Natural convection

[jim hatfield]

I am designing a tunnel boring machine power center. Ive been able to calculate ventilation for natural convection but the customer wants filters. I need to know how to combine the static pressure of the filters with the ventilation open area. Anyone know how this is done?

 

[EnergyProfessional]

Filter manufacturer should provide data. Note that pressure drop rises as the filters fill up. i doubt you can filter air without a fan. Unless you built a mile high chimney.....

 

[chicopee]

EP has it right. Get literature on filters and you'll note the graphs showing the relationship between static pressure and the rate of air flows which is much greater than values from natural ventilation. Perhaps a water spray may at the boring machine may be a better selection. Back in time,from my perspective, on our job sites we used water spray to reduce dust emission when we cut into bridge concrete piers or when we used hydraulic hammers on bridge concrete abutment walls to the satisfaction of state inspectors, OSHA, and state environmentalists.

 

[GT-EGR]

Never done this before and would expect that natural convection would have a tough time pulling through filters, unless you’ve got a big convective force driving it.

Here’s my 10 cents on how I’d approach it.

I don’t mathematically know where each formula would come from - but if you have your filter free convective airflow calculated you somehow then have the pressure increase that the convective transfer is “pushing” your airflow through with.

With that airflow and a specific filter selected, you can easily get the pressure drop of your filters from the manufacturer. Subtract that from the pressure boost of convection, and you will have a new airflow through the system.

However this airflow will then be lower, which means you have to recalculate your filter resistance, which will resist less because your flow decreased. This becomes an iterative process or Im sure you could set up some formulas to do this quicker.

 

[miningman]

P=R*Q*Q, as in pressure = resistance * square of the quantity