Mechanism of ventilation energy dissipation in homogeneous roadway

The essence of roadway ventilation resistance is energy dissipation. In order to study the ventilation energy dissipation,the steady flow in homogeneous roadway is taken as research object and the principle of fluid mechanics is used as analysis basis. Analysis is firstly carried out for energy dissipation as the ventilation in laminar and turbulent flow respectively,and the similarities and differences between them are identified. Then the essence of non-rotational and rotational flow are analyzed by the energy dissipation of fluid between plates and cylindrical walls. Finally,the formation and mechanism of ventilation energy dissipation are analyzed from a microscopic perspective. The relationship between various parameters of roadway and ventilation energy dissipation is established and the effect of vortex on the energy dissipation in turbulent core region is analyzed. It is found that the energy dissipation rate of laminar flow per unit length of roadway is directly proportional to the square of average velocity and the dynamic viscosity,and independent of roadway radius. The turbulent energy dissipation rate of roadway per unit length is directly proportional to the cubic of average velocity,frictional resistant coefficient,radius and air density. Locally,the energy dissipation rate per unit volume is equal to the product of the shear velocity gradient squared with dynamic viscosity for any fluid motion. The essential difference between turbulent flow and laminar flow is that the vortex existing in turbulence increases the local shear velocity gradient leading to an increase in energy dissipation rate. The energy dissipation in the turbulent core area is proportional to the cube of the average velocity in the roadway,because the initial kinetic energy of the vortex is proportional to the square of the velocity,and the frequency of vortex generation is proportional to the velocity. With the increase of wall roughness,the radius and initial kinetic energy of the vortex generated on the bottom boundary of laminar flow and turbulent core energy dissipation rate also increase.