Air Flow Distribution At The Longwall Faces - Air Velocity Distributions In Longwall Faces - Introduction

The generation and transportation of the airborne dust are mainly governed by the velocity and the movement pattern of the ventilation air in the longwall face. Generally speaking, the higher the air velocity, the more the airborne dust will be generated and the longer the period of the dust of certain size will be carried away from the source. In order to effectively prevent the production and the spread of the airborne dust, The airborne dust concentration distribution in the longwall face must be known in advance. Before the dust concentration distribution can he predicted theoretically with confidence, the air velocity distribution pattern of the ventilation air in the longwall face area must be determined first. However, the complicated, time-dependent and unpredictable mining conditions along and around the face area make the theoretical studies of the problem rather difficult. For instance, one of the factors commonly affecting the air velocity distribution at the longwall face is the air leakage, either into or from the gob area. The leakage quantity and the location of occurrence differ from mine to mine, face to face, and time to time. They depend not only on the compactness of the caved roof fragments in the gob, but also on the degree of obstructions in the working space and in the return entry. Another obstacle to the theoretical studies about the velocity distrbution is the complicated boundary conditions of the ventilated spnce which is very difficult to represent accurately in mathematical forms. In this paper, the air velocity distributions measured in four longwall faces are presented. A statistical model for each longwall face is also derived for prediction of air velocity distribution in the longwall face.