TechStuff Classic: How Refrigerators Work

This episode originally published on March two, thousand thirteen. So let's listen to how fridges work. I totally forgot and I need to chill out, so let's let's let's hear it. We're gonna talk about refrigerators then. And here's the interesting thing, guys.

If you listen to the episode that Chris Pallette and I did quite some time ago about air conditioners, podcast is going to sound very similar to that because the technology is used in air conditioning systems and the technology is used in refrigerators are essentially the same, just one is a more small and controlled and um not for people usually usually right. No, there's some notable exceptions to that. We are not going to talk about those guys, because

that's creepy and probably belongs in another podcast. Okay, so we're not talking about people in refrigerators today, although now I can't think of anything else. Um, but no, no, no, first let's start with what the definition of refrigeration is. So it's defined as the process of achieving and maintaining a temperature below that of the surroundings. And the aim of it is to cool some sort of space or

object to a required temperature. Right, because bacteria grow most rapidly in this and it's it's called the danger zone actually of in between. I now I have a new thing filling my head. But okay, yes that I had debatably better than than okay, well excellent, but so yeah, the danger zone is in between forty degrees fahrenheit and a hundred and forty degrees fahrenheit, which is a four point four to sixty degrees celsius. And and in that

temperature range, bacteria really just groove out. They can they can more than double in in twenty minutes, and the population just explodes. And and bacteria and for things like you know, food stuff that that we would consume that's not necessarily a great mix that can lead to some pretty nasty contamination. It can lead to some really serious health problems. And uh, and this is why refrigeration is

such a big deal. I mean, clearly, before we had any kind of refrigeration, we had to look at different ways to preserve food. Otherwise, you pretty much had to get food from the source and consume it right away immediately or as close to immediately as possible. Or you had to get so that it would yeah, so it wouldn't spoil as quickly, or you had to salt it like crazy so that again the salting would would inhibit the bacteria from from from reproducing so quickly. And even

in refrigeration we still have that that process. It's just slowed down quite a bit, which is why you cannot leave food in a refrigerator indefinitely. It will eventually go bad. Um and then just like in that great Far Side cartoon, the potato salad will hold up the catchup when potato salad goes bad. So the trick here, though, is how do you create this cool environment? This this cold environment because adding heat two things is easy. Taking heat away

not as easy, less less easy. And also before I get all my physicist friends sending in messages about the use of the word heat. I do apologize. We're going to be using it in the vernacular quite a bit because that's really what everyone's familiar with. But to be clear, an object does not possess heat. It has a temperature, but it doesn't possess heat. An objects will have internal energy as a result of molecular motion, and heat is

really the description of an energy transfer process. And you go from a high temperature object to a lower temperature one. That is the basic concept of heat. It's really an energy transfer. So when we say, like this object's got a lot of heat to it, uh, that's a that's a completely colloquial way saying it. So I do acknowledge that. I apologize. But if you really want someone who's going to be a stickler for science, go bug Robert Lamb because he loves that the stuff to blow your mind. Gay, Um,

Robert's awesome. I love Robert. So, yeah, that's the way heat works. Though you have high temperature low temperature, then heat moves from the high temperature to the low temperature. It does not go the other way around, right without without some sort of external force working on the system. This is essentially one of the basic laws of thermodynamics. And so you've got this, uh, you've got a way.

You have to find a way of creating a lower temperature environment to pull heat from or to for heat to transfer from the objects that are inside a refrigerator to make them cool. So that's the basis of refrigeration. But you know, to get to that point, we had to do a lot of stuff and we had to understand a lot about physics for this to become what

we now all kind of take for granted. Yeah, So to to get started, I guess we can talk about what the predecessor was to the modern refrigerator, which was the ice box, right, or you know, going going way back in time, you had you had people not even making ice boxes, yes, just collecting ice and putting it next to stuff. Yeah, or like maybe you know, you might have a seller that you'd put ice into, or you might just have a hole in the ground, or you may just like if you were in a part

of the world where there was a significant amount of snowfall. Uh, we here in Georgia are not in that part of the world. We did have some snow the other day, I could see a bare trace of it next to my steps. Some of it landed in my hair when I walked my dog. That was That was about it. But if you were in a place where they get a significant amount of snow and they're large snow banks, then one of the things you might do is store

some food inside the snow. They're bury it in the snow, and just hope that nothing comes along to to grab that food. Or Yeah, if if you've got an ice house, you can preserve some of the ice with a sawdust or wood shavings. Later on, cork was used to insulate it for a few months anyway, until temperatures warmed up enough.

Right right, Yeah, you could. You could definitely slow the process, insulated enough from the heat of the outside environment so that it would preserve it, you wouldn't lose too much in melt off. It took a while before people started to figure out the best ways to keep ice from from melting too quickly. And it's interesting because just as they were really getting getting very good and making sure they kept ice uh cold for as long as possible,

even in hot environments. Uh, that's when the mechanical refrigeration technology had started to really take off and it became less important. Yeah, and these were happening simultaneously, which is really fascinating to me. It was in seven five that the first refrigerating machine was produced. I believe it could

make small amounts of ice in the lab. Yeah. Yeah, to to really understand well, first of all, the word refrigerate, I found the I found the earliest use of it, which was or at least earliest recorded use that I could find, which was from fifteen fifty. But it was all about using chemicals and water. People were discovering that if they added certain chemicals to water for some reason, the temper sure the water would drop. So if you were to put something in a container of water that

had this chemical in it, you could cool that's something. Now, if that's something was unprotected food and that chemical was poisonous, that was not necessarily a great thing. But if that's something where I don't know, a bottle of wine and you happen to be French, this was a great way

to cool your wine. And in fact, in the Renaissance, these cooled drinks became very popular, to the point where if you added chemicals to water it would drop the temperature enough that if you put something in it that that you could turn on a regular basis, you could actually make ice this way. Um. Yeah, so this was

kind of an early ice maker. Not efficient, not good for producing ice on any kind of large scale, but it was one of those things that the rich people really enjoyed, and really those were the only ones who had any chance of getting at it. Um. But yeah, it was just before your the refrigerator unit type thing you were talking about from the seventeen seventies. Seventeen fifty five is pretty much when we talk about the origin

of the idea. That's when William Cullen made his machine with which you used a vacuum UH and UH ether to UH to create this UH environment where he would put water into a container, put a smaller amount of ether in there, put a essentially a vacuum bell jar on top, you know, a pump with a pump on it. By creating the vacuum, the ether would start to boil off.

And when the ether was boiling off, when it was vaporizing, he noticed that the temperature was going down in the water and in fact, by when the ether would continue to boil off, the water would start to turn into ice. Now we'll talk about why that is a little bit later, but this was one of those early observations that started to lead people into thinking, you know, if we harness this in some way, pretty cool. You're doing it too here, there's no way to avoid it. Vocal baumb join us together,

we will rule the galaxy. Jonathan. We need to we need to chill out. Yes we do. Okay, alright, not too fast, too fast. You gotta gotta pace yourself here. Um So, anyway, this does form the basis. This, this idea of vapor pulling out heat somehow, that is what was the very basis of mechanical refrigeration. It would be quite a while before the mechanical refrigerators would start to become a real thing. Uh, I have in eighteen o three, you have a Thomas Moore obviously, not that one different

Thomas Moore UH of Maryland. In fact, he received a U. S. Patent for a refrigerator. Now this was not the same thing as mechanical refrigerators that would come later. But that same year that was when the domestic ice box was invented.

So three you get the domestic ice box. This was usually a wooden cabinet that you would put a block of a large block of ice into the top, and then you would keep your food and consumables in the bottom part of this cabinet, and convection would essentially keep because because heat rises and cold sinks, the which is which we know is the generalization generalization, yes, but but in general in this particular case, yeah, you've got you've got the dense the dense cold air going down and

the and the less dense warm air moving up. Because yeah, but we we understand that is a gross over generalization. But for the purposes of this podcast, it's effective enough. Yeah, you keep that ice on top. You have a like a drip tray on underneath, because hey, that ice is melting um, and so you would collect the water which you would not just pour into the top where it would magically become ice again. Essentially, once that ice was gone,

you had to go out and buy more ice. And actually the ice trade was really huge right around that time. In eighteen o six, I think Frederick Tudor began his his ice empire. He was called the Ice king Um when he started cutting chunks out of the Hudson River in various ponds around Massachusetts and then exporting it as far as China and Australia, in India and India. Yeah. Also what's interesting is that India was the way the way they were producing ice in India at this time

was through a process called nocturnal radiative cooling. Right, I was reading about this this it took me a while to grasp how that work. I still did not understand it. So I mean what I what I understand that basically they were doing was putting water in shallow clay trays and setting it outside under the open sky overnight and then in the morning ice would be there. Yeah. What what essentially is happening is that the uh it's there is another physical process going on here. But you've got

you've got a tray of water outside. The sky needs to be clear because what's happening is the heat is radiating from the water out into the atmosphere and escape that way. Now, if there are clouds, then the heat can radiate back down too, because it's like an insulator. It'll it'll end up insulating the earth and you end up you don't get us. But otherwise, even if the the ambient temperature outside is still right around freezing or just above freezing. You can still freeze water that way

under a clear sky. It also helps if it's a very dry climate. Right. And and from what I understand that it's important that it's a that it's an earthenware tray because that way you get some of them, well, you have to have that insulated effect there as well. It's the earthen tray and there's usually hay underneath it, some kind of compressed Yeah, so it's it's interesting that that was the way that India was producing ice, but that was not a very again, a very efficient way

of producing ice. You couldn't produce a lot of it, and uh there was a big demand. So Tutor was really raking it in by harvesting ice in the United States, just natural ice. Not he's not producing it in any mechanical means. He's actually going out and digging it up, packing it in wood shavings and that sort of stuff, cork, that kind of thing, shipping it to the other side of the world, and making huge bank off of it,

huge bank. And I want to mention that also right around this time, in UH seven, ammonia was first liquefied in a laboratory, right, which will becoming point um, So just keep that in your heads for a second and um. And then also in eighteen o five, right before Tutor began his big ice trade, um Oliver Evans described did not create, but described a closed at their vacuum refrigeration system. Yeah.

So this is the same sort of of mechanical system that would eventually become what we use in refrigerators, most refrigerators, I'm saying refrigerators in general, but there are different types. Yeah, well, we'll mention a few, but but the we're focusing on what most of us have available in like in our kitchens. Uh, and maybe our basement if Okay, I'm not gonna go back there. It's dark base to a dark place. Voco bomb really early on, I'm very fond of that of

that documentary American Psycho. Okay, that's fair, All right, guys, we're gonna take a quick break. I'm gonna go raid the fridge and we'll be right back in. This is interesting that the Michael Faraday was working again with liquid ammonia, and that's when he started realizing that liquid ammonia, which ammonia is naturally at room temperature is a gas, right, because it boils it at like negative twenty seven degrees fahrenheits. So, so to to liquify it, you have to compress it.

You have to pressurize it to make it a liquid. And he realized that when it went from liquid back to gas, it caused cooling and so again and another important part of this mechanical refrigeration. Now, in one a German physicist by the name T. J. Cbeck discovered that if you have two junctions of dissimilar metals kept at two different temperatures, it induces electromotive force or electric currents.

So what that means is that let's say that you have a junction of a copper wire and an iron wire, all right, and then you have a second junction where the iron wire is attached to a second copper wire. And let's say you were to heat up that, uh, that first junction, and cool down the second junction, perhaps put some ice on it, you would actually induce electricity

to flow through that wire. Now that's important because in eighteen thirty four, uh Peltier discovers that if you do the opposite, if you put electricity through a series of wires that have these kind of junctions on one side will heat up and the other side will cool down exactly and then by up to I think forty degrees fahrenheit. It all depends on what kind of material material you're using. UH.

In fact, this sort of is called the Peltier effect. Actually, but this sort of effect is dependent upon the types of metals or or materials you're using and UH their purity. UH. If you're using pure metals, the effect is pretty small, so small as to not be very useful. It's interesting in the laboratory setting, but not terribly useful. Also, if you're using pure metals, they tend to be very good thermal conductors, which means that that that difference in temperature

will not maintain itself for very long. You will eventually have the the heat will move from the high temperature to the low temperature and balance that out. UH. Meanwhile, if you were to use an insulator, then you wouldn't get the effect, so it would take years before anyone would find a way to make that useful. But that is used that that same technique is used in some little portable refrigerator things like the kind of stuff you might plug in to your your car outlet. Sure. Yeah.

Basically you just get a whole bunch of these junctions set up. You put the hot ones outside the unit, the cool ones inside the unit. Fridge. Yep, that's exactly it. So so spoiler alert, that's how that one works. But we thought it i'd be interesting to talk about that, But that's that was what caused was the basis of that sort of refrigerator. UM. And that same year, in eighteen thirty four, Jacob Perkins developed a vapor compression cycle refrigerator using either. So you got a lot of people

working on patent for it. Happened that year and h eighteen forty four you had John Gory proposing an air cycle refrigerating machine for making ice. UH eighteen fifty you had Rudolph Clausus who said heat can never pass from a colder to a warmer body without some other change connected there with occurring at the same time. This is what I was talking about at the top of the podcast. It's kind of a rewording of the second law of thermodynamics.

It's related to that. So that's one of the principles that guided refrigeration as well. UH. In eighteen fifty one, our buddy John Gorey from back when he had proposed that air cycle refrigerating refrigeration machine to to create ice. In eighteen fifty one, that's when he got the another patent for mechanical refrigeration. And in eighteen fifty five Alexander Twining starts his first commercial ice making plant using vapor compression refrigeration. We'll explain what that is in more detail

in a little bit. Eighteen fifty six, commercial refrigeration begins in industries like brewing and meat packing. Now, commercial refrigeration did not necessarily mean they were using mechanical refrigeration. They could be using natural refrigeration, as in going out and buying lots and lots of ice and packing stuff in it. Um. It's interesting to me that brewing picked up on this really quickly, like like the brewing companies were like, we

want beer that tastes good. It's as though alcohol technology is something that drives industry in some way. Yeah, the meat packers were slower to follow, which is disturbing. Spoiled meat was something everyone was used to write. But and if you're drunk enough, you don't care. Okay, got it, I understand now as someone who does not imbibe alcohol, it was just completely foreign to me. But I don't

eat meat either, so what do I care? Um. Also, we're no longer in the eighteen fifties, as it turns out, But yeah, meat pagging was slow to adopt this technology, but it did start it back in the eighteen fifties, and the majority of plants wouldn't switch to mechanical refrigeration until about nineteen fourteen, and by then you were getting into a really like a booming time of refrigeration. But

backtracking just touch. In eighteen fifty nine we had a Ferdinand car of France who developed an ammonious slash water refrigeration machine. Eighteen sixty eight you had Peter van der Wide. Uh. He patents thermostatically controlled refrigeration systems. That's going to be important when we get to the modern refrigerator. Eighteen seventy Carl Lynn publishes a paper called the Extraction of Heat at Temperature by Mechanical Means, and he designs the first

practical portable compressor refrigeration machine in eighteen seventy three. Uh. In eighteen seventy seven, that was the peak of the ice trade so in the US that it hit its peak, right, and the late eighteen seventies, the United States was exporting almost almost a quarter of a million tons of ice to other countries. So uh, yeah, a lot of ice

leaving the United States. Um, and uh it's interesting to me that at this point where the ice trade is at its peak, but mechanical refrigeration is already in its infancy. The only reason that mechanical refrigeration even started to take off, it wasn't because the technology was getting great. It's because

the ice trade was starting to encounter problems. Once it gets to about the eighteen nineties or so, Like, if the ice trade had not encountered problems, then even with the technological advances in mechanical refrigeration, we may not have seen refrigerators in the United States for another you know, I don't know, four or five decades, but so yeah, and that what happened with was that as people were essentially mining ice, you know, cutting away ice from these

rivers and ponds, they were starting to uh exhaust the clean sources of water and so more and more of the ice. The demand was was growing, right, and the supply was diminishing, not that we were running out of lakes and rivers and stuff. It's just the demand was so great and great that there wasn't enough to go around. Yeah, there's not there's only that are frozen and the Hudson

is really big and stuff. But yeah, I mean when you're talking about a quarter of a million tons, right, so you're talking about tons of ice that might have things like sewage in not so great when you're using it in the meat packing industry as not maybe not such a big advantage over spoiled meat. Um. Yeah. So uh, it's because the ice industry was starting to have these issues that we began to see the rise of mechanical refrigeration. One was when a trade journal called Ice and Refrigeration

began to publish. Nineteen o four was when the American Society of Refrigerating Engineers was founded. By the way the American Society of Refrigerating Engineers, I learned, was about engineers who were experts in refrigeration. It was not a society that would actually refrigerate engineers. Because the way it was worded it was confusing. I find that difficult to believe. Jonathan. I think you should check your Storvices American Society of

Refrigerating Engineer. It does sound like you're just shoving a guy with a hard hat into a fridge, and that brings us back to American Psycho. Nineteen eleven, General Electric introduced the first domestic refrigerator. Depending upon whom you ask, we should also point out that when we've got these dates and saying who brought out the first one, etcetera, etcetera, there's some dispute in them, and it all like I've

seen conflicting time. The history, and especially uh scientific in corporate history tends to be written by the victors and um. So therefore, sometimes you know, yea in different reports differ about exactly who won that right, and you know, exactly nineteen according to some sources, that's the first electric refrigerator.

According to actually frigid Air's timeline, I can tell you specifically, nineteen sixteen was when models like the Kelvinator and Servel were introduced, and in nineteen eighteen General Motors purchased Guardian Refrigerator Company and renamed it frigid Air. So nineteen eighteen was when frigid Air as a thing became a thing like it existed before, but it didn't exist in like, it didn't have the frigid name. And Frigida is where we get the word fridge from. I do believe, I

believe so. And it's also they that's the company that developed free On, which we will talk about a little bit in just a moment. Yeah, yeah, so way up in the nineteen thirties, we've got like one other point to cover before then I've got I've got a couple more, actually, because I've got I've got three. In the twenties, here we go, Oh my goodness. In the USA there were about twenty five million domestic refrigerators, only seventy five thousand

of which were mechanical. So these refrigerators, some of them were more like the ice box refrigerator, right. I remember, I remember watching like Lassie growing up that that the mom and Lassie had an icebox, not not a fridge. Random mom in Lastie, not the mom and Lassie from all, I thought Lastie had its own fridge. I'm like that

dog was luckier than I was. Ninety seven was the first porcelain on steel cabinet refrigerator, which is that's the one I always think of, like the nineteen fifties refrigerator, the big porcelain ones looks a little bit like a rocket. Yeah, mine, mind is minds a steel refrigerator. I've got the same les steel thing going now, so but I don't see

I remember the one, the porcelain ones. Uh. The line was when Frigidair introduced the first home food freezer, and it was a chest style freezer, so you know, not the not the upright type, not not incorporated into a refrigerator. Um. And that was right around that time is when uh, frigid Air starts to introduce chlorofluoral carbons, right. I believe that DuPont had developed it's also called a free on. Yeah,

that's the patented specific lora flora carbon that Frigidair introduced. Um. And yeah, before then, um, some of the very early fridges, I believe we're using sulfur dioxide. Yeah, sulfur dioxide, methyl chloride, ammonia. Yeah. And these are all chemicals that are toxic, super toxic.

So whenever there were accidents, and you know where human accidents happen happens, uh, then sometimes people were really badly injured or even they died even as a result of being exposed to these sort of chemicals, and so there was a big incentive for companies to develop refrigerants that we're not toxic, and so that was the reason why

companies were looking into something like a chloral fluora carbon. Now, later on we would learn other downsides to chlora flora carbons, which we'll talk about in a second um, which is why we don't use them anymore. Now. In nineteen thirty one, that was the first use of free on as a refrigerant. So it was kind of introduced in ninety nine and it was being incorporated into the design and mechanical refrigerators, and in the first refrigerator freezer combo with the freezer

having its own separate section was introduced. So you that was where you know, you would open up the fridge part or you would open up the freezer part um. And in ninety nine, Soviet engineers discovered a way to create thermoelectric refrigeration systems using the the Peltier effect by using semiconductor material because you know, like I said, those pure metals weren't producing enough of an effect for it

to be useful in any way. They found that by using semiconductor materials, they could create a pure differential that was effective enough for it to be used for something science. So yeah, they actually started creating refrigerators using that thermoelectric system rather than the vapor compression system that was being used pretty much everywhere else. Also in A nine the business was so booming that seven million refrigerators were being

produced in the US annually. Nice and in fact, my timeline ends at nineteen because I didn't write down specifically the bit about the nineteen seventies, where right around nineteen was when we started figuring out the chloral flora carbons were starting to accumulate in the atmosphere. Yeah, and eat through the ozone layer, which is not the science for that,

that's right, right, but that it was. It was in fact harming the ozone layer, and that was what gave the incentive for us to develop something besides that, which is why these days hydrofluora carbons or isopu tane or yeah, those are the those are the main two to be used because they don't have the same environmental impact nor did they have the same toxicity levels as the previous refrigerants before free on, Yeah, ammonia and things are still

used in industrial capacity because they assume that someone who has, you know, um, five thousand dollars to drop on a refrigerator is going to or five thousand dollars more on top of what you would normally spend, is going to take a little bit better care with the care of it and not you know, let the dog eat through the back end. Yeah, it's it's it's one of those things. Also where you're talking about efficiency as well, Ammonia is

a very efficient refrigerants. So that's that's you know, when you're talking about a large scale production, efficiency ends up being the difference between a profitable year and a disaster. Yeah, especially when you've got health inspectors coming through making sure that you do not have any food that is entering that danger zone that I talked about, right, So that that kind of brings us up to speed to the general refrigerator of today. Let's take a quick break to

thank our sponsor. Okay, so I think it's time we start talking about the actual process of refrigeration and how the modern day refrigerator in general works. Do you mean the technology of it, Like we're like we're a tech as if we were talking about the stuff that is techy talk. So so you're using essentially the refrigerator cooling system is a closed system, right, it's a closed system. Think of it as a series of tubes. So it's its own internet, but a series of tubes that are

all connected to one another. There there's no external venting or anything or intake. So you've got a system where you're using a refrigerant like we were talking about in those early days. Yes, some sort of some some sort of of material that at room temperature is a gas, but when you pressurize it, you can make it a liquid.

And that's the key. So um, if you if you're having trouble understanding how this works, think about like you get some rubbing alcohol and put a little bit on your skin, and you're gonna feel that it it feels very cool. And that's not because the rubbing alcohol itself is at a cooler temperature. Yeah, that the liquid in the bottle, when you hold the bottle, it can feel like it's the simply the same temperature room right. But but the thing is that rubbing alcohol will start to

evaporate at room temperature. So when you put it on your skin as it evaporates. You're gonna feel your skin cooled down that evaporative effect. It's as the the liquid is turning into a vapor, it's pulling heat, uh through part of that physical reaction endothermic reaction. The energy that is required to turn something from a liquid to a vapor. Um sucks in energy heat energy from the air around and you've got the higher temperature generated by your body,

so that's where that heat can come from. It can pull the heat from there to help fuel this reaction. Essentially, again we're kind of oversimplifying, but yeah, but we're also not not physic system, so we also don't have visual effects to show you what we mean, which makes aside from our own gesticulation, which is really only benefiting us. Yes, we can. We can also do the safety dance in here. Apparently that's that's what it looks like whenever I start talking, Um,

that's just the way I am. But okay, So you've got the coolant in your refrigerator, which is called a refrigerant. The coolant moves through a series of coils and through different parts of the system. The coolant is either going to be in a liquid state or a gas state. Now you have to think of this system in its various parts so on. It's kind of hard to say on one end of the system because really, in a way, this is kind of like a big circle. So you don't have a start and an end. Really, I think

it's easy to start with that. With the compressor, that compressor. So yeah, I've got a compressor. The compressor is, of course does what it sounds like it does. It compresses compresses the gas. So it's uh, well it compresses the coolant at the the time. Yes, it's a gas, it's compressing it, so it's coming in through Uh, it's pulling in gas and compressing it. Now, remember we said that heat is not a thing that an object possesses. Instead,

an object possesses some sort of internal energy. So if you were to pressurize something like a gas, if you were to pressurize a gas, uh, or you were to heat up that gas, you would increase the molecular movement there and just from being just from observing the gas itself, without having any knowledge of how it got that way, you would be unable to tell whether it had achieved its internal motion through heat, pressurization, or some combination between

the two they would be indistinguishment. They all like the same, right. So essentially, what I'm saying is that compression and heat gets you the same result. So you are compressing this gas and as a result, the temperature of that gas goes those up, all right, So you then create this long series of coils. This is on the outside of the fridge. The compressor is right ready, the edge of

the fridge. It it draws the air in, it draws the gas, right sorry, draws the gas from the fridge out to the outside, compresses it and then yeah, and then it proceeds up through the series of coils coils. And you keep in mind, like I said, this is totally a closed system. This this gas is not exposed to the interior of your refrigerator. There's it's always in in tubes essentially, it's always in pipes. So it's going through After it gets compressed, it's heat heats up. It

doesn't it isn't heated up. It heats up through the compression, uh, and then it goes through this series of coils. As it goes through the series of coils and the outside the refrigerator, it starts to lose some of that it you know, the heat moves from the coils to the surrounding atmosphere, right that that that is the purpose of these coils to to cool down this air to the

point that it going to gas. Okay, I just don't want it to be too too vague, but yes, yes, exactly, it's it's cooling down the gaseous coolant, right because because at this point that that compressed gas is at a higher temperature than the ambient air around it. So if you were to touch one of these coils, you would feel it was very hot. We don't necessarily recommend doing No, don't do it. And this also shows that the refrigerator is only going to work if it's in an environment

that is cooler than what the coils are. Like if if for some reason you put a refrigerator in the middle of a volcano, then the forty degrees it probably wouldn't do well because because then you have the temperature of the surrounding environment is higher than the temperature of the coils, the heat transfer would move in the opposite direction, would never cool down. So so clearly you have to

have a cooler temperature in your environment. In this case, it's in your kitchen, and your kitchen, while even when you're looking full blast feels like it gets pretty warm, is nowhere near as hot as those those coils are. First, Um, when the gas is compressed, so as it moves through uh, it starts to cool down, and it begins to condense, and under that compression, under that pressure, this condensed cooler gas becomes a liquid. Because as you increase the pressure

on a liquid, you also increase its boiling point. So if you were to take a uh, let's let's take water. Okay, So water boils at two and twelve degrees fahrenheit or one hundred degrees celsius, So much easier to talk in terms of celsius. Although I'm totally I'm so used to everything else being in fahrenheit that water is the only thing that makes sense to me in celsius. So that's because I'm an ignorant American alright, so uh and I'm not saying all Americans are ignorant. I'm saying I am

so anyway. Um, So at a hundred degrees celsius, that's normally when water would boil, right of water under one atmosphere pressure. If you were to increase the pressure on that pot of water. Let's say let's say we somehow put a pressure cooker around this this pressure canister around this pot of water and increase the pressure on that water. That would also increase the boiling point, so you would actually have to go over a hundred degrees celsius in

order to get that water to boil. The same sort of idea here. You've got this compressed gas, you've got condensed down into a liquid. That means the boiling point has gone up. So as long as that that liquid is under pressure, the boiling point is higher than it normally would be. That's why it can be a liquid. Right, all right, So you've got this liquid, it would normally be a gas at this temperature. How do you make

this liquid suddenly magically make everything cool again? Well, you've got to have a valve, an expansion valve Juel Thompson or our Juel Kelvin, depending on on how how you want to say that. Uh, Lord Kelvin. Lord Kelvin, Yes, came up with this with this ingenious little valve concept where if you have a high pressure liquid on one side and a very tiny hole right and a low pressure area on the other side stuff happens. Right. What happens is that liquid will pass through that expansion valve

once it gets to the area of low pressure. Now you don't have the pressure on there anymore. Once the pressure is gone, that boiling point goes back down to where it normally would be. Now again, with the refrigerants you're using in the refrigerator, that boiling point is way lower than room temperature. Yeah, yeah, negative twenty eight degrees fahrenheit or negative thirty three degrees celsius. So that's when this liquid would normally boil off into a gas. Okay,

here's the other the cool thing about boiling points. Let's say that you are magically inside an oven. Don't ask me why you went in there, but you're okay, for some of you, you're very heat resistant. Okay. Now you've got you have that pot of water from the pressure experiment earlier, because you don't like to waste now, right,

especially not water. It's a it's a precious resource. So you've you've taken that pot of water with you into the oven, and you're watching the water and the temperature inside the oven is four hundred degrees and you're watching the water boil and you you have a thermometer inside the water. It doesn't have any contact with the metal or anything. It's just measuring the temperature of the water.

The temperature of the water. Even though the oven is four hundred degrees temperature, the water is still going to be assuming regular pressure two twelve degrees fahrenheit one degrees celsius, because that water cannot physically cannot go above that temperature. Not not a liquid form, no, because as when you're in liquid form, you can go only up as high as the boiling point and then you turn in again.

So so the water itself is at one hundred degrees celsius so to you, because you know you're in the four hundred degree air, to you, the water would actually seem cold, right. So that's the whole idea is that once it goes down to this boiling point, the temperature actually drops dramatically. So it goes through the expansion valve. The liquid, the highly pressurized liquid, goes through this expansion valve,

hits the area of low pressure, immediately boils off. And because most from what I've read, about half of it boils off. Well, yeah, because again you're getting into this low pressure system, which means that now that that uh that it's no longer confined by the high pressure, which means now it can it can boil off into its vapor form, which means that it starts pulling in the heat to essentially be part of this uh, this process. Yeah.

As as the process happens, it pulls in heat necessarily because that is where the energy for the process comes from. So what what that means for your refrigerator is that the interior of your refrigerator, all the heat that's contained

within the interior refrigerator moves to these sucked into the pipes. Yeah, so that the same series, same sort series of coils that you would find on the outside of refrigerator, something similar to that is on the inside of your refrigerator, only there, instead of putting heat out, it's pulling heat in because it's pulling heat in from the interior of your your refrigerator and free sir. There's just there's really just more length of it and your freezer than there

isn't your refrigerator. That's the difference there. Yeah. So so so yeah, this liquid, this half liquid half gas is running through the coils inside the body of the fridge and fans are blowing air across the coils through the food part of the fridge, which which continues to to vaporize the rest of the liquid into gas and continues to pull more heat more heat. Yep, and that's what makes the refrigerator cold. So really it's not that it's

not that the refrigerators pushing cold in. It's pulling heat out. So that's something because, i mean, which is so cool when you open up refrigerator and you feel that little blast of cold air, you just think, oh, there's something magically and there's the same Yeah, that's not what's happening. So but it is really neat to think about that that's all going on at the same time. So you're

really you're talking about too closed systems. The closed system of the interior of the refrigerator where all your food is, and the closed system of the actual coolant that's moving through. And um, yeah, that's that's the basic idea. Oh and once it it once the gas gets to the end of that part of the cycle, you know, it's it's

completely in gas form, it's no longer pressurized. That's when the compressor pulls that gas through to move it all the way through the system again, So it's reusing the same coolant over and over and over again with with no waste. Right, assuming there are no leaks in the system, you're good to go. If you've ever had to have a refrigerator or freezer unit, if you had to had coolant added to it, this happens frequently I've seen with

air conditioning systems or climate systems. Then that means there's probably there has to be a leak somewhere in there because it is a closed system, and otherwise you shouldn't really have any loss, at least not any appreciable loss. So that's the basic way of fridge works. I find it super interesting. I almost said cool, and I almost did it. I almost did. I didn't want to do that. I think, did I do that a second ago? I apologize.

I apologize for accidental puns guys, But uh, you might be wondering, Okay, well, my refrigerator allows me a set a temperature, right, like I can choose to either go super cold. Yeah, for for my freezer, I wanted to be as cold as possible. Or you might think, well, no, that's gonna use up a lot of energy. I'm gonna be a little bit. But when when the stuff in your cheese or alway starting to frost over and you

start going like, yeah, this is bad. So what what governs that is what's called a thermo couple, which is essentially a thermometer and a switch. So the thermometer detects the temperature the interior of the refrigerator, and when it drops below whatever the temperature set to, it turns off electricity to the compressor. So the compressor stops, which means this whole cycle that we've been talking about stops, and then if the temperature creeps up above it again, it

turns electricity back on. Yeah. So that's when if you've ever heard your refrigerator just kind of kick on, that's what's going on in you know, the more modern ones do this really efficiently, so you don't have it happen as frequently or as dramatically. I remember an old refrigerat it or I had where you thought that, you know, perhaps Steven Spielberg was filming Poltergeist for in your kitchen

every time I kicked in. Yeah. Modern fridges also do contain small, low wattage heaters, which just keeps the evaporator coils at the correct temperature and not frosted over um, which which I find also fascinating. Just yeah, like like fridges contain heaters, that's the thing that they do. Yeah, And you know, obviously refrigerators can have lots of other bells and whistles on them. Of course. Sometimes literally, my

my refrigerator does ding. Uh if I like, if I am using the there has a water dispenser, right, so it intakes water from my my house's water system and puts it through a filter, and then I can get a nice clean glass of water. But if you open up a the other door, it's a it's a double door refrigerator. The open of the other door it cuts

the water off. You can't you can't dispense water while the door is open, and if you have depressed the water dispenser, it will bring at you and mercilessly chide you for trying to do two things that are not compatible.

Because I frequently forget. While I'm getting a glass of water, I'm thinking, you know, it would go great with this water that enormous hunk of cheese that's in my refrigerator, And then my refrigerator tells me that yes, indeed, that would be lovely, but you need to wait until you've either gotten the cheese or finished getting your glass of water. You cannot do both at the same time. That's great. I love it when electronics chide man by love I

mean hate. I hate that thing. Well, and there are other kind of interesting uh like additions you can get. LG has a beer chiller. Yeah, that's so. This is this thing. I actually got to see this in person at sea. I think it one like the innovator or yes, it did it did It won one of the Innovation awards. Uh and uh So this is like a tiny little thing chamber within the refrigerator part itself. It's called a

blast chiller. Yeah, it's designed it's designed to take a well, the demo was a can of beer from room temperature to ice cold within about five minut and uh and essentially it's doing the same process we talked about right here. It's just that I imagine there are more of those coils. It's a very small chamber and very controlled. Yeah, there's

their fans involved. I mean it's it's they're they're they're trying to increase the circulation of air and the and the surface area that the cold coils have so that it pulls heat as efficiently as possible, so that you can have your frosty beverage when you want it, or at least five minutes after you thought about it. Um, and that's assuming you want one can if you want to, it's going to take about eight minutes because it's more for it to more heat for it to disperse um.

But yeah, there's there's stuff like that. And then they're smart refrigerators, right, Yeah, now you can you can have your fridge tell you what's in it and what kind of recipes you can make with that, and yeah, and send information to other elements in your home, assuming that they are made by the same company and are compatible are willing to talk to each other. Yeah. So the idea here, of course, is that it's not a new idea. It's one of those things that people have been trying

various to implement in various ways. But now that we have smartphones, it's a little bit it's a little easier, yeah, because you can you can connect a smartphone to a refrigerator and scan things in that way. That was that was the big issue, right, was that how do you tell a refrigerator what's inside of it? If you have to stay in there and manually input onto probably a really miserable touch pad on the refrigerators surface, exactly like how many bananas you have? I don't. I never want

to do that. I don't put bananas in the refrigerator. I do not put it to thinking. Okay, well, foco bomb, I've found your problem. Uh no, but you you are, you are correct that that that's that's the barrier, right, How do you make it so easy? And you know, there were people who are talking about why don't you put r F I D chips and or strips of some sort onto various products and then you could just

have it scanned when you put it in. But then other people are saying, wait, if you have r F I D chips, you can end up tracking everything that someone buys, whether they want to be part of a customer you know not. Yeah, And there are people who are very sensitive about that. And I can completely understand. You know, I personally I don't worry about it that much. But that's just because that's who I am. I'm waiting to do it so that I can get sent yogurt coupon, right,

you know. But but I'm I'm totally understand the people who are like, no one has any business knowing what I buy. I go out and I buy it. I buy it with my money. It's my exchange. That's all that. That's where it should end. And I totally respect that. But so that that the r F I D thing never really I mean, I've seen some implementations of it, but I don't expect that off the ground because it would also require the entire food industry to change, right,

All the packaging would have to change. And that's when you look at that across every single company that makes food that's designed to go into a refrigerator. That's a lot of money that that would require billions of dollars

of investment from various companies. Yeah, for for relatively low usage point, I think, yeah, especially right now because we're talking about you know, right now, I don't think there are that many people who have smart refrigerators, and again, like to get one that's really useful that can work with something else, like say you're your oven so that you know, you pull up a recipe on your refrigerator and it's it's telling you what you can make based

upon the ingredients that you that it knows that you have available, and you say, yes, that's what I want. I'm gonna make chicken ala king, and you have pushed the button, and then it could actually again if it's part of this this sort of network system could send information to the oven so that the oven starts to pre heat to the correct temperature to make chicken ala king right while you are actually pulling the materials out

so that you can prep them for for cooking. So this way ends up making the whole experience more efficient and could even potentially, uh, you know, send another note out to your cell phone the next time that you're in a shopping market and and say, hey, by the way, you really like this one thing because you you made it like fourteen times in the last two months, but maybe you want it again, or or maybe you're out a chicken, uh and we're planning on doing something else

later this week. Maybe you need to buy more chicken. Yeah, it just tells you go out there and buy more chicken. Now. The the thing that I find interesting is that we're talking about this. These are kind of future applications. They're really coming into practice now. Uh, and we'll probably see more of that in the next maybe five or ten years. It's gonna take a while before this technology to to get out there far enough for it to be pervasive.

Especially you know, once you buy a big appliance like a refrigerator, you want that to last for a while, not something you replace every couple of years, ety year kind of can. I definitely can't be. So I think this is one of those those things that we're gonna see kind of played around with, like high end homes and that kind of stuff. I don't I don't imagine I'll be buying a smart refrigerator anytime the near future

unless I just win the lottery or something. I'm like, I don't know what else to do with this for everyone, right, like just knock on random doors, guess what you want today? Yeah, I don't know otherwise, But it is interesting to me because I sit there and I think about the time back when people were like, well, we could buy them mechanical refrigerator, but ice is so available, so he knows what will happen um anyway. So that's that's how refrigerators work, alright, guys.

That wraps up this classic episode of tech stuff, How refrigerators Work. I hope you enjoyed it. If you have suggestions for future topics of tech stuff, please let me know. You can let me know on Facebook or Twitter. The handle for both of those is text stuff hs W and I will talk to you again really soon. Text Stuff is a production of I Heart Radio's How Stuff Works.

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