| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
02 Apr 2006 05:22:30 PM |
| Object: |
Household physics question |
....Especially for those of you who are up on evaporation physics: Why
is it that when the dishwasher has completed its cycle, the plastic
items are never completely dry? All glass, metal and ceramic dishes and
utensils are dry; all plastic items are covered in adhereing water
droplets.
Andy
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| User: "Sam Wormley" |
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| Title: Re: Household physics question |
02 Apr 2006 06:36:10 PM |
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wrote:
...Especially for those of you who are up on evaporation physics: Why
is it that when the dishwasher has completed its cycle, the plastic
items are never completely dry? All glass, metal and ceramic dishes and
utensils are dry; all plastic items are covered in adhereing water
droplets.
Andy
Water wets of glass, metal and ceramic dishes... spreading out... more
surface area... evaporating faster.
Water beads up on plastic... less surface area... evaporates slower.
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| User: "OG" |
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| Title: Re: Household physics question |
02 Apr 2006 06:40:45 PM |
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"Sam Wormley" <swormley1@mchsi.com> wrote in message
news:KdZXf.77517$oL.40402@attbi_s71...
at@2walla.com wrote:
...Especially for those of you who are up on evaporation physics: Why
is it that when the dishwasher has completed its cycle, the plastic
items are never completely dry? All glass, metal and ceramic dishes and
utensils are dry; all plastic items are covered in adhereing water
droplets.
Andy
Water wets of glass, metal and ceramic dishes... spreading out... more
surface area... evaporating faster.
Water beads up on plastic... less surface area... evaporates slower.
Also possible higher thermal capacity of glass & ceramics and conductivity
of metals increases the timescale/temperature available for evaporation.
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| User: "John Lorimer" |
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| Title: Re: Household physics question |
02 Apr 2006 08:09:15 PM |
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adding to Sams correct comments;
Specific heat can also be interpreted as a measure of how well a substance
preserves its temperature, i.e. "stores" heat, hence the term "heat
capacity" and thus the glass, metal and ceramic dishes and utensils dry
faster due to the higher stored heat.
http://en.wikipedia.org/wiki/Specific_heat_capacity
Regards,
John
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| User: "The Ghost In The Machine" |
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| Title: Re: Household physics question |
02 Apr 2006 07:58:47 PM |
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On Sun, 02 Apr 2006 15:22:30 -0700, at wrote:
...Especially for those of you who are up on evaporation physics: Why
is it that when the dishwasher has completed its cycle, the plastic
items are never completely dry? All glass, metal and ceramic dishes and
utensils are dry; all plastic items are covered in adhereing water
droplets.
Andy
That might be it right there. The droplet has to extract heat from
somewhere (for water, about 40.7 kJ/mol or 2.26 MJ/l) in order to convert
from liquid to vapor. Glass and metal hold heat and allow it to transfer
from the metal or glass to the water droplet, evaporating it. However,
plastic doesn't hold heat well; ergo, droplets.
And then there's the issue that the vapor has to actually escape; hence
the vents in the top part of my dishwasher.
--
#191,
It's still legal to go .sigless.
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| User: "" |
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| Title: Re: Household physics question |
02 Apr 2006 11:34:56 PM |
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Long chain hydrocarbons and especially plastics have very high heat
capacity. Water needs to absorb heat to evaporate because the heat goes
latent into the vapor. Very difficult to pull any heat out of a piece
of plastic when everything is at thermal equillibrium. It takes much
more time.
And I'll tell ya another thing, you never, ever want to get any molten
plastic on you skin. It can burn you much worse than other equally hot
materials. You also get a double whammy from a steam burn because it
wants to condense on your skin and so you get all of that latent heat
as a kind of reverse bonus.
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| User: "" |
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| Title: Re: Household physics question |
04 Apr 2006 12:11:26 AM |
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Thanks to all who responded.
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