequently, the properties of the inviscid core and the near-wall (laminar) boundary-layer regions have to be calculated simultaneously. The resulting problem is formulated for both regular (ideal-gas-like) fluids and dense gases. Differences and similarities of the resulting flow pattern with respect to the well-known classical Laval nozzle flow are presented for perfect gases, and the regularizing influence of viscous–inviscid interactions, is examined. Furthermore, the analogous problem is considered for BZT fluids in detail as well. The results indicate that the passage through the sonic point in the inviscid core is strongly affected by the combined influence of nozzle geometry and boundary-layer displacement effects suggesting in turn an inverse Laval nozzle design in order to obtain the desired flow behaviour.

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