Transient turbulent diffusion of admixtures at the faces of tunnels and workings after ventilation is started up

Conclusions

• 1. Investigation of the process of clearing faces when ventilation is switched on after the detonation of explosives reveals that the laws of diffusion of admixtures in the mixing zone are more complex than had previously been supposed (i.e., than the exponential law). The exponential law, and the logarithmic formula for the air flow rate which follows from it, are correct for relatively short distances between the supply tube and the face,l/D=1.0–1.5. For larger distances (from 1.5 to 4.0), clearing of admixtures from the face is best represented by the error integral function (13).

• 2. From considerations of aerodynamics and rapid clearing of faces from noxious gases, and also of production technology, it is best to locate supply tubes at a distance equal to the range of the jet, given by$l/D = 1.0\frac{{\sqrt {S_t Sw} }}{a}$, while the required air flow rate for ventilation of the face in a given time interval after the detonation of the explosives must be calculated from (18) and (19).