Keeping stuff cold & ice vs. dry ice.

[dcampen]

Next month I am going to be car (truck) camping for 7 days/6 nights in the desert of SE New Mexico. While I can pretty much survive for this period on foods that do not need refrigeration I would like to have a couple of cold beers in the evening. Also, now, my wife insists that she wants to go with me and she would like better food than what I can survive on.

So, I am planning on bringing 2 - 50 qt., Igloo brand coolers. While these coolers claim to be able to hold ice for up to 5 days in 95F temperatures this must be if they are filled with a solid block of ice; my experience has been that the cooler is good for about 3 days. While there is allegedly a general store that may have ice about an hours drive away from where I will be camping I would rather avoid this 2 hour round-trip drive as I expect my days to be rather full.

So, my question is, does anyone have experience with using dry ice when car camping for extended periods? If I fill a 50 qt. cooler with dry ice would there be any hope that it would last significantly longer than wet ice?

 

[mike_d]

If I fill a 50 qt. cooler with dry ice would there be any hope that it would last significantly longer than wet ice?

i have no experience with this, but from a purely theoretical viewpoint, i'd say dry ice is a bad idea. the amount of heat that one pound of ice can absorb (that's is to just take ice at 32F and turn it to water at 32F) is 3200 calories. one pound of dry ice is a little more than half that: 1900 calories per pound. once the try ice sublimes, it turns into CO2 gas and goes away, so you don't get any more cooling other than the subliming of the dry ice. when wet ice turns into water, you still have 32F water in the cooler, so that will help keep things cold until the water warms up to the outside temperatures.

so overall, per pound, wet ice is at least twice as good as dry ice.

if your experience is that you can get 3 days out of your cooler, and you need to only get 2 more days or so out of it, then maybe just a few little changes can really help. during the day wrap the cooler in as many blankets as you have, even use your sleeping bag. this will significantly slow down the heating from the outside, and that could really help give you some more time. also, make sure that anything you put in the cooler is already cold (preferbly frozen), so you don't need to use any of ice to cool stuff down. that may be enough to give you the extra time.

 

[dcampen]

the amount of heat that one pound of ice can absorb (that's is to just take ice at 32F and turn it to water at 32F) is 3200 calories. one pound of dry ice is a little more than half that: 1900 calories per pound.

Where did you get these values? I have found web sites that claim that dry ice has twice the "cooling capacity" of ice.
http://www.uigi.com/carbondioxide.html
(4th paragraph)

once the try ice sublimes, it turns into CO2 gas and goes away, so you don't get any more cooling other than the subliming of the dry ice. when wet ice turns into water, you still have 32F water in the cooler, so that will help keep things cold until the water warms up to the outside temperatures.

All good points. Also, since the dry ice is colder thus giving a larger temperature gradient, heat will transfer into the dry ice chest more rapidly.

 

[mike_d]

i know for sure that the water value is right. i verified that from a couple of data sources...water has a heat of fusion of 80 cal/g which is about 3200 cal/lb

i'm less confident about the dry ice numbers. i can't find much of a concensus. but i did find one other site that agrees with the numbers you posted. so 571.3 kJ/kg is about 6200 cal/lb which is almost twice, as you say.

so i don't know what to believe just yet, the best source to find data is www.nist.gov. i just haven't been able to find the thermodynamics tables.

but i still think water is the way to go. you're right with the larger temperature gradient, you're going to lose (well gain) heat moure quickly. but let's ignore that for a second.

i'll use the 95F ouside temperature figure that you posted, and i'll assume that it's that temperature all the time. of course it'll get damn cold at night in the desert, but i'm going to ignore that. and right now, lets ignore any food that you would have in the cooler.

if we have dry ice AND all the gassous CO2 stays around to help cool:

1lb CO2(solid) at -110F -> 1lb CO2(gas) at -110F (6200 calories)
1lb CO2(gas) at -110f -> 1lb of CO2(gas) at +95F (9500 calories)

total = 15700 calories

1lb H2O(solid) at 32F -> 1lb H2O(liquid) at 32F (3200 calories)
1lb H2O(liquid) at 32F -> 1lb of H2O(liquid) at 95F (14300 calories)

total = 17500 calories

so even if all the gas stayed around to help cool, you'd still not be as good as water.

if you want to double check my calculations: (which you should, i can't verify that i did everything right, especially since i just did it real quick on a sheet of paper in front of me) here are the numbers i used

heat of fusion of H2O 80cal/g = 3600cal/lb
heat of sublimation of CO2 = 136 cal/g = 6200 cal/lb
specific heat of CO2(gas) = .011 cal/g/F = 51 cal/lb/F
specific heat of H2O(liquid) = .55 cal/g/F = 250 cal/lb/F

 

[dcampen]

From the Handbook of Chemistry & Physics I get a value of 80cal/g for the heat of fusion of ice (equals 36,000cal/lb or 144 BTU/lb).

Also from the Hand. of Chem. & Phys.: 1 BTU = 252 cal.

From this web site:
http://www.ccpidryice.com/dryice/specs.php
I get a value of 246 BTU/lb for the heat of sublimation of dry ice (equals 62,000 cal/lb).
Also from this web site, I get a density of dry ice of 98 lb/cu. ft. which would give me (246X98=) 24,000 BTU from the sublimation of 1 cu. ft. of dry ice.

The density of ice is about 57 lb/cu. ft. so the heat of fusion of 1 cu. ft. of ice should be (144X57=) 8,200 BTU.

So if I can believe the values from the above referenced web site, then, per volume, dry ice has about 3 times the cooling capacity of water ice.

 

[dcampen]

heat of fusion of H2O 80cal/g = 3600cal/lb
heat of sublimation of CO2 = 136 cal/g = 6200 cal/lb

You are slipping a decimal point. But so far we agree on the ratios.

I will have to go over your calculations for the cooling capacity lost to the escaping, cold CO2 gas.

On a side note, I determined the other day that a 1 lb propane cylinder, like I use for car camping, contains 20,000 BTU the equivalent of the heat of sublimation of 1 cu. ft. of dry ice. What I need is a portable ammonia cycle refrigerator like they sometimes use in RVs. I wonder what the efficiency of an ammonia cycle refrigerator is?

 

[mike_d]

i guess i should learn to keep my orders of maginitude correct . since i can't seem to multiply, i'm going to just trust the numbers you say and concede that it looks like dry ice is better than wet ice. something i would never have expected.

 

[waskillywabbit]

ARB Cooler

Just buy an ARB refridgerator and be done with it! :xnuts:

:guitar2:

 

[84runner]

i have a little insight on this matter. i work at a taxidermy and when we ship frozen carcasses to different countries we always use dry ice. it doe skeep things cooler longer, proven fact. HOWEVER, with using dry ice make sure meats or other such products don't come into direct contact with the ice or it will create freezer burn. we use paper as a buffer between the ice. you also won't have to worry about water getting into food with dry ice.