FE Exam Review - Fluids - Hazen Williams / Manning Equations

[@keloomie]

Another quick note for the Value of "C". Page 297 in Handbook 10.0.1 reveals the value should be 130. From my experience Ductile Iron Pipe is usually concrete lined so using 140 may be correct in a real world scenario. I just wanted to point this out for FE test takers!

[@zack-kr3uz]

the cm value is incorrect for manning's equation. should be 1 for SI units not 1.486

[@directhubfeexam]

Hi Zack, you are right! Sorry for the mistake. Keep it up man.

[@rickcarr8253]

@@directhubfeexam So answer is B (163 m^3/s)

[@shamanaveed9329u]

I got the answer with manning equation 163.14m3/sec. The value of K in SI system is 1.

[@keloomie]

Hello, When I calculate the Manning Equation I continue to get a different answer, please let me know what I am doing wrong! Q = (K/n)* (A) * (Rh^2/3) * (S^1/2) => (135.09) * (15.90) * (1.08) * (0.104) = 241.25 m^3/sec. Thanks for your time.

[@directhubfeexam]

Hi Kyle, your answer is right. This is my mistake for not double-checking the calculation. The correct answer should be around 243.75 m^3/sec. I will make sure to double-check my work in future videos. Thank you!

[@keloomie]

@@directhubfeexam Your welcome and no worries... Your videos are very helpful and engaging. Keep it up!

[@05adeleon]

@@keloomie I believed the answer is 163.3 m^3/sec, the mistake is we are using metrics units in this problem and the Value of K should 1.0 instead of 1.486 that is on SI units, that will change the result of problem. BTW, These videos are very good and helpful @direct hub

[@andreahodge6539]

When do you use Hazen Williams and when do you use Mannings if its not specified in the problem?

[@directhubfeexam]

Good question. Here is a table summary: snipboard.io/Jbr3C5.jpg

[@Yunalee0605]

Where can I find the roughness coefficient used in the Manning's equation? I only found the Hazen-Williams coefficient in the reference manual...

[@directhubfeexam]

That will be given to you in the problem statement. It is not in the latest 2022 FE Handbook

[@Yunalee0605]

@@directhubfeexam Thank you so much for the quick reply. Your videos are helping me greatly, thank you!

[@directhubfeexam]

@@Yunalee0605 Thanks Yuna! I am glad these videos are helping as you're preparing for your FE! Keep up the great work

[@saeedehlotfi2576]

Hi. Is "C" value gonna be specified in the problem? because there is no table for different types of concrete such as smooth except the one showing 130 for just concrete in FE handbook. This was annoying because with C=130 you will get the wrong answer which is 165 !!

[@directhubfeexam]

Yeah it will always be given to you.

[@saeedehlotfi2576]

@@directhubfeexam thanks. there is another issue I would like to let you know. in the manning equation you mistakenly used USCS K and I think you needed to use the SI unit which is K=1. Anyway, I really thank you for the amazing videos. I am learning a lot from you.

[@directhubfeexam]

@@saeedehlotfi2576 Oh crap, sorry about that. You are right! Thank you for pointing that out. I'm glad you find these videos useful. Keep up the good work!

[@saeedehlotfi2576]

@@directhubfeexam sure. Thanks again

[@danithaman4610]

@@saeedehlotfi2576 the K value for the SI version is 0.849. See page 185

[@knightfn3508]

The k value for Manning is 1 not 1.486 thanks

[@happyluv6]

hi, Where did the seconds come from in the first solution?

[@pinkie224]

Why are the Hydraulic Radius(s) different when using two different equations. Hazen Williams the Rh is pi*4 and in the Manning's equation the Rh is 4.5/4. Thanks

[@directhubfeexam]

Hi David, the hydraulic radius should be the same for both. For a circular pipe at full depth flow, Rh = d / 4, where d = pipe diameter.

[@pinkie224]

@@directhubfeexam What is the correct answer for this problem with the corrections from the comments?

[@directhubfeexam]

@@pinkie224 Hi David, For the first one (Hazen), if you use the same C = 140 (the one I used) you should get: Q = 178 m3/sec For the second one (Manning), I had a mistake by using the wrong K value. K should be 1.0. You should get: Q = 164 m3/sec I'm definitely redo a video for this lol

[@pinkie224]

@@directhubfeexam all good thank you!

[@directhubfeexam]

@@pinkie224 thanks man!

[@foroughi1988]

When we use darcy and when we use manning.

[@directhubfeexam]

- Darcy if friction factor is given - Hazen Williams coefficient is given - Manning if manning coefficient is given

[@madridi891]

sorry S is friction slope, not the earth slope which is the head loss/ the length of the pipe you were right

[@directhubfeexam]

Thanks for clarifying! Good stuff

[@adamrayan7892]

This question dosent have word serach index , its confusing if you not said will be use William q.

[@directhubfeexam]

The Hazen Williams equation applies in this case since the table for the Hazen Williams coefficients is given. I hope this makes sense.

[@kylecatman7738]

You used the USCS units for "K" when it's 1.0 for SI units

[@directhubfeexam]

Sorry about that. Old video that should’ve been corrected. I hope the steps were still clear though. Thank you for practicing with me!

[@danithaman4610]

Why are a lot of videos in this playlist "private." If you dont mind me asking

[@directhubfeexam]

@@danithaman4610 please shoot me a message on through my website DirectHUB.net

[@directhubfeexam]

[e-mail]

[@malaynawingert8783]

Thank you so much!!