ANALYTICAL APPROACH TO ESTIMATION OF WATER BUILD-UP EFFECT IN MINE VENTILATION SHAFTS

Abstract

The relevance of the study is caused by the need to reduce the additional aerodynamic load on the main fans associated with the occurrence of pressure drop caused by water build-up effect in mine ventilation shafts. This negative effect can lead to significant increase in the air resistance of the mine and to subsequent unstable operation mode of main fan. Avoiding this effect is important not only for energy save mine ventilation, but also for preventing emergency stop of the main fan. Purpose: finding out the causes and mechanism of the water build-up effect with obtaining qualitative and quantitative estimates of the pressure drop value depending on the air velocity, shaft depth and intensity of the groundwater inflows. Objects: ventilation shafts. Methods: analytical modeling of moisture condensation and droplet movement in an ascending air flow in ventilation shaft; comparative analysis of experimental and model data. Results. The authors have analyzed the experimental data on formation and movement of droplet moisture in the ventilation shafts of various mines. It is noted that the water build-up effect is observed in the range of air velocities from 7 to 12 m/s, but in some cases the effect is absent even despite the presence of thick fog and abundant condensation of moisture on the surface of the shaft lining and other equipment. Three possible scenarios of the effect are considered: accumulation of a large number of drops of a certain size hanging in the air; drops of large size fall along the entire depth of the shaft with a source of moisture release in its upper part and multidirectional movement of drops depending on their size with a source of moisture release located at arbitrary depth. It is established that the first two models do not allow us to obtain a quantitative estimate of the water build-up effect value due to the uncertainty of the fractional composition of drops, the critical size of which increases the pressure drop to infinity. This drawback was eliminated in the third model by introducing the droplet size distribution function, which made it possible to obtain quantitative results. It is proved that the release of moisture from the air cannot be the cause of the water build-up effect, and the cause is the ground water flows into the shaft with intensity of an order of magnitude higher than moisture condensation. Based on the results of numerical modeling, it is shown that the maximum pressure drop occurs when surface groundwater enters the shaft.

Keywords

• mine ventilation
• moisture condensation
• hydrostatic cooling
• water flows
• pressure loss
• aerodynamic drag
• natural draft
• fractional composition