Pressure drop thru a flexible hose 1

[presso]

Is there a way to have an estimate of the pressure drop through a 25' hose. I did a first calculation assuming first all the length of the hose was straight (which must be almost never true...) and second assuming that the hose has the same caracteristics of the pipe it is connected to since I could not find a way to obtain a value for K. What would be the difference between my assumptions and the real deal? Is it possible to find tables or data such as pages A26 to A29 of Crane for hoses?

Thank you!

 

[Davidorias]

I think, if your calculation doesn't need much accuracy, it's enough to use the roughness of the inner rubber and the shape coefficients. You can get the values in a fluid mechanics book, or in a good handbook of mechanical engineering.

 

[Cockroach]

Yeah, Davidorias is on the right path. It doesn't matter whether the hose is straight or wound, the gas still needs to travel the bore length, LENGTH being the key here.

Ideally the solution to your problem is a nonlinear relation between the Bernoulli Equation and Continuty. The iterative approach is to assume large, infinite upstream reservoir and thus, velocity of the upstream fluid is zero. Consequently, the Torricelli Principle drops out of the analysis, a statement between the exchange of kinetic and potential energies. You can apply a correction factor to this, typically 3% loss or CV=0.97 for fluids.

With the first approximation to velocity as found above, compute the Reynolds Number. Depending on ReD greater or less than 2300, the transition from laminar to turbulent flow need be established. Given that condition, the friction factor can be computed from the Prandtl Equation and used to compute head loss.

Now you can modify the first iterative solution by the addition of head loss into the Bernoulli Equation and solving for dP, again, upstream velocity is small or "zero". This will give you very reasonable answers within scientific error.

I have written an Excel spreadsheet to take account of computer iterations, therefore the physical convergence of the solution set. Depending on the boundary conditions, usually the convergence is fast, say three or four iterations. You can get into instabilities, but thankfully these are few case studies. Follow the approach I have used above, this is exactly how the code was originally written. Unfortunately the spreadsheet is propietary and not for public release, but the model itself is found in many books dealing with fluid dynamics.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[aviat]

Parker Hannifin produces a Fluid Power Design Engineers Handbook that gives presure drops formulas and charts. It depends on type of hose and fluid as well as other factors, but I'm sure that if you contact them they could help you.

 

[presso]

Thank you all!
I will try all that!

 

[JEB66]

I. E. Idel'chik published a lot of his work in this area ina a book entitled. Handbook of Hydraulic Resistance - coefficients of local resistance and of friction.

 

[TBP]

If it's for air or water, and you just need to ballpark it, pick up a "Handyman In Your Pocket". Lee Valley Tools has them on for about $14 Cdn. An amazing amount of basic reference info for a few dollars.

 

[makeup]

Reading this with interest:

I am sitting here with the hydraulics handbook: It says:

Losses at bends do not lend themselves to definative mathematical analysis and solutions and are invariably based on empirical data. There are changes depending on the radius of curvature or the bend (R) relative to the tube bore (d). As a generalisation there are no effective losses in bends of R/d of 8:1 or greater with turbulent flow: In the case of laminar flow, some loss will be experienced at values of R/d of 20:1 or less, increasing with deacreasing R/d ratio: Approximate values are:

equivalent straight length of pipe = 2xbend for turb
= 5xbend for lamin

hope this helps, how near do you have to be?

 

[presso]

I just needed a rough figure confirming / infirming a pressure problem with operators using some hoses in parallel. Thanks to all your suggestions I obtained a number confirming our hypothesis, the new operating procedure is already in the works!