Pressure drop in pipe sections
Pressure drop in pipe sections
(OP)
When calculating pressure drop in long pipes I've used the following formula.
dp = 7.57*(q^1.85)*(L)*(10^4)) / ((d^5)*p) (1)
where
dp = pressure drop (kg/cm2)
q = air volume flow at atmospheric conditions (FAD) (m3/min)
L = length of pipe (m)
d = inside diameter of pipe (mm)
where
dp = pressure drop (kg/cm2)
q = air volume flow at atmospheric conditions (FAD) (m3/min)
L = length of pipe (m)
d = inside diameter of pipe (mm)
It's probably something silly buy I've just noticed it doesn't appear the units balance.... what's up with that?
Thanks,
Slader99





RE: Pressure drop in pipe sections
RE: Pressure drop in pipe sections
This came from the engineering toolbox website
The pressure drop in compressed air lines can be calculated by using the formula
dp = 7.57 * q^1.85 * L * 10^4 / (d^5 * p) (1)
where
dp = pressure drop (kg/cm2)
q = air volume flow at atmospheric conditions (FAD) (m3/min)
L = length of pipe (m)
d = inside diameter of pipe (mm)
p = initial abs. pressure (kg/cm2)
They even gicve you a handy calculation box - http://www.engineeringtoolbox.com/pressure-drop-co...
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pressure drop in pipe sections
Any equation with kg/cm^2 must have a cg term buried in there to get the bastardized force units back to a mass. Somehow the developer deleted the friction term (or assumed it as a value that can be rolled into the constant). For "long" pipes I wouldn't use any equation without an explicit friction term. But I wouldn't use any equation that I didn't know the underlying assumptions and could verify that my current case satisfied those assumptions. I use empirical equations all the time, but I always make sure that I'm not extrapolating outside the original dataset. They call that "Engineering".
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Pressure drop in pipe sections
RE: Pressure drop in pipe sections
I agree, we all use some rough and ready calces, but "long" pipes with compresisble fluids need to be analysed properly. A simple fixed formula like this doesn't work.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pressure drop in pipe sections
Independent events are seldomly independent.