Modern Plumbing - Heaters and PumpsWater/air mixture becomes compressible
Corrosion
Pipe Sizing
Velocities high enough to carry air to the point of separation.
Above 2 ft/sec will carry air bubbles with liquid stream
Below 0.5 ft/sec will allow bubbles to rise by buoyancy in spite of the downward flow
Need effective air control.
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Water
Water
Water velocities greater than 2 feet per second will move entrained air downward. Air will rise in downward water flows at velocities of 6 inches per second or less.
(Gil Carlson. 1981. The design influence of air on hydronic systems. ASHRAE TRANSACTIONS 87(1):1293-1300.)
Air
Air
Venting
Purging
High temperature
Low pressure
Low velocity
Centrifugal action
EFFECT of PRESSURE and TEMPERATURE
Lowest pressure /highest temperature: this is the Point of lowest solubility
Example at 40 psig (ie: right out of faucet)
At 60 degrees F = 8% air by volume
Now heat the water up...
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EFFECT of PRESSURE and TEMPERATURE
Lowest pressure /highest temperature: this is the Point of lowest solubility
Example at 40 psig
At 60 degrees F = 8% air by volume
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EFFECT of PRESSURE and TEMPERATURE
Lowest pressure /highest temperature: this is the Point of lowest solubility
Example at 40 psig
At 60 degrees F = 8% air by volume
RESULT: At 195 degrees F = 4% air by volume....where did the air go? RELEASED INTO THE SYSTEM
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CHILLED WATER SYSTEMS
Lower temperatures so air pockets are less likely to lockup system
Corrosion still a concern
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In Line Air Separators
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Rolairtrol
Rolairtrol Centrifugal Air Separators
Rolairtrol: For 2” thru 24” pipe; ASME Code construction; spinning water stays to outside of vessel, the lighter air rises through middle. The percent of entrained air removed per pass is published (air elimination efficiency)
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