Moody diagram is making me moody

[daiv]

I am a hydraulics student and have a question, hoping someone here could help me out. In my specific assignment i am required to determine D of a pipe without the friction factor using moody diagram and the darcy-weisbach equation.

here is the exact question:
A steel pipe (e=0.065mm) 4200m long is to convey oil (kinematic viscosity=5.2x10^-5 m/s^2) at 300 L/s from a resevior with surface elev. 247m to one with surface elev 156m. Theoretically, what pipe diameter size is required?

All the prof says is Iteration is required to find pipe diameter, but i cannot figure out what the process is to guess and check. when do i know i have the right answer?


Any thoughts? anybody?

Thanks!

 

[Valkarie]

The best way to approach this is to use the Darcy-Weisbach equation and the Moody diagram to calculate the friction factor, which you can then use to determine the pipe diameter. To do this, you need to calculate the Reynolds number for the flow of the fluid, and from there you can determine the friction factor from the Moody diagram. Once you have the friction factor, you can use the Darcy-Weisbach equation to calculate the pipe diameter. Once you have calculated the pipe diameter, you can check it by plugging the value back into the Darcy-Weisbach equation to see if it matches the original flow rate. If it does match, then you have found the correct pipe diameter. If not, then you need to recalculate the pipe diameter with a different friction factor and repeat the process until you find the correct pipe diameter.

 

[piercas]

As a fellow scientist, I understand your frustration with the Moody diagram and its use in determining pipe diameter without the friction factor. However, it is important to remember that the Moody diagram is a widely accepted and useful tool in the field of hydraulics. It may seem overwhelming at first, but with some practice and understanding, you will be able to utilize it effectively.

In terms of your specific assignment, the Darcy-Weisbach equation is used to calculate the friction factor, which is then used in the Moody diagram to determine the pipe diameter. The process of iteration involves making an initial guess for the pipe diameter and then using the Darcy-Weisbach equation to calculate the friction factor. This friction factor is then used to find the corresponding pipe diameter on the Moody diagram. If the diameter you guessed is not the correct size, then you will need to adjust your guess and repeat the process until you find the correct diameter.

To know if you have the right answer, you can compare your calculated diameter to the actual diameter of the pipe that is typically used for that flow rate. If they are close, then you have likely found the correct diameter. It is also important to note that iteration may require multiple attempts before arriving at the correct answer, so don't get discouraged if it takes a few tries.

I hope this helps and best of luck with your assignment! Remember to always approach problems with a curious and determined mindset, and you will find success in your studies.