The Naked Scientists

The Naked Scientists Forum

Author Topic: Why Does Heating This Suck In The ClingFilm ?  (Read 2184 times)

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Why Does Heating This Suck In The ClingFilm ?
« on: 13/11/2007 17:02:37 »
Dearest Peeps Of International Plastic Wrapping Fun & Luff,

See this bowl of yummy veggies ?




Nice isn't it ?..Notice how veggy like and ready to be zapped by microwave hugs they are ?


But, when ewe heat it.....heat expands yes ?....the clingfilm expands to create a dome......so why does the clingfilm get sucked in onto the vegetable AFTER the cooking is done ?..surely it should continue to expand or maintain it's dome like structure eh ?


I've sent an email via a Medium to Sir Christopher Wren ( he's an authority on domes)...but I got an 'out of office' reply !!

Can ewe help me ?




 

lyner

  • Guest
Why Does Heating This Suck In The ClingFilm ?
« Reply #1 on: 13/11/2007 18:15:26 »
Loadsa pressure when the water inside's boiling.
This forces some steam and air out past the film / bowl gap.
When it cools, the steam condenses and the pressure is lower - atmospheric pressure pushes in and, because it is pushing inwards on the (by now soft) film, forms a better seal than before and keeps the pressure inside, low. Hence the dome.
They always tell you to put a tiny hole in the film to stop the vacuum-pak effect.
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Why Does Heating This Suck In The ClingFilm ?
« Reply #2 on: 14/11/2007 12:56:50 »
Loadsa pressure when the water inside's boiling.
This forces some steam and air out past the film / bowl gap.
When it cools, the steam condenses and the pressure is lower - atmospheric pressure pushes in and, because it is pushing inwards on the (by now soft) film, forms a better seal than before and keeps the pressure inside, low. Hence the dome.
They always tell you to put a tiny hole in the film to stop the vacuum-pak effect.

THAN YOU THANK YOU THANK YOU very much !!....I understand !!

YAYYYYYYYYYYYYYYY !!
 

The Naked Scientists Forum

Why Does Heating This Suck In The ClingFilm ?
« Reply #2 on: 14/11/2007 12:56:50 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length