Unexpected results: side by side "ice box" test

[Tod Mills]

A while back someone on another bulletin board suggested conducting a test with ice in an ice chest.

So, I bought two styrofoam bait buckets (cheapest things I could find for the test) and a second electronic thermometer to go with the one I already had. I plunged the thermo probe through the center of each foam lid and added equal amounts of ice (measured with a cereal bowl) to each bait bucket. The ice in the first bait bucket was tossed directly into it, resting on the bottom. The ice in the second bucket was placed atop the lid of a pan which was tilted to allow the meltwater to drain into the bottom of the bait bucket.

What I found, with two rounds of the test, is that the ice lasted very close to the SAME AMOUNT OF TIME. I was surprised. I would've guessed that the ice in the meltwater would've melted significantly sooner.

Not surprising was that the thermometer in the second bucket read temperatures on the order of 10 degrees lower. Not surprising because the thermometer probe was much closer to the ice.

I want to repeat this test with a bit of a variation: the ice in the second bait bucket supported with something more open. The lid nearly sealed off the upper and lower halves, leaving just a small gap, plenty for water to drain, but not much for air circulation.

I also want to "pre-chill" the bait buckets so that factors such as cooling the mass of the shelf don't come into play.

Any other suggestions for the tests?

[Neil Gordon]

Any other suggestions for the tests?

Fill two identical ice chests with beer and cover with ice. Invite everyone from the board over to talk about sailing.

[Steve Laume]

I don't see how over all temperature could vary much in either bucket. If you allowed the cold water to drain as it melted the dry bucket would be warmer. For short trips I always liked the idea of starting out with as much frozen or very cold food as possible and frozen milk jugs for ice. I really hate having ice and melt water in a cooler along with food and worst of all, bait. I had a bad experience with mullet water in a cooler on a youthful fishing trip to Hatteras once. I think the ideal solution to the ice and melt water problem would be to contain and retain it in the ice box. By draining it off we are giving up all the cooling effect of the near freezing temp water. That is a fair trade for not having it slosh around with the milk, cheese, fish and steak. I would like to find some thing like those water carriers that look like a big cube with a handle and a drain. The difference with the ice carrier is that it would need to open to be able to add the ice. If you take this to the patent office I want a few of these things and some beer to go with em, Steve.

[Carl Thunberg]

Hi Tod,

Actually, this result shouldn't come as any surprise. It boils down to basic thermodynamics. For ice to go through a phase change requires the introduction of heat. Ice in a cooler is not super-cooled. It's at or near 32 degrees. Ice and melted water are at roughly the same temperature. The melted ice has no excess heat to give off. Therefore, it shouldn't make any difference in the overall length of time it takes to melt a block of ice whether you siphon the water off or not. The insulation does a good, but not perfect, job of preventing heat from the outside. If there is any effect of the ice being in contact with the water, it may be because the water has a greater surface area in contact with the floor of the cooler, and therefore has greater exposure to heat from external sources.

Phew! I need a beer .

[Cathy Monaghan]

Tod,

Don't forget to use block rather than cubed ice in the icebox on your boat. Cubed ice will melt almost immediately compared to block ice. Three blocks of ice, if kept out of the melt-water should last 4-5 days in a well-insulated box.

Try your test with a couple blocks of ice of equal size and density. Let one sit in the water and let the other sit above it. Keep the meltwater in each bucket. It's the meltwater that keeps the stuff in the bottom of the icebox cold. And since cold air sinks, you want the ice up high so that the cold will start out near the top and sink to the bottom, keeping the entire box cool. If the ice is down at the bottom, the coldest area of the box will be the bottom and the stuff up high (like your produce which should be in a basket or something up out of the water) will be in the warmer part of the box and that's the stuff that really needs to be kept coolest.

Have fun and let us know what happens.


Cathy

[Oswego John]

Hi all,

Many years ago a student asked "Is all ice at the same temperature or can ice be at different temperatures?" The answer is that ice can, indeed, be at different temperatures. Can you see where this post might be heading?

Here are some views that can muddle this thread, throw a few logs on the fire and possibly stimulate your thought. By the way, feel free to disagree with whatever you think may be contrary to what I say.

I think that we might all agree that still, sweet water above 32° F won't freeze. The same water will start to freeze below 32° F. If this same volume of water is subjected to a temperature of, say, 30° F for a prolonged period of time, there will be a volume of ice measuring 30° F.

If the same volume of water is subjected to 20° F, it will, in time, be a volume of ice that is 20° F. The same volume of water, when subjected to zero° F, will become a volume of ice that measures 0° F

Water freezes from the outside surface inward. Until frozen for a long enough duration, the core of the volume can be warmer than the exterior surfaces, even may still be liquid. In time, the volume of ice will be of the same temperature throughout.

When this same volume of ice is exposed to temperature that is warmer than 32° F, it begins to melt from the outer surface first, then inwardly.

Through less than perfect insulation and repeated opening and closing of the box, warmer air enters the box and raises the boxe's ambient temperature and the melting cycle begins.

It is not rocket science to realize that the 30° volume of ice will melt in a short time. The 20° F volume of ice will melt more slowly, and the zero volume of ice will last the longest.

To better understand what's going on, picture a northern pond in early winter. The pond water is at least 33° F or higher. As the outside air drops to 30° F, the water on the surface begines to freeze. Nothing changes below the surface. As the temperature drops to 20° F, the surface becomes colder and the thickness of the ice increases. After an extended time and/or the temperature drops to zero, the ice temperature lowers and it's thickness increases.

The reverse happens when the temperature warms up in the springtime.

Some of the bottom line (not all) is that the temperature of the ice that you use , the degree and effeciency of insulation in place, the outside air temperature and the frequency of use of the box all affect the length that ice will last.

More to be said about draining melt water or not at a later post.

O J

[barnettg]

OJ,

It really is thermodynamics! One calorie (cal) is the amount of heat required to raise the temperature of 1 gram of water (or ice) 1 degree Celsius (C), but a gram of ice at 0 C (32F) must absorb 80 cal of heat to convert it to 1 g of water at 0 C (Its heat of fusion). So it takes as much heat to convert a 32F block of ice to a 32F pool of water as it takes to increase the temperature of the same 32F pool of water to 176F. It is the heat absorbed by the ice as it melts that keeps your goods cold - not the temperature of the ice.

Glenn

[barnettg]

The heat absorbed by the ice as it went through the phase transition of solid to liquid would be sufficient to raise the temperature of an equal mass of water by 176F, but since it started at 32F the final temperature would be 208F or nearly boiling! Yes...science is stranger than fiction.
Glenn

[Tim Mertinooke]

I wonder if the guys trapped up in this weather station are mentally sparring over the same things you guys are right now? Right now it is -12 degrees with 91mph winds. Even the Minnesotans who read this are shivering. Click the link for an update, but I'm warning you it's addicting. Tim

www.mountwashington.org

[img]http://www.mountwashington.com/pictures ... ington.jpg[/img]

[Oswego John]

Hi Tim and all,

Mt. Washington is something else, truly awesome. Several years ago, my late wife and I were touring upper New England, concentrating mostly on New Hampshire.

I remember that it was Columbus Day weekend which, if I remember correctly is also the same time that Canadians celebrate Thanksgiving. It also happens to be high season fo the fall foliage color show.

We rode the chairlift to the top of Wildcat Mountain, which is across the valley, to the east of Mt. Washington. (MW) I was taking some great photo shots when my wife asked me what was going on on the top of MW. Here I was, on a beautiful autumn day, clad in just chinos, shirt and sweater, looking through binoculars at a fierce winter storm raging atop MW.

I thought that it would be wise for us to get off the mountain with a storm approaching. I mentioned this to the lift attendant and he said not to worry, that these storms were a common occurence. He mentioned that the mountain was so huge that it often times created it's own weather.

I have friends that would often ski into late June or early July in the Tuckerman Ravine, on the shady side of MW. Talk about a deep snow base.

By the way, I took some great shots of "The Old Man Of The Mountain" earlier on that trip.

http://www.nh.gov/oldman/

Think spring,

O J

[Neil Gordon]

I wonder if the guys trapped up in this weather station are mentally sparring over the same things you guys are right now?

The guys on top of Mt. Washington worry about getting trapped outside in a sudden snow squall. I read a story about one of them several years ago who was caught outside that way while checking instruments. His eye lids froze shut and was lucky to find his way back inside.

There's a lesson for us in keeping a good weather eye even as we worry about our melting ice.

[Tim Mertinooke]

There is a prestigious club up there called the "Century Club". One is initiated once they successfully circumnavigate the station in winds that exceed 100mph without falling. It's an exclusive club even for those who work there. Fortunately there is plenty of opportunity in a typical winter. Time to reef.

[CruiseAlong]

I believe you will find that a "ventilated" pan spacer will also not increase the ice life....the energy to melt the ice must come from the outside world..i.e. outside the cooler...and they are the same. A variation which may work is to cover the ice with a thin sheet of plastic which may break up the thermo pumping between the top warmer space of the cooler and the lower cooler volume of the cooler. Given the equal coolers (insulation thickness, type of insulation, etc.) and refrigeration loads (things to cool), that is the only mechanism which would work to keep the upper slighly warmer air volume from circulating down.