Mathcad confused when solving equations with units in them.

[isharma]

Dear All,

I was trying to solve the variable d, diameter of the pipe.

I could not get the solution. Can any one help me to solve in mathcad.

[LucMeekes]

If you want to solve symbolically, it's better to keep the symbols (by having them undefined), rather than their values.

Besides, the symbolic solver does not work with units, it treats them as (undefined) variables.

Normally assignments (Like V:=Q/A) are not allowed inside a solve block. Only equations (with the bold equals-sign) are.

Success!
Luc

[Fred_Kohlhepp · Accepted solution]

Sorry, I don't like your equations.  Try this:

Note:  LAMINAR FLOW ONLY!!

[isharma]

Thank you for your kind response.

I worked as per your suggestion, I simplified the equation and I got the answer as below.

However, as the Re value I found above 2300 , its turbulent flow. I tried to solve these equations to find ID.

I can not simplify here the equations. There fore, I need to go by Solve or Find function. It will be helpful if you can guide here.

[Fred_Kohlhepp]

Your units don't balance:

(Reynold's Number does:

So you still have something fundamentally wrong.  If you get Reynold's Number you can approximate the Friction factor.  See Attached

[isharma]

As per your suggestion, I solved the unit issue.

Thanks for your sheet. However I am looking for my answer in different way.

My problem is to find the diameter of the pipe.

First I equate the friction factor equation to laminar flow equation to get the diameter. Once I got the diameter , I back calculated the Reynold;s number.

As the R value greater than the laminar flow, I am interested to find the diameter from the turbulent flow equation.

I need to find the value of d1= diameter of the pipe from the equations. However, mathcad showing no result found. Please help me out.@

[LucMeekes]

Then try like this:

Does this meet your expectations?

(Oh, it will not solve symbolically... )

Luc

[LucMeekes]

Or just (below the definitions of all constants):

Success!
Luc

[isharma]

Thanks LucMeekes for your input and math cad sheet.

However, your sheet doesn't yield any result in my mathcad version 14.

It is showing as shown below only.Please let me know what could be the reason or did i miss anything to get the result.

[isharma]

This equation also not yielding.

Can you please look into it as well.

[isharma]

I got the answer as per your sheet.

Thanks a lot for your kind help.

This forum is really helpful.I learnt a lot from you guys while solving this problem.

Thanks once again.

[LucMeekes]

And the Reynolds number is above 2300, so no laminar flow:

Luc

[Fred_Kohlhepp]

Best I can do; given pipe length and pressure drop, find diameter and velocity.  Not thrilled about the accuracy.