Discharge Blower Reverse Flow
Discharge Blower Reverse Flow
(OP)
In discussion with my colleagues regarding the possibility of installing a dilution air blower on a vent stack, the following question arose:
Let's say a dilution blower is provided that has a deadhead pressure of, say, 3 psig, and the vent stack is in the middle of relieving an emergency event. The relief event is such that the stack pressure is 10 psig at the inlet due to the relieving gas flow (close to where the dilution air blower would discharge into the stack).
My colleagues seemed to think that by providing a "Y" connection would somehow prevent backflow through the blower. I contended that unless the stack were provided with some kind of venturi or other design to accelerate the gas and drop local pressure below 3 psig, the blower would experience back-flow through it.
My overall contention and understanding of a blower is that if discharge pressure is higher than the deadhead pressure, it will experience backflow.
Let's say a dilution blower is provided that has a deadhead pressure of, say, 3 psig, and the vent stack is in the middle of relieving an emergency event. The relief event is such that the stack pressure is 10 psig at the inlet due to the relieving gas flow (close to where the dilution air blower would discharge into the stack).
My colleagues seemed to think that by providing a "Y" connection would somehow prevent backflow through the blower. I contended that unless the stack were provided with some kind of venturi or other design to accelerate the gas and drop local pressure below 3 psig, the blower would experience back-flow through it.
My overall contention and understanding of a blower is that if discharge pressure is higher than the deadhead pressure, it will experience backflow.
RE: Discharge Blower Reverse Flow
RE: Discharge Blower Reverse Flow
An interesting example I came across recently is the Tesla valve which is essentially a solid state diode to gas flow.
RE: Discharge Blower Reverse Flow
RE: Discharge Blower Reverse Flow
RE: Discharge Blower Reverse Flow
You seem to be saying that even if I had this Y connection, but it discharged to atmosphere (no blower), there would be no flow through it because the momentum of the relieving stream would prevent the gas from “turning around”. I find that to be an unbelievable assertion. Adding a blower to that pipe only changes the static pressure the gas flow is fighting against. You are essentially asserting, if I understand you correctly, that gases will not always flow from high pressure to low pressure. If that is a fundamental error on my part, please explain why.
We are currently designing this stack to handle a range of relief conditions, and dilution air is one means of achieving sufficient velocity for dispersion for some of the smaller relief cases. This question arose during that discussion regarding what kind/pressure the blower would be needed.
RE: Discharge Blower Reverse Flow
Daniel
Rio de Janeiro - Brazil
RE: Discharge Blower Reverse Flow
But not 10 psig. No way.
without an NRV suitably rated you will get backflow.
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