Abstract
Mine ventilation measurements using with SF6 as tracer gas were carried out at Kushiro Coal Mine operated by Taiheiyo-tanko Co., Ltd. in 1997, in order to investigate the flows in the inclined airway and its network flows from the inlet portals to the main fan. The photo-acoustic gas monitor of SF6 with high sensitivity of 10 ppb resolution of gas concentration was used to measure gas concentration-time curves. Two injection methods were applied to measure airflow in the inclined shaft by stepwise gas injection, and the ventilation network flows by pulsed injection of the tracer gas from the inlet portals. The effective gas diffusion coefficient in the single mine airway has been investigated by the measurement and numerical simulation results, and it was evaluated as 20 m2/s that is almost same order to that of Taylor's equation. On the other hand, the effective diffusion coefficient in the large scale of mine ventilation network has been evaluated as 200 m2/s that is one order larger value to Taylor's one. As the result of the measurements, the effective diffusion coefficient in mine ventilation airways has been evaluated as one order larger than usual turbulent diffusion coefficient (≈ 2∼25 m2/s) , and the average traveling velocity of tracer gas was about 70% to the average airflow velocity to the flow passes. Authors have presented a possible mechanism of the large effective diffusion coefficient and delay of the gas travelling in mine airways, that are generated by weak re-circulated flows formed in dead spaces and roads connecting main airways without airflows.Furthermore, the revised equation and numerical method for gas concentration-time curves in mine network ventilation flows has been presented which was extended from the Taylor's equation to evaluate effective diffusion coefficient of a single flow channel, and it has been shown that the presented model can be used for matching with the measured results including gas diffusion characteristics of mine ventilation airflows.
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