Pressure of fluid leaving a syringe

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Discussion Overview

The discussion revolves around determining the pressure of a fluid as it exits a hypodermic needle, with a focus on the relationship between the diameter of the needle and the flow rate. Participants explore relevant equations and principles that could apply to this scenario.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant seeks an equation to calculate the pressure of fluid leaving a syringe, mentioning the diameter of the needle and the flow rate as known variables.
  • Another participant suggests using Bernoulli's equation but notes that additional information, such as the diameter of the plunger and the force applied, is necessary.
  • A different participant argues against using Bernoulli's principle, stating it is inappropriate for this scenario due to the flow not being inviscid and recommends looking into Poiseuille flow instead.
  • A later reply expresses gratitude for the assistance and indicates a resolution to their inquiry, though it does not clarify the specifics of their findings.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the appropriate method to calculate the pressure, with differing opinions on the applicability of Bernoulli's equation versus Poiseuille flow.

Contextual Notes

Participants highlight the need for additional parameters beyond the diameter and flow rate to accurately determine pressure, indicating that assumptions about flow characteristics may be critical.

nerdguy
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I am trying to find an equation to find the pressure of a fluid as it leaves a hypodermic needle when all I have is the diameter of the hole the fluid is discharging from and the flow rate. Can anyone point me in the right direction? I think this should be simple but I have spent a couple of hours trying figure this out. I would like to find out what the pressure would be going into say an IV line of the same dimension as the hole of the syringe if that makes sense. I appreciate any ideas. Thanks for your time.
 
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Using Bernoulli's principle here is a bad idea. Bernoulli only holds for inviscid flow and at these scales, the flow isn't even close to being approximately inviscid. Look up Poiseuille flow. That ought to get you started.
 
Thank you for the help. I think I figured it out. Science rocks!
 

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