Understanding the Science Behind Refrigeration

by Megan Ray Nichols 

How many times have you gotten up, opened your fridge, looked in for a minute for something to eat, then closed it again without taking anything out today? If we discount the fact that leaving the fridge door open wastes up to 7 percent of the appliance’s energy use when was the last time you thought about your fridge or your air conditioner and how they work to keep your home and snack food cool? How did the milk in your fridge make it from the cow that created it to your home without spoiling? Let’s take a closer look at the cool (pun intended) science behind refrigeration that we so often take for granted.

Why is Refrigeration Important?

We all know that we keep our milk in the fridge to keep it from spoiling, but how does keeping it cold make sure that you’ve got a fresh dairy topper for your morning Frosted Flakes?

We’ve been keeping food cold since prehistoric times. Even cave dwellers realized that if they kept their food in a cool cave or packed it in the snow, it would last longer. Thankfully, we don’t have to wait for a snow day to keep our food cold these days — most homes in developed countries have at least one refrigerator, with 23 percent having two or more.

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Why Do Pipes Freeze in Winter?

by Megan Ray Nichols 

It’s one thing that no homeowner wants to deal with, but it’s often the reality during cold winter months — frozen pipes. In addition to cutting off water to the home, these pipes can also burst, causing water damage. Why do pipes freeze in the winter, and what can you do to prevent them from getting cold enough to freeze? What should you do if the pipes burst? Here are some tips and tricks to help you get through the winter with your plumbing intact.

Why Do They Freeze?

First, why do pipes freeze?

Like most things filled with water, they freeze when the temperature drops below the freezing point of water — 32 degrees Fahrenheit or 0 degrees Celsius.

With pipes, there are two more variable to consider — movement and expansion. It’s harder for water to freeze if it’s in motion. That’s why lakes will freeze at 32 degrees, but it takes much lower temperatures to solidify rivers and waterfalls.

If a section of your pipe starts to freeze, the water expands. This behavior is an anomaly in nature because most liquids don’t grow when they solidify. Water, however, will become denser until it reaches a point just before freezing, then it will start to expand again. In a confined space like the inside of a pipe, this extra pressure doesn’t have anywhere to go, so it will cause the tube to split.

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Newtonian vs. Non-Newtonian Liquids

By Megan Ray Nichols

If you’ve seen any viral videos in the last few years, you’re probably familiar with the concept of non-Newtonian fluids — liquids that are fluid when moving slowly but when struck with force, they take on a solid consistency. Videos have gone viral of people filling entire swimming pools with a mixture of water and cornstarch, allowing them to literally run across the surface of the water. What is the difference between a Newtonian fluid and its non-Newtonian counterpart, and where might you encounter these fluids in your daily life?’

Newtonian vs. Non-Newtonian Liquids

First, what is the difference between Newtonian and non-Newtonian fluids?

Newtonian fluids have a constant viscosity that doesn’t change, no matter the pressure being applied to the fluid. This also means they don’t compress.

Non-Newtonian fluids are just the opposite — if enough force is applied to these fluids, their viscosity will change. These fluids are broken up into two categories — dilatants, which get thicker when force is applied, and pseudoplastics, which get thinner under the same circumstances.

These can be further broken down into rheopectic and thixotropic categories. Rheopectics work like dilatants in that they get thicker when force is applied. Thixotropic materials get thinner, like pseudoplastics do. The difference here is that the latter two categories are time dependant. The viscosity doesn’t change immediately but changes slowly over time as more and more force is applied.

Newtonian Fluids in Daily Life

These fancy names might sound like something out of a science fiction novel, but they’re really just the scientific names for things you encounter in your daily life. What Newtonian fluids have you encountered today?

If you took a shower this morning or had a drink, then you’ve already encountered the most common Newtonian fluid — water! Water does not change viscosity no matter how much pressure you put on it — it also cannot be compressed, so the amount of pressure you can put on water as a Newtonian fluid is negligible.

Other common Newtonian fluids include mineral oil, alcohol and gasoline.

Non-Newtonian Fluids in Daily Life

For this section, we’re going to break it down into the four categories of non-Newtonian liquid that we listed above.

Dilatants are probably the most well known nonnewtonian fluids. They become thick or almost solid when force is applied to them and are made up of water mixed with other materials. Oobleck, the colloquial name for a mixture of water and cornstarch, is probably the most well-known, but quicksand and silly putty also fall into this category.

Pseudoplastics might not sound very appetizing, but you probably have a bottle of one in your fridge right now. That’s right — ketchup is a non-Newtonian fluid. The fact that the viscosity changes as each new ingredient is added to the mix makes it tricky to mix ketchup on a large scale.

Now we get into the weird non-Newtonian fluids.

Rheopectic fluids get thicker in relation to the pressure being applied to them and the time that the pressure is being applied. The best example of a rheopectic fluid is cream. With enough time and pressure, cream becomes butter.

Thixotropic fluids are similar to pseudoplastics in that they get thinner as pressure is applied to them, but it’s also dependant on the time that the pressure is being applied. Things like cosmetics, asphalt and glue all fall into the thixotropic category.

It might seem like this is useless information, but it can actually be very useful, especially if you’re ever in a restaurant that still uses glass ketchup bottles. Simply remember that ketchup is a non-Newtonian pseudoplastic and will get thinner as more force is applied to it. Give that bottle a couple of good thumps, and you’ll be in French fry heaven.

Sources:

https://www.youtube.com/watch?v=RIUEZ3AhrVE

https://blog.craneengineering.net/what-are-newtonian-and-non-newtonian-fluids

https://www.philamixers.com/news/how-condiments-are-made/