Many ore mines that have an active aerodynamic connection of underground workings with the surface through the caving zone are ventilated by the injection-suction method. In this method, by regulating the operation of the suction and discharge fan, it is possible to create in the area adjacent to the caving, the so-called zone of zero depression. In this zone, the effective depression is extremely low, so there should be neither air suction from the surface nor air escape from the mine to the surface. The actual large size of the caving area and the occurrence of local natural draughts do not allow for the complete elimination of air movement through the caving. Air may move upward in one part of the caving and downward in another, but in much smaller quantities than with a single fan. Thus, the zero-depression zone created by the blower-suction method of ventilation serves as a measure to control air suction through the caving zone. At mines in the northern regions, the position of the zero depression zone plays an important role in improving the atmospheric conditions of these mines, reducing the entry of cold air from the surface ...

Methane emission within the excavation area depends on the operation of mining machines, atmospheric pressure fluctuations, collapse of rocks of the main roof, irregularity of air supply, etc. Regardless of the influence of these factors, the methane content in the outgoing jet of the site should not exceed 1%. Consequently, it is necessary to supply to the site such amount of air Qpred that would ensure compliance with the requirements of Safety Rules at any combinations of these factors.

Topics of research work of the Department of Mine Ventilation and Safety Engineering of the Leningrad Mining Institute is aimed at ensuring normal ventilation of mines, creating in mine workings safety conditions and such sanitary and hygienic working conditions that would allow to achieve maximum productivity.

The question of the dependence of local resistance coefficients k on the roughness of the walls of air ducts is one of the little studied issues of practical aerodynamics. Most aerodynamics courses provide values, sometimes very detailed, of coefficients k for a number of local resistances - turns, sudden contractions and expansions, but are not indicated Usually, how to use these coefficients: should they be taken as constant, independent of the roughness of the walls of the air duct, or, conversely, should they be considered variable values, related in some way to the coefficient of friction on the walls of the air duct. The work done by the authors made it possible to clarify the relationship between the coefficients of local resistance k and the coefficients of friction a of air on the walls of the air duct. The previously accepted dependence turned out to be incorrect and must be replaced by another (see article). The turning resistance coefficients given in various courses should be increased for rough concrete fastening by 8-10% and for workings secured with staggered door frames by 25-30%. The correctness of formulas (11) and (12) for other types of local resistance requires verification.

In 1936, in the laboratory of mine ventilation, associate professor V. B. Komarov and assistant A. A. Geskin carried out work to determine the resistance coefficients of turns of ventilation pipelines while simultaneously narrowing them. This work set itself the task of determining the resistance coefficients of turns of channels mine fans, designed in various ways. The work was divided into two parts: a) determination of the rotation coefficients with simultaneous compression of the air stream, b) determination of the rotation coefficient with simultaneous expansion of the air stream. This work presents the second part of determining the resistance coefficients of channel turns. The work done by the authors makes it possible to clarify a number of provisions related to the design of fan channels when fans operate to pump air into the shaft.