Martin Griffith

Hi Fred, The Goal Seek can be used to adjust multiple airways. The reason the unit changes to percentage for multiple airways is that the Goal Seek applies a multiplier to the changing parameter on the adjusting airways. Sometimes the multiple airways do not start at the same value, so the multiplier will retain the pre-existing ratio. Therefore we change the unit to percentage. If you start the 2 adjusting airways with a ratio of 2:1 in the Refrigeration property, the Goal Seek result will retain a 2:1 ratio. This can look a little strange when your parameter starts at zero. In these cases, the Goal Seek will guess an initial value (usually 1), so you can get some very strange percentages, as you have in your example. This is because the Goal Seek doesn't know anything about what will happen before it launches. I think I could improve this; if the pre-existing ratios are 1:1 then we don't have to report percentages. This should be easy to implement, we'll do it for the next version.

Hi, This is most likely down to the fact that the Goal Seek is only adjusting the sensible heat source, while the Heater is adding a mixture of heat and moisture. Though both solutions return the same dry bulb temperature, check the wet bulb temperatures, they are likely very different. With the Heater, it will take the fuel yield of H2O and inject that into the air as well; furthermore, there is a difficulty with these features where we are only setting either dry or wet bulb and not the other; we need to make assumptions about the other. In the context of Heaters, these assumptions are based around their use in colder environments So it depends on what you are trying to do. One difficultly you have is that to adjust for a drybulb temperature, you can add sensible heat, or you can simply change the amount of moisture in the air. The dry bulb temperature can depend strongly on this; wet bulb temperatures are more often the focus in underground environments because they have a more direct relationship to the energy inputs, as well as having limits that are more easily calibrated to the limits of human exposure. In short, what are you trying to model with this heat input?

Hi Fred, we changed it to monthly since the post above was made

Hi Stefano, Thanks for your message. This is probably because the airway being referenced does not exist in each stage. The Show All option can only point to one airway (indicated by the 1063814 in your image). The solution is to duplicate the message box and then change the stage selection in each so that each stage has its own message box. Ideally you wouldn't have to do this, so in a future version of Ventsim we will make it so that if the airway is not found in the current stage, then it looks for an airway in the current stage at the same location. But for now you will have to do what I describe above and make a duplicate message box.

Hi Fred, Thanks for your message. We don't save the Annual Flywheel data to the model because it's quite a lot of data and increases the size of the file. So you have to rerun it every time you reopen. I understand that you may want to save it to the model, particularly on a very large model which may take a long time to run. What we can do in a future version of the software is add the data to the model save, but prompt the user and only save it if the user wants. We do something similar already with the monitor data from Dynamic Simulations. We will do this in a future version, I will let you know when. For now, you will have to rerun the flywheel simulation after loading your model.

Hi Thomas, It doesn't do much at the moment. We added it so that users could divide their fans into Primary and Secondary, since most often it's the Secondary/Auxiliary fans that users are trying to save power on, and for the potential to help Ventsim Control work out which are the Secondary fans. But there isn't much you can do with it yet. There is a small mention of the Primary/Secondary breakup in the Summary form, but we need to add more here, such as what is the power breakup between the Primary and Secondary fans. So more development to be done. I think the first thing to do would be to add some more information in the Summary form, and to add something in the Advanced Find Select. Any other ideas you have for it would be welcome!

Hi Fred, Thanks for bringing this to our attention. This error sometimes occurs when you are working across different monitors, with different screen resolutions. Generally, if you move or generate the image in the screen that you originally started Ventsim in then it can work. Nonetheless, we will try to get it to work regardless, in a future update.

Hi Benedict, It should work fine, you would just need to check the settings shown in the image below. Allow surface temperature adjustments, set your temperatures, check your atmospheric lapse rate and make you have your Surface Datum Elevation above sea level and Surface Datum Minegrid correctly set. Some information in these links: http://ventsim.invisionzone.com/topic/75-elevation-in-ventsim-density/?tab=comments#comment-182 http://ventsim.invisionzone.com/topic/465-setting-up-a-heat-simulation/?tab=comments#comment-877

Many mines operate a paste fill system, where mined rock is mixed with a paste to create Paste Fill, which is then pumped or fed underground to fill in underground voids and stopes. This mining method is becoming more common, due to its advantages for waste management and the reduction of surface subsidence. But getting the paste underground can be difficult and must be carefully managed. Pumpsim can help. Pumpsim can simulate pipe flows for a range of fluids, including non-Newtonian fluids, such as paste fill. A non-Newtonian fluid is one whose viscosity varies as a function of the shear rate. This means that the rate at which the fluid shears, or gives, will depend on how hard you push it. Furthermore, there might be low shear stresses under which the fluid doesn't move at all and behaves like a solid. A good example is toothpaste. A blob of toothpaste will behave like a solid and sit on top of a toothbrush (low shear stress), but will flow like a fluid when you squeeze it out of a tube (high shear stress). By contrast, water (a Newtonian fluid) has a constant viscosity with shear rate and will give under any applied shear stress. These different viscous behaviours are best described using the below graph. (https://en.wikipedia.org/wiki/Non-Newtonian_fluid) The viscosity is the gradient of the line. For a Newtonian fluid, the gradient is constant. For the others, it varies. Paste fill is often described using the Bingham plastic model; this model incorporates a constant viscosity at stresses above the yield stress. Below the yield stress, it behaves as a solid (this is analogous with the toothpaste example above. The other model that is often used for Paste fill is the Herschel-Bulkley model, which resembles the Bingham pseudoplastic curve in the image above. This introduces a third parameter beyond the Bingham model, adding an exponent to achieve the curve. When working with Paste Fill at a mine site, you will generally have access to a consultant report on your specific paste fill mix; this report may give parameters for either a Bingham or Herschel-Bulkley model of your paste. You can enter this definition into Pumpsim and then set that as your working fluid. When working with Paste Fill in Pumpsim, you build your model exactly as you would a standard Pumpsim model for water. The only difference is that you then change the fluid type of your pipes to your Preset Paste Fill Fluid. To define your fluid, open the Liquids tab of the Preset Form. In the example below I've added two paste fill mixes, Paste Fill B (Bingham) and Paste Fill HB (Herschel-Bulkley) An important note here is that the units of Viscosity/Consistency are not strictly correct for the Herschel-Bulkley model, so the viscosity can't really be compared to the Bingham; also, the yield stresses between the two models are not really synonymous. The best way to compare the two fluids is to plot the shear stress to shear rate variation, as I've done here in Excel: We can see from the graph that the two models give roughly the same outcome, depending on what shear stresses we are working with. When you are working with your model, you can return the wall shear stress as a property on your pipes and refer back to this graph to see where your system is operating. In a future version of Pumpsim, we are going to add a tool to generate this graph for your fluids. But in the meantime if you want help generating this graph, please contact us. Once you have your fluid defined, simply set the Fluid Type on the pipe to the right type. When using non-Newtonian fluids, the friction factor calculation is more complex, but Pumpsim will handle all of this as part of the simulation. When working with non-Newtonian flows, Pumpsim will give different warnings around cavitation. Cavitation occurs when pressures are low in pipes, and air bubbles form; for paste this manifests as slack flow (horizontal) and free-fall (vertical). The model can be used to predict where such problems might emerge. Useful properties to examine when working with paste are the frictional pressure loss per metre and the wall shear stress. In some paste fill systems we have worked with, the operators have had a target frictional loss in their pipes, and the model can be used to locate parts of the system where the loss is too high or too low. Another useful tool is the Hydraulic Gradeline Graph, which you can generate from the Shortest Path Tool. Any questions about paste fill, please let us know.

Hi Felipe, We'd be happy to give you a demonstration. Send us an email at ventsim@howden.com. There are a few resources online that showcase the software. You can start on the website www.pumpsim.com. Also, there is a Pumpsim webinar in Spanish you can watch here: https://ventsim.com/webinars/

Hi, yes it sounds like you are on the right track. The Surface Datum Rock temperature is not something you can directly measure, its value should be extrapolated from the underground borehole measurements.

Hi Frédéric, Thanks for your message! Investigating this, the diffusivity is a function of the rock density, specific heat and thermal conductivity and is indeed read-only. I think the "Optional" comment on the density is a relic of an earlier version of Ventsim where you could specify the diffusivity. Thank you for bringing this to our attention, we will clean up the descriptions in the next version of Ventsim to make it clearer. I'll post here again when the version is out. Have a great day as well.

Buenos dias, Podemos decirle si nos dice su número de licencia; tambien, podemos liberar la licencia. Envíenos un correo electrónico y podemos ayudarlo más: ventsim.support@howden.com

Hi Nathan, The feature is broken. I've just fixed it, the version with the fix in is Ventsim version 5.4.5.0 available here: https://ventsim.com/download/minor-releases/ The intention of the feature is to generate cubic function fits to get smoother fan curves and to use all the available ten points. For example: Thank you for bringing this to our attention.

Hi, New in Ventsim 5.4.4.8 is the Auto-Regulator feature. This is a new Resistance type option. This resistance option can be used as a replacement for an Orifice or Regulator resistance type, but rather than having a set opening, it takes a Target Flow. The Auto-regulator will then adjust the opening to achieve that flow. If the Target Flow can not be achieved (ie, more pressure is needed) then the Auto-regulator will set to 100% open and the flow will solve at some airflow less than the target. Additionally a warning will appear, telling you that the Target Flow has not been achieved, such as in the example below, where I've set an unachievable Target Flow. To model this previously, some of you may have used the Fixed Flow option on the Fan tab with the Restrict Only option on. The Auto-regulator has the advantage that in scenarios where extra pressure is needed to achieve the flow, as well as getting the warning, you will also get a realistic flow rate. For the Auto-regulator, you have to choose a type. This can be the Orifice-Equivalent, which follows the same resistance-to-opening function as the Orifice Resistance Type; or you can choose one of the preset Regulators. Either way, you will also be shown either the calculated orifice area or regulator opening on the Edit Box. We see this feature being used to model ventilation systems that will have some sort of Ventilation-On-Demand service; or to help during the ventilation design phase, in a similar way to how Fixed Flows are currently used. Please let us know how you go with the Auto-Regulators and if you have any feedback or suggestions.

A question that comes up from users sometimes is: what is the effect of fog density on the mine ventilation system? Ventsim Heat Simulation already predicts fog, but it only does it really for the purpose of modelling visibility. Usually the effect of fog on air density, and then by extension the mine ventilation system and fan performance, is not significant. In Ventsim, fog concentration has a maximum value of 1200 mg/m3; if condensation of water out of the air results in the fog exceeding this limit, then this extra condensation is simply removed from the system, with an assumption that it falls out of the air or onto the airway walls and floors as droplets of water. 1200 mg/m3 is equal to 0.0012 kg/m3, which is a 0.1 % variation on standard air density, so not something we are likely to notice in our fan performance. However, there are some situations where this fog limit may not be valid. In a long exhaust shaft with a high air velocity and a large decompression, fog formation is likely. Dynamic water suspension is possible for shafts speeds roughly in the range of 7 -12 m/s. This is where condensing water builds up and is suspended and carried up the shaft; but not carried fast enough, with the amount of condensation building up to a sufficient weight that is falls down the shaft. The process can then repeat, putting a detrimental varying load on the ventilation fan. Ventsim already has a feature to warn the user when shaft speeds occur in this range (Settings | Simulation | Airflow | Water Suspension Checking) Another possibility at velocities greater than 12 m/s is that the condensation is carried all the way out of the shaft. In this case the density increases over the length of the shaft, putting an extra load on the fan. To model this we've introduced 2 new settings: Settings | Simulation | Airflow | Water Suspension Carry Condensate During Heat Simulation, this setting will enable the carrying of condensate as fog (condensate = 0) in vertical (>80 degrees) shafts, meaning it is passed from one airway to the next and builds up as it goes. But it will only happen in high velocity rising shafts, that is, at velocities greater than the Settings | Simulation | Airflow | Water Suspension Upper Limit Settings | Simulation | Airflow | Water Suspension Adjust For Condensate This setting will take the fog and add its density to the air density in every airway in the model during an Air Simulation. In a rising air column (and in tandem with Settings | Simulation | Airflow | Water Suspension Carry Condensate), this could be sufficient to have an effect on fan performance. If this feature interests you or you have any questions about it, please get in touch.

Hi Ivan, Yes, you can use the Error Box to select all the airways with errors on them and edit them together. In the image below, I have 36 errors. I click Select All and Edit on the Error Box and then I can select Close End on the Edit Box and apply the change to 36 airways with the one edit.

I can't say exactly, we have a lot of development on. But I imagine sometime later this year.

You can try changing the air density in the Environment Settings to 998 kg/m3, but the rock heat exchange is designed for exchange with air, doing calculations of temperature, pressure and density based on standard psychrometric functions for air, not water. So I can imagine some problems around air wet bulb and dry bulb temperatures that Ventsim is used to working with. You could try it and see what sort of numbers you get and whether they make sense.

Hi Robin, Thanks for your message and interest in the waterway feature. It's hard to tell what is happening. Is this a natural ventilation driven model? Do you have any airflow? If there is no airflow, then it probably won't simulate any heat exchange. If you want to send me the model (ventsim.support@howden.com) I should be able to work out why it's not working. As for the inclined airways, it may be that the waterways are simply hidden. Try clicking W to switch to wireframe mode. Just a note, that the waterway feature models heat exchange between the exposed water surface and the air, it won't handle heat exchange between the water and the rock wall. As for your other question, and related to the previous point, Ventsim won't simulate the heat exchange in a tunnel filled with water. We will likely have a feature in the future which simulates the exchange between an insulated water pipe and an airway.

With the increase in interest in Battery Electric Vehicles in underground mines, we've introduced a feature to help model the heat produced. A new type of heat input is available: Electric Vehicle Power This input works in the same way that the Diesel Power input works, taking the power of the motor as the input and then calculating the heat produced, taking into account the motor efficiency and the amount of moisture produced. The default Electric Vehicle Efficiency is 95%. For Diesel Power, we have a Water-to-Diesel ratio to determine how much of the heat produced is given off as latent heat. The Ventsim default value of the Water-to-Diesel is 6, which reflects the moisture produced by the fuel burning, but also the increased moisture that results from the operation of the truck; typically a truck will operate in a moist environment, carrying wet rock and churning a wet road. Similarly for an electric vehicle, a significant part of the heat will be given off as moisture, despite the electric motor producing only sensible heat. To reflect this we have another setting, the Electric Vehicle Latent Heat Factor, default value of 50%. This means that half of the heat given off by the truck will be emitted as latent heat. This factor will likely need to be adjusted to reflect mine conditions; a drier mine might reduce the factor, a wetter one increase it. If your model has a lot of electric vehicles and the dry bulb temperatures are too high or low, it could be that this factor needs calibrating. So in the case shown in the image, the electric truck of 350 kW power output is working with a 50% utilisation factor, with a motor efficiency of 95 % and a latent heat factor of 50%. Therefore Average engine output = 50 % of 350 kW = 175 kW Heat output = 175 kW / 95% = 184.2 kW Latent heat output = 50% of 184.2 kW = 92.1 kW Sensible heat output = (100 - 50)% of 184.2 kW = 92.1 kW More discussion of this calculation can be found here: If you have any questions on this feature or anything to suggest, please get in touch by replying to this thread or emailing us at Ventsim.

Hi Ivan, The best resource we've found for this is Fire and Combustion textbooks. I'm not aware of any online source. Is there a particular type of fuel that you're looking for?

Hi Ivan, this thread might be interesting for you:

Thanks for the info Neil, 135,000 airways is certainly one of the bigger models out there. With really big models some performance issues can appear that we don't see for more common size models (<20,000 airways), so let us know if you there is a tool, feature, graphic or mouse action your using that lags or seems to be taking more time than it should.

Hi Emmanuel, There is no feature to do this. The volume flowrate is not adjusted for condensation. Do you have a scenario where the amount of condensation is large enough that it makes a significant different to the flowrate? If so, what sort of numbers? Is this in a shaft? We could have a look at adding something, or coming up with a suggestion to model it.