# Homework Help: Loss coefficient K in a pipe?

1. Jun 16, 2016

### ipocoyo

1. The problem statement, all variables and given/known data

2. Relevant equations
N/A

3. The attempt at a solution
Usually we are given a table, but how do we calculate the loss coefficient between 2 different pipes with different diameters? In this case, between the 5 and the 3 cm^2 pipes?

2. Jun 16, 2016

### SteamKing

Staff Emeritus
The K-factors for a given diameter of pipe are proportional to the fourth power of that diameter, as described in this article:

http://www.pipeflowcalculations.com/pipe-valve-fitting-flow/flow-in-valves-fittings.php

The usual method is to express the K-factors or equivalents for the system in terms of one common pipe size.

3. Jun 16, 2016

### Staff: Mentor

You should be able to look up the equation for the loss coefficient for the transition between two pipes of different diameter. Do you not have a text book?

4. Jun 16, 2016

### ipocoyo

5. Jun 16, 2016

### ipocoyo

My textbook just says to refer to appendix for K values. It doesn't say anything between the transition of 2 different pipes with different diameters.

6. Jun 16, 2016

### SteamKing

Staff Emeritus
The K-factor for each length of straight pipe is f (L/D). Call one K-factor K-3 for the 3-cm. pipe and the other K5 for the 5-cm. pipe.

Now, according to the relation

$\frac{K_a}{K_b}=(\frac{d_a}{d_b})^4$

If you make Ka = K3, then Kb becomes K5. Putting the value of the K-factor for the 5-cm. straight pipe into the relation will give you the equivalent K-factor as if the 5-cm. pipe was actually 3-cm. pipe.

7. Jun 17, 2016

### Staff: Mentor

What geometries does it give K values for?