How do you calculate hydraulic diameter?

[leonita]

Hi, I just confuse how to know this hydraulic diameter, would you mind to help me?
hydraulic diameter is for reynold calculation then heat transfer coefficient.
Thank you

 

[Travis_King]

The hydraulic diameter is the cross-sectional area of the flow divided by the wetted perimeter. The basic form is: D(h)= 4*A / P(w). For a circle, that just becomes D(h) = D, for other shapes it varies. Here's a page from Engineering Toolbox: http://www.engineeringtoolbox.com/hydraulic-equivalent-diameter-d_458.html

I'm not sure what level of work this is though. It could be as simple as figuring out the hydraulic diameter of that geometry, but it could also require you to account for possible phenomena like "vena contracta"; though most likely not.

 

[leonita]

Thank you for your reply. In my case, I used Hydraulic Diameter of Rectangular Tubes or Ducts.
However, the size of the rectangular tubes is different (decreasing). We can see it in the picture above.
In the first, size is 1.5 cm x 2.6 cm then it will decrease until 0.3 cm x 2.6 cm.
Do you have any suggestion?
Thank you

 

[Travis_King]

The definition uses the "cross sectional area".
Can you think of a way to calculate the total area of the opening (including the triangular/trapezoidal areas on the ends)?