Geometrical Optimization And Performance Of Diffuser Attached To Mine Ventilation System

Aimed at the problem of large structural resistance of MV(Mine Ventilation) diffuser and its low efficiency of MV, this paper proposes a BS(Bitangent Streamline) diffuser, and it is concluded that an approach to optimization of the geometry and geometrical parameters, and the approach optimizes the flow field of BS diffusers, and the performance of a BS diffuser is improved. These contribute to the increased efficency of MV.Firstly, on the basis of the deep investigations, it is concluded that the problem of energy-saving MV, and it is proposed that one approach to energy-saving MV through the optimization of MV diffusers. In application of mass and energy conservation, the geometry and parameters of a diffuser are defined, and the geometries and parameters affect the flow field, and the flow fields affect the performance of a diffuser. In order to assess the performance of a MV diffuser, used of fluid dynamics, it is deduced that the ideal ratio of static pressure, the realistic ratio of static pressure, the ratio of structural resistance, the ratio of net earning and et al.Secondly, BS diffusers are designed. On the basis of the technical requirements and special safety standard, a diffuser of main mine fan is constrained by short length of axial direction, curved wall and slope outflowing. The function of flowing magnitude is constructed by virtual sink and non-even paralleled inlet flow. The stream function is deduced from the function of flowing magnitude in application of the conjugated relationship. Applied of the boundary conditions, the streamline outline function is deduced from the stream function. In order to avoiding increasing too fast curvature of the curved outlines, it is deduced that the inner and outer outline functions assuming corresponding relaxation coefficients. On the basis of the inner and outer outlines, the outlines of streamline walls are proposed. The BS(Bitangential Streamlines) diffuser consists in guide-line, curved wall line and extending-line, and the straight lines are both tangential to the curved wall line; the BS diffuser is new type of curved wall diffuser.Thirdly, the optimzations of geometry coupled with geometrical parameters of BS diffusers. Through numerical simulations, it is concluded that the inner flow and outflowing distributions of BS diffusers should be more reasonable. Assessed by static pressure ratio, structural resistance and net earning ratios, the geometries of BS diffuser are optimized, and it is found that the optimization of the area enlarging ratio is from 2.20 to 2.35. The experimental system and automatic testing system were built in a laboratory room, and it is tested that the peroformances of three geometries and their changed parameters of BS diffusers, it is fount that the optimized diffuser of the best performance, and its area enlarging ratio is 2.28. In order to analyze inner and outflowing flow fields of optimized geometrical parameters of energy-saving diffusers, the momentum and kinetic energy coefficients were discussed through the numerical simulations. As far as circular section, rectangle section and gradually increasing sections of energy-saving diffusers, the above two ratios are discussed with the increases of the Reynolds number and the numerical values of the axial length, and it is found that two ratios in the outflowing section of a diffuser should be affected by the ratio of width to height by itself, the Reynolds number and the historical condition of the inlet flow. Furthermore, by the virtue of the deduced formula of approximately calculated the boundary layer thickness, through the analyzing the changing boundary layer thickness, it is concluded that: the change of the boundary layer thickness adjacent to the inner curved wall is gentler than adjacent to the outer curved wall; the larger the inlet velocity, the larger are the oscillation amplitude and frequentness of the boundary layer thickness; the larger is the difference between the values and the optimized geometrical parameters of energy-saving diffusers, the larger are the oscillation amplitude and frequentness of the boundary layer thickness. Analyzed the change of the static pressure in application of the consisting formula, it is concluded that: the change of the static pressure gradient vertical to the inner curved wall is gentler than vertical to the outer curved wall; the larger the inlet velocity, the larger are the oscillation amplitude and frequentness of the static pressure gradient; the larger is the difference between the values and the optimized geometrical parameters of energy-saving diffusers, the larger are the oscillation amplitude and frequentness of static pressure gradient. Therefore, it can be deduced that the improvement of MS diffusers should be only an approach by the optimization of geometrical parameters coupled with flow fields.The optimizations of performance coupled with geometrical parameters of diffusers. Using the theoretical analysis and engineering boundary conditions, the design method of a diffuser is improved; the geometry of a diffuser is optimized by numerical calculations; it is optimized that geometries and geometrical parameters of diffusers; it is concluded that the approach to the optimization of BS diffuser geometry and geometrical parameters arround the performance.