pressure in 2 tanks
pressure in 2 tanks
(OP)
For this case, i have a distribution chamber which is continuously filled with water with head 7m to feed a clarifier with head 6m. my concern is the pressure for point A in this drawing
.
if it will be the difference between the two levels or will be the total head in the distribution chamber.
note that this system isn't static.
. if it will be the difference between the two levels or will be the total head in the distribution chamber.
note that this system isn't static.





RE: pressure in 2 tanks
You should have been able to solve this by observation.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: pressure in 2 tanks
Ted
RE: pressure in 2 tanks
your drawing is somewhat simplified, but as you say it isn't static, so we have to take your figures on trust.
Your static pressure measurement may well be affected in this instance by velocity head if the velocity is fast enough - see things like this http://www.chemicalprocessing.com/articles/2012/ge...
https://en.wikipedia.org/wiki/Hydraulic_head
You can often ignore it, but when you only have 1m head difference, it's not a lot.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pressure in 2 tanks
Really?????? What in the drawing would make you think that the two levels are possible? For a static condition, regardless of the hole size, the two levels have to be the same if there is a connection between the two tanks. For a dynamic condition, the difference will be the pressure drop between the two tanks. The pressure at point A will NEVER be the average of the two heights. It cannot be.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: pressure in 2 tanks
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: pressure in 2 tanks
Because the OP said so, one side is a tank being "continuously filled with water" so it must be going somewhere and he or she says "note that this system isn't static". If it isn't static then it's dynamic or flowing. The drawing is lacking in important details such as showing the flow in and out or sizes or flow path, but we can only deal with what we get.
The wording is unfortunately underneath his picture, but too many don't seem to have read that bit?
If you assume the bit between them is a pipe and point A is half way along and the pipe is flat then why isn't the head / pressure halfway between the inlet head and the outlet head??
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pressure in 2 tanks
If it were static the situation would be impossible. If it is dynamic then there is something (a valve, a filter, a strainer, an orifice, etc.) in the cross connect and if you take Point A on the downstream side of the dP then it reads the lower value. If you take it on the upstream side of the dP then it is the higher pressure.
Whatever is causing the dP would by its nature be non-steady-state and predicting the pressure within a varying element is pointless. Even if the dP were due to friction in a small pipe, dP due to friction is anything but linear along the pipe (closer to a fifth power function) so picking Point A in the exact center of that pipe would give you a number a lot closer to 6 m than 7 m.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: pressure in 2 tanks
OK, so you're saying there can be a point that is the average of the pressures, then; it's just not in the middle?
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: pressure in 2 tanks
I fully agree -if this was static it wouldn't work.
We don't know anything about the cross connect - it could be a pipe, a small channel or any data such as size, length etc, all we know is that there is a head difference of 1m between the two tanks. Now assuming this is liquid at a steady flow rate then the pressure drop per unit length is the same at the inlet as it is at the outlet if nothing changes ( diameter, surface roughness, shape etc). DP due to friction is constant for a liquid filled pipe.
"Whatever is causing the dP would by its nature be non-steady-state" - how do we know this - the OP has stated a single figure for the head difference, not "varies between X and Y" so it looks pretty steady state to me...
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pressure in 2 tanks
The velocity head can not be measured with a pressure gauge. You need a pitot tube to measure velocity head.
However, the hydrostatic pressure will depend on the elevation. If the pipeline is relatively level, the hydrostatic pressure will be constant. If there is significant elevation difference, then there will be differences in pressure due to the elevation. For those applications, the elevation head will have to be added to the static pressure.
For the application that you have proposed, the total energy will be midway between the tanks. The velocity should be relatively low for this application.
RE: pressure in 2 tanks
For gas (where I usually work, not that it has anything to do with this question), dP/length varies considerably from point to point down a line, and the lion's share of the total pressure drop happens early in the line. I was in a hurry this morning and improperly applied that same logic to liquid. For a gas it won't ever be in the middle. Liquids are generally assumed to have constant density so they will have constant dP/length down the entire line, and the average will occur somewhere very near the center.
LittleInch,
It has been my experience that things (all things in gas, everything but pipe in liquid) that cause a dP are imposing a market basket of forces on the flow and the pressure profile is always shifting within a device like a filter or a control valve. If it is just pipe (can't be a channel because there is non-trivial pressure on it and a channel would drain both tanks), then I suppose Point A would be the average of the two pressures.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: pressure in 2 tanks
Anyway what OP should do is assume that the loss is symmetrical (not entirely true since inlet loss is not the same as outlet loss. If you wish to compensate for this then you need to know the flowing velosity) and then just take half the difference in elevation (then pressure would be in m/in/feet water column) and if necessary convert this to pressure in the unit of his/hers preference
Best regards, Morten
RE: pressure in 2 tanks
flowing velocity should be fairly easy if you know the inlet rate and assume a quasi stationary problem (its SS but it wont go on forever) and the pipe diameter. A good approximation of inlet loss (from pipe to tank) is 1 velocity height and outlet (from tank to pipe) is 1/2 velocity height. Velocity height is V^2/2g and you can deduct that from the measured level difference - the remainder will be the loss in the pipe itself. The half that and add the "outlet" loss and convert (if required) to a pressure unit and you have you answer (assuming that A is a the middle of the pipe connection the two tanks.
Best regards, Morten
RE: pressure in 2 tanks
RE: pressure in 2 tanks
neglecting entry and exit losses