In this work, the combustion process of chromium powder in the co-flow filtration mode was studied. The effect of nitrogen-containing gas flow rate on the nitridation of combustion products is shown. The effect of the amount of argon in the nitrogen–argon mixture on the burning rate and the burning temperature of the chromium powder is shown. It was found that an increase in the percentage of argon in the nitrogen–argon mixture can lead to the formation of an inverse combustion wave. The actual burning temperature is higher than adiabatic burning temperature in the co-flow filtration mode, thus the phenomenon of superadiabatic heating is observed. The phase composition of the obtained combustion products was studied. It was shown that the forced filtration mode allows for synthesizing non-stoichiometric Cr2N nitride.
Abstract. In this paper a two-phase (gas -solid particles) swirling turbulent flow in the separation chamber of a centrifugal apparatus is considered. The results of mathematical modeling of flow at different settings are shown.This paper presents a two-phase (gas -solids) swirling turbulent flow in the separation chamber of the centrifugal apparatus with an additional supply of gas (Fig. 1). Through the section A-A the gas flow is supplied with particles having radial and tangential velocity components. Through the section B-B an additional supply of gas without solid is provided. The flow in the vortex chamber is axisymmetric by its nature.Through the section C-C the swirling flow together with the gas fraction of fine particles leaves the working area of the vortex chamber. Through the section B-B the incoming gas stream filters larger particles of the particulate fraction, returning finer particles to the working zone of the classifier. Large particles, due to the predominance of the centrifugal force over the aerodynamic force, leave the vortex chamber through the cross section B-B. All solid walls of the apparatus can rotate about the axis O-Z, giving additional rotation of the gas flow with the solid phase and thereby aligning the field of circumferential velocity vector components. To describe the swirling gas flow in the separation chamber a set of the Reynolds equations is used. For its closure the generalized Boussinesq model is applied according to which the Reynolds stresses are considered to be proportional to the mean flow strain rate and the coefficient of eddy viscosity νt. Thus, the system of Reynolds equations in the cylindrical coordinate system in the conservative dimensionless form for an incompressible viscous fluid taking into account the axial symmetry (*/* = 0) can be written as follows:*ru r * + * *r (ru 2 r ) + * *z (ru z u r ) − 1 Re * *r r(1 + ν t ) *u r *r + * *z r(1 + ν t ) *u r *z = = u 2 − r *p *r + r Re *ν t *r *u r *r + *ν t *z *u z *r − u r r 2 (1 + ν t ) − 1 N j =1 j j (u r − w rj ) Stk ; a Corresponding author:
The combustion of the titanium and chromium powders in the co-current filtration mode was considered. We considered an original equipment that allows us to study the combustion of metal powders in a co-flow gas stream. It was demonstrated that the proportion of argon in a binary gas mixture has a greater influence on the burning temperature of titanium powder than the specific flow rate of the gas mixture. It was found that the actual burning temperature of chromium in the forced filtration mode is higher than the adiabatic temperature and the phenomenon of superadiabatic heating takes place. This method has high energy efficiency and allows you to get nitrides without the use of high pressures. It was found that co-current filtration promotes the formation of Cr2N nitride.
In this work, we considered an original setup that allows us to study the combustion of metal powders in a co-flow gas stream, and also presents the results of experimental studies on the combustion of chromium powder in a confined nitrogen-containing gas stream. This method has high energy efficiency and allows to get nitrides without the use of high pressures. The study of chromium combustion is justified by its high melting point at a relatively low exothermicity, which eliminates the influence of melting of the initial powder and synthesis products on the filtration process. This article presents the results of combustion of chromium powder with particle size δ = 63÷80 µm and δ = 500÷1000 μm. X-ray phase studies of the obtained powders were carried out. The effect of nitrogen-containing gas consumption on the degree of nitriding of combustion products is shown. It is established that the forced filtration mode allows the synthesis of non-stoichiometric chromium nitride Cr2N. The nitrogen content in the obtained Cr2N samples reached 9.6%.
This paper presents a numerical study of a two-phase swirling turbulent flow in a separation element of a vortex chamber. The paper considers a process of fractional separation in the separation chamber with three particular features in its design. The main feature is the separation mobile element located at the outlet of the separation area. Changes in the position of this element can affect the boundary size and the sharpness of the separation. The second feature of the considered separation chamber is the presence of a rotating element along the vertical axis. This element helps to align the field of the circumferential velocity component. The third feature of this chamber is the presence of a branch pipe for the auxiliary gas flow supply intended to push the particles away from the chamber wall and to blow the separated particles in order to prevent them from agglomeration. In this work, the trajectories of the motion of fine nitride particles are calculated taking into account the turbulent diffusion effect. A possibility to control the boundary size of the particles, when moving the separation element located at the outlet of the vortex chamber, is demonstrated. Numerical study results show that the turbulent pulsations cause significant changes in the separation process and affect the boundary size and the sharpness of the separation.
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