Tuesday, March 07, 2006

Food Science 101: Refrigeration Technology

I spoke about this topic on Podcast #27. An article in the October 2005 issue of National Geographic Magazine explains the history of artificial refrigeration, a history propelled by pollution. Once the natural ice used in old times started to become polluted with industrial waste, the need for an industry to produce clean and dependable ice was necessary.

Industrious inventors came up with ways to produce ice and to cool foods, which led to using coolants to propel refrigerators. This in turn produced problems from the highly toxic sulfur dioxide and ammonia used in early refrigerators. Scientists next developed "safe" chlorofluorocarbons, which we later discovered to be eating holes in the ozone layer! Even the safer replacements, hydrofluorocarbons and hydrochlorofluorocarbons (say that ten times fast!) turn out to be greenhouse gases.

"Steven Garret of Pennsylvania State University has helped develop a thermoacoutic refirgerator that uses sound waves to compress helium, a harmless gas. The gas doesn't have to go through a phase change into a liquid and back again, because just explanding and compressing does the trick of sucking heat out of the compartment. The fridge's engine is so loud it would set your hair on fire. But thanks to insulation, it barely hums."

At the opposite end of the the technology spectrum:

"A women's group in Sudan is distributing the zeer pot, a storage container that's essentially two nested clay pots with a narrow gap between them filled with sand. The sand gets soaked with water, which, as it evaporates, chills the inner container so effectively that food that would normally spoil in two days can last two weeks.

It's not complicated, and it works in the desert, a long way from electricity, thermoacoustic refrigerators, or anything as exotic as natural ice."

I guess these zeer pots work on the same principle as the evaporative "swamp" coolers we used to cool the house while I was growing up in New Mexico.

Here's a link to an article about zeer pots.

And an article from Penn State explaining their thermoacoustic technology, which is being used in developing a new freezer for Ben & Jerry's Ice Cream!


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