Roughness value for rubber hose

[packdad]

I see this question come up from time to time, but I don't think I've ever seen a definitive answer. I didn't find a good answer using the keyword search function. Anyone know what range of roughness values (or friction factors) to apply to rubber hose for the purpose of calculating flow rates? Would clean commercial steel pipe be a good approximation?

 

[sjohnr]

Is it really rubber hose or some type of plastic?

I have used an absolute roughness figure of 0.7 micron in the past for hose having a liner extruded in nylon.

 

[packdad]

Well, you know, I'm not entirely sure. It's red and it's flexible, but it's also pretty smooth. I guess it could be either...?

 

[sjohnr]

Any markings? Manufacturer? Part number?