Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 10-04-2012, 16:33   #1
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 4,198
Images: 4
Ice to keep something from freezing?

Just a thought type of question.

If I wanted to prolong something from freezing in below 0*F ambient temperatures, wouldn't it be better to place in an insulated ice box with a large block of ice than without any ice?
__________________

__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 10-04-2012, 16:39   #2
Registered User
 
S/V Illusion's Avatar

Join Date: Oct 2007
Location: Lakewood Ranch, FLORIDA
Boat: Alden 50, Sarasota, Florida
Posts: 1,693
Re: Ice to keep something from freezing?

It's a matter of temp gradient. A warm insulated box will stay warmer without ice. A cold box (below freezing temp) will warm in the presence of ice. The practical answer to your question is - it depends on variables like volume, temp gradient, efficacy of the insulator of the box, leakage, etc...
__________________

__________________
S/V Illusion is offline   Reply With Quote
Old 10-04-2012, 17:49   #3
Registered User
 
Ziggy's Avatar

Join Date: Apr 2008
Location: U.S., Northeast
Boat: Contessa 32
Posts: 1,421
Images: 2
Re: Ice to keep something from freezing?

Quote:
Originally Posted by S/V Illusion View Post
A cold box (below freezing temp) will warm in the presence of ice.
It depends on the temperature of the ice. If the ice is colder than ambient the box will get colder when you put the ice inside. If the ice is warmer than ambient, the box will warm up. But the ice box temperature will not rise above freezing as long as there is any ice in it.

If you want the box to stay above freezing, put some liquid water in it.
__________________
... He knows the chart is not the sea.
-- Philip Booth, Chart 1203
Ziggy is offline   Reply With Quote
Old 10-04-2012, 19:31   #4
Senior Cruiser
 
Wanderlust's Avatar

Cruisers Forum Supporter

Join Date: Aug 2005
Location: NSW Central Coast
Boat: Lagoon 410
Posts: 499
Re: Ice to keep something from freezing?

You would do better if you put water in there. Most foods freeze at a lower temperature than water, in which case the water will freeze first. The additional mass also shares the heat loss, so the time will be longer.

But the bigger benefit of water is the fact that it takes about 80 times the energy to freeze as it does to drop it 1 degree Celcius. So while the internal temperature may drop steadily to 0 degrees, it will not get colder until the water has frozen.

However. while the above may be true theoretically, there will be a slight difference in practical usage. The inside temperature will drop slightly below zero, as there needs to be a temperature differential for the freezing to occur.

Seawater freezes a couple of degrees lower than fresh water. So if what you don't want frozen has a still lower freezing point, then choose seawater.
__________________
Steve
Wanderlust is offline   Reply With Quote
Old 11-04-2012, 08:57   #5
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,331
Re: Ice to keep something from freezing?

Quote:
Originally Posted by deckofficer View Post
Just a thought type of question.

If I wanted to prolong something from freezing in below 0*F ambient temperatures, wouldn't it be better to place in an insulated ice box with a large block of ice than without any ice?
Surely it would depend on the substance involved. For instance, if the something is say nitrogen or even petrol, then it really doesn't matter.

I would be using the ice to mix in my drink or keep the beer warm.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is online now   Reply With Quote
Old 11-04-2012, 11:11   #6
Registered User

Join Date: Dec 2006
Posts: 249
Re: Ice to keep something from freezing?

Putting ice in lowers the temperature of the ice box to 0 c. If the ambient temperature is the same in the boat, and ice box, ie enough to freeze stuff ie below 0 c that will warm the box. If that is not the case then it will cool it.
Presumably the box starts warmer than the ambient. Eventually they would reach the same. For shorter times, the ice would cool the box bringing it closer to freezing. Heat transfer slows as the temperature difference declines, but that would happen anyway so that doesn't make a difference. All that happens is the ice cools the box closer to ambient lessening the time to freezing.
__________________
chris_gee is offline   Reply With Quote
Old 11-04-2012, 12:36   #7
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
Re: Ice to keep something from freezing?

Is this a test Bob? I know you are also a marine engineer who knows this stuff.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 11-04-2012, 13:44   #8
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 4,198
Images: 4
Re: Ice to keep something from freezing?

Quote:
Originally Posted by David M View Post
Is this a test Bob? I know you are also a marine engineer who knows this stuff.
David,

BTW, I'm just a dumb deckie.

Everything you have taken the time to post is always spot on. I was reflecting back to a physics class at CMA, had Jim Wheeler, who still teaches there, and my recollection was there is always a large energy jump when changing states, i.e., a liquid to a solid or gas. So, I think if you were in very cold ambient temperature (well below freezing), then a volume of water in the insulted ice chest would give the longest time before other items in the cooler would freeze. When the water froze, then as ice, would continue to keep other items from freezing until evaporating (a gas), then you no longer have any mass that can give off heat and the outside temperature will equalize with the inside and your stored items would freeze.

So, you see David, I'm not sure and was bouncing this off of others. Now that you found this thread, I will know for sure, so step me through it.
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 11-04-2012, 15:13   #9
Head in a locker
 
Cavalier's Avatar

Cruisers Forum Supporter

Join Date: Dec 2010
Location: Houston, TX
Boat: Beneteau 461 47'
Posts: 879
Images: 1
Re: Ice to keep something from freezing?

Quote:
Originally Posted by deckofficer View Post
Just a thought type of question.

If I wanted to prolong something from freezing in below 0*F ambient temperatures, wouldn't it be better to place in an insulated ice box with a large block of ice than without any ice?
Think in terms of energy and specific heat capacity and the whole problem gets easier.

The 'heat capacity' (sometimes known as thermal capacity) of a substance is the amount of heat required to alter the substance's temperature by a given amount. Specific heat capacity (SHC) of a substance is similar but also takes into account the amount of heat required per unit mass of the substance. The SI units for SHC are J per gram kelvin - J/(g.K)

Water at -10degC (water ice) has a SHC of 2.11 J/(g.K)
Water at 25degC (pure water) has a SHC of 4.181 J/(g.K)
SeaWater at 25degC (1.03SG saltwater) has a SHC of 3.985 J/(g.K)

Note that water-ice requires much less heat per unit mass to alter its temperature than pure water at roughly room temperature. The same is true in reverse and in that sense ice would lose, to a colder environment, its thermal energy at a higher rate than liquid water.

Looking at the numbers above, putting the food in a sealed container in water at room temperature in an insulated container would take much more time to freeze than the same situation but with an equal mass of ice inside: The liquid water simply has more initial thermal energy to be lost than the ice (which is already cold).

Obviously, this seems like a no-brainer, as in food it is the water content which freezes (in a freezer) and not the more solid food matter. The fats will stiffen etc, but not much is happening to your flour for a while... the water in the cells of the organic foods (such as an apple) will freeze and expand and rupture the cell-walls, so when it's defrosted it looks like a sad watery mess and tends to discolor and ruins quicker.

What you may be thinking of when you hark back to physics lessons is the vapor-pressure of gases above a liquid as a medium/transport for energy loss.

As school kids we used to run inside and fill up a cup with hot water to throw on the ground outside (to make a skid-pan) instead of cold water as the steam coming off the hot water initially would act as a much more efficient transport drawing thermal energy away from the mass of water. Cold water on the otherhand would more readily form a layer of ice on the surface but in the process would create an insulative barrier reducing the rate at which the thermal energy in the remaining liquid water could be lost to the cold air above. The hot water would generally freeze solid quicker than the cold water!

Ice is a better insulator than liquid water, but liquid water starts off with more energy initially - so for the same mass will take longer to freeze.

Hope this made sense
__________________
"By day the hot sun fermented us; and we were dizzied by the beating wind. At night we were stained by dew, and shamed into pettiness by the innumerable silences of stars."
Cavalier is online now   Reply With Quote
Old 11-04-2012, 15:15   #10
Head in a locker
 
Cavalier's Avatar

Cruisers Forum Supporter

Join Date: Dec 2010
Location: Houston, TX
Boat: Beneteau 461 47'
Posts: 879
Images: 1
Re: Ice to keep something from freezing?

Quote:
Originally Posted by deckofficer View Post
BTW, I'm just a dumb deckie.
No such thing as a dumb deckie!
__________________
"By day the hot sun fermented us; and we were dizzied by the beating wind. At night we were stained by dew, and shamed into pettiness by the innumerable silences of stars."
Cavalier is online now   Reply With Quote
Old 11-04-2012, 16:33   #11
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,331
Re: Ice to keep something from freezing?

Quote:
Originally Posted by Cavalier View Post
Think in terms of energy and specific heat capacity and the whole problem gets easier.

The 'heat capacity' (sometimes known as thermal capacity) of a substance is the amount of heat required to alter the substance's temperature by a given amount. Specific heat capacity (SHC) of a substance is similar but also takes into account the amount of heat required per unit mass of the substance. The SI units for SHC are J per gram kelvin - J/(g.K)

Water at -10degC (water ice) has a SHC of 2.11 J/(g.K)
Water at 25degC (pure water) has a SHC of 4.181 J/(g.K)
SeaWater at 25degC (1.03SG saltwater) has a SHC of 3.985 J/(g.K)

Note that water-ice requires much less heat per unit mass to alter its temperature than pure water at roughly room temperature. The same is true in reverse and in that sense ice would lose, to a colder environment, its thermal energy at a higher rate than liquid water..................................
Hope this made sense
Cavalier, is the emphasised part above a typo? If not, can you explain a little more as I don't understand how (pure) water could be at -10degC.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is online now   Reply With Quote
Old 11-04-2012, 17:05   #12
Head in a locker
 
Cavalier's Avatar

Cruisers Forum Supporter

Join Date: Dec 2010
Location: Houston, TX
Boat: Beneteau 461 47'
Posts: 879
Images: 1
Re: Ice to keep something from freezing?

Quote:
Originally Posted by Wotname View Post
Cavalier, is the emphasised part above a typo? If not, can you explain a little more as I don't understand how (pure) water could be at -10degC.
Hi,

It's not a typo.. more of a terminology oddity.. i put "water ice" to differentiate it from "Nitrogen ice" (as some people call it).. but it's still good old H2O, just in solid form. The point was to show that the SHC of ice is actually much lower than water. When you start trying to introduce heat into ice the near-crystalline structures start to dissociate quite quickly into clumps approaching liquid form -this happens locally to the heat source at first (i.e. outside in), and ice - being solid, is not capable of convecting like liquid water - the transmission of heat through ice is a somewhat different mechanism than liquid water.

On another note, you can get liquid water down below 10degC, and not in ice form if you're willing to add other components such as salt (NaCl) or Glycol (anti-freeze) compounds.

Phil
__________________
"By day the hot sun fermented us; and we were dizzied by the beating wind. At night we were stained by dew, and shamed into pettiness by the innumerable silences of stars."
Cavalier is online now   Reply With Quote
Old 11-04-2012, 17:12   #13
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 4,198
Images: 4
Re: Ice to keep something from freezing?

Phil,

You bring up another mind puzzler. We all know water will boil at lower than 212F / 100 C, if in a container that is brought into a vacuum. We do that all the time to make potable water using discarded heat from the engine. Can the freeze point of water be altered by a pressure other than atmospheric? I.e., a vacuum or pressure vessel?
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 11-04-2012, 17:25   #14
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,331
Re: Ice to keep something from freezing?

Quote:
Originally Posted by Cavalier View Post
Hi,

It's not a typo.. more of a terminology oddity.. i put "water ice" to differentiate it from "Nitrogen ice" (as some people call it).. but it's still good old H2O, just in solid form. The point was to show that the SHC of ice is actually much lower than water. When you start trying to introduce heat into ice the near-crystalline structures start to dissociate quite quickly into clumps approaching liquid form -this happens locally to the heat source at first (i.e. outside in), and ice - being solid, is not capable of convecting like liquid water - the transmission of heat through ice is a somewhat different mechanism than liquid water.

On another note, you can get liquid water down below 10degC, and not in ice form if you're willing to add other components such as salt (NaCl) or Glycol (anti-freeze) compounds.

Phil
Well I learn something new every day - Nitrogen ice - never heard the term before! I would have guessed it was a bad way of expressing "solid nitrogen"!

For me, water is liquid H2O, ice is solid H2O, "water ice" is a mixture of liquid H2O and solid H2O both at 0 degC and cant exist at any other temperature. I am using H2O to denote pure water as you rightly pointed out that when pure water is compounded by other substances, the numbers change.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is online now   Reply With Quote
Old 11-04-2012, 17:33   #15
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
Re: Ice to keep something from freezing?

Quote:
Originally Posted by deckofficer View Post
David,

BTW, I'm just a dumb deckie.

Everything you have taken the time to post is always spot on. I was reflecting back to a physics class at CMA, had Jim Wheeler, who still teaches there, and my recollection was there is always a large energy jump when changing states, i.e., a liquid to a solid or gas. So, I think if you were in very cold ambient temperature (well below freezing), then a volume of water in the insulted ice chest would give the longest time before other items in the cooler would freeze. When the water froze, then as ice, would continue to keep other items from freezing until evaporating (a gas), then you no longer have any mass that can give off heat and the outside temperature will equalize with the inside and your stored items would freeze.

So, you see David, I'm not sure and was bouncing this off of others. Now that you found this thread, I will know for sure, so step me through it.
Wheeler is still there?...wow. Lloyd Kitazono is still there also. Once in a while I take one of his oceanography classes out on the research boat and show them how the professionals do it.....LOL. He is a great guy. We have all kinds of sampling gear and electronics to impress them...

Yeah, I remember the additional energy it takes to jump from a solid to a liquid state for water and the giving up of energy in the opposite direction. I'm not sure how much it would work in the scenario you described. Maybe give Jim a call

http://www.ratemyprofessors.com/Show...jsp?tid=343809

http://www.ratemyprofessors.com/Show...jsp?tid=707608
__________________

__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 01:44.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.