In Response to The Wood Burning Alternative Refrigerator Project.
I'm not sure, but I think Dale Degler's going to blow his head off with that wood-burning contraption! These fridges are designed to be used with a small flame. When you hit them with intense heat — such as that of the wood fire you pictured — you're going to boil the water, not only lowering efficiency to the point where the machine won't work, but building up steam pressure in the unit to destructive levels.
BOOM! Thar' she blows! And the explosion will have an added bonus, lots of ammonia, a toxic compound.
H. Hartzog. Bellingham, Wash.
You're right, H . but only partway. The intermittent absorption refrigerator does work. In fact, the "Icy-Ball" model (also mentioned in the article), was a widely used, dependable commercial product. And it was heated by being placed over a fire.
However, our illustration of the unit's inner workings was somewhat more poetic than accurate, As you say, nobody should set the ammonia-water pan right next to a giant blaze like the one pictured. Application of heat to a wood-burning fridge should be gentle and predictable. The whole point of the system, after all, is to boil the ammonia without boiling the water.
The heat-accepting side of an intermittent absorption machine would probably be best kept along the edges of a moderate fire. (It doesn't take a lot of heat to turn the ammonia to vapor, just a steady application of low-level heat. Again, the idea is to warm the pan, not boil the water.)
I might as well add, too, that no one should experiment with mechanisms such as this unless he or she really knows what they're all about. Dale Degler — as you'll recall — is a qualified heating and air conditioning technician (even if our artist isn't!). If your experience with refrigeration units more closely parallels that of our artist instead of Dale Degler's background, you'd be well advised to lay back and let the "folks who know" build and test the first intermittent absorption coolers.
And I expect to keep you posted on that work. Here, for example, is a refrigerator — similar to Dale's — that was designed many years back by another MOTHER reader, Stephan A. Sieradzki. Note that Steve's freezing mechanism has a built-in cutoff that operates automatically just in case that pot of ammonia and water does get too hot. — MOTHER.
Stephen A. Sieradzki, designer of the Wood Burning Refrigerator
Twenty-three years ago, while living in Europe, I designed a simple refrigeration unit with two tanks joined by a length of pipe. The assembly was mounted on a pivot in such a way that the condenser-evaporator could move in and out of an icebox, while the boiler absorber-tank moved correspondingly to and from a location over a gas flame. The system is gravity operated, fully automatic, and could be adapted for operation with any heat source (including solar).
Anyway, my diagram tells the story better than I can. It shows the unit in cooling position. From there, the cycle goes like this:
When most of the ammonia has been absorbed by the boiler, the added weight overcomes the force of the lower magnet, allowing the assembly to pivot into the position shown by the broken lines. In that mode, the pipe depresses the control rod, opening the gas valve to the burner.
Ammonia is driven from the boiler and condenses inside the evaporator. When enough of the coolant liquid has collected in the second chamber, the weight shifts again overpowering the upper magnet and swinging the setup back into its cooling phase. With the pressure thus removed from it, the control rod shuts off the flow of gas.
During the heating cycle, the opening in the ice chest is kept sealed by the counter weighted inside closure. If the ammonia pipe overheats-indicating a malfunction a link in the safety pad melts, causing an immediate shut off of gas to the burner.