Initial Air Flow Rate Research Articles

Airflow disturbance induced by coal mine outburst shock waves: A case study of a gas outburst disaster in China

We explore the magnitude of airflow disturbance in mine roadways induced by gas outburst shock waves. Outburst shock wave propagation in the near-field of the outburst source is established and simulated in three dimensions using FLUENT. The effects in connected but distal roadways are represented by a simplified one-dimensional network model and solved by Flowmaster. A Mesh-based Parallel Code Coupling Interface (MPCCI) is applied to couple the three-dimensional (near source) model and the one-dimensional (distal) model. The coupled model is verified by theoretical analysis and against observations from a coal and gas outburst incident comprising 2887 tonnes of coal that occurred in the Jiulishan coal mine, China and general characteristics of outburst events explored. Simulations demonstrate that airflow disturbance induced by outburst shock waves in the coal mine is principally controlled by the shock wave overpressure and fan pressure provided by the main fan. Of these, the shock wave overpressure exerts the dominant impact. The larger the shock-wave overpressure, the more rapid the decrease of airflow in the roadway branches and the larger the ultimate airflow decrease. Furthermore, the arrival time of the minimum air flow rate is delayed. When the fan pressure is large, the ability to resist airflow disturbance is enhanced and the area subject to countercurrent flow is reduced. The initial air flow rate and the restored air flow rate show less correlation with the shock wave overpressures. However, they are both significantly affected by the pressure of the main fan. This work presents a novel approach for the study of airflow disturbance in underground ventilation networks in coal mines caused by coal and gas outbursts and provides guidance for the design of outburst prevention facilities.

Concept and validation of a novel approach for producing large batches of reference material of ambient aerosols on filters

A novel method for preparing reference material of aerosol particulate matter (PM) on filters was developed by using the concept of very high volume, multiport sampling, and this was subsequently applied to produce more than 300 well-characterised units. The dedicated sampler built for this purpose features a 0.94-m-diameter, vacuum-tight main chamber with a total of 349 monitor ports, each holding a 37-mm-diameter, cellulose acetate-nitrate ester (CA) membrane filter with a nominal pore size of 0.8 microm. At a pressure difference of about 130 hPa across the filter cassettes, the total initial air flow rate was 350 m3 h-1 (1.0 m3 h-1 per filter). Investigations into the variability of filter parameters showed that the flow resistance of CA filters is mostly determined by and proportional to their blank mass, with a mean uncertainty of about 5%. Total suspended particulate matter (TSP) was sampled for a total of 50 h using 349 selected filters with a relatively narrow spread in blank mass. The mean TSP mass per filter thus produced was 3.35 mg. Corrected for small differences in blank mass of the filters, the normalised aerosol masses per filter of 96% of the samples exhibited normal distributions with standard deviations of only 2.1 and 3.4%, depending on details of the normalisation procedure. Within the limits of the technique, a variation of aerosol mass with radial distance from the centre of the sampler is not clearly evident. The results provide evidence that the multiport approach allows large batches of particulate matter on filters to be produced in a reliable manner.

High velocity impact of particles on a target — an experimental study

In order to study communition in a jet mill, an experimental rig was built to investigate the breakage phenomena. Particles were accelerated with air in a nozzle to velocities ranging from 120 to 250 m/s and collided with a target. Energy loss during impact was evaluated by measuring particle velocities before and after impact. Two different systems for measuring particle velocities were implemented. The first one was designed to work at very low loading (particles are considered to hit the target individually). The velocities are measured by a high shutter speed video camera (up to 1 μs). The particle traces on a frame were analysed by an image analyser. The second method, used for medium to high solid loading, consists of two sets of emitter-receptor optic fibres. Signals, collected by a 500kHz acquisition card, are cross-correlated in order to obtain the velocity. Influence of solid loading and initial air flowrate on characteristics of broken particles were evaluated. The influence of target nature and orientation were established.