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.
By contrast with the aminomethylation of thiourea by formaldehyde and primary amines to form 5-substituted 1,3,5-triazinane-2-thiones (see studies [1,2] and references therein) the aminomethylation of urea has not attracted so much work [3-10], the most recent being published in 1991. Because of the possibility of different condensations involving urea and formaldehyde [11,12] cyclic urea Mannich bases are better obtained not by a three-component condensation of urea, formaldehyde, and the corresponding primary amine [3-5, 7] but rather using 1,3-dimethylolurea (DMU) (1) [13], prepared from urea and formaldehyde, which then condenses with a suitable primary amine [7,8] or by condensing urea with the previously prepared dimethylol derivative of a primary amine with or without isolation of the indicated intermediate product [9]. The N-methylene derivative of a primary amine [10] may be used in place of the latter. Ethylenediamine and ethanolamine have been used [3][4][5] as bifunctional amines in a three-component condensation and ethanolamine and N,N-dimethylethylenediamine [7] in the condensation with DMU. In all four cases the expected 5-substituted 1,3,5-triazinan-2-one cyclic Mannich bases were obtained.
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