Time for Primary Ventilation system to reach steady state (Natural Primary Ventilation)

[Sam La Macchia]

I was wondering if any documents / research papers exist that are able to predict the time it takes for any Primary Ventilation system to reach steady state under natural circumstances (once all primary and secondary fans are turned OFF). Hot air rises, so I imagine this will be an important factor within an sort of prediction / formula / prediction?

 

Many other factors exist too:

- Mine Resistance due to drive / void sizes

- Ambient surface temperature/s

[Martin Griffith]

Hi Sam, 

Thanks for starting the discussion. I'm not aware of any research papers on this, although I know there are some network fluid solvers that incorporate inertia. 

We've tried at looking at this in Ventsim a few times, incorporating the inertia of the ventilation into the simulation is something we'd like to do somehow in Ventsim, but we haven't managed it yet. 

One approach you can do is to make an estimate of the total kinetic energy of the airflow in the mine at the moment that you turn the fans off. You can then make an estimate of the resistance of the mine and calculate the rate of energy loss to friction and to surface exhaust as a function of flow rate. You can get a rough estimate this way of the time to go to zero flow. I did this once a few years ago, I'll try to find it in my notes and post it here. 

But this doesn't incorporate natural ventilation pressure resulting from heat and density changes. Again, you can do these things roughly; you can simulate the steady state condition where fans are off and calculate the time to reach that total energy state, rather than an energy state of zero.

Another factor is the change in rock strata heat transfer. This heat transfer depends strongly on airflow rates. If you change the airflow rate, the heat transfer will change; but rock strata can take a very long time to reach steady-state, probably much longer than the airflows. If you switched off all ventilation, it could take a long time for the rock walls to heat back up to the VRT, and therefore to reach a steady state.