Fluid Dynamics of a fuel cell??
11-26-10, 10:46 PM
#1
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Fluid Dynamics of a fuel cell??
Ok so i got my new fuel cell i have the 2 sump holes on the bottom and the vent on top.
my problem is will the return work against sixteen gallons, im thinking no.
if this is true i thought i might run a tube from the bottom to above the tank and use that as a vent. and run the return through the vent on top.
I think i got it right but just checking with you guys to double check it.
my problem is will the return work against sixteen gallons, im thinking no.
if this is true i thought i might run a tube from the bottom to above the tank and use that as a vent. and run the return through the vent on top.
I think i got it right but just checking with you guys to double check it.
11-26-10, 11:28 PM
#2
Not sure if the return on the bottom would be a problem (I assume it would be ok, return usually has a tube that drops down so the fuel doesnt constantly waterfall back into the tank), but the vent idea definately wont work.
Vent has to be above the fuel level or else the fuel will get pushed out instead of air/vapor.
Vent has to be above the fuel level or else the fuel will get pushed out instead of air/vapor.
11-26-10, 11:35 PM
#3
My return in my cell goes back in the top but it feeds into a surge box with trap doors so it always is feeding back below the surface of the fuel. What that means to your problem, I don't know, but I would give it a try. At worst it may just effect your fuel pressure regulator setting to compensate for a little 'backpressure' in the return system. My gut feeling says it will be no problem.
11-26-10, 11:50 PM
#4
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Not sure if the return on the bottom would be a problem (I assume it would be ok, return usually has a tube that drops down so the fuel doesnt constantly waterfall back into the tank), but the vent idea definately wont work.
Vent has to be above the fuel level or else the fuel will get pushed out instead of air/vapor.
Vent has to be above the fuel level or else the fuel will get pushed out instead of air/vapor.
even if the vent attaches from the bottom of the tank as long as it is ran above the tank like say 12 inches above it it would not be an issue.
11-26-10, 11:54 PM
#5
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My return in my cell goes back in the top but it feeds into a surge box with trap doors so it always is feeding back below the surface of the fuel. What that means to your problem, I don't know, but I would give it a try. At worst it may just effect your fuel pressure regulator setting to compensate for a little 'backpressure' in the return system. My gut feeling says it will be no problem.
Im going to put a flow pressure tester on the return line and get the exact number so i can then get the math
Return Pressure VS. 16 gallons of standing fluid????
If the pressure can force the fuel back in then ill be happy and im not oppesed to puting a micro inline pump on the return line but thats more math.
11-27-10, 12:22 AM
#6
I don't think there would be a problem running the return to the bottom, that is also the source (= pressure).
11-27-10, 12:57 AM
#7
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hmmmm, well i can always drill another hol for venting if im really worried but a confirmed yes it will work from a person who has this set up, is what im lookin for
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11-27-10, 02:27 AM
#8
If you route the return to the bottom of the tank, it will have to over come the 'head' pressure. Head is the standing column of fuel by weight that the returning fuel has to push against. To calculate the head, find the weight of fuel in lbs/cu.ft., divide by 12 cubed then multiply by the depth of the tank. That will yield the weight of head in psi.
For example, water weighs a little over 64 lbs/cu. ft.. Divide by 12 cubed, (1728), yields .037 lbs/cu. in. Multiply that by say a 10" tank depth and the head is .37 psi. Fuel is lighter than water but I don't recall it's specific weight.
If you don't want to do all the math, add a return line with a drop tube within an inch of the bottom of the tank as close to the feed out line as possible. On the other hand, an approximately 1/3 psi of head isn't much to push or fight against for the returning fuel as it will also have some head along with it's return psi because it's returning from a higher level than the bottom of the tank.
You now know most of what I still remember from fluid dynamics taken 20 years ago, lol.
For example, water weighs a little over 64 lbs/cu. ft.. Divide by 12 cubed, (1728), yields .037 lbs/cu. in. Multiply that by say a 10" tank depth and the head is .37 psi. Fuel is lighter than water but I don't recall it's specific weight.
If you don't want to do all the math, add a return line with a drop tube within an inch of the bottom of the tank as close to the feed out line as possible. On the other hand, an approximately 1/3 psi of head isn't much to push or fight against for the returning fuel as it will also have some head along with it's return psi because it's returning from a higher level than the bottom of the tank.
You now know most of what I still remember from fluid dynamics taken 20 years ago, lol.
11-27-10, 10:47 AM
#9
The fuel return at the bottom doesn't have to contend with "16 gallons," it only has to contend with the relative pressure based on the depth of the fuel, times the density of gasoline, times force of gravity over a 1 square inch area (if you want your answer in PSI).
The formula that gives the P pressure on an object submerged in a fluid is:
P = r * g * h
where
r (rho) is the density of the fluid,
g is the acceleration of gravity
h is the height of the fluid above the object
P = r * g * h
where
r (rho) is the density of the fluid,
g is the acceleration of gravity
h is the height of the fluid above the object
Example: Based on the density of sea water (64.1lbs/ft^3 or 0.038lbs/in^3), pressure increases by one atomsphere (15.4PSI) for every 33 feet of depth.
Looked at another way, a column of sea water 1 sq. inch in cross section and 33 feet high weighs 15.4 lbs at one G. That works out to 0.4667 pounds per foot of depth.
If your tank were one foot deep, then, and filled with sea water, the return line at the bottom of the tank would see a total static pressure (if the tank is properly vented!) of less than 1/2 PSI relative.
Gasoline's a lot less dense than sea water (roughly 0.026lb/in^3).
Figure 0.026 times the depth of your fuel cell and you'll have the static pressure in PSI at the bottom of a full (and vented) cell.
Keep in mind that if your lines drop additional inches, you have to count those. But you also get 'credit' for the height above the tank bottom at which your fuel enters the return.
11-27-10, 11:13 AM
#10
If the regulator and carb are higher than the tank, the pressure in the return line will be higher than at the bottom of the tank. The source and the return being in the same location equalize each other. If the carb was lower than the tank, the pump would have the positive pressure of the feed line to equalize the negative pressure of the return.
Running the return line from the top of the tank to near the bottom(stock configuration) is the same as running the line to the bottom, the pressure is the same however you get there.
Divin beat me to it with a more scientific explanation. I need to type faster.
Running the return line from the top of the tank to near the bottom(stock configuration) is the same as running the line to the bottom, the pressure is the same however you get there.
Divin beat me to it with a more scientific explanation. I need to type faster.
11-27-10, 01:11 PM
#11
Lives on the Forum
Deadhead the carb so you can eliminate the need for a return. Not sure how to do this, but heard it was simple. Sterling owe you any favors? 
.
.
11-27-10, 09:10 PM
#14
Or just run it like it's designed, I don't think they designed and built it wrong.
In the stock configuration the supply and return are at the bottom of the tank, they only enter at the top.
Calculations are not needed, with the supply and return in the same place you're just moving fluid in a loop.
In the stock configuration the supply and return are at the bottom of the tank, they only enter at the top.
Calculations are not needed, with the supply and return in the same place you're just moving fluid in a loop.
11-28-10, 02:03 PM
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Or just run it like it's designed, I don't think they designed and built it wrong.
In the stock configuration the supply and return are at the bottom of the tank, they only enter at the top.
Calculations are not needed, with the supply and return in the same place you're just moving fluid in a loop.
In the stock configuration the supply and return are at the bottom of the tank, they only enter at the top.
Calculations are not needed, with the supply and return in the same place you're just moving fluid in a loop.
11-29-10, 10:14 PM
#16
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the tank i think wsa designed with a v8 in mind the fuel line size out of the tank is half inch. im reducing it to my sizes and thats the kicker will that effect return flow.
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