Odd behavior of chilled water circulator w/ high elevation gain
Odd behavior of chilled water circulator w/ high elevation gain
(OP)
See attached PDF for general piping layout. The idea is that the chiller unit cools the incoming water which is then pumped ~100ft in the air to cool a piece of equipment at higher pressure. My return line is filled with bubbles and unpredictable behavior which I have never observed in lab settings.
I had run this system in a shop before, all components tabletop with minimal elevation gain, with water. I was able to tune the bypass needle valve to hit the flowrate I needed, while staying within our pressure ratings of the pump, and there was no funny business in the water return line (bubbles, cavitation, noise etc).
Now it is installed in "real life" and must move 50/50 water+glycol up 100 feet to cool a piece of equipment in 3/8-1/4 copper tube. The return line has the flowmeter (standard rotameter with clear plastic so bubbles are easy to see). My return line is filled will all kinds of nonsense like chaotic bubbles, jumps, whooshing. Very inconsistent.
At first I thought the bubbles were trapped in the line and working their way out, but after running ~4 hours they are as bad as ever. Is there cavitation in the line, or lowering of the vapor pressure on the return line downwards forming bubbles? I need to nail a certain flowrate and I need to use my bypass needle valve to tune it.
http://files.engineering.com/getfile.aspx?folder=4...
I had run this system in a shop before, all components tabletop with minimal elevation gain, with water. I was able to tune the bypass needle valve to hit the flowrate I needed, while staying within our pressure ratings of the pump, and there was no funny business in the water return line (bubbles, cavitation, noise etc).
Now it is installed in "real life" and must move 50/50 water+glycol up 100 feet to cool a piece of equipment in 3/8-1/4 copper tube. The return line has the flowmeter (standard rotameter with clear plastic so bubbles are easy to see). My return line is filled will all kinds of nonsense like chaotic bubbles, jumps, whooshing. Very inconsistent.
At first I thought the bubbles were trapped in the line and working their way out, but after running ~4 hours they are as bad as ever. Is there cavitation in the line, or lowering of the vapor pressure on the return line downwards forming bubbles? I need to nail a certain flowrate and I need to use my bypass needle valve to tune it.
http://files.engineering.com/getfile.aspx?folder=4...





RE: Odd behavior of chilled water circulator w/ high elevation gain
RE: Odd behavior of chilled water circulator w/ high elevation gain
RE: Odd behavior of chilled water circulator w/ high elevation gain
Let me change the scenario on you. We have a twin system which is acting just about right, maybe such that the siphon analogy doesn't fit..?
System #2
Same plumbing, but the low pressure drop part at height (100ft) is exchanged for a high pressure drop device (many small capillary tubes for radiant heat dissipation).
The outlet pressure is ~175 Psi with flow rates ~.5 L/min, fully closed bypass valve. Same vented reservoir. The flow back to the chiller is more uniform, lacking bubbles. Is a cascading chug-chug-chug happening, but damped out before reaching the rotameter?
If we are in a pinch, it seems to me as long as we can say there is orderly flow to our target device then we can feel confident heat is dissipated (although precise flow rates may not be known - delta T over device IS known however.)
RE: Odd behavior of chilled water circulator w/ high elevation gain
RE: Odd behavior of chilled water circulator w/ high elevation gain
Plug three of the four atmospheric vents you've shown; I'm not sure it matters which three, but I'd certainly plug the two at the top.
Mike Halloran
Pembroke Pines, FL, USA
RE: Odd behavior of chilled water circulator w/ high elevation gain
RE: Odd behavior of chilled water circulator w/ high elevation gain
An alternative is to place a back pressure valve at the foot of your riser to maintain a pressure equivalent to 100ft, about 3bar, 45psi. This will fill your pipe and maintain it above atmospheric pressure. Long term running in this mode will cause damage, fatigue of bends and equipment and is generally a bad idea.
By the way, your pump looks like it is operating way off the end of it's curve, but at that power probably won't matter too much.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Odd behavior of chilled water circulator w/ high elevation gain
RE: Odd behavior of chilled water circulator w/ high elevation gain
Ii suppose the best question would be: is there an off the shelf component to prevent this action which doesn't involve a pressurized reservoir? LittleInch mentions a back pressure valve - does this go on the return side before rotameter?
Photo of rotameter attached.
http://files.engineering.com/getfile.aspx?folder=e...
RE: Odd behavior of chilled water circulator w/ high elevation gain
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Odd behavior of chilled water circulator w/ high elevation gain
RE: Odd behavior of chilled water circulator w/ high elevation gain
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Odd behavior of chilled water circulator w/ high elevation gain
They both have beef with flowmeter placement and air vent valves. Its a little troubling that neither seem to be particularly worried about the 32 foot water column limitation. I might have made some incorrect assumptions about how the chiller and reservoir are vented.
Developing....