Anyone work with liquid flow, tubing size flow dependence

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Discussion Overview

The discussion revolves around the effects of tubing size on liquid flow rates in a closed system involving a pump and a reaction vessel. Participants explore the relationship between tubing diameter, flow rate, and pressure dynamics, considering both volume and mass flow rates.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether a change in tubing size will affect flow rate due to pressure, noting that the system is closed and will equilibrate over time.
  • Another participant asserts that the volume flow rate will remain the same, as the fluid has no alternative path, despite the differing diameters of the tubes.
  • A third participant discusses that while mass flow will remain constant, volume flow may vary if the liquid is pressure sensitive, and notes that flow velocity will be lower in a larger pipe compared to a smaller one.
  • This participant also raises concerns about potential issues such as cavitation and entrained vapor bubbles at higher flow velocities in the smaller pipe.
  • A later reply expresses gratitude for the clarification, indicating some initial confusion about the topic.

Areas of Agreement / Disagreement

Participants express differing views on how tubing size affects flow rates, with some asserting that volume flow remains constant while others highlight potential complications related to flow velocity and pressure sensitivity. The discussion does not reach a consensus.

Contextual Notes

Participants acknowledge that the behavior of the liquid may depend on factors such as flow velocity and the properties of the liquid, but these aspects remain unresolved in the discussion.

rwooduk
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I want to use a pump to have solution moving through a reaction vessel at a set flow rate. But the problem is the outlets FROM the pump are very small 1/6" (0.4cm) inner diameter, and the vessel INLET is GL14 thread size (1cm inner diameter).

Schematic

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Problem

VyeU6OI.gif


Pump

https://www.coleparmer.co.uk/i/mn/7316033

My question is will a change in tubing size effect the flow rate due to pressure? My initial thoughts are yes, however it is a closed system, so although there is pressure present as the pump "pushes" the liquid through it will after a short period of time equibrilate.

However when I visualise it the flowing fluid from the small tube will disperse into the big one and there will not be the same flow rate in the bigger tube.

Any thoughts on this?
 
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rwooduk said:
However when I visualise it the flowing fluid from the small tube will disperse into the big one and there will not be the same flow rate in the bigger tube.
Volume flow rate will be the same (it's got nowhere else to go).
 
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Mass flow will remain the same . Volume flow will usually remain the same unless the liquid is pressure sensitive (for example soap suds or a volatile chemical)

Flow velocity will be lower in large pipe than in small pipe .

Apart from the above it depends on the flow velocity in the small pipe . Low velocity probably no problems at all . Higher velocity possible problems with cavitation and entrained vapour bubbles .
 
Last edited:
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^^ okay many thanks for the comments! not sure why I got confused on this one, but thanks again for helping clear it up.
 

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