Head loss through air intake duct piping

[VFreshEngineer]

Hello,

I try to calculate pressure drop through rectangular ducting (sound baffle), which will be placed on air inlet. I'm new to this and need some guidance.

Screenshot for reference:

I found formula for calculatig equivalent hydralic diameter for rectangular shaped duct on Engineering toolbox - Link
Since the duct has 4 openings, I only considered flow through one opening to simplify. I devided required air volume flow (2 m3/s) by 4 and used Engineering Toolbox excel template

According to the template I've got head loss of 1316 Pa/100m. To calculate the total head loss through duct channel I've used following equation:
Pdiff = 1316/100 * Length of duct channel * Number of openings

I've got head loss that equals to 26 Pa. Seems a bit low, but it's a half meter duct ... so it seems realistic.
I'm tottally green in this field and will appriciate all the support I can get.

General inputs
Opening's height: 800 mm
Opening's width: 62,5 mm
Length of duct channel: 0,5 m
Number of openings: 4
Required min. air flow: 2 m3/s

Attaching Excel spreadsheet for reference.

 

[LittleInch]

It's actually less than that as you've multiplied the pressure loss/ 100m by 4 - these are in parallel so you don't need to do that as the pressure drop is the same for all 4 assuming equal flow.

It does seem a little low alright as you're doing 10m/sec through those slots, but eng tool box is usually pretty good.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mrev23]

Include entrance/exit losses as the air speeds up / slows down to enter/exit your rectangular flow path.

Hints here:

https://www.engineeringtoolbox.com/minor-loss-air-ducts-fittings-d_208.html

Suggest doing some searches related to entrance and exit losses.