Each summer we attempt to raise a small garden at our house. This past year our green beans did well, and we were able to “put some up” to use later in the year. To our delight, when we opened a jar of the green beans this winter, they tasted almost as fresh as when we had picked them. They were much better than what we had been getting from the grocery store cans.
What does “put some up” mean? It means “to preserve the food for future use.” Many of us probably have a refrigerator in our home. A refrigerator is a device that helps us preserve food. We may take the refrigerator for granted, but when you look back at its history, you’ll see that it’s only been around since the early 1900s. The invention of mechanical refrigeration systems not only improved the quality of life for many people, but it also led to some other inventions, such as air conditioners.
The World Before Mechanical Refrigeration
Preserving food has always presented a challenge to man. In some locations crops can be grown year-round, so there is always a fresh supply, but in most locations the growing seasons are cyclical. You grow the crops part of the year, harvest them when they are ripe, and preserve enough to last until the next crop comes in the following year. A number of things could go wrong. The food could become spoiled, in which case it cannot be eaten. The food could become contaminated with bacteria, fungi, or microorganisms that could be harmful or fatal. Man has invented a number of ways to work around these problems.
Grains are staple foods. They can be eaten in their field state or dried and ground to make breads. People learned very early on that if grain was dried properly, and if it was stored in buildings that kept it dry, it would not spoil very quickly and would last until the next season. A number of fruits can also be dried to lengthen the time they can be stored. Bacteria need water to survive, so if food is sufficiently dry, bacteria cannot thrive in it. Drying is one method of preserving food.
Root and tuber type foods, like potatoes, did not lend themselves well to drying in the early days. Instead, they could be stored for extended periods of time by keeping them in dry, dark, cool environments. This was best accomplished by digging underground cellars or by using the insides of caves. Such foods could still spoil, but the conditions greatly slowed down the decaying process, and they would last a lot longer than if they were just left to sit out.
Meats presented some problems. If they spoiled and became infested with bacteria colonies, they would be health hazards that could poison or kill people who ate them. Drying meat works, but other methods, including smoking, salting, and curing, were also used to preserve it. These methods control bacteria growth by limiting the moisture, like drying, but also through the introduction of chemicals that kill the bacteria.
But what if you want to preserve something, such as milk, that will not keep for a long time and does not lend itself to one of these methods? Or what if you have some food you want to store for a short time, or you don’t have the time or materials to dry it, smoke it, cure it, or salt it? What will you do then? You’ll just put it in the refrigerator!
Early refrigerators were similar to today’s ice chests. People would mine ice and snow in the mountains, transport it to their locations, and place it either in a cave or in an underground chamber. Often, they would line the location with straw before putting the ice and snow in. This would insulate it and make the ice and snow last longer. These storage locations were the first “refrigerators.”
The World of Mechanical Refrigeration
Hauling ice and snow into caves and underground chambers is great if you have the ice and snow to bring in, but that is not the case in all places. People began to look at ways to create “cold.” This area of study falls under the discipline of mechanical engineering and is called “thermodynamics.” The term “thermo” means heat, and the term “dynamics” means motion. Thermodynamics is the study of controlling the motion of heat.
Scientists understood that heat was a form of energy. The more energy something had, the more heat it generated. In order for something to become cold, it must lose some of its energy. Refrigeration, as it turns out, is not a matter of creating cold, but rather of taking away heat. It is a thermodynamic process. The heat moves from one object to another. The first object gets colder, while the second object gets hotter.
God built a refrigeration system into each one of us. It’s called “sweat.” When we sweat, beads of perspiration build up on our bodies. Here’s the ingenious part: When the sweat evaporates off of our skin, it causes heat to transfer from our bodies into the atmosphere! Sweating is a thermodynamic process.
Scientists began experimenting with ways to control evaporation. They learned that there were some materials that, when properly controlled, could move a lot of heat, resulting in a lot of cooling. This led to early refrigerating devices. A classic example, which was used into the early 1900s and still shows up on occasion at flea markets, is called the “Icy Ball.”
The Icy Ball was invented in the early 20th century as an affordable refrigeration system for the average household. It used two metal spheres connected by an inverted, U-shaped metal tube. One of the spheres was called the “cold” side, and the other was called the “hot” side. The Icy Ball worked on a principle known as “gas-absorption.” It had no moving parts and required no electricity! Here’s how it worked.
The Icy Ball had to be regenerated once every 24 hours. This means it had to be “charged” so it could operate. The cold side sphere was filled with pure liquid ammonia. The hot side was filled with pure water. Ammonia vapor would fill the inverted U-tube. The liquid water on the hot side liked to absorb ammonia vapor. As it absorbed the vapor, the pressure in the tube decreased. This caused the pure liquid ammonia on the cold side to start to evaporate.
As it evaporated, the temperature would drop. In operation, it would drop to as low as 19º F. The hot side would start heating up—but this had to be controlled. If the hot side got too hot, it would quit absorbing the ammonia vapor, and the refrigerator would stop working. To remedy this, metal cooling fins were welded on the hot side sphere. This allowed air in the room to cool the hot side so it could continue to absorb ammonia vapor, thereby keeping the refrigeration process running.
The Icy Ball, once regenerated, would be lifted into place so that the cold side sat inside a chest, much like an ice chest. This refrigeration action kept the inside of the chest cold, making it a refrigerator.
Some very good pictures of this, including an exhibit of the Crosley Icy Ball at the Smithsonian Institute, can be seen at http://crosleyautoclub.com/IcyBall/crosley_icyball.html.
As people began to try to improve refrigeration systems, they tried a number of different materials in addition to ammonia. These included methyl formate, methyl chloride, and sulfur dioxide. But there was a problem: These materials were all hazardous. As refrigerators began to develop into household appliances, accidents occurred. Some refrigerators would spring leaks in the cooling system and release the chemicals into the home. People were killed by methyl chloride poisoning into the early 1900s. To solve this problem, scientists at DuPont invented a chemical called Freon. Freon made an excellent refrigerant, and it was safe to people if it was accidentally released. Years later, it would be hypothesized that Freon was damaging the earth’s ozone layer, resulting in the elimination of Freon as a refrigerant.
The World After Mechanical Refrigeration
As the demand for refrigeration grew, new methods and techniques were developed to continue to improve upon the systems. The two main types of refrigeration systems used today are the vapor cycle and the gas cycle systems. The refrigerators we have in our homes are vapor cycle systems. They work in a manner very similar to the Icy Ball, except that motors inside our refrigerators keep the process running so that we don’t have to regenerate the vapor. It is a cycle, meaning it repeats itself. The liquid evaporates, creating cooling, and is then compressed and condensed back into a liquid. It cycles back around and evaporates again, creating more cooling.
In the gas cycle system, we never have a vapor in one side and a liquid in the other. Cooling is achieved by expanding and compressing the refrigerant vapor. This method is used in a device some of us may have in our homes called a “heat pump.” It is an efficient way to do cooling when you don’t need to reach freezing temperatures. When is this useful? When you’re air conditioning a house!
There are now small, portable coolers that use thermoelectric cooling, or the Peltier Effect. In the Peltier Effect, when certain solid state materials are placed together and an electric current is run through them, a reaction starts which results in a transfer of energy. The end result is an electronic device that produces cooling.
A new method, being studied in the laboratory but not ready for commercial application, is called Magnetic Refrigeration. There is even a way to use sound waves in a pressurized gas to produce heat transfer. This is called Thermoacoustic Refrigeration.
The Cold, Hard Facts
• Celsius (formerly known as Centigrade) – A temperature measurement scale where 0º C is the freezing point of water and 100º C is the boiling point. The scale was invented by the Swedish astronomer Anders Celsius around 1742.
• Fahrenheit – A temperature measurement scale where 32º F is the freezing point of water and 212º F is the boiling point. The scale was invented by the German Physicist, Daniel Gabriel Fahrenheit. No one knows exactly why he came up with this scale. There are many theories, though!
• Kelvin – A temperature scale where 0 K, also called absolute zero, is where all thermal energy ceases. The scale was invented by the Irish physicist, William Thompson, the First Baron of Kelvin. It is also referred to as a thermodynamic scale. Each degree Kelvin is one degree Celsius.
• Rankine – A temperature scale where 0º R is absolute zero (just like the Kelvin scale), but each degree Rankine is one degree Fahrenheit. It was invented by the Scottish physicist William John Macquorn Rankine.
Ray and Gale Lawson have been homeschooling their three children since 1995. Ray holds a B.S. in Electrical Engineering from the Virginia Military Institute and works for Washington Safety Management Solutions, LLC. Gale holds a B.S. in Mechanical Engineering from the University of South Carolina and is a full-time mom and teacher. They are members of Breezy Hill Baptist Church in Graniteville, SC. Questions, comments and suggestions are always welcomed and can be emailed to them at firstname.lastname@example.org (Gale).
This article was originally published in the May/June 2008 issue of Home School Enrichment Magazine. Visit http://homeschoolenrichment.com/ to request a FREE sample issue today!