Adjust system resistance curve of electronics enclosure

[cef3rd]

I have the system resistance data for an electronics enclosure (power supply) with Width, Height and Length. I need to approximate the system resistance curve for a similar enclosure but with reduced W and H and more or less same no. of components. Are there empirical equations out there that can be used with reasonable assumptions? Are there studies on how a change in enclosure dimensions affect the overall system resistance of an electronic enclosure?

 

[chicopee]

To me system resistance implies ventilation is that what you are talking about?

 

[ko99]

cef3rd,

I assume you're trying to estimate the airflow vs pressure curve through a power supply.

Most accurate is to test or model the new power supply, of course, but if you can estimate the change in open area you can get a rough resistance curve. Not sure I can explain it very well via email but I'll try:

Look down the tested power supply in the direction of airflow. "Open area" is the unobstructed area available for airflow (WxH minus obstructed area). Since the open area can change dramatically along the depth, choose the cross-section with the lowest open area (often this occurs at a vent shared with the power receptacle, etc).

Next, estimate the open area for the new supply.

At a given volume flow (CFM), the velocity change is the inverse of the area change (ie, if open area is cut in half, velocity doubles).

For turbulent flow, pressure is proportional to velocity squared. You can use this to estimate the new pressure curve (ie, if open area is cut in half, velocity doubles and pressure increases by a factor of four).

Good luck,

ko (

http://www.ecooling.biz)