AIR VELOCITY CALCULATION

[VEEKRISH]

Hi. Does anybody know of a mathematical method of computing the velocity of air at a specified distance from the Air Outlet ? Application is a Laboratory where we need to maintain a velocity of 20 FPM at the Occupied Zone. Temperature of primary air being supplied will be about 55 deg F. Assuming we use a Laminar Flow Outlet with an intial face velocity of 70 FPM, I need to evaluate at what distance from the outlet, I can expect the Velocity to be 20 FPM. Alternatively, if mounting height is known, what should be the Face Velocity to achieve the velocity of 20 FPM at the occupied zone, say 6 feet from the Terminal.

 

[walz]

Two entirely different subjects

Fluid flowing inside the duct, and the other is outise the duct in free environment.

CFD is the answer. I guess the only answer.... have a CFD analysis for this LAB, get the pretty images which shows the velocites as well temperature of every region inside the room

 

[EnergyProfessional]

the diffuser manufacturer might have (approximate) data for their product. this of course not accurate and CFD is left to do.

 

[walz]

What diffuser manufacturers mention at the most is the throw in feets of air stream out of a diffuser of certain type and size at a certain air flow rate.

 

[EnergyProfessional]

Walz: I didn't double-check, but they must state what the velocity at that distance is. the diffuser throws indefinitely, it's just that the velocity goes to near 0 at some point.

there may be a standard velocity they will refer for. Let's say 5 fpm is standard, so each diffuser has a different distance at which velocity is 5 fpm.

anyway, talking to a diffuser rep might be a good start.

 

[VEEKRISH]

Thanks, guys.Most Terminal Manufacturers do provide throws to Terminal Velocities of 50-100-150 FPM. I just wanna check if there is a method to evaluate the ditance at which the velocity could be a pre-determined value.

 

[walz]

Veekrish

Are you looking only for a mathematical formula??

I mean can you measure the velocity at site at a desired distance from diffuser. You can use anemometer or a flow meter device.

 

[VEEKRISH]

Walz, what I am looking for is a Formula which I can use at the design stage. Am not looking at measuring at an actual site. Thanks.