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

Abstract

One of the topical problems of coal power engineering both from the point of increasing efficiency and ecological safety of heat energy production and need to utilize low-grade coals and coal wastes is the development of combustion technology for coal in the form of a coal-water suspension (CWS). The technologies of CWS combustion place high demands to the spraying devices (nozzles): absence of narrow fuel channels, which can be locked; low fuel velocities relative to the solid walls, which will reduce abrasive wear. The authors of the paper propose a 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 in 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. It is shown that in the entire investigated range of excess air pressure, the converging annular jet turns 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 operation of a liquid fuel nozzle, such a return flow will contribute to the effective destruction of a liquid jet and formation of a highly dispersed two-phase flow. With an excess air pressure in the nozzle of 1 bar, a sound annular converging jet is formed at the nozzle outlet; with a further increase in pressure, the outflowing jet becomes supersonic, the oblique shock waves are formed there, and the axial jet acquires a barrel-like shape with formation of the Mach disks. Such a complex spatial arrangement of the flow (both in the toroidal vortex and outside it) ensures efficient dispersion of liquid fuel in this nozzle.

Characteristics of Alcohol-Coal-Water Slurries Spraying

“…Measurement error, taking into account possible sources of error (such as: local velocity gradient; droplet displacement; optical effects, etc. ), did not exceed 8 % for PIV similarly to [16] and 2 % for IPI method. Schematic diagram of the stand for jet recording of coal-water fuels during coaxial spraying is shown in Figure 2.…”

“…Techniques for high-speed visualization of jet characteristics (droplet velocities, sizes, and concentrations) of sprayed coal-water fuels are similar to those described in [16]. Registration of the structure of the steady flow of sprayed fuel slurries and their velocity was performed by the PIV method (Particle Image Velocimetry).…”

Ignition of coal‐water fuel droplets with addition of isopropyl alcohol

“…Intensive erosion of the spray devices occurs during atomization of coal-water suspensions due to the high concentration of coal particles. 53 Introduction of alcohol into the composition of coal-water suspensions, as shown by specially conducted experimental studies, leads to a decrease in the viscosity of the suspension and surface tension. Addition of 5% (by weight) of isopropyl alcohol to the fuel leads to reduction of suspension viscosity by 3% to 5% in comparison with conventional coal-water fuel.…”

“…It should also be noted that the introduction of alcohol in the composition of coal‐water fuels leads to the solution of another problem of CWF. Intensive erosion of the spray devices occurs during atomization of coal‐water suspensions due to the high concentration of coal particles 53 . Introduction of alcohol into the composition of coal‐water suspensions, as shown by specially conducted experimental studies, leads to a decrease in the viscosity of the suspension and surface tension.…”

Influence of Spray Nozzle Operating Parameters on the Fogging Process Implemented to Prevent the Spread of SARS-CoV-2 Virus

“…The list of the elements applied in the experimental setup was standard for testing of the compressed air nozzles utilizing the PIV technique. A similar method of configuring the test stand was also presented in [28,[38][39][40]. A detailed specification of the equipment used during the measurements is presented in Table 1.…”