Keeping the ice chest cold

[floattuber]

Not a terribly important subject but I thought it would be a fun one.

To keep the ice chest cold on extended camping trips do you want to empty the water from the melting ice or keep it in there?

My thoughts are to keep the cold water in the ice chest because the sun has to heat up the mass of the water and the ice. But the flip side is that water is a better conductor of the heat so it ends up melting the remaining ice faster.

 

[JStephen]

Buy two identical ice chests, try it, and report back. Or suggest it to the Mythbusters.

 

[MintJulep]

I'd say drain it. Convective coefficient between water and inside wall is much higher than between air and inside wall.

Same reason a bottle of beer will cool much faster in a bucket of ice water than in the freezer.

 

[dcasto]

I've always kept the water because you are dumping cooling. The ice chest is suppose to stop the heat transfer.

 

[IRstuff]

I'd dump the water. The increased thermal conductivity from the water simply makes it tougher for the ice chest itself to keep in the cold. It would probably also help, a bit, to put the chest on a couple of rails, to limit the external thermal conduction.

TTFN

FAQ731-376

 

[tkordyban]

Keep your ice in the plastic bag from the convenience store. When it melts, the water does not make contact with the ice chest walls, so the convection with the inside wall does not change.

 

[magicme]

keep the water up to a point because it takes longer to heat up that mass of water, then dump the water as soon as it's warmer than you want the beer to be.

keep a wet towel covering the cooler.... keep it wet.

magicme



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there's no place like gnome.

 

[DickRussell]

I suppose it would depend on the cooler design, and the relative contributions to total "R" of outside film coefficient, foam insulation, and inside film coefficient. Then there is the matter of separate areas for heat transfer: wetted and unwetted inside foam surfaces. The contact of water with the foam at the bottom of the cooler will provide a better coefficient (less R) for that part of the total area, but that part of the total R for that area may be insignificant. As long as there is ice and water, and the heat transfer is relatively slow, then the water and ice temperatures will stay at 0 C. Once the ice has just about melted, then having the mass of the water will be an advantage.

Better designs? Thicker foam at the bottom and partly up the sides to compensate for the water contact. An internal ice container, made of aluminum, to keep meltwater from contacting the foam. Of course, "better" depends on whether the purpose of the cooler is to cool things placed into the cooler or to keep cool things already prechilled before placement into the cooler. But the OP did specify "camping trip."

 

[mechengdude]

Solution:

Drink all beer before ice melts...use a funnel if needed. have fun.

 

[jbwick]

iirc heat conduction through a wall (the cooler) is dependent only on the delta T. Then the heat transfer would be constant regardless of the contents. That being the case you would be better off with the water.

It would seem that the conductivity of the water would only be an issue if there were significant mixing of the ice-water-beer.

There are many variables to consider imo this would be an interesting science fair project for a young student.

 

[dvd]

I vote dump the water. Air inside the cooler is a better insulator than water. There is more than convection on the outside of the cooler, condensation on the outside of the cooler seems to stay below the water line.

 

[IRstuff]

heat conduction through a wall (the cooler) is dependent only on the delta T

Only true if delta T is constant. Air and water result in different delta T, since air, being less conductive, sucks up more of the delta T, leaving less delta T across the insulation. This is the reason that double pane windows are more efficient at insulating.

TTFN

FAQ731-376

 

[MintJulep]

heat conduction through a wall (the cooler) is dependent only on the delta T

True if your boundary is the interior surface of the wall.

If we are considering the heat transfer out of the beer to the ambient air, then you have to consider the convective film coefficient. Water's will be much higher than air.

 

[jbwick]

IRstuff are you suggesting that the cooler wall is permated by air or water depending on the contents of the cooler?

MintJulep I assumed at the intial state the contents of the cooler were at a uniform temperature and the ambient air is the higher temperature. Hence heat would travel from the outside and eventually to the beer.

All of the energy reaching the contents must pass through the wall. Granted the contents will eventually warm and the delta T will shrink but it will be slow (if the cooler is any good). So which can absorb more energy and increase in temperature the least?

 

[MintJulep]

This is actually a non-trivial problem isn't it? Transient, multiple heat transfer modes in parallel, as well as mass transfer.

Heat enters the cooler's exterior skin via combined convection, radiation and conduction if in contact with some solid such as the ground or a picnic table.

Passes through the exterior skin via conduction.

Passes to the insulation. If we assume bonded closed cell insulation we can simplify to conduction.

Passes to inner skin, same simplified assumption.

From the inner skin:

Convection to the air.

Lets start with 100% ice, 0% water. Conduction where the ice is touching the inner skin.

Conduction to any beer containers that may be in contact with the skin.

Radiation to ice and beer containers.

Ice begins to melt.

Add convection from skin to water, water to ice and water to beer containers.

Add radiation between water and inner skin, water and any ice that remains "high and dry", and between water and beer containers.

As the ice melts, the volume occupied by H2O decreases, leading to infiltration of warm outside air.

Obviously the initial conditions will affect all of this as well.

On thing is clear however, in summer conditions, by the time the system reaches a steady-state condition the beer will be too warm to drink (unless you are British).

 

[magicme]

MintJulep has nailed the problem statement .... and it is far from a trivial problem (but a fun problem that would be a great lab project for a heat transfer course .... hmmmm)

magicme



------------------------------------
there's no place like gnome.

 

[IRstuff]

I'm assuming that the wall has either water or air on one side and air on the hot side. When you do the 1-D heat flow path, you'll find that the interior air consumes more of the total delta T from the ice to the external air, therefore, there's less delta T across the insulation in that particular case, and therefore, there's less heat transfer.

Using some typical, yet arbitrarily chosen, numbers, water results in 28 W/m^2 transferred through the insulation, while air results in 17 W/m^2 transferred through the insulation. A difference in 10ºC in the delta T across the insulation between water and air on the inside.

TTFN

FAQ731-376

 

[magicme]

IRstuff

it seems you are disregarding the masses (water versus air). it takes a lot longer time to change the temperature of a cooler filled with cold water than a cooler filled with cold air ... i did not run any numbers but i think that would offset the differences in conduction (water vs air).

i think mass is a big factor in this problem.

magicme

------------------------------------
there's no place like gnome.

 

[unclesyd]

I have solved the problem through Edisonian Research and astute observations. I don't go fishing on boats that don't drain the water off their coolers.

I do considerable deep sea fishing in the Gulf of Mexico with numerous extended trips of 2 to 4 days where the ice has to last. I drain the water off all coolers both large and small and use a wooden grid in the bottom of all coolers to insure they drain.

On the larger boat we go to great lengths to insure the coolers drain and that they are air tight and are only opened when it is required. On one of the boats we have a box that holds about 1500 pounds of ice and we can stay 4 days and still arrive with fresh fish. On the larger boat we can carry about 60,000 pounds of ice and can stay about 20 days.

Anecdotal:
Several years ago I had an acquaintance that believed in keeping water in his cooler. While in a fishing tournament he caught a 22+ pound red snapper. He put the fish in his cooler and started for home. He broke down and had to be towed to the dock. While checking the fish at the scales the weigh master deemed that the fish had soured therefore it must have been caught before the start. All his ice had melted and and the warm fish soured in the 5 hrs it took to get to the dock. A 11 pound Red Snapper won the tournament and the $1,000 prize.

 

[dcasto]

let me rephase the question slightly, do you drtain the water off your homemade ice cream maker?

The reason to drain the water off the ice in a boat iw weight and room (for the fish).

You drain water you are loosing energy unless the water is warmer than outside the box.