Experimental and numerical investigation of aerodynamics of a pneumatic nozzle for suspension fuel

• Published in: The International journal of heat and fluid flow 2019-06, Vol.77, p.288-298
• Main Authors: Alekseenko, S.V., Anufriev, I.S., Dekterev, A.A., Kuznetsov, V.A., Maltsev, L.I., Minakov, A.V., Chernetskiy, M.Yu, Shadrin, E.Yu, Sharypov, O.V.
• Format: Article
• Language: English
• Subjects: Dispersion of liquid; Gas flow structure; Nozzle for coal-water slurry; Numerical simulation; Particle image velocimetry; Velocity measurements
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/j.ijheatfluidflow.2019.04.013

•Converging annular jet forms the straight and recurrent cumulative axial jets.•Toroidal vortex is formed in the diffuser.•Annular jet is characterized by the presence of shock-wave structures.•Mach discs are forming in the initial region of the axial jet.One of the topical problems of coal power engineering both from the standpoint of increasing efficiency and ecological safety of heat energy production and the need to utilize low-grade coals and coal wastes is the development and enhancement of combustion technology for coal in the form of a coal-water slurry (CWS). The technologies of CWS combustion place high demands on the spraying devices (nozzles): there should be no narrow fuel channels to avoid clogging; low fuel velocities relative to the solid walls, which will reduce abrasive wear. The authors of the paper propose and investigate a novel pneumatic nozzle based on the use of the properties of near-wall and cumulative jets of liquid and gas and Coanda effect, which meets the basic requirements for CWS injectors. Aerodynamics control plays the determining role in the efficiency of pneumatic nozzle operation. In this paper, the structure of a single-phase gas flow generated by the proposed pneumatic nozzle is studied under different regime parameters using the experimental and numerical methods. The studies were carried out using the particle image velocimetry (PIV) and mathematical modeling of the flows by means of the DES and RSM turbulence models. In the entire investigated range of excess air pressure, the converging annular jet is shown to turn into the concentrated one and forms the direct and return cumulative axial jets in the nozzle near the axis of symmetry. Due to interaction of the return and annular jets in the diffuser, a toroidal vortex is formed. At an excess air pressure of 1 bar in the nozzle, a converging annular sonic jet is formed at the nozzle exit. With a further increase in pressure, the outflowing jet becomes supersonic. At that the oblique shock waves are formed, and the axial jet acquires a barrel-like shape with formation of the Mach disks. Spatial arrangement of the flow (both in and outside of the toroidal vortex) contributes to efficient dispersion of liquid fuel in the proposed nozzle. The obtained results of the study of a single-phase gas flow structure justify the effectiveness of this nozzle for the formation of a fine multiphase flow during the CWS spraying. [Display omitted]