Does the small size of a hole affect fluid flow rate?

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Discussion Overview

The discussion centers on the effect of orifice size on the fluid flow rate of oil between two chambers. Participants explore theoretical considerations, potential experimental setups, and the implications of fluid dynamics principles, particularly in relation to small diameter holes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant seeks to calculate the fluid transfer rate through a small orifice and notes the need for additional information such as oil density for a precise solution.
  • Another participant suggests considering the Reynolds number to determine the flow type, indicating that flow is laminar for Re < 2300 and turbulent for Re > 2300.
  • A different participant references ASME MFC-14 for flow through small orifices but expresses doubt that the orifice size in question is adequately covered, particularly regarding the coefficient of discharge (Cd) at small Reynolds numbers.
  • One participant proposes setting up an experiment with a pressurized reservoir and weighing scale to measure output flow, mentioning existing research on the flow of viscous substances through small holes.
  • A participant raises a question about the initial conditions of the chambers, specifically whether chamber #2 is full of air, which could complicate the flow dynamics.
  • Another participant clarifies that both chambers are full of oil and assumes the flow will be very slow due to a weak spring.

Areas of Agreement / Disagreement

Participants express differing views on the setup and implications of the flow dynamics, particularly regarding the initial conditions of the chambers and the applicability of existing flow equations to very small orifices. No consensus is reached on the best approach or solution.

Contextual Notes

The discussion highlights uncertainties regarding the applicability of standard equations for flow through orifices at small diameters, the significance of Reynolds number, and the initial conditions of the fluid chambers. These factors remain unresolved.

Who May Find This Useful

This discussion may be of interest to those involved in fluid dynamics, engineering applications related to fluid flow, and experimental physics, particularly in contexts involving small orifices and viscous fluids.

pbiebach
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I would like to calculate the rate at which fluid(oil) is transferred from one chamber to the other.
Note the orifices is in the range of 0.0030 to 0.0760 in I'm wondering if the very small size of this hole requires any special consideration.

http://myimgs.net/images/oyfi.jpg

I realize more info such as oil density and dimensions are required for a exact solution, however I would like to determine a general solution into which I can substitute these values.
Any hints to get me on the correct path or even better a sample calculation would appreciated.

Note this is not a homework question.
 
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You might consider the type of flow to be expected for oil flowing through the small diameter hole using the definition of Reynolds number and the physical properties of the type of oil considered. If Re < 2300 flow is laminar, above it is expected to be turbulent.
Go on from this point.
 
ASME MFC-14 handles flow through small orifi but I am thinking that this is even too small for that. I have a copy at my desk which I don't have access to right now. That being said, the flow will still follow orifice equations. The tough part is to find out what the Cd of the small orifice is, especially with what will be pretty small Re.
 
I suppose a real experiment would not be difficult to set up: pressurized reservoir, small orifice and weighing scale (to measure output flow) On the other hand, there must have been done extensive research on flow of viscous substances through small holes if one considers automated dispensers for glues, hot melts etc
 
I'm confused about the setup. Is chamber #2 initially full of air? I would expect air bubbles to form at the orifice and rise to the top of chamber #1. Not a simple problem at all.
 
Both chambers are full of oil, single fluid problem, no air involved. also the spring is weak so we will assume the flow to be very slow.

happy new years everyone
 

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