A couple questions regarding pressure drop

[kosig]

First, I am very confused as to the difference, if any, between head loss and pressure drop/loss. Can someone help me?

Also, I know that the Darcy-Weisbach equation for head loss due to friction is h_f=fL/D*V²/2g

and you can plug that into get an equation for delta p that is
dp=fL/D*pV²/2

And this is dimensionally correct. My company says that for our applications all flow will be turbulent Re>4000 and the equation for the friction factor can be approximated to
f=(.0337*v^.25)/(V^.25*d^.25) Which I am assuming is from the Colebrook equation.

So my problem is, when I plug this into the equation for delta p I get an equation which is not dimensionally correct. Why? And what does it mean?

 

[minger]

They are often times used somewhat interchangably. Head typically has units of length, while pressure has the typical force/area units. The terminology probably comes from the Bernoulli Equation, we can be written such that each term has units of pressure
$$p + \rho\frac{V^2}{2} + \rho g z = C$$
or of units of length:
$$\frac{p}{\rho g} + \frac{V^2}{2g} + z = C$$
You'll find that often times in pipe flow or industries such as that, you'll find pumps and suchs in terms of head.

As far as what they physically mean, they are essentially the same thing, one divided by specific weight.

 

[kosig]

Alright that makes sense. What effect does a change in height have on pressure drop? For instance, I have a tube that is carrying a fluid and the tube starts at a pump and connects at a filter below. The tube has a large radius bend.

 

[vajihehdaei]

what is the diffrance between pressure drop and head loss,exactly?thanhs

 

[alphy]

First, let's clarify the difference between head loss and pressure drop. Head loss refers to the decrease in the total energy of a fluid as it flows through a system, due to factors such as friction, bends, and changes in elevation. Pressure drop, on the other hand, specifically refers to the decrease in pressure that occurs as a fluid flows through a system. In practical terms, head loss and pressure drop are often used interchangeably, but it's important to understand the distinction between the two.

Now, regarding your equations, it's important to note that the Darcy-Weisbach equation is a general equation that can be used to calculate head loss in a variety of flow situations, including both laminar and turbulent flow. However, for turbulent flow (Reynolds number > 4000), the friction factor can be approximated using the Colebrook equation, as you mentioned. This is a commonly used simplification that is valid for most practical applications.

When you plug the simplified friction factor equation into the Darcy-Weisbach equation for head loss, you should still get a dimensionally correct equation. If you are getting an equation that is not dimensionally correct, there may be an error in your calculations or in the values you are using for the variables. It's important to double check your work and make sure all units are consistent.

If you are still having trouble, it may be helpful to consult with a colleague or a subject matter expert to review your calculations and provide further guidance. Remember, as scientists, it's important to ensure that all equations and calculations are dimensionally correct in order to accurately represent the physical processes at play in a system.