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It is hard to say whether the added duct solved more of the problem or if the plenum extension did. Extending the plenum indicates the engineer thought system effect was adding too much pressure drop and reduced the system effect (pressure drop) by extending the plenum. Dual feed loops are not all that uncommon in commercial installations and are used in large chilled water and air systems to reduce fan or pump horsepower. Another advantage especially in water systems is that properly designed back feeding the coils is possible when part of the system needs to be shut down for repairs.
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The hose going around the world depends on water volume Vs pipe or hose size. Friction loss drops out if the pipe is big enough because water seeks it's own level which is the science behind it. When a river receives a lot of water from rain it develops a hump which the laws of physics tells us it cannot not hold in one place. The hump develops it's own head because the water insists on being level. As a result the hump trying to level out helps accelerate water flow. If you pump water into the pipe you have developed enough head to create the hump which will level out. Assuming the water doesn't evaporate it will eventually come out the other end because friction loss gives way to the water seeking to be level. I don't know how many years it would take.
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Water friction loss in pumped mains is calculated assuming the entire hydraulic radius of the pipe is wetted. In the example of the level pipe going around the world this will not happen so friction loss calculations are out the window.
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Originally Posted by
WAYNE3298
Water friction loss in pumped mains is calculated assuming the entire hydraulic radius of the pipe is wetted. In the example of the level pipe going around the world this will not happen so friction loss calculations are out the window.
Don't you think friction losses would apply until the pump runs out of head like in horizontal applications?. Seems the water would begin to level and any pressure would be lost. I'm applying what happens in a horizontal pipe loop. Friction still needs accounting for. Even a trickle has resistance Que'No?!
I'm sill looking for a hose.
About the duct: The plenum extension was only enough to accommodate the new duct for the doughnut. I thought the reverse thinking was clever. Like if Mohamed won't come to the mountain, bring the mountain to Mohamed.
Some people do this reversal almost automatically when confronting a problem. It's uncommon. There was often a saying in meetings to "Think out side the box". This can be said forever but still won't get many results. It's called creativity and is rare even though the solution is often obvious.
I like surprises.
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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Friction head can only exist as long as water is moving thru the pipe. Friction head cannot stop all water flow because the velocity would be zero resulting in zero friction head. Vertical static head can stop all flow but friction head can't.
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There we go, that's how you say it. As I mentioned elsewhere, I intuitively knew that a hose around the world would not create so much friction loss as to create no flow.
I was going to hit it with a simple empirical example, but this is of course the better way to say it.
Originally Posted by
WAYNE3298
Friction head can only exist as long as water is moving thru the pipe. Friction head cannot stop all water flow because the velocity would be zero resulting in zero friction head. Vertical static head can stop all flow but friction head can't.
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OK y'all, the question is not done yet.
Let's say we change the medium from a fluid to air. An air tight duct, say glued PVC, is run
around the same world. Remembering fan laws and pump laws apply. Would you expect any air to come out the other end?
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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The first thing you have to know is that fans and pumps have no brains, they do what the system allows. If the system allows a fan to put air into a duct that is leak proof and it doesn't come out the other end where does it go? A fan or pump can approach shut-off but friction loss by it's definition cannot stop all airflow because you HAVE to have velocity to develop friction. It may take 8 or 10 years but without leaks the air has to come out the other end.
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Originally Posted by
hvacker
OK y'all, the question is not done yet.
Let's say we change the medium from a fluid to air. An air tight duct, say glued PVC, is run
around the same world. Remembering fan laws and pump laws apply. Would you expect any air to come out the other end?
I still stand by my first rebuttal. Friction loss cannot cause flow to stop completely. If you were to graph it out, it would appear hyperbolic, getting infinitely closer but never reaching "zero flow".
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When you calculate and show friction loss graphically it becomes a system curve. That doesn't tell you where the flow would end up being in this case. What it would tell you is the dynamic static pressure you need for various airflows. Once the system curve crosses the fan curve you are above the design static pressure needed for the fan to deliver design airflow. There are two system curves calculated for a fan which are design and actual. The actual system curve is calculated from field measurements. I don't know of any way to calculate airflow that causes friction loss equilibrium.
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Originally Posted by
WAYNE3298
The first thing you have to know is that fans and pumps have no brains, they do what the system allows. If the system allows a fan to put air into a duct that is leak proof and it doesn't come out the other end where does it go? A fan or pump can approach shut-off but friction loss by it's definition cannot stop all airflow because you HAVE to have velocity to develop friction. It may take 8 or 10 years but without leaks the air has to come out the other end.
I'll play with this awhile. What I'm pondering is we know that we can create system in a duct where static pressure doesn't exist and only velocity exists as In some factual situations the air will collapse into a jet. We've talked about this earlier. With a vena contracta situation, where duct friction won't normally apply (I said normally as you might have some secrete sauce where it does)
All that's needed to deal with the ?? is when the velocity pressure reaches zero does all air movement cease? Or is your position that the velocity pressure never reaches zero? If there were a super instrument that could measure any pressure would I expect to see movement? Maybe a super thermometer as where there's movement there should be some temperature.
This exploration is interesting. Thanks to all for indulging me.
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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Originally Posted by
shellkamp
I still stand by my first rebuttal. Friction loss cannot cause flow to stop completely. If you were to graph it out, it would appear hyperbolic, getting infinitely closer but never reaching "zero flow".
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About your curve: Never reaching zero has a built in problem. In our experience everything has a zero.
I remember a question where a ball was being held four feet off the ground and dropped. The question was does the ball ever hit the ground? In our experience, of course it does because we can set up experiments to prove it does.
But because mathematically every distance can be cut in half, the math says the ball never does reach the ground.
One solution said that there is a moment in space that can no longer be divided. Not all agree.
Because the graph has no zero I'll take that to mean your on the side of the ball never reaching the ground.
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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hvacer,
I agree this is an interesting conversation. Another theory about dropping the ball is if you drop it enough times it will eventually go up instead of down. I don't believe that for a second but some professor came up with it and I thought you might find it amusing. The ball falling half way to the ground is one way used to explain half life of uranium ect. The system curve zero is without the fan running so the curve starts at the zero-zero point on the graph. What the system curve tells you is how much pressure you need to obtain a specified amount of airflow. The curve itself never ends but has no use beyond desired airflow. The flow at shut-off head can also be zero but can only happen if you have a shut-off valve. Yes there will be velocity pressure in our example albeit pretty small. Shut-off head (or zero airflow with the fan running) doesn't fall on the system curve but instead is represented on the fan curve where it meets the Y axis.
The orifice flanges that create the vena contracta do have pressure drop. Orifice flanges are not only used for flow measurement but also to restrict air and water flow. The only place I know of where restrictive orifices are still used is in commercial de-aerators for non-condensables venting.
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Originally Posted by
WAYNE3298
The first thing you have to know is that fans and pumps have no brains, they do what the system allows. If the system allows a fan to put air into a duct that is leak proof and it doesn't come out the other end where does it go? A fan or pump can approach shut-off but friction loss by it's definition cannot stop all airflow because you HAVE to have velocity to develop friction. It may take 8 or 10 years but without leaks the air has to come out the other end.
I'll play with this awhile. What I'm pondering is we know that we can create system in a duct where static pressure doesn't exist and only velocity exists as In some factual situations the air will collapse into a jet. We've talked about this earlier. With a vena contracta situation, where duct friction won't normally apply (I said normally as you might have some secrete sauce where it does) all needed to deal with the ?? is when the velocity pressure reaches zero does all air movement cease? Or is your position that the velocity pressure never reaches zero? If there were a super instrument that could measure any pressure would I expect to see movement? Maybe a super thermometer as where there's movement there should be some temperature.
The reason in my mind as to why the air/water never reaches the other end is also air. Atmosphere would become the major resistance. Just like my race car only able to ge so fast because it can't overcome air resistance. For the race car there are many other limiting reasons.
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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I think I ended up with two partial posts. Teach me to eat dinner in between posts. Or I'm getting old and am repeating myself.
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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Overcoming atmospheric air pressure is not a factor but remember air resistance doesn't stop your race car but does limit how fast you can go. Remember in a vena contracta the airstream quickly recovers from the diameter reduction, if it didn't it couldn't be used for flow measurement and the airstream contracts because it hits a sudden reduction in the duct which temporarily increases the velocity because the same amount of air is moving thru less area. You need to reduce the duct area suddenly to generate the vena contracta and the reduction creates the velocity needed but also adds pressure drop. I have heard several engineers argue that the beta ratio dictates the outcome. That is one discussion I stayed clear of because that statement told me they had never calculated the size and related pressure drop expected to determine air or water flow. Beta ratio is the baseline for calculations but there are empirical values that are part of the final sizing. Remember also that the air entering the fan is at atmospheric pressure and you add pressure at the fan discharge in order to move it.
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Originally Posted by
WAYNE3298
hvacer,
I agree this is an interesting conversation. Another theory about dropping the ball is if you drop it enough times it will eventually go up instead of down. I don't believe that for a second but some professor came up with it and I thought you might find it amusing. The ball falling half way to the ground is one way used to explain half life of uranium ect. The system curve zero is without the fan running so the curve starts at the zero-zero point on the graph. What the system curve tells you is how much pressure you need to obtain a specified amount of airflow. The curve itself never ends but has no use beyond desired airflow. The flow at shut-off head can also be zero but can only happen if you have a shut-off valve. Yes there will be velocity pressure in our example albeit pretty small. Shut-off head (or zero airflow with the fan running) doesn't fall on the system curve but instead is represented on the fan curve where it meets the Y axis.
The orifice flanges that create the vena contracta do have pressure drop. Orifice flanges are not only used for flow measurement but also to restrict air and water flow. The only place I know of where restrictive orifices are still used is in commercial de-aerators for non-condensables venting.
I know students need to watch what they say to a Professor. I remember saying to my Philosophy Professor, when a question about consciousness came up and I suggested that consciousness is in everything. "Do you mean that this chair has consciousness?"He asked me. I said "It seems to have enough consciousness to remain a chair."
Then he kicked the chair across the room.
He had everyone's attention at that point.
Any student that argues with a Professor has a distinct disadvantage. The student is not aware that they are a mouse and the Professor is a cat.
The question of how high is up? Some might say up goes on forever only to find out up is 274 miles. After that it becomes "out".
Maybe just hold fast to the idea that there are just tendencies to exist.
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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The statement I liked was "if you reach the end of space what is on the other side". Another one said what is electricity and one guy raised his hand to give him an answer. The prof yelled "the smartest person in the world doesn't know what electricity is and your going to tell me". He was really a fun person and it made sense when he explained what he meant.
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Originally Posted by
hvacker
About your curve: Never reaching zero has a built in problem. In our experience everything has a zero.
I remember a question where a ball was being held four feet off the ground and dropped. The question was does the ball ever hit the ground? In our experience, of course it does because we can set up experiments to prove it does.
But because mathematically every distance can be cut in half, the math says the ball never does reach the ground.
One solution said that there is a moment in space that can no longer be divided. Not all agree.
Because the graph has no zero I'll take that to mean your on the side of the ball never reaching the ground.
I'm certainly not speaking of theoretical physics here. So long as that fan is running and airflow is not fighting gravity (going up) - the flow will never actually get to zero.
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Originally Posted by
WAYNE3298
The statement I liked was "if you reach the end of space what is on the other side". Another one said what is electricity and one guy raised his hand to give him an answer. The prof yelled "the smartest person in the world doesn't know what electricity is and your going to tell me". He was really a fun person and it made sense when he explained what he meant.
Not wanting to exactly go there but I seem to remember an explanation of that question was (and maybe just my mindset in some mid 60's chemical abyss) but space being visualized as living on the film of a bubble where inside the bubble is empty time and empty space. So in my little rocket ship I simply glide on film of the bubble and never reach the end.
I also remember reading in a book by the healer Edgar Cayce was similar to, Man demands a beginning so here's one. No end in sight,
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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