% of Salt Solution for freezing

Submitted: Wednesday, Feb 01, 2006 at 14:27
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G,day all,

just found some pretty good small 1ltr strong plastic containers which I plan to use as ice bricks in an esky.

I was wondering what amount of salt to add per ltr to achieve the desired extra freezing effect?

I know that saturated (ie wont dissolve more) is best, but wondered if anyone had a good amount per ltr that they use and gives them a benefit?

Thanks

Rgds

Ron
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Reply By: robak (QLD) - Wednesday, Feb 01, 2006 at 14:41

Wednesday, Feb 01, 2006 at 14:41
I don't have the amnswer but have a question.

From what I can remember salt lowers the melting point of ice. So my question is what is the benefit of having ice melt below 0 degrees C?

R.
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Follow Up By: robak (QLD) - Wednesday, Feb 01, 2006 at 14:43

Wednesday, Feb 01, 2006 at 14:43
Ron,

I found some information for you.

10% salt solution freezes at -6 degC
20% salt solution freexes at -16 degC

Not sure if thats of any help.

Cheers,

R.
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Follow Up By: Ron173 - Wednesday, Feb 01, 2006 at 14:56

Wednesday, Feb 01, 2006 at 14:56
Robak,

thats exactly what I was looking for, ta muchly!

Guess you worked out why I want to do it, put salt in your water container before freezing and it gives it a lower freezing point, so aids in keeping cooler a bit longer.

Not sure on all the physics of it, but a bit of digging on here will turn up that it works in our favour.

I just wasnt sure of the best ratio to mix up.

Thanks again

Ron
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Follow Up By: robak (QLD) - Wednesday, Feb 01, 2006 at 15:08

Wednesday, Feb 01, 2006 at 15:08
Well, I've always been a little confused over this and I'm sure somebody has answers because a slat solution is used in many A/C systems in buildings.

My confusion is:

ICE is a heat sink that basically absorbs heat. Does salty ICE absorb more heat and therefore keep things cooler longer?

If I had two blocks of ice. One with 20% salt and the other just plain water, both at -20 degC. The salty ice will melt when the temperature gets to -16 and the plain ice will stay solid until the usual 0degC.

So from what i can work out, with salty ice you'll just get very cold water (below 0 deg C) in your esky sooner.

Somebody out there must know.

R.

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Follow Up By: Ron173 - Wednesday, Feb 01, 2006 at 15:20

Wednesday, Feb 01, 2006 at 15:20
LOL!

I cant fault your theory, sounds true, but somehow its not.

Its got to do with time I think, you'd need to do the two blocks thing with two seperate eskys, otherwise they would be merging energies.

So assuming two eskys, starting at outside ambient of say 30deg, the one with frozen water will have released all its 'coldness' sooner than the one with brine, so although melting point lower, it should take longer and hence keep food/beer colder longer.

But then again, I'm no scientist LOL!!

Ron
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Follow Up By: robak (QLD) - Wednesday, Feb 01, 2006 at 15:27

Wednesday, Feb 01, 2006 at 15:27
Ron, this is starting to hurt my head.

It might not release all of it's coldenss sooner. They'll both be at, say -12 degrees but one will be ice and the other water.

To put in another thing. The greatest heat absorption is in the chage of state from Ice to Water and not so much in the change of temperature. So maybe the the Salty ice changing to water (at -16deg C) absorbs more heat then normal ice changing to water (at 0 deg C). So you may be right.

I might try an experiment at home one day.

Anyway, lunch is over and I have to get back to my menial work.

Cheers.

R.
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Follow Up By: Ron173 - Wednesday, Feb 01, 2006 at 15:42

Wednesday, Feb 01, 2006 at 15:42
No worries

I am fairly certain I am right, I just dont know why!!!!!!!!!!

Its actually quite well documented in camping tips etc on a good number of sites, so thats why I'm fairly sure the practicality of it works, I just dont know how to prove the theory! LOL

Guess I might try some home experiments on time to defrost with and without as i have a good accurate RTD thermometer, and since salt is not expensive, R and D cost should be acceptable!

Someone on here will prob have a theory, theres plenty on web but they all get WAY to technical to be bothered reading more than a few lines.

Rgds

Ron
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Follow Up By: Member - Captain (WA) - Wednesday, Feb 01, 2006 at 15:45

Wednesday, Feb 01, 2006 at 15:45
Hi Guys,

When you have ice (fresh or salty water), it takes approximately 2 joules (J) of energy (heat) to raise it 1C per gram (specific heat of ice). But to change its state from ice to water, it takes 335 J per gram (latent heat). Now when its a liquid, it takes 4J per gram (specific heat of water).

Now what does this mean? Assume we start at -20C and end up at 5C, when we have 1 gram of ice (no salt) we have:

20C x 2J x 1g (specific heat ice) = 40J
335J x 1g (latent heat) = 335J
5C x4J x 1g (specific heat water) = 20J
total = 395 J

when using 20% salty water (melts at -16C) :
4C x 2J x 1g (specific heat ice) = 8J
335J x 1g (latent heat) = 335J
21C x4J x 1g (specific heat water) = 84J
total = 427J or ~8% more energy

Thus the salty ice gives you ~8% more cooling for nothing. But the other big advantage of salty ice is that it stays at -16C for ~80% of the time (as opposed to 0C for ice) while the ice is melting (melting ice is what takes a lot of heat energy).

I hope this makes sense and explains the advantages of salty ice!

Cheers

Captain
(Chemical Engineer)

PS. Some assumptions have been made in the above to simplify the explanation, but only alters the final values by a few%.
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Follow Up By: Ron173 - Wednesday, Feb 01, 2006 at 15:53

Wednesday, Feb 01, 2006 at 15:53
Captain,

Top Bloke!

I knew someone would have the theory to back it up, well done.

PS is there any advantage in going beyond 20%? I was planning to add 200grams of salt to 800ml of water and heat to dissolve, then pour into container, is that the way to go?

Ron
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Follow Up By: Member - Captain (WA) - Wednesday, Feb 01, 2006 at 16:02

Wednesday, Feb 01, 2006 at 16:02
Hi Ron,

Salt reaches saturation in water at just over 20%, so there is no benefit in going any higher (you will see undissolved salt in your water if you go too high).

Your method sounds spot on, heat will certainly decrease the time taken to dissolve the salt.

Cheers

Captain
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Follow Up By: robak (QLD) - Wednesday, Feb 01, 2006 at 16:06

Wednesday, Feb 01, 2006 at 16:06
captain,

That makes perfect sense. So the big benefit is that it changes state at a lower temeprature, right?

Thanks for your reply.

R.
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Follow Up By: Ron173 - Wednesday, Feb 01, 2006 at 16:08

Wednesday, Feb 01, 2006 at 16:08
Excellent.

Plan to seal these containers and freeze and refreeze many times from Engel to esky, so wanted to get it right first time.

Thanks a lot, I'm sure this post will also help others who have heard of adding salt but werent sure on method / merits.

Rgds

Ron
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Follow Up By: Member - Captain (WA) - Wednesday, Feb 01, 2006 at 16:20

Wednesday, Feb 01, 2006 at 16:20
Hi Robak,

If we assume we lose say 100J heat loss per hour, after approx 4 hours both "eskys" will be at 5C (assuming 2 eskys with 1g ice / salt ice in this example). But if you look at the time line, then;

After 1 hour;
ice = 0C
salt ice = -16C

After 2 hours;
ice = 0C
salt ice = -16C

After 3 hours;
ice = 0C
salt ice = -16C

After 4 hours;
ice = 5C
salt ice ~ -10C

After 5 hours
ice = 55C
salt ice = 40C

This is better represented as a graph, but I think you get the idea. The salt ice has kept the frozen food at a lower temperature for MUCH longer, but once the ice melts, it makes little difference (the idea is to have enough ice that it doesn't completely melt).

Cheers

Captain

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Follow Up By: robak (QLD) - Wednesday, Feb 01, 2006 at 16:34

Wednesday, Feb 01, 2006 at 16:34
Captain,

That's exactly the kind of graph I imagined. Thanks for your help.

I have another question for you. Actually two. (I got this info off the net so it could be wrong)

1. Since disloving salt requires heat and salt comes back out of solution at -21 deg C, would it be beneficial to freeze your salt solution below -21C and then when the salt re-disolves at -21C it absorbs heat and keeps the solution cooler for longer?

2. I suspect there is no benefit in draining water from an esky because, you're throwing out a heat sink. ie. Ice will stay longer but overall the air in the esky will be warmer sooner (especially with brine). ????

Cheers

R.
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Follow Up By: Member - Captain (WA) - Wednesday, Feb 01, 2006 at 16:54

Wednesday, Feb 01, 2006 at 16:54
Hi Robak,

1. No, when a salt solution goes below -21C (depends on salt concentration), it forms pure ice crystals and NaCl.2H20 crystals (a eutetic mixture as opposed to a homogeneous solution). When it melts, the latent heat is the same.

2. Correct (sort of). Draining the water will remove the heat sink, but until the ice has melted, the water will remain at 0C (or -16C). Once all the ice has melted, the remaing water still requires heat to raise its temp.

Cheers

Captain
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Follow Up By: Ron173 - Wednesday, Feb 01, 2006 at 17:50

Wednesday, Feb 01, 2006 at 17:50
Captain,

just trying to mix this now, and finding its a milky colour with a slight sediment, should it go clear if fully disolved?

I tried removing 200ml and replacing with fresh not much difference, my kitchen scales may be out n got too much salt in I think, I'm sure when I did this stuff at school (long time ago) it should go clear?

Thanks

Rgds

Ron
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Follow Up By: Member - Captain (WA) - Wednesday, Feb 01, 2006 at 18:06

Wednesday, Feb 01, 2006 at 18:06
Hi Ron,

Milky colur is fine, any sediment is excess salt.

Cheers

Captain
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Follow Up By: Bonz (Vic) - Wednesday, Feb 01, 2006 at 22:50

Wednesday, Feb 01, 2006 at 22:50
Captain, I have to dispute your comment that water will not take more than 20% salt. I went swimming at Minkey Mia while waiting for the dolphins and got a mouthful I am sure it was more like 90% salt, it was THE saltiest water I have ever tasted. I would be prepared to accept as low as 80% but no lower! Great info and excellent for a technophile like moi.
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Follow Up By: Member - Davoe (Widgiemooltha) - Thursday, Feb 02, 2006 at 01:11

Thursday, Feb 02, 2006 at 01:11
I dont get it either coz as far as I know saline water doesnt freeze! what you say - yep thats right why do you think icebergs are fresh. what happens is the freshwater freezes further concentrating the ue salt in the unfrozen water until it becomes to saklty to freeze. Ever eaten ham that has been frozen ? you can taste the fresh ice crystals as being seperate from the frozen meat. same as freezing a pickled leg of pork it stays a bit soft with fresh ice crystals iin it and unfrozen saline sections giving it a lumpy feel
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Follow Up By: Member - Captain (WA) - Thursday, Feb 02, 2006 at 13:11

Thursday, Feb 02, 2006 at 13:11
Hi Davoe,

Saline water does freeze, just got to get it cold enough (below -21C depending on salt concentration).

You are right about frozen brine, it forms pure ice crystals and NaCl.2H20 crystals, a eutetic mixture as opposed to a homogeneous solution. It is actually quite technical and I simplified the matter to try and provide an easily understanable explanation. It doesn't change the above calcs I did, but it does happen in a slightly different manner.

So what you actually have is frozen brine crystals (NaCl.2H2O) and frozen pure ice. But depending on the initial concentration, you will have a varying amount of ice and salt crystals. That is why you have the lumpy pickled pork leg, some sections have frozen ice while others have brine, but still below 0C.

The difference is the pork leg stops the salt migrating and does not give the appearance of a homogeneous mixture, unlike an iceblock situation where species migration allows the lot to behave in a homogeneous manner.

I hope this explains things for you.

Cheers

Captain
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Reply By: Rigor - Wednesday, Feb 01, 2006 at 16:23

Wednesday, Feb 01, 2006 at 16:23
A reply to Robak, the salty water or "brine" in A/C or refrigeration system is simply a medium to move the heat from one point to another . eg in a large system the cost of refrigerant (freon) would be huge because of the volume required therefore chill the brine and pump it to the desired location for whatever purpose.
Cheers Dave L.
AnswerID: 152300

Follow Up By: robak (QLD) - Wednesday, Feb 01, 2006 at 16:38

Wednesday, Feb 01, 2006 at 16:38
Thanks for the info Dave.

(and Freon is a CFC isn't it?)

Cheers
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Reply By: geocacher (djcache) - Wednesday, Feb 01, 2006 at 16:27

Wednesday, Feb 01, 2006 at 16:27
Off course once you do that to it you can't drink the water either though. In 90% of cases it's probably not an issue - but if you broke down in a remote dry area and needed to wait a few days for help it might be.

Dave
AnswerID: 152301

Reply By: Member - Guy (QLD) - Wednesday, Feb 01, 2006 at 16:48

Wednesday, Feb 01, 2006 at 16:48
I used to use "brinies" two litre milk containers, when going deep sea fishing, just had 3-4 in an 80 litre evacool, would then tip a few litres of sea water in once we were out , the fish would come home at the end of the day nearly frozen.Just wash the bottles of and return to freezer, they worked great. Some lessons I learned , if you are going to use maxium saturation salt solution then you need a good freezer to get them solid,we had a large chest freezer and I would have to put them down the bottom up against the wall of the freezer, as for the hot water method, I used to get salt from the butcher, it was called flossy salt from memory it desolves quite easly in just cold tap water, you'll notice the difference in temperature of the water as you add the salt. Also discovered one day after washing the brinies I let them stand to drain off , at this time they were just liquid the fresh water on the outside froze. Just thought I would pass on my experience.
Cheers & good luck
Guy
AnswerID: 152308

Follow Up By: Ron173 - Wednesday, Feb 01, 2006 at 17:41

Wednesday, Feb 01, 2006 at 17:41
Great,

all very interesting, and if you ignore minor extra electric costs in freezing longer, something for nothing.

Rgds

Ron
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Reply By: Member No 1- Wednesday, Feb 01, 2006 at 18:36

Wednesday, Feb 01, 2006 at 18:36
its not worth the effort
AnswerID: 152328

Follow Up By: Ron173 - Wednesday, Feb 01, 2006 at 21:50

Wednesday, Feb 01, 2006 at 21:50
Hey nude nut, (not no1!....indeed!!!!!!!!!!!! you wish!!!!!!)

you must need a lot of return for your efforts, how hard is it to add salt to a freezing bottle for extra performance????? lots of effort eh? I really dont think so, and Captains excellent description of the benefits surely is plain to see?

Then again guess your just chasing the 'stirring up posters' factor.

I along with others found it very informative, if you dont think so, fair do, you dont need to post a negative comment like that.

Ron
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Follow Up By: Bonz (Vic) - Wednesday, Feb 01, 2006 at 22:55

Wednesday, Feb 01, 2006 at 22:55
Hmm Nudie knows stuff, I am interested in the extra information he has behind those glasses that lead him to this assertion.
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Follow Up By: Eddy - Wednesday, Feb 01, 2006 at 23:09

Wednesday, Feb 01, 2006 at 23:09
NUMBER 1 MEMBER!

I owe owe something.
I sent my nearest & dearest this text message this morning.

"Men have two emotions: Hungry and Horny. If you see him without an erection, make him a sandwich."

The leader of the oposition demanded to know "Where did that come from!"

I replied with pride, ME!

I will forever be in your debt.

ps. Daughter reckons me & the leader might be back on speaking terms by 2009!

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Reply By: Mike DiD - Wednesday, Feb 01, 2006 at 23:07

Wednesday, Feb 01, 2006 at 23:07
Most domestic freezers only go down to -15 deg don't they. If you use too strong a brine, won't you have trouble freezing it ?

Mike
AnswerID: 152395

Follow Up By: Member - AdrianLR (VIC) - Wednesday, Feb 01, 2006 at 23:29

Wednesday, Feb 01, 2006 at 23:29
This is an important point - having very cold but NOT frozen brine is no use as to get the heat absorption you must go from the solid state (ice) to the liquid state (water). Might be worth an experiment in your own fridge to make sure that the solution you make up actually freezes.
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Follow Up By: Ron173 - Thursday, Feb 02, 2006 at 07:18

Thursday, Feb 02, 2006 at 07:18
Thats a very true point.

You do need a very good freezer, and its wise to experiment first to make sure you can achieve it.

If problems freezing, just remove some brine and add fresh in known quantity therefore reducing concentrate.

Once you know what you can easily freeze, your on a winner.

I intend to ensure that whatever concentrate I'm using, my Engel can freeze it, will try that tonight, doubt it will struggle much though, as even empty it can reach -22deg c.
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Reply By: Gronk - Thursday, Feb 02, 2006 at 10:21

Thursday, Feb 02, 2006 at 10:21
Just my two bobs worth, I bought a downunder fiberglass esky and froze two wine bladders,one with water and one with salty water(about 10%) and filled with beer and four 1litre frozen water bottles. The bladders were laid down on the bottom of the esky side by side and after two days the water bladder was still frozen solid and the salty one was completely melted,so now I just freeze water and they seem to last approx 4+ days before melting
AnswerID: 152468

Reply By: flappa - Thursday, Feb 02, 2006 at 10:43

Thursday, Feb 02, 2006 at 10:43
So , what is the ACTUAL benefit , not a theoretical benefit ?

Does Salty Ice take days/week/months longer to thaw out , or is it a few hours ?

IMO , I like being able to use the cold water for other purposes , rather then just chucking it away.
AnswerID: 152476

Follow Up By: robak (QLD) - Thursday, Feb 02, 2006 at 11:15

Thursday, Feb 02, 2006 at 11:15
Flappa,

from what I understand...

Salt water will not not really keep your esky colder for longer

BUT
With normal ice your esky will be at 0 deg C
With Salty ice it will be at -16 deg C (depending on your concerntration of salt)

Hope I got that right

Cheers

R.
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Follow Up By: flappa - Thursday, Feb 02, 2006 at 11:24

Thursday, Feb 02, 2006 at 11:24
So then , whats the point ?

I'm guessing that with the salty water , will keep frozen things frozen for longer , whereas , normal ice will allow frozen things to thaw from the start ?

What would it matter for a weekend/long weekend , as you want things to thaw anyway ?
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Follow Up By: robak (QLD) - Thursday, Feb 02, 2006 at 11:34

Thursday, Feb 02, 2006 at 11:34
I think everyone has to weigh up the pro's and con's for themselves.

I can see your point of the water being unsuable after it has melted but i find that the water in my esky by the end if full of crap like bits of cabbage and carrot mixed toegther with some sand and meat juices.

Generally any food that has been colder lastes longer. And it's good to have a bloody cold beer after a day of driving.

One other point to note is that you don't have to use salt. I think most things that dissolve will work, like sugar.

R.
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Follow Up By: Ron173 - Thursday, Feb 02, 2006 at 11:46

Thursday, Feb 02, 2006 at 11:46
Hey Robak,

why not start a seperate % sugar thread?? LOL

Ron
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Follow Up By: flappa - Thursday, Feb 02, 2006 at 12:30

Thursday, Feb 02, 2006 at 12:30
I freeze milk/cordial bottles , because I hate floaties.

Water can then be used as required.

I can see the point of "lasts longer" over a week/multi week trip , but over a weekend . . . I see no great benefit (IMO).

I dont seem to need -16 to get a nice cold beer ;)
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Follow Up By: Member No 1- Friday, Feb 03, 2006 at 08:26

Friday, Feb 03, 2006 at 08:26
as I said....why?...not a negative comment just a bloody waste of time and money...i know salt is cheap hehehe but my time is worth money

Robak your theory about drinks being at only 0 may is not always so
have a 90 litre coleman that i can fill with -20 to -25 c ice (never really measured it my fingers stick to it....and by the time i get to sturtvale some of my cans are frozen and thats in 35 ambient...and they are not in contact with the ice but are at bottom of esky partitioned off from the ice by the dividing plate one gets with the esky...i guees they freeze due to low temp ice?
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Follow Up By: robak (QLD) - Friday, Feb 03, 2006 at 09:48

Friday, Feb 03, 2006 at 09:48
Hi Nudie

Yes you're right it's not always so. At first the temperature will be lower then 0. But will quickly get to zero with normal ice. ie once some of the ice turn to water your fridge is at zero.

I've never used salt in ice befor but now I think I will.

Cheers

R.
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FollowupID: 406409

Reply By: DiesAl - Thursday, Feb 02, 2006 at 14:18

Thursday, Feb 02, 2006 at 14:18
This also sounds like a good way to extend the life of your water ice (the way some people use dry ice)

Cheers
AnswerID: 152513

Reply By: rocketsalad - Thursday, Feb 02, 2006 at 16:27

Thursday, Feb 02, 2006 at 16:27
I just noticed that one of my "Esky all purpose refreeze ice pack"s had sprung a leak and yep....salty water. Judging from the taste id say about 50% ......yuk.

rs
AnswerID: 152541

Reply By: Member - Duncs - Thursday, Feb 02, 2006 at 23:23

Thursday, Feb 02, 2006 at 23:23
Ok Let's get practical.

Years ago my brother bought me one of those 4 bottle wine cooler/esky things. You know the one it has plstic bottles that act as dividers inside that you fill with water and freeze to keep the chardy cold. A friend also had one.

He filled his bottles with salt water for the reason expressed above. I filled mine with Cottee's Fruit Punch Cordial. It may have been some other flavour but you get the idea.

At the end of the day my mates kids were drinking salt water and mine had a nice drop of Cottee's. We both had nice cold chardy for the entire day, but my kids love me.

Duncs
AnswerID: 152633

Reply By: Trekkie - Friday, Feb 03, 2006 at 00:28

Friday, Feb 03, 2006 at 00:28
And for those that got lost in the tech details - KISS - the point of this post is to get your Tinnies colder for longer
AnswerID: 152643

Reply By: Ron173 - Friday, Feb 03, 2006 at 12:43

Friday, Feb 03, 2006 at 12:43
MY SUMMARY ON THIS POST WOULD BE:-

Firstly thanks to all who chipped in, it has been very informative and interesting.

I have learned a few things, and tried a few things, regarding the salt issue.

Firstly from direct practical test I found that it is indeed true that a 20% salt solution will take a long time and very low temps to freeze. (feel good nudie? you were to an extent correct! LOL)

Also it was noted a couple of posters found salt water inside reuseable freezer blocks... interesting

Freezer blocks dont take forever to freeze (you know the blue ones)

It would also appear that the only real advantage apart from a minor time extension, is a colder esky, which may not be all that great.

The above said, I would conclude that it COULD be advantageous to use a SMALL concentration of salt, more like 5%, which is probably similair to what you get in the freezer bricks, that way you will get slightly better temps without needing an ice age to freeze it solid.

And one other point, I would never use it in free blocks, ie always in a sealed container for reuse.

THE END

Rgds

Ron

PS My next question is a long debated one, so dont want to start another thread but wondered can you do a poll on here? so you just state your pref A or B?

prhaps someone can tell me?

My question is to drain your esky water or not? I've heard all the sides, I'm just interested in numbers on each side rather than individual ideas?

AnswerID: 152708

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