Optimizing Flow in a Networked Manifold System

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Discussion Overview

The discussion revolves around optimizing airflow in a networked manifold system with multiple blowers and varying inlet and outlet configurations. Participants explore the implications of inlet diameter on flow rates, the effects of system design on performance, and the relationship between blower specifications and airflow capacity. The conversation includes both theoretical considerations and practical applications.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning
  • Experimental/applied

Main Points Raised

  • Some participants assert that conservation of mass dictates the inlet flow must match the total outlet flow, raising questions about the feasibility of achieving high flow rates through a small inlet.
  • Others challenge the initial flow rate assumptions, suggesting that the blowers' performance may not support the claimed flow rates due to the reduced cross-sectional area at the inlet.
  • A participant proposes that the maximum flow through a 3-inch orifice could be limited to 1894 scfm under specific conditions, indicating the need for detailed analysis rather than simple estimations.
  • One participant introduces a new scenario involving larger fans and a diverging duct shape, asking for expected flow rates under these conditions.
  • Multiple requests for system drawings indicate a need for visual clarification of the described setups, suggesting that the current descriptions may be insufficient for accurate analysis.
  • A participant mentions running an airflow analysis program, providing a specific pressure drop result but expressing uncertainty about its application to fan performance.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of achieving high flow rates through the given inlet size, with no consensus reached on the actual performance of the system or the implications of the design choices made.

Contextual Notes

Limitations include the lack of specific blower performance curves, assumptions about air density, and the need for detailed analysis to accurately predict airflow behavior in the described systems.

dilipbhanu
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Hi, A chamber (manifold type cylinder) has 1 inlet and 8 outlets of 3 inch diameter each.

8 suction blowers are connected to the chamber's outlet. Each blower's suction flow rate is 1000 cfm.

what will be the flow rate through the inlet of the chamber (diameter = 3 inches).

Will the inlet flow rate reduce because of reduced cross section? What should be the chamber's inlet diameter to receive 4000, 6000 and 8000 cfm ?
 
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Is this homework?
 
Dear DrClaude,

I am a individual and have been breaking my head for months to solve this. Appreciate some help
 
Obviously, conservation of mass requires that if the outlet flow is 8,000 CFM, the inlet must also be 8,000 CFM (assuming the air density doesn't change much). But the flow numbers sound impossible for such a small inlet unless the blowers are extremely high static pressure. Are those just the ratings or have you actually measured the flow? Do you have the specs of the blowers? Do you have a sketch of the system you can post? What is the purpose/function of the system?

I'm moving the thread to mechanical engineering.
 
Dear Russ_watters,

Each blower with a inlet port of 3 inches (area 12.56 sq inches) pulls 1000 CFM when open to atmosphere. when 8 blowers are connected in parallel in a chamber, they will require 12.56*8=100.48 sq inches of cross section inlet

But the chamber inlet is 3 inches (12.56 sq inches) means the cross section area for the network of blowers has reduced. Will the 8 blowers be able to pull 8000 cfm through the 3 inch inlet or will the cfm of blower network reduce ?
 
dilipbhanu said:
Each blower with a inlet port of 3 inches (area 12.56 sq inches)
Is that 3" or 4" diameter? Check your numbers.
...pulls 1000 CFM when open to atmosphere. when 8 blowers are connected in parallel in a chamber, they will require 12.56*8=100.48 sq inches of cross section inlet

But the chamber inlet is 3 inches (12.56 sq inches) means the cross section area for the network of blowers has reduced. Will the 8 blowers be able to pull 8000 cfm through the 3 inch inlet or will the cfm of blower network reduce ?
The airflow will certainly be greatly reduced. How much depends on the exact specs of the fans and ducting. This is not something you can rule-of-thumb: a detailed analysis is required.
 
If this problem is treated as a box with a 3" diameter orifice, with an orifice coefficient of 1.00, in one face and with the blowers inlets directly connected to the box; then, even if the blowers' were capable of reducing the box interior pressure to 0 psia, assuming an (atmospheric) 14.7 psia, 65°F air source, the maximum possible flow through that 3" orifice would be choked flow at 1894 scfm. (I have an orifice flow program for just this type of analysis)
 
Last edited:
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Sorry for reverting late. please allow me to redraft the question with some updated data

I have 2 exhaust fans that can handle 1000 cfm each. Diameter of each fan is 12 inches. I need to fit these 2 inside a duct in parallel. Hence the duct cross section will be 12x24. But the suction side of the duct can only be 12x12. Hence we see that the duct from the inlet to where the 2 blowers sit, is a diverging shape. If I fit a bell mouth at the inlet that is 12x12, the shape looks like a venturi.

Q1. In this given condition, what is the ideal cfm that i can expect ?
Q2. What if there were 4 or 6 fans in parallel ?

Regards
Dilip
 
Please provide a drawing of the entire system. I can't picture it from your description and can't tell if you've made changes or just added elements to it.
 
  • #10
russ_watters said:
Please provide a drawing of the entire system. I can't picture it from your description and can't tell if you've made changes or just added elements to it.

Dear sir,
please have a look at the rough drawing and advice
 

Attachments

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  • #11
I have run an air flow analysis program using a round orifice with an equivalent area to your 12" x 12" square restriction and an orifice factor of 1 (100% efficient) that shows that there will be a best case 1 psia pressure drop across that restricted entry at a 20,000 scfm flow rate. Unfortunately, I don't know how that result may be applied to determine its effect on the fans' performance.
 
  • #12
dilipbhanu said:
Dear sir,
please have a look at the rough drawing and advice
Is this still connected to the system described in the first post? Do you have a fan curve for the fans? At what static pressure can they produce 1000 CFM?
 

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