Question About Cold Retaining Metal
AlWahrabi
I was thinking of experimenting this hot Summer with placing various chunks of
metal in my freezer and...more or less using them like ice. Putting them in my
cooler and seeing if they kept items nice and cold --without the side effect
which ice has (melting to liquid).
If I'm not making myself clear, I mean...would iron or steel or brass or lead
or what metal would likely "hold its cold" the longest?
John Manders
it.
However, to answer your question, Heat absorbed = specific heat x mass x
temperature rise
The metal with the largest specific heat will remain cool the longest
assuming that it's shape and thermal conductivity are not limiting things.
A better way is to involve a phase change like freezer blocks. The advantage
of ice is that it absorbs a lot of heat just by melting. Get a flexible
container, put some water in it and use that.
John
"AlWahrabi" <alwa...@wmconnect.com> wrote in message
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AlWahrabi
Manders>>
Okay...what metals might those be?
AlWahrabi
the highest value of density times specific heat. Copper is a good one. Ed
Ruf>>
So, you're saying: copper (once placed in the freezer and chilled overnite) is
a metal that will take a LONG time to lose its cold temperature? Longer than,
say, iron or steel?
I appreciate the several replies, and in the meantime I am reviewing old
postings. It seems like at least 2 parameters are at work: Specific Heat AND
Thermal Conductivity.
Each year, when I buy dry ice for cooling in my vehicle, I notice that dry ice
is a very POOR conductor of cold. Dry ice appears to have to be directly ontop
of something, in order to chill it. Something one inch away from the dry ice is
warm, while...whatever it is directly in contact with it is super-chilled...but
only at that one point of contact with the dry ice.
dlzc1 D:cox T:net@nospam.com N:dlzc D:aol T:com (dlzc)
"AlWahrabi" <alwa...@wmconnect.com> wrote in message
news:20040520052751...@mb-m14.wmconnect.com...
Using google advanced and searching for
all words: density metal table
exact phrase: specific heat
URL:http://metals.about.com/gi/dynamic/offsite.htm?site=http://www.apo.nmsu.edu/Telescopes/SDSS/eng.papers/19950926%255FConversionFactors/19950926%255FMProperties.html
They call specific heat "heat capacity", for some reason. As John Manders
said, you would look for some mass times the specific heat, or on a unit
volume basis, density times specific heat.
You may also want to consider "metering" the cold out slowly (thermal
conductivity), so that it feels cool longer, but doesn't freeze you out for
a short period of time.
David A. Smith
Michael
change from solid to liquid that makes ice a good source of cooling.
to put things in perspective, assume that you cool 1 pound chunks of copper
and ice to 0F.
Question: how much energy do you have to put into each of them to heat up to
60F??
Answer: Copper: 5.64 BTU; Ice: 188.1 BTU
The ice absorbs about 33 times as much energy as the copper.
Brian Whatcott
sodium, then aluminum.
But better yet is a material that gets its coolth from a change of
state: you'd never guess:
a plolythene bottle filled with water and frozen.
Brian W
On 20 May 2004 05:50:44 GMT, alwa...@wmconnect.com (AlWahrabi)
wrote:
Brian Whatcott
aluminum 886
sodium 1180
porcelain 755 (!!! but poor conductivity)
Brian W
On Thu, 20 May 2004 06:24:48 -0400, Ed Ruf <egruf_...@cox.net>
wrote:
>On 20 May 2004 09:27:51 GMT, in sci.engr.mech alwa...@wmconnect.com
>Excluding phase change, for a given volume, it will be the material with
>the highest value of density times specific heat. Copper is a good one.
>________________________________________________________
>Ed Ruf Lifetime AMA# 344007 (Use...@EdwardG.Ruf.com)
>http://EdwardGRuf.com
AlWahrabi
you won't be impressed with the results of your experiment--it's the phase
Yes, I understand that frozen water (ice) would be best, cause it requires
calories of heat to change state from ice to water. But, it is sloppy and
always leaks (in the back of my truck, each Summer).
dlzc1 D:cox T:net@nospam.com N:dlzc D:aol T:com (dlzc)
"AlWahrabi" <alwa...@wmconnect.com> wrote in message
news:20040521005025...@mb-m05.wmconnect.com...
If you have good ventillation, you could then use solid carbon dioxide,
which sublimes from solid direct to gas...
David A. Smith
Paul Skoczylas
> calories of heat to change state from ice to water. But, it is sloppy and
> always leaks (in the back of my truck, each Summer).
Huh?! I've never, ever, had a plastic pop bottle (either 600 mL or 2 L)
leak on me when refilled with water. Bags of ice always leak--there's
nothing you can do about that, but put water in pop bottles and freeze them
the night before your trip (just as you would do with your metal block), and
you'll have something far more effective, taking up less volume, and
weighing less, while working faaaaar better. Plus when they melt, you've
got a source of fresh water--often useful when you venture into the
boondocks!
-Paul
Brian Whatcott
wrote:
>On Fri, 21 May 2004 01:17:06 GMT, in sci.engr.mech Brian Whatcott
><bet...@sbcglobal.net> wrote:
>
>>On Thu, 20 May 2004 06:24:48 -0400, Ed Ruf <egruf_...@cox.net>
>
>>>Excluding phase change, for a given volume, it will be the material with
>>>the highest value of density times specific heat. Copper is a good one.
>>>________________________________________________________
>>>Ed Ruf Lifetime AMA# 344007 (Use...@EdwardG.Ruf.com)
>>>http://EdwardGRuf.com
>
>>Ahem....copper 380 joules per kg .degC
>>aluminum 886
>> sodium 1180
>> porcelain 755 (!!! but poor conductivity)
>
>
>Ahem, // ..... // per
>unit volume. Given the density difference between copper and aluminum, it
>wins hands down. One of the reasons the heatsink copper scramjet models we
>test at work are made of copper.
>________________________________________________________
>Ed Ruf Lifetime AMA# 344007 (Use...@EdwardG.Ruf.com)
>http://EdwardGRuf.com
Ed,
I cut out the personal invective from your interesting response above,
and offer this explanatory note. Hope it helps.
I'd like you to take the opportunity to think a little more about your
response.
1) TERMS
"Specific" is a keyword in physics for "per unit mass"
so...
Specific heat times density means
heat capacity / mass X mass/volume
=
heat capacity per volume.
Your sentence "For a given volume, the material with highest specific
heat times density" [gives the highest heat capacity]
means
"For a given volume, the material with highest heat capacity per
volume" gives the highest heat capacity.
I think you can see that this statement is not a deduction or
conclusion, but a recasting of terms.
2) FIGURE OF MERIT.
... more importantly, if you are going to fly something as an
engineering proposition, you work out a figure of merit.
Where the desired objective is maximizing heat capacity, it costs
something to get the item aloft, and that cost is mass.
So the reasonable figure of merit in your ram-jet case is heat
capacity per mass which is - guess what? called specific heat
capacity.
That's why recip valve stems are sodium filled, and engine cases not
exposed to high temperature are...aluminum. They are not ever copper,
which has a lower figure of merit for the application.
Sincerely
Brian Whatcott Altus OK
Johnathan Standridge
Everyone is debating how long any metal will stay cold, but I wonder, will
copper leach out into the drink, and if so, is that really safe? Just to be on
the safe side, I'd say iron or someone said porcelain. Personally, I'd love to
see someone make some neat porcelain drink coolers.
--
for full context, visit http://www.polytechforum.com/mech/question-about-cold-retaining-metal-2621-.htm
lucid
> eriment--it's the phase change from solid to liquid that makes ice a good
source of cooling. MBush>>
> Yes, I understand that frozen water (ice) would be
timewethink
--
For full context, visit https://www.polytechforum.com/mech/question-about-cold-retaining-metal-2621-.htm
dlzc
On Tuesday, August 9, 2022 at 7:45:05 AM UTC-7, timewethink wrote:
> I recently bought two types of Arctic Ice brand freezer blocks,
> one freezes at 28.4ºF one freezes at 5ºF, would it be better to
> use one of each, so the state change occurs at different times
> as the contents warm (say over 2 days) or 2 of the same, so
> that the state change occurs at the same time but takes more
> energy?
Maximize insulation, minimize temperature difference.
I also had a crappy "cool bag" that I somehow thought was "water proof". The ice was melting, and the water was dripping out the bottom... so it could not conduct / convect heat to the walls of the "cool bag". One bag of ice lasted for almost a day, and food was cold the entire time. Don't get that with the typical styrofoam cooler.
David A. Smith