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Issue with modelling internal flow of industrial factory

Question asked by William Ching on Oct 11, 2018
Latest reply on Oct 14, 2018 by William Ching

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Hi,

I am trying to simulate an industrial factory with heat sources however i cannot get the correct results. I keep on receiving ridiculous values from the solver. My input is 38.9 degrees into the roller shutter, thats my boundary condition.

Also, I am wondering whats the difference between initial conditions and boundary conditions, if i put them both as the same temperature, humidity etc. would that affect the result?

And i am using fans to improve the ventilation while also modelling natural ventilation. I have attached my model below.

It would be much appreciated for any inputs to get realistic values.

Thanks

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ASSEMBLY CNC FACTORY WITH FAN.SLDASM.zip232.7 KB

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Janko Stellaard Oct 12, 2018 4:31 AM
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Please add the parts to the zip-file, only the assembly-file is not sufficient
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- William Ching @ Janko Stellaard on Oct 12, 2018 11:21 PM
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  Hi Janko,
  
  thanks for your reply. I have zipped the files below. I have trying to perform simulation using these two cnc machines as heat sources from the motor. I am not sure when to set the flow freezing for permanent option? Also i am using the boundary condition through the roller shutters opened as v=2m/s inlet velocity and environmental pressure. I have used fan curves to get my fan but not sure if my selection is correct, any helpful tips would be much appreciated. Issue with modelling internal flow of industrial factory
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  - SOLIDWORKS FLOW WITH FAN.zip3.3 MB
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Mark Keown Oct 12, 2018 11:04 PM
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Keep it simple and slowly build in details.
Assuming all the heat goes into the air. (This is an incorrect assumption but I will keep going. You will have heat transfer through the building walls).

Some air is entering the box and the same amount of air must leave the box. The amount of power that the air picks up must be the same as the amount of power you are putting into the simulation. Use the below relation to get an idea of what is going on. We are not checking if Flow is correct we are checking if your inputs are correct.

It looks like you have 36,750 watts going into the box. So if for example if deltaT is say 30°, G would need to be ~4k m^3/sec air What are your fans rated at?
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- William Ching @ Mark Keown on Oct 12, 2018 11:26 PM
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  Hi Mark,
  
  Thanks for your email.
  
  I have used adidbatic walls as the factory is a unit connected with other concrete walls. I have inputted 28000W to each of the two CNC machines coming from the motor heat. I am using a roof exhaust and supply fan to improve the ventilation. my required airflow is 2666L/S with 10 ACH for factory. I was not sure about the input for fan selection for the static pressure hence i used 100 PA static.
  Any help would be appreciated. thank you
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  - Mark Keown @ William Ching on Oct 13, 2018 5:17 AM
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    In the engineering data base select fans.
    Create a user defined fan and enter the fan curve from the manufactures fan curve plot. Flow Simulation will figure out the operating point.
    In most systems like this - the biggest flow resistances is at the grill / filter air entrance to the building (enclosure) and the exit grill, ducting, ... Have the air inlet low as possible (at floor level) and the air exit high as reasonable to take advantage of natural convection.
    
    I was just at a new cafe with all new gear in the kitchen. The fans over the stove pulled enough vacuum that people could not push the front door open. This problem did not last but a day or so - but don't make the same error.
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    - William Ching @ Mark Keown on Oct 14, 2018 12:55 AM
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      Hi Mark,
      
      I am using mechanical roof ventilation (Supply and exhaust) not displacement ventilation, as it is not suitable/practical for this factory due to high ceilings at 6m. What would be an optimal range for static pressure for fan selection if i have the required airflow rate and i do not have measuring equipment.
      
      Thank you
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