Setting up a Heat Simulation

[Customer]

Hi, 

I want to model the heat and temperatures in my mine. What do I need to do first to setup a Heat Simulation in Ventsim?

[Craig Stewart]

It’s important to calibrate your model for heat with known measurements where possible, before extending the model deeper for future predictions. 

Your surface temperatures, pressures and rock parameters need to be entered into the SETTINGS > SIMULATION > ENVIRONMENT section.  Ensure the SURFACE DATUM value is correctly referencing the Z Coordinate where you have taken the surface pressure and temperature.  Once you enter these values, the surface AIR DENSITY and all associated underground densities are automatically calculated – you do not need to enter this.  Rock parameters such as conductivity and diffusivity can be measured by a laboratory, however if this data is unavailable, examples of common rock properties are available in the Ventsim manual.

 Your measured underground rock temperatures need to be used to calculate the geothermal gradient (difference in temperature per 100m vertical) and project the temperature gradient back to the surface level to establish the SURFACE ROCK TEMPERATURE – which also needs to be entered in the SETTINGS > SIMULATION > ENVIRONMENT section also.  Measuring the surface rock temperature after blasting is not ideal – it may be ok but it is likely to have cooled a little.  The gold standard is to drill a hole in the side wall near the blasting face, and measure the temperature at the back of the hole with a probe (at least 3m deep).

 To calibrate the model to your actual underground temperatures, you will need to consider any diesel or electrical activity in the mine beyond just the rock strata, auto compression and fans (all of which Ventsim calculates automatically).   A good guide to establishing the correct amount of diesel engine power to put in to the model is to estimate the diesel fuel usage by the mine per day, and then calculate the fuel usage per operating hour (for example if the mine uses 25,000 litres per day and works 12 hour shifts, then the diesel usage for operating times (let's assume 9 hours per shift) will  be 25000 / 18 hours = 1388 l per hour)  Use the HEAT CALCULATOR in the TOOLS menu in Ventsim to convert that to Diesel Engine kW, and then spread these heat sources through the working areas of the model using either a number of point sources, linear sources, fuel burn or activity tracks (these are all options in the HEAT section of the EDIT box).

 Focus on getting the WET BULB temperatures correct initially.  Once you have a model that has good validation with the WET BULB measurements, you can then focus on the DRY BULB – the most significant factor affecting the DRY BULB is the WETNESS FRACTION assigned to the airways (or SETTINGS > SIMULATION > ENVIRONMENT if you haven’t directly set the wetness fraction in the airways).  Increase the wetness fraction to increase evaporative cooling and decrease dry bulb.  You will find this will not normally change wet bulb temperatures significantly and therefore you should be able get the dry bulb to change to match your measurements.  You may need to adjust different airways in the mine with different wetness fractions.

 Once you have these factors correct you should then be in a good position to use the model with confidence for future planning.

 

Hope that helps

Craig