signman replied:

As Pof. Sumner Miller would say.."Why is it so..."

porl replied:

Do it again with the salt thing. I would do it right now cept i don't have polystyerene cups and no ice and i dunno how much salt to put in.

Member - Jay Gee (WA) replied:

And you came to this conculsion because.........?

Browser replied:

Hi Ron173,

You have shown that ice lasts longer if you drain away the water but what about the temperature? I always find that a beer in an ice slurry is colder than when it is simply sat on ice. So what is important to you? Longer lasting ice or colder beer!!!!!

regards,

Browser

Moose replied:

G'day Ron
Dr Karl would say that doing the experiment only once proves nothing. Ambient temp obviously has an effect. Try again at higher and lower ambient. Do it in an esky since you are saying that what happens in the poly cups can be assumed to also occur in an esky. Eskies not usually 100% polystyrene. Also eskies have lids which should be better insulated than a piece of glad wrap!
However I would have thought that the fact that the water you added was above freezing would obviously hasten the melting of the ice.
Good on you for coming up with the idea. Back in the old days of actually using an esky I always emptied the water without really wondering about it scientifically - just did it because the food floating in the water was detrimental to its edibility.

Bega Photographer replied:

OK, it does seem to uphold the theory.

How about trying the following to confirm it:

Put out two styrene cups with just ice. When the ice is about half melted, tip the water out of one and then see how they perform. I'd be pleased to hear the outcome. I suppose, of course, that I could do this for myself, but it's easier and more reliable to put it on to such an expert as you, Ron.

I recall, as a boy before we had a fridge and the iceman came once a week. The block of ice sat in the top of the icechest on a platform about half an inch high. The melted ice drained into a bucket. Now I know why.

I'd also appreciate some insight about keeping ice and frozen meat.

I'm going on another wilderness landscape photography trip to outback South Australia in August. Traveling on an ATV (four wheel motorbike) I don't have much spare space or carrying capacity.

I'd like to take some frozen lamb chops this time to go with the beans, damper, and black tea.

I have a 5liter drink esky with a large, square lid which is polyurithane insulated and seems to be not too bad for it's insulative properties. I wondered about putting the frozen meat and an ice pack in one of those flexable picnic packs, inside the esky. Are the picnic packs any good for this or do they just keep your sandwiches cool for an hour or two?

Regards,
Laurie.
Wilderness Landscape Photography

Member - John L G replied:

Hi Ron

Too much time methinks but that may be another matter.

Question: The water you added to the ice blocks - was that room temperature water or chilled water just above freezing temperature as melted ice would be?

That may provide a slightly different story as the total thermal mass may take longer to thaw ---- or not perhaps!!!!!!!!!!!

If all else fails turn on the Engel with the beer barrel inside.

John G

Lone Wolf replied:

As quoted by Member Number 1..."water conducts heat better than air...thats why the ice melts faster" Now, he is also one of the proponents of emptying the water from an esky, he is also a refrigeration dude, so I am not going to argue his points.

I will however, say this...

Water conducts heat better than air. So, if you've got just ice in the esky, and drinks, and air, how is the air going to conduct the temperature differential to the drinks?

If you've got an Ice / water slurry, it is quite evident to see how the differential can be carried out.

I am also led to believe, that if you keep ANYTHING, in an esky or fridge, other than air, it is going to be more efficient, ergo keeping the cold water within the confines of the esky.

I really think, that a controlled experiment, needs to be carried out, to see, once and for all, what method KEEPS GOODS IN AN ESKY THE COLDEST, not, what keeps the ice the longest, we want COLD GOODS, which is by way of thawing ice.

So, two identical eskies, two lots of produce, two identical thermometer probes, and some weighed ice.

I am not going to do this experiment, I'll leave it to someone else, who can then bask in the EO Mythbuster Limelight.

May the better esky win....

The gauntlet has been thrown down...

Wolfie

Member - Jack replied:

I may be wrong but it was pointed out to me that salt does lower the freezing temp of water ..... so you get colder tinnies . Gotta be a good thing.

But ............................. (and there's always one of these) .......................

It therefore has a lower melting point, so turns to water sooner.

Oh, how I do miss Prof Julius Sumner Milner ......

Jack

The Explorer replied:

Another couple of questions

Does ice frozen in and Engel last longer than that frozen in a Waeco?

Are wide ice cubes better than skinny ones?

Just curious
Cheers
Greg

tojo replied:

I've heard Dr karl on the radio talking about how hot water will freeze quicker than water at ambient temperature apparently there is many theorys on it but now one really knows . Dr karl had his own but l cant seem to recall it , l have never actually tried it my self but Dr karl is one smart cookie .
Any test pilots ? .

andoland replied:

Ron,

Good experiment but I don't think you can draw the conclusion from this experiment that you should drain water from the esky for best results. What you have demonstrated is that the water in the cup contained more energy than the air in the other cup.

Here is some maths.
Lets assume cold water put into the cup was about 50mL and was say 2 degrees (i.e. just above freezing). The specific heat of water is 4.18 J/g/C. We know the water did no freeze so it did not reach zero degrees. Lets say the final water temperature after 2 hours was 1 degree so the water temp reduced by 1 degree.

To calculate the amount of energy the water gave up, and hence the amount of enegry the ice absorbed:

Energy, q = mass X specific heat x change in temperature

So for the water, mass = 50 g (water has a density close enough to 1000 kg/m3)
specific heat = 4.180
change in temp = 1 degree

therefore q = 50 x 4.18 x 1 = 209 J, i.e. the ice absorbed 209 Joules of energy

Now for the other cup. This cup contains air only so the ice has to absorb energy from the warmer air. If we assume the same volume of air (50mL) as for the water, then there is 0.06g of air being cooled. The specific heat of air is 1.009 j/g/C. We will assume the air was at 25 degrees and cooled down to 1 degree. The amount of heat absorbed by the ice from the air is:

q = 0.06 x 1.009 x 25 = 1.6 J, i.e. the ice only absorbed 1.6 joules of energy from the air.

This maths does not take into account heat loss through the cup walls.

So the ice with water in it absorbed 139 times as much energy, but this energy was absorbed COOLING THE WATER DOWN. If you have ice in your esky that melts to water, then the water is at 0 degrees and will stay at that temperature until the ice has completely melted. Therefore, the ice will not be absorbing energy to cool this water down so this is a different scenario to the experiment that you did.

There is some more thermodynamics could be done to show whether you are better off draining water out or not, based on the specific heat of water versus the latent heat of fusion in the ice, and the differences in temperature between an ice slurry which will be at 0 degrees and ice without water around it which will be less than zero degrees. You also have to take into account then convection and conduction because water is a much better heat transfer medium than air, i.e. cold water will cool an object down much quicker than air that is the same temperature. But, it is Friday afternoon and I left Uni too long ago to remember how to do the calculations anyway.

Have I confused everybody sufficiently?
Ando

Vivid Adventures replied:

complex subject.

The water transfers heat (from the outside of the esky through the esky walls to the water body) and from the goods in the ice box to the water body (keeping them cool) better than air transfers the same heat.

So if the items need cooling first, the water - if it is colder than the items - will do it better - the air, on the other hand is likely to be warmer than the water, so even though it is not as effective, it may actually be transfering some heat (warming them up) into the items (and the ice) to start with, until the air gets cold enough.

So, in the end you need to decide what you care about - if you care about cold ice, cold water, cold air, cold esky, cold car or cold goods!

The best way is to get everything (esky included) pre-chilled (put it all in a freezer, and start with the goods as cold as you can have them) - then it just gets down to the air-tightness and insulation of your esky.

The salt disolving has a heat of solution in water, so it extracts heat from solution (I think this is called exothermic). KNO3 is better - 4x better at cooling I think. On the other hand, LiCl is endothermic and heats the solution something like 20x as much as NaCl (salt) decreases it's temperature! Exactly how much depends on how much salt, and the temperature of the water and the salt!

The usual questions though, should be how much heat your two polystyene cups could absorb

I'd hazard to guess that in most situations, the "only water" one is still more capable of cooling stuff than your "4 ice cubes" (and a lota air) one.

Ciao for now
Andrew.

gramps replied:

Ohhhh my head hurts :(((( Knew I should'nt have started reading this thread.

Ron, You're gunna burn for this :))))))))

Member - Camper (SA) replied:

Whacko! real science on the Forum!
I'm with Arnoland. There are more variables here than one can poke a stick at.
Including heat required to increase temp of ice, latent heat required to melt ice and heat required to raise temp of water.
Try repeating experiment and seeing how long it takes for the contents of each cup to reach ambient temp. My money is on the cup with water and ice because ultimately after the ice melts there is more water to raise to ambient.
Ain't this excitin'?
Camper

Member - Bware replied:

Those in favour of the 'slurry method' must realise that the water is not below 0 c, that's a fact, and I like my beer a bit colder than that. Also, the more slurry the less ice the higher the slurry temperature.