Concrete duct static loss 1

[camago]

I want to know how to calculate the static pressure losses in a concrete duct.

Thanks

 

[ChasBean1]

Use the calc. here:

http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm

and the roughness table here:

http://www.efunda.com/formulae/fluids/roughness.cfm

It looks like concrete is a little of a shot in the dark depending on smoothness (listed as roughness of 1000-10000...

 

[camago]

Thanks very much Chasbean1,

Do you think that I can also calculate the friction loss with the ductulator and the use a correction factor depending on the velocity from HVAC rules of Thumb?

 

[ChasBean1]

It gets a little hairy between laminar and turbulent flow. The friction factor will affect head loss linearly and the change in friction will be linear with laminar flow. But when flow is turbulent, the relative roughness of the pipe comes into play. Using an equation I have from old notes, f when turbulent is a function of:
1 / [(2 log(relative roughness))^.5]
Maybe try crunching the math using the difference in roughness between galvy and concrete by setting up some values for head loss:
H = (f*L*V^2)/(D*2*g), where L is length of pipe, D is diameter, g is gravity (most of this you can make constant). If you get any results from the comparison, pls. post and let us know.