The influence of the piston effect in subway tunnels depends on a train speed, the geometry of a tunnel and a train, the types of air flow caused by mechanical ventilation and other variable characteristics. Tables and graphs of changes in air flows generated by the effect of the piston are presented depending on the speed of a train and the degree of fill rate of a tunnel. It is noted that the piston effect is characterized by two phases. At the first stage, the piston effect and the processes of changing physical fields are non-stationary whereas at the second stage, the processes become stable. The speed of the circulation flow created by the piston effect, in accordance with the fill factor of a tunnel, is characterised by a linear relationship; the degree of its growth is directly proportional to the speed of a train. Based on the results from the present paper it is possible to calculate the velocity and consumption of an air flow in an underground space. The maximum value of air flow carried out by the piston effect does not exceed 90-100 m 3 /s. It corresponds to the stationary phase of motion, when the tunnel filling factor α = 0.35 and train speed is in the range of 40-45 km/h. Based on the obtained numerical simulation results, technological parameters for metro ventilation systems can be calculated more accurately.
It is established that the geothermal field of a massif around underground structures located above the neutral layer is non-stationary because of the influence of solar radiation. Below the above marked layer, the formation of the geothermal field of the subsoil is due to the process of depths and is stationary. The definition of these fields is necessary for the performance of the thermal physical calculation of the ventilation and the specification of the air consumption of the underground facilities of the metro by the thermal factor. The paper gives formulas, tables and graphs with the help of which it is possible to reliably determine the sought-for geothermal fields
In this article presented an analysis of the hazards caused by the influence of strong fires in the road tunnels. Have been considered the main factors that affect the reliability of the results of definition of the period of time during which there is the possibility of evacuation of people. The dependence of the period of time marked by the characteristic parameters of fire: from the power of spatial localization and duration of the ascending phase of its development. The paper noted that the duration of the evacuation period, will be less than the duration of the ascending phase of development of a fire and also noted that this period tends to narrowing due to the influence of turbulent diffusion fluxes. In this paper it is assumed that the turbulent diffusion fluxes occur between the zones in which the ruling are toxic carbon gases of fire and fresh ventilation air flow.
According to modern technologies of construction and operation of transport tunnels, it is assumed in the present work that drainage of water does not occur inside the membrane in the area of reinforced coating of the tunnel and here takes place a non-stationary process of transfer of hygroscopic mass (moisture) together with а similar process of heat transfer between the ventilation stream and the surrounding mining massif. Thus, we have to deal only with the sorption mass content in the pores of the massif and the water in the explicit form in the tunnels can only be in exceptional cases as local sources and therefore, their influence on the ventilation flow should be considered separately. The paper provides results of mathematical modeling of heat and mass transfer processes as well as graphs and nomograms, which can be used to define non-stationary coefficients of the heat and mass transmission required for thermal physics calculation of underground ventilation. The additional flows initiated by the Soret and Dufour effects usually strengthen the main flows, but in practice one can find a case where it is not necessary to take into account the effect of additional flows. Based on the analysis of processes, the criteria that determine the numerical value of these show the case when accounting for additional flows of Soret and Dufour is mandatory. The marked effects can be ignored when 106 Lα=1.
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