Tracking Spread of a water jet out of a downward-facing pipe

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Discussion Overview

The discussion revolves around calculating the spread of water from a downward-facing pipe, focusing on the dynamics of fluid discharge into the atmosphere. Participants explore various models and approaches to understand the area covered by the water jet, considering both simplified and complex scenarios.

Discussion Character

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

Main Points Raised

  • One participant seeks to determine the radius of the water spread from a pipe with known diameter, volume, and pressure, requesting both simplified and complex models.
  • Another participant suggests modeling the spread as an expansion into a larger diameter pipe, but expresses doubt about this methodology.
  • Some participants consider examining the flow in two dimensions, although they struggle to find relevant equations or sources.
  • There is a proposal to treat the water jet as a projectile, acknowledging the complexities involved in tracking fluid dynamics in two dimensions.
  • Concerns are raised about whether the water jet spreads or converges, with one participant comparing it to the behavior of a running faucet.
  • Participants discuss the flow rate and pressure conditions, noting the high speed of the water jet and expressing uncertainty about the accuracy of the stated values.
  • One participant emphasizes the potential danger of the water jet, suggesting that aerodynamic drag may play a significant role in the behavior of the water spread.
  • There is mention of plans to conduct a physical demonstration and use an ultrasonic sensor to measure flow, indicating ongoing exploration of the topic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the behavior of the water jet, with multiple competing views on whether it spreads or converges, and uncertainty remains regarding the accuracy of the parameters involved.

Contextual Notes

Participants acknowledge limitations in their understanding of fluid dynamics, particularly regarding the effects of pressure, velocity, and aerodynamic drag on the water jet's behavior.

Charles Winston
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Hey folks, I'm back with a new question.

If I have a pipe of known diameter, with a known volume of water at a known pressure discharging downwards into atmosphere, how can I calculate the radius of its "spread". That is, how can I find what area beneath the discharging pipe is being covered with water?

A simplified, idealized model, along with a more complicated derivative would be equally appreciated.

Thanks!
 
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Charles Winston said:
Hey folks, I'm back with a new question.

If I have a pipe of known diameter, with a known volume of water at a known pressure discharging downwards into atmosphere, how can I calculate the radius of its "spread". That is, how can I find what area beneath the discharging pipe is being covered with water?

A simplified, idealized model, along with a more complicated derivative would be equally appreciated.

Thanks!
What are your thoughts on this so far? Is this a homework problem?
 
So far I've tackled it a few different ways.

First approach is to model it as an expansion into a pipe of diameter equal to the desired coverage, but I'm thinking that methodology is flawed. Essentially, Q1*A1 = Q2*A2.

Second is to examine the system in two dimensions, but I've yet to be able to track down equations or any sources for it. Entirely possible I just don't know what I'm looking for.

I've also tried to treat it as a projectile, but tracking that in two dimensions for a fluid is somewhat tricky.

This part of a company project, but just one step out of a dozen or so.
 
Are you sure that it spreads rather than converging?
 
I can't be sure, but the outlet diameter is 3/4" with a flow rate of 350 gpm. Pressure unknown, but above atmospheric. Would a stream in those conditions behave like, say, a running faucet (i.e. converge) or spread? This I'm not sure of.

On Monday I'm going to have a demonstration of the flow pattern, but it would be difficult from that to determine with any degree of certainty what its spread would be, as the water is at around 180°F.
 
Charles Winston said:
I can't be sure, but the outlet diameter is 3/4" with a flow rate of 350 gpm. Pressure unknown, but above atmospheric. Would a stream in those conditions behave like, say, a running faucet (i.e. converge) or spread? This I'm not sure of.

On Monday I'm going to have a demonstration of the flow pattern, but it would be difficult from that to determine with any degree of certainty what its spread would be, as the water is at around 180°F.
According to this, it's traveling at extremely high speed, 260 ft/sec. Is this about what you were expecting?
 
I hope that the audience is well separated / shielded from that water jet. The velocity pressure is over 450 PSI, and if such a jet hit somebody, it would (not could) kill them.

You could try treating it as a projectile. A cylinder of water at a velocity, subject to gravity and air drag along the sides. Ignore air drag on the leading and trailing ends. I expect that gravity force will be small compare to aerodynamic drag, and that the air drag will explain why spray comes off the sides. But that's just a guess. I have not done any calculations. And I'd like to know how it turns out. Can you get us a photo?
 
Chestermiller said:
According to this, it's traveling at extremely high speed, 260 ft/sec. Is this about what you were expecting?
In all honesty, I've got reason to suspect that these stated/given values might not be accurate.

Monday in addition to a physical demonstration, I'll be taking an ultrasonic sensor to the pipe bank to get the flow. There's no infrastructure for that in place currently.

jrmichler said:
I hope that the audience is well separated / shielded from that water jet. The velocity pressure is over 450 PSI, and if such a jet hit somebody, it would (not could) kill them.

I'll be sure to get pictures, maybe even with a thermographic camera!

Thank you for the drag consideration. That's out of my expertise. I'll be looking into that.
 

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