|Cold as Ice....How cold is that?|
|Also...be sure to read about "fast food" ice.....And what it means to "siphon".
All on this page!
|Hopefully, reading this page will be more interesting than watching paint dry, the grass grow, or water freeze!
As mentioned elsewhere on this site, I've worked on just about anything there is to work on. One of those things happens to be commercial ice cube machines, often found in taverns and restaurants. Over the years, I learned some interesting things about ice. You should know this too, so you can impress your buddies, if nothing else!
First, you have to know a few things about hot and cold. I'm going to use water for a simple comparison of how heat flows. You know that without any help, water will only run downhill. As long as water is available at a higher level, it will continue to flow to a lower level naturally. If the water from the higher level "fills up" the lower level to the point where lower level becomes the same height as the higher level, the water will no longer flow. But if either the height of the upper level is increased, or the lower level decreased, the water will begin to flow again.
Heat flows in very much the same way. Just as water only flows downhill, heat will only flow from hot to cold, never from cold to hot. If you have a block of metal heated to 100 degrees, and you place it against another block of metal that is 50 degrees, heat will immediately begin flowing from the hot block, to the cold block. This will cause the hot block to start cooling down, and the cold block to start warming up. At a certain point, both blocks will become the same temperature, and the flow of heat between them will stop. Adding, or removing, heat from either one of the blocks, will cause heat to start flowing between them again, always FROM the warmer one TO the colder one.
Now's a good time to clarify where "cold" comes from. People sometimes tell me their refrigerator or air conditioner isn't making any "cold". Technically, there is no such thing as making "cold". What cold really is, is a lack of heat. Just about any object that does not produce heat, will tend to be at the same temperature as it's surroundings. To make that object colder, you have to remove some of the heat from it. This makes the object less "hot", in other words, colder. The most common way to remove heat from an object is to place it in cooler surroundings, such as the cold air in a refrigerator, or cold water. Then the heat from the object will flow into the surroundings. Also, the bigger the difference in temperature between an object and it's surroundings, the faster the heat will flow.
OK then, so where does the cold air in the fridge come from, you may ask. Someday I'll devote an entire page to exactly how a refrigerator works. But for now, I'll give you the short version. A liquid with a very low boiling point, often called Freon, is capable of absorbing heat at low temperatures, as it boils into a vapor (similar to steam) inside a sealed container within the refrigerator. This causes the container to become very cold, as it's heat is transferred to the Freon. Now that the container is colder than the surrounding air, heat will flow from the air, to the container, causing the air to become colder. So where did the heat go? As the Freon boils into a vapor, the heat becomes "trapped" in the vapor. The vapor is drawn away by the refrigerating mechanism, located outside of the cabinet, which "concentrates" the heat up to a temperature higher than the room temperature. This allows the heat to be transferred to the air in the room. That's why the coils on the back of your fridge get hot! Once the heat is removed from the vapor, it turns back into a liquid (condenses) and the liquid goes back inside the fridge to do it's job all over again.
You hear the term "BTU" a lot, but you probably don't really know what it means, yet! A BTU or British Thermal Unit, is simply a term to describe a given amount of heat, much the same way a "gallon" describes a given amount of milk. You know about how big a gallon is. Here's how "big" a BTU is: It's the amount of heat you have to add to one pound of water, to make the water get warmer by 1 degree Farenheit. Likewise, removing one BTU of heat from one pound of water will make the water cooler by 1 degree. (A pound of water is about 16 fluid ounces, or a pint.)
If you have 1 pound of water, and you add 10 BTU's to it, it will get 10 degrees warmer.
If you have 10 pounds of water, and you add 10 BTU's to it, it will get 1 degree warmer.
A gallon of water weighs about 8.5 pounds, so you would have to add 8.5 BTU's to it to make it get 1 degree warmer.
An average electric household water heater adds a little over 15,000 BTU's per hour to the water, and if the heater holds 50 gallons, that's about 425 pounds of water. So you have to add 425 BTU's for each degree the water is heated. Saying you want to heat the water by 50 degrees, from 70 to 120 degrees, you have to add 425 x 50 = 21,250 BTU's to the water. So it will take more than an hour to do this. On the other hand, a gas water heater is typically 35,000 BTU's per hour, so accomplishing the same task as above would only take about 40 minutes.
OK, so now you know what a BTU is, let's talk about ice!
Many people think that water simply turns to ice at 32 degrees. But really, there's more to it than that. As you now know, if we have a pound of water that is let's say, 62 degrees warm, we have to remove 30 BTU's from it to cool it down to 32 degrees. What do think will happen if we remove 10 more BTU's from it? Think it'll freeze solid? Think it'll cool down to 22 degrees?
None of the above. A thin film of ice will form at the coldest point on the water. If we don't add or remove any more BTU's from the water, it will stay like that indefinitely. If we remove another 10 BTU's, the ice film will become thicker. But the water will still be 32 degrees! Interestingly, once our pound of water is cooled down to 32 degrees, we have to remove 144 BTU's from it to turn it into solid ice! And even after we do that, it will still be 32 degrees!
The trick is the "change of state". I mentioned earlier about heat getting "trapped" in Freon as the Freon changed from a liquid to a vapor. In the case of ice, the "change of state" is a liquid (water) changing to a solid (ice). During the change of state, a whole lot of extra BTU's can get "trapped" or stored in a substance, without causing a temperature change. This is called "latent heat". In the case of our ice, it helps to look at what happens as it melts. While it is in the process of changing from a solid to a liquid, a pound of ice will "soak up" or remove 144 BTU's from it's surroundings. Even though the water resulting from the ice melting is still 32 degrees, the same temperature the ice was, it now contains the extra 144 BTU's of latent heat. Therefore, to turn this water back into ice, even though it's already 32 degrees, we still have to remove that extra 144 BTU's!
Once the water is frozen into ice, it can still be made colder, by removing only about 1 BTU per pound again. If this ice is stored in your freezer, it will cool down to however cold your freezer is, usually around 0 degrees.
So to summarize the above, each time we remove 1 BTU from our 62 degree pound of water, it gets one degree colder. After we've removed 30 BTU's, our pound of water will be 32 degrees. Now we have to remove 144 BTU's from it to make it turn into ice, but this won't change the temperature, it'll still be 32 degrees. We can remove still more BTU's to make the ice colder if we wish.
As you can see, 32 degrees is an important temperature when talking about ice. But just because we have 32 degrees, and water, does not mean we have ice. Additional heat has to be removed to form ice, and additional heat has to be added to melt it.
You probably also see that ice is most useful for maintaining temperatures at about 32 degrees. Even if we start with a pound of ice frozen to 0 degrees, after it soaks up only 32 BTU's, it will warm up to 32 degrees. Then while remaining at 32 degrees, it will soak up 144 BTU's as it melts. (That'll keep your drink cold for quite a while.) Once it's all melted, it simply behaves like water again, getting 1 degree warmer for each BTU added.
You probably still want to know more about ice, right?
If you put a 5-gallon bucket of water in your dog's house on a cold night, it will release 6,120 BTU's of heat into the dog house as it freezes into ice. Hey, it's better than nothing. If it gets warm enough during the day, you can set it outside to thaw (for free), and be ready for the next night. Otherwise, you'd have to bring it inside your house where it can "take back" that 6,120 BTU's.
Leaving the faucet run on cold nights: Many people believe that if water is running or moving, it won't freeze. While it's true that leaving the faucet run a trickle will prevent the pipes from freezing, it's not simply because the water is moving. The real reason is because that wherever the water is coming from, whether a well or a city water plant, it is considerably above freezing temperature at it's source. If you have a constant flow, this will keep bringing this warmer water through the pipes, keeping them above freezing temperature!
By the way, if your pipes freeze, you thaw them, NOT un-thaw!
In a commercial ice machine, water is circulated with a pump, over a freezing plate. This slowly builds a slab of ice or a batch of ice cubes. But in this case, it's the same water going round and round again and again. At the beginning of an ice making cycle, the machine fills with water, at whatever temperature the local water supply is, generally 50 or 60 degrees. The refrigeration system quickly cools it down to 32 degrees, and then the ice starts forming. The circulating water will remain at 32 degrees through the remainder of the cycle, even though the freezing plate, and the ice forming on it, will be colder than that.
If you want to check the accuracy of a thermometer (one that is capable of reading 32 degrees), you can do so with ice water. Fill a glass with ice cubes, then add water to cover the ice. Insert the thermometer bulb or probe in the ice water, near the top of the glass, and if your thermometer is accurate, it will read 32 degrees F. Note that the water can be a few degrees warmer at the bottom of the glass, defying the notion that heat always rises!
Oh yeah, in case you didn't know, adding salt to water makes it freeze at a lower temperature. So you can make ice that will cool below 32 degrees, but probably wouldn't taste too good in your drink. That's why they put salt on the roads in the winter. In addition to lowering the freezing point of water, it will also melt existing ice, then it will lower the freezing temp. of the water created by that ice melting.
FAST-FOOD ICE: You go to McDonalds, and order a 16 ounce Coke. You get a half a pound of ice in the cup, plus some soda. When you're done eating, there's still about a quarter pound of ice in your cup. You throw everything in the trash can..
My point: For every 4 people that do this, that's 1 pound if ice / water going in that garbage can. Probably happens 40 times an hour, so that's 10 pounds per hour. Multiply that by X amount of hours, multiplied by X amount of fast-food joints, which results in X amount of TONS of ice thrown in the trash everyday. Not that a little water in the garbage will hurt anything. But, the kid that takes the trash bag out to the Dumpster has to carry the extra weight. And the garbage truck has to carry the extra weight, using more fuel and making more pollution. Probably most important though, is that someone has to pay by the pound to dump it in a landfill.
Stacks and stacks of $100 bills wasted every day, paying to bury water!
Of course an easy fix would be to have a little sink by the trash can, and encourage the customers to dump out their cups before tossing them in the trash. I usually eat my fast-food in my truck. Then I dump the ice out of my cup outside, before tossing the cup.
Athough this has nothing to do with ice, I've found people that don't know what it means to "siphon" a liquid. (Sometimes it's spelled "syphon") A farmer neighbor was baffled by news reports that people were stealing fuel by siphoning it out of cars and farm tractors. He asked me what "siphon" means. I explained that by putting one end of a hose in the fuel tank, then by sucking on the other end of the hose with your mouth (not recommended!) or a siphon pump, until the fuel starts flowing, you start a siphon that will continue by itself, as long as the fuel level in the tank is higher than the fuel level in the container you're siphoning into. He said "that's impossible, the fuel would have to go uphill by itself".
To demonstrate, I filled up a bucket of water and set it on top of the bulk milk tank. Then I took the 5 foot garden hose off of the milkhouse faucet, and put one end in the pail, all the way to the bottom, and let the other end hang down by the floor. Of course I hadn't "started" the siphon yet, so they were looking at me like I was nuts! One of the boys said "there's no way you're going to get that water out of that pail through that hose!" So I proceded to grab the lower and of the hose and give it a good suck with my mouth. This draws the water in the hose up and over the top of the pail, and once the water starts going down in the hose outside of the pail, the weight of the water going down will create a suction strong enough to continue to pull the water up and over the top of the pail. You should have seen the look on their faces!
I also ran into more people that didn't understand siphoning, when I was wiring a new house for them at about age 10. They had a sump pump in the basement, with a garden hose hooked onto it that went outside and into a water tank for horses. When they were working on the house, they ran the sump pump with a generator to empty out the basement. But when they would come back the next day, the basement was flooded again, and the horse tank empty. I explained that without a check-valve on the pump to prevent water from flowing backwards, as soon as the pump shuts off, the water from the tank would flow by siphoning, back through the hose and the pump, into the basement. Our quick-fix was to arrange the end of the hose above the tank, rather than in it, so only the water in the hose itself could drain back into the basement, not the whole tank full!
For a siphon to work, the liquid to be siphoned must be higher than the liquid level in the receiving container, if one is used. The greater the difference in height, the faster the flow. The hose must be filled with the liquid, with no air in it. I'ts not important how deep the upper end of the hose is submerged in the liquid, as long as it's not allowed to suck any air into the hose, which would stop the siphon. Another way to start a siphon is to put the entire hose in the liquid to be siphoned and allow the hose to fill completely. Then plug one end of the hose tightly with your hand or finger, and take that end over the top of the container, and down below the liquid level, outside of the container. When you unplug the hose, voila! Of course I'm talking about water, in an open-top container such as a barrel or a swimming pool.
One More Tidbit! You set two 5-gallon buckets on the ground. It doesn't matter if they're 2 feet apart or 200 feet, as long as they are both the same height. You fill each one half-full of water. Then you take a piece of hose that is completely filled with water, and without letting any water out of (or air into) the hose, you place the ends of the hose over the top, and then down in and near the bottom of each of the 2 buckets. and fasten them so they stay there. It doesn't matter if the hose is laying on the ground between the buckets, or if it is several feet up above them, but there can't be any leaks in the hose. Now what?
Within a short time, depending on the size and length of the hose, the water level in the 2 buckets will "equalize", that is, they will be the same distance "above sea level". If you add or remove some water from either one of the buckets, within a short time, they will equalize again. In other words, if you take 1 gallon out of bucket "A", a half a gallon will flow from bucket "B" into bucket "A" to make them both the same level again! This is relying on an "automatic" siphon, which stops when both levels are equal, but starts again by itself if the levels are not equal. This will work indefinitely as long as no air is allowed to enter the hose.
When you try this for yourself, and it does not work, it's because you have some air in the hose. Any air will screw it up. (Hint: a "clear" hose can help you see if there's air in it.) And if it does work, but it "equalizes" with more water in one bucket than the other, it simply means that both of your buckets are not the same height above sea level, the one with more water in it has to be raised up higher.
Don't let your brain freeze, make sure to visit the <home> page and siphon off some more interesting stuff!