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Old 11-10-2012, 18:52   #31
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Re: Which do you suppose is more efficient?

I only have coolers (the one's that say they hold ice for 5 days ). I pack one with food, drinks and ice. The other will fit 3 bags of ice and dry ice. I pull out a bag of ice every day or so and restock the food and drink cooler. I can go 3 days in 90+ degree weather with this set up.
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Old 11-10-2012, 19:24   #32
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Re: Which do you suppose is more efficient?

Actually, I have done one better on a very cold night backpacking, where the bottle stayed in the sleeping bag for awhile.

I also have spent cold nights where my German Sheppard wanted in the bag, then too warm - wants out, then in...all night long...


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Better would be to pee in a bottle and keep it in the tent. So long as the bottle is at a higher temp than the air, it will give off heat to the air, thus helping to warm the tent. Peeing outside just looses those calories.

The thing with water is it has a huge energy density (the amount of energy it takes to heat or cool it by one degree. Air is around .001 vs water at 4.2 J/cm^3. This means it takes roughly 4200 times as much energy to heat up a given volume of water compared to the same volume of air.

Again, as you let water out of the box, you let air in. The air which is nice and warm will quickly drop in temprature, while the stuff inside increases. Further, as heat is transferred into the box, that heat energy has very little mass to heat up, except for the stuff, because the air warms up so easily.
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Old 11-10-2012, 19:56   #33
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Originally Posted by witzgall
Physics dictate that you drain the water. Otherwise, the water, which is very effective at heat transfer, will hasten the melting of the rest of the ice.

On a similar note, imagine that you are camping in a tent, and it is cold outside. You have a full bladder, and are wondering "Should I go outside and pee out all of that warm liquid, surely it is keeping me warm?". The answer is to go outside and relieve yourself, your body is burning calories to keep that stuff warm, it is not warming you.

Chris
Try it. You'll figure out you're wrong (about the ice... always empty the full bladder). The water acts as a thermal mass, and continues the cooling process.
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Old 12-10-2012, 05:41   #34
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Re: Which do you suppose is more efficient?

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Try it. You'll figure out you're wrong (about the ice... always empty the full bladder). The water acts as a thermal mass, and continues the cooling process.

Even though water is a dialectic fluid (and thus remains at the same temp as the ice until all of the ice melts), it has always been my assumption that any box is not insulated enough to overcome the effects of the water hastening the transfer of heat to the boxes surface.

Maybe I just always had badly insulated boxes/icechests.

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Old 12-10-2012, 07:27   #35
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Even though water is a dialectic fluid (and thus remains at the same temp as the ice until all of the ice melts), it has always been my assumption that any box is not insulated enough to overcome the effects of the water hastening the transfer of heat to the boxes surface.

Maybe I just always had badly insulated boxes/icechests.

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I can tell you without a doubt that I go through less ice when I keep the water. And my beer at the bottom is colder than the beer sitting ontop of the ice bag. To me, that's the most important.
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Old 12-10-2012, 07:37   #36
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Re: Which do you suppose is more efficient?

Good Question and answers...have often wondered about this myself...
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Old 12-10-2012, 10:09   #37
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Re: Which do you suppose is more efficient?

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Good Question and answers...have often wondered about this myself...
And after reading it all I still wonder.
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Old 12-10-2012, 13:25   #38
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Re: Which do you suppose is more efficient?

I just don't understand the debate. The science is so clear it's frustrating, so I will go on to some authorative sources...


EVERY SINGLE COOLER MANUFACTURER RECOMMENDS KEEPING THE WATER IN THE ICE CHEST.

Yup, every one. Best practice is to only drain the water when adding more ice, and even then, just drain enough water to be able to add the new (this assumes the water is still at 32 degrees, if it has warmed get rid of it).
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Old 12-10-2012, 14:04   #39
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Re: Which do you suppose is more efficient?

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I just don't understand the debate. The science is so clear it's frustrating, so I will go on to some authorative sources...


EVERY SINGLE COOLER MANUFACTURER RECOMMENDS KEEPING THE WATER IN THE ICE CHEST.

Yup, every one. Best practice is to only drain the water when adding more ice, and even then, just drain enough water to be able to add the new (this assumes the water is still at 32 degrees, if it has warmed get rid of it).
Oh I don't know. They just make coolers.

You should hear what Toshiba help told my son. And they are computer whizzes.
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Old 13-10-2012, 09:34   #40
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Re: Which do you suppose is more efficient?

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Oh I don't know. They just make coolers.

You should hear what Toshiba help told my son. And they are computer whizzes.
Regarding specs,claims and perfomance, I think most products represented claims are over the top...at least the aircraft and boating business seems to be...they never seem to represent the true performance of a given craft...story tellers!..
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Old 13-10-2012, 10:31   #41
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Re: Which do you suppose is more efficient?

The rate of heat transfer due to convection depends on a temperature difference between the fluid and the wall of the box that is in contact with the fluid.

One must look at the other important heat transfer mechanism which is the conduction of the heat through the insulation.

There are other heat transfer to consider but the most important is the conduction. The rate of heat transfer through the insulation is a function of the conductivity and thickness of the insulation and the temperature difference between the outside of the insulation and the inside. The inside is roughly at 0 deg C if the ice is slowly melting and there is water.

In the steady-state, lid on box, ice slowly melting, it doesn't really matter if the water is present or drained...as long as there is ice.

When the ice is used up if water is present as heat transfers into the box the water slows the warming. More water slower rise in temperature. The relatively high specific heat and mass of the water require much more heat to change temperature than air or food in the box. That is because the heat flowing into the box and raising the temperature is governed by the mass times the specific heat of the water.

Because the inner wall temperature of the box is very very close to the water and air temperature in the box the difference in the amount of heat transfered by the water compared to air due to the difference in the coefficient of convection is negligable. In other words the temperature gradients are small and the process is not governed by the convective process but rather is governed by conduction through the insulation.

So in conclusion...as long as there is ice in the box it doesn't practically matter if the water is present. In the end game, when all of the ice is gone then it matters and the water will help to keep the box cold for a longer time.

However, once your ice is consumed you are within a day or so of getting too warm anyway even if the liquid water bought you some hours.

The cooler manufacturers recommend leaving the water in because it is common for coolers to use up all the ice and the cold water will buy some amount of time for picnic'ers and campers on the weekend. In their time frame the water is important.

In a cruisers time scale I think it is less important because a cruiser will need to maintain ice over the long haul. I think the potential heath risks (blood and food soaking in the water, leaking zip locks, etc.) outweight the benefits.
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Old 13-10-2012, 10:37   #42
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Re: Which do you suppose is more efficient?

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Even though water is a dialectic fluid (and thus remains at the same temp as the ice until all of the ice melts), it has always been my assumption that any box is not insulated enough to overcome the effects of the water hastening the transfer of heat to the boxes surface.

Chris
Think about the above statement...and remember there is always ice at both the North and South Poles. Well maybe not the North Pole in the future.
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