## Open Channel, Partially full pipe flow in excel. Please help!

## Open Channel, Partially full pipe flow in excel. Please help!

(OP)

Hello,

I am looking for a way to use excel to calculate the velocity in partially full pipes. I noticed that it had been a previous topic and I am hoping that darth051 will respond to this message and help me with this problem. I am stuck on the hydraulic radius. I would greatly appreciate your response. Thank you so much.

You may email me at: "kga" followed by @profile-eng.com

Thank you again!

I am looking for a way to use excel to calculate the velocity in partially full pipes. I noticed that it had been a previous topic and I am hoping that darth051 will respond to this message and help me with this problem. I am stuck on the hydraulic radius. I would greatly appreciate your response. Thank you so much.

You may email me at: "kga" followed by @profile-eng.com

Thank you again!

## RE: Open Channel, Partially full pipe flow in excel. Please help!

## RE: Open Channel, Partially full pipe flow in excel. Please help!

Unfortunately I don't have access to the spreadsheets at the moment but here is the basic method:

1) Set up a table for %full depth based on a pipe diameter of 1. Depth increments of 0.01 are what I traditionaly use.

2) For the depth calculate the water area and wetted perimeter. You'll need to dig out your geometry formulas to find the equations. (Don't forget that the formulas will change once you are over half full.)

3) Calculate hydrualic radii for each depth.

4) Calculate the % Velocity based on the full flow velocity. Since its a ratio, the slope factor drops out.

5) Calculate the % Capacity based on the full flow capacity. Make this column the column immediately to the left of the %Velocity column. (% Capacity = % Velocity * Area which you already calculated.)

6) Use Excel's VLookUp function to search the table for the closest % Capacity and return the corresponding % Velocity.

7) Use your full flow velocity and the the % velocity to determine your partial flow velocity.

You end up with a Workbook that has 1 Spreadsheet containing the "Partial Flow Table" and 1 Spreadsheet where you do your calculations.

You can always refine your spreadsheet further by setting up another Table containing the standard pipe characteristics you use. Let the first column of that table be the size & material of pipe with the other columns the diameter(s), area, etc. Then name your list of pipes (Insert Name Define). Use Data Validation to use your named list of pipes as a selection list in your spreadsheet. This forces you to pick from a list of known pipes. You can then use VLookUp to pull the pipe properties from your pipe table automatically.

David

David Dietrich

KMK Consultants Ltd

Windsor, Ontario, Canada

## RE: Open Channel, Partially full pipe flow in excel. Please help!

siblak

## RE: Open Channel, Partially full pipe flow in excel. Please help!

I would never design a pipe to use Q less than 0.3Qf, for economics. By the time Q/Qf = 0.3, d/D already is approx. 0.45 and v/vf is around 0.75.

In fact, I try to design for much better than Q/Qf = 0.3, so basically I am almost always dealing with v/vf > 0.85 or 0.9. Very rarely does this small differtial benefit the client.

Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”

-Steve

## RE: Open Channel, Partially full pipe flow in excel. Please help!

Sure it would be cheaper for the private sector developers to install the pipes at a shallower slope and therefore less depth but the public sector which looks after maintenance isn't willing to pick up the cost to keep flushing the system every couple years to keep it operating correctly.

David Dietrich

KMK Consultants Ltd

Windsor, Ontario, Canada

## RE: Open Channel, Partially full pipe flow in excel. Please help!

for a circular pipe:

Area = (D**2)* (O-sinO)/8 Where O is theta- the angle in radians form by the top width (T) (line across the water surface) from the center of the pipe.

The top width (T)= D*Sin(O/2)

Wetted perimeter P = DO/2

Hydraulic radius = D/4*(1 - SinO/O)

Hdraulic depth = (D/2)* ((O-SinO)/Sin(O/2))