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Mon Jul 29, 2019, 06:58 AM

serious technology question

From "Our Times: America Finding Itself" (Mark Sullivan, 1927, Scribner's), page 488:

".....that led to an early device for artificial cooling; a physician in a Florida town, whose wife was sick.....found that he could reduce the temperature of the sick-room by setting a vessel of ammonia on the top of a step-ladder and letting it drip....."

Why, and how, would this work, making a room cooler?

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Reply serious technology question (Original post)
imwithfred Jul 2019 OP
rampartb Jul 2019 #1
rahtruelies Jul 2019 #2
imwithfred Jul 2019 #3
SatansSon666 Jul 2019 #5
SatansSon666 Jul 2019 #4

Response to imwithfred (Original post)

Mon Jul 29, 2019, 07:17 AM

1. amonia can be used as a refridgerant in hvac systems (R17 if memory serves)

common in commercial applications in mid 20th century.

but it might take more than a "drip." to absorb the heat from a florida room in summer.



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Response to imwithfred (Original post)

Mon Jul 29, 2019, 07:27 AM

2. As the cooling fluid falls it will evaporate and absorb heat from the air. I have seen this done

with misting water in outdoor restaurants. Thing is that ammonia is toxic so I am not sure what the doc's setup really was..................

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Response to rahtruelies (Reply #2)

Mon Jul 29, 2019, 07:50 AM

3. ".....evaporate and absorb heat from the air....."

I assumed, without knowing for sure, it had something to do with evaporation of water from the air.

The history of the Sandhills of Nebraska is jammed with examples of primitive cooling methods used by the sodbusters, but I'd never heard of this. Since summers here are usually very hot and dry, while summers in Florida are apparently usually hot and damp, I speculated from that.

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Response to imwithfred (Reply #3)

Tue Jul 30, 2019, 07:07 AM

5. Water in the air is already evaporated.

It can cool and condense to form water droplets again, when this happens the thermal energy absorbed through evaporation is released.
When that water evaporated it required thermal energy to change it from liquid to gas.
This is called the latent heat of vaporisation.
While you heat up a liquid, say water, it's temperature will rise, but when it changes from liquid to gas it stays the same temperature even though it need roughly 4 times the energy just to break the bonds between the water molecules, not the molecules themselves, the bonds holding the water molecules together. So no change in temperature is seen in the phase change. The energy for the phase change, in your case, ammonia, takes heat from the room to break the bonds between the NH3 molecules, thereby removing thermal energy (heat) from the room.
I've worked with ammonia quite a bit. It doesn't make for a very pleasant experience having NH3 vapor filling the room you are working in.

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Response to imwithfred (Original post)

Mon Jul 29, 2019, 08:09 AM

4. When the ammonia changes phases from liquid to gas

Thermal energy is given to the ammonia from the warm air, slightly cooling it.
Not sure how much ammonia you would have to evaporate to cool a room, but that would be the science behind it is my guess.

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