Flow between two tanks 3

[MissFerjo]

I have one verticle tank and one horizontal tank that are connected together in an "L"-shape. There is a hole between the two tanks that will allow oil to move from the horizontal tank to the verticle tank and vice versa. I need to size this hole in order that the oil in the horizontal tank does not exceed a certain level as it heats up and expands, instead, when the oil heats up and expands, it will reach a certain level, thereafter, it will move into the verticle tank. The knowns I have are the density of the oil at various temperatures, the volume of the verticle tank, the volume of the horizontal tank. I planned on making a guess on the hole size, then I was going to calculate the delta P, then based on that, calculate what head is required for that solved delta P. I am very confused if this is the right strategy or not, and if so, exactly how to do it. Any help would be appreciated. Thanks!

 

[MikeHalloran]

Sizing the hole won't do what you seem to want.

Locating the hole, might.

Locate the hole vertically such that its top is at or a little below the level you want to maintain. Then as the oil in the horizontal tank rises, air will be trapped above the oil as soon as it occludes the hole, and any further expansion will cause flow into the vertical tank. The level in the horizontal tank will rise a little as the air is compressed by the pressure represented by the gravity head of the difference in levels between the tanks.

This doesn't work if the top of the horizontal tank is vented in any way.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[MissFerjo]

Thanks for the info. Actually, at the top of the verticle tank is a "spill over" hole. If the oil level in the verticle tank reaches this level it exits through the spill over hole and back into the horizontal tank. In knowing this, does your proposed strategy still work? Thanks!

 

[quark]

I couldn't understand the actual setup about the horizontal and vertical tanks. If the vertical tank is to help the overflowing liquid, you will waste good volume of the vertical tank.

Locating the hole is rather easy. You know the initial volume of oil and the height of liquid column in the tank. You get the final volume of the oil at the increased temperature from the density data and calculate the new liquid column height. If you want to size the hole, check the time rate of volume increase from one height to another height and this is the flowrate you require to pass through the hole.

But this seems to be a redundant exercise unless you explain the system in detail.

Regards,

 

[MissFerjo]

Please see my picture below (I am not sure if there is a way to import a picture or not).
I know the volume of V-Tank.
I know the volume of H-Tank.
I know the density of the oil.
As the oil the heats up, the volume increaes. As this happens, I cannot have the oil in H-Tank go above the solid line. It must evacuate into the V-Tank. If the level in the V-Tank continues to rise, there is a vent at the top that will drain it back into the H-tank. I need to size the hole so the oil flow behaves in this manner. Does this help?

V-Tank
_____
| |
| |
| Spill Over
| ---->
| |
| |
| | ___________ Oil not allowed above line
| | |
| Hole |
| <---- <---- |
| | | H-Tank
|_____|____________|

 

[MissFerjo]

Please see my picture below (I am not sure if there is a way to import a picture or not).
I know the volume of V-Tank.
I know the volume of H-Tank.
I know the density of the oil.
As the oil the heats up, the volume increaes. As this happens, I cannot have the oil in H-Tank go above the solid line. It must evacuate into the V-Tank. If the level in the V-Tank continues to rise, there is a vent at the top that will drain it back into the H-tank. I need to size the hole so the oil flow behaves in this manner. Does this help?

V-Tank
_____
| |
| |
| Spill Over
| ---->
| |
| |
| | __________ Oil not allowed above line
| | |
| Hole |
| <---- <---- |
| | | H-Tank
|____|___________|

 

[quark]

This is where you lost. The main potential for the flow to occur is the differential head. It can be pressure head, static head or velocity head. In your case this is static head of the liquid. Irrespecitive of cross sectional area of the two tanks, height of liquid column remains same when you are equalizing the two tanks. If at all liquid column rises in the vertical tank beyond the equalizing hole, there is a corresponding rise in the horizontal tank.

The height of spill over line in the vertical tank should not be above the oil not allowed line on the horizontal tank. This is irrespective of whether the tanks are pressurized or not, in a gross sense.

Regards,

 

[MissFerjo]

Thanks for the info. I made some calculations, and I was able to come up with the delta P across my orifice (assumed area). Now I need to find the delta h, any idea on how to do that? Can I find the delta h from the delta P, or do I have to find velocity through the hole first? Thanks!

 

[MissFerjo]

Actually, I think I found the answer to my question.

http://www.engineeringtoolbox.com/static-pressure-head-21_610.html

What do you think??
Thanks!

 

[quark]

You didn't answer my 31st March post. Don't get me wrong, we generally don't discuss fundamentals in these forums unless they are tricky and this is also against the rules of the forum.

The link you provided doesn't talk about your specific issue. The head difference is the difference in heights between the maximum possible oil height and the bottom of the hole, if the oil level in the vertical tank is not above the bottom of the hole. Otherwise, you have to consider the height of oil level in the vertical tank instead of hole bottom height.

These two links will be of some help to you.

http://www.efunda.com/formulae/fluids/draining_tank.cfm#calc

thread378-116505

Regards,

 

[MortenA]

MissFerjo

If there is no "check valve" function in your "hole" (the lower one where oil is supposed to flow from horz. vessel (rightmost) to vert. vessel (leftmost)) - then the level in the two vessels will always be the same (the level in the one of the tank may be slightly higher in order to "create head for flow").

If you do have a check valve - then the oil could NOT flow back (left to right) - but it would on the other hand never get above the max level experienced in the rightmost vessel. How could it? What would "drive it"?

Best regards

Morten