SCALE-MODEL STUDIES OF THE TRANSPORT OF AIRBORNE POLLUTANTS ON COALFACES

Studies have been carried out to investigate airflows in coalmine models, with special regard to the transport of airborne pollutants, and to examine how they relate to what happens at full-scale in an actual underground mine. If such models can be shown to provide data representative of actual mine ventilation engineering, then they can provide cost-effective alternatives to full-scale investigations. The work set out in the first instance to identify the properties of: (a) the bulk airflow and associated transport of airborne pollutants along a longwall coalface; and (b) the transport of material out of regions that were partially enclosed or poorly ventilated (e.g. in the cutting zone, in headings). For the former, an appropriate quantity is the dispersivity of the coalface airflow, for the latter the mean retention time. Both quantities may be rendered non-dimensional with respect to dimensions characteristic of the system and to velocities of the airflow. Their behaviour in relation to a third dimensionless quantity, the flow Reynolds' number, is also important. Experiments were performed, using smoke or dust tracers, to investigate how these properties are interrelated and how they scale between small-scale and full-scale systems. They were carried out in a 1/10-scale laboratory model, in a full-scale surface model, and underground in an actual coalmine. The basis of most of the experiments was the 'tracer decay' method, in which the transport properties of the aerodynamic system under investigation were determined from observations of the changes in tracer concentration with time immediately following the removal of the tracer source. During these experiments, the feasibility of using small-scale models to investigate ventilation problems was clearly indicated and preliminary scaling relationships which may be used as an initial basis for predicting the transport and local build-up of pollutants in mines were developed. It is expected that applications of the ideas and methodology described will be relevant to other industries.