What’s happening and why (water flow within a container)

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SUMMARY

The discussion focuses on the mechanics of water flow within containers, specifically examining the behavior of water in PET and HDPE bottles when small holes are punctured at the base. When the cap is sealed, the water does not drip due to the creation of an airtight seal, which maintains pressure within the container. Upon opening the cap, the release of pressure allows water to flow through the holes. The conversation also highlights that scaling up to a five-gallon HDPE container introduces complications, likely due to factors such as surface tension and material properties.

PREREQUISITES
  • Understanding of fluid dynamics principles
  • Familiarity with material properties of PET and HDPE
  • Knowledge of pressure differentials in sealed containers
  • Basic concepts of surface tension in liquids
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  • Research fluid dynamics in sealed systems
  • Explore the impact of surface tension on fluid flow
  • Investigate material properties of HDPE versus PET
  • Learn about pressure differentials and their effects on liquid behavior
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This discussion is beneficial for designers, engineers, and anyone interested in fluid mechanics, particularly those working with container designs and liquid flow systems.

SLA
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Hi all

I’m from a design background and I have a number of questions in relation to water flow within a container (e.g. coke bottle and larger). I punch a few small holes in the base of the (PET) coke bottle and then I fill it up with water, once I have done that, I place the cap back on the bottle. The water within the bottle has stopped dripping from the base, and when the cap is opened, the water flows through the holes of the base. What forces are doing this? Is it the airtight seal that has repreasuriezed the container? Or is it hole size 2mm. Alternatively, perhaps it’s something else like material selection or the design profile of the container? This method works fine for some containers (HDPE and PET) 2 litres up to 5 litres. So now, I’ve scaled up the project to a five-gallon HDPE container. It has failed to act in the same way as the other containers. Why?
 
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Surface tension is going to be a big factor here. What is the goal of your design? Do you want the water to flow only when the lid has been opened?
 

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