how does it work?
http://cs.trains.com/trn/f/743/p/259513/2914629.aspx#2914629
RME posted a nice diagram at that link that shows how it works.
Even better is an article published in Trains back in the fifties which actually describes the process. I'm sorry, but I am unable to tell just which issue. Paul North, can you help us?
Johnny
DeggestyEven better is an article published in Trains back in the fifties which actually describes the process. I'm sorry, but I am unable to tell just which issue. Paul North, can you help us?
I'm sure he can - but in the meantime, check the August 1951 issue, Wallace W. Abbey, "Steam Cools your Train". (There is a steam-ejector diagram on p.16)
chad s thomas how does it work?
Thanks to Chris / CopCarSS for my avatar.
The way it works is that a jet of steam into a tube -- the ejector -- draws a vacuum. The vacuum causes a pool of water inside the unit to boil at a cool temperature -- the higher the vacuum in the unit, the lower the boiling point. That boiling/evaporation of water draws away heat, providing the chill for air conditioning.
The stack on a steam locomotive works the same way -- the jet of exhaust steam draws a vacuum (the draft), which pulls combustion air through the firebox, flues, and up the stack. When the locomotive is stationary, a valve opens a jet of live steam to keep the draft and hence the fire going.
Steam is also used to provide chilled water for air conditioning in many large commercial buildings. There, something called "absorption cycle" air conditioning is used. The steam supplies heat that provides the motive power to a refrigeration cycle without any mechanical compressor -- I believe it involves ammonia being "absorbed" into water. There are refrigerators for RVs working on the absorption cycle driven by a butane flame, but that is not how the A/C on trains had worked.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul Milenkovic The way it works is that a jet of steam into a tube -- the ejector -- draws a vacuum. The vacuum causes a pool of water inside the unit to boil at a cool temperature -- the higher the vacuum in the unit, the lower the boiling point. That boiling/evaporation of water draws away heat, providing the chill for air conditioning.
That's about half the magic of the system, the other half is compressing the resulting steam so that the steam will condense at a higher pressure. The latter is related to how a steam injector works.
The basic technology was developed by a Frenchman by the name of LeBlanc, who then sold patnts rights to Westinghouse. The real trick was learning enough about supersonic flow and the transitions between supersonic and subsonic flow to make a diffuser to slow down the flow to sonic speed and then continue on as a subsonic diffuser. The reduction in velocity then boosts the pressure so that condensation can occur at a higher temperature than the water being cooled. The article on the LeBlanc system in a 1917 issue of The Electric Journal stated that the reject eat was limited to about 50F higher than the "cold" side. The same article mentioned that a "ton" of cooling capacity needed about 35 lbs/hr of steam.
Why supersonic flow? If the ejector flow was subsonic, then some of the molecules could diffuse back to the vapoartion chamber, raising the pressure and the boiling point.
The basic rationale for the steam ejector system was that steam for steam heating was already available, thus reducing the load on the axle driven genetators.
- Erik
Murphy Siding chad s thomas how does it work? "Holy cow! Is it groundhog's day already? Hi Chad!" Sho' nuf! Popcorn Popper, and all, Terrific! Hi Chad!"
"Holy cow! Is it groundhog's day already? Hi Chad!"
Sho' nuf! Popcorn Popper, and all, Terrific!
Hi Chad!"
Excellent answer! Succint and in lay-man's terms.
I attended a seminar on absorption chillers when I worked for Hartford Steam Boiler. After the seminar, I concluded that they worked by magic. Twenty years later, I still don't have a clue!
54light15After the seminar, I concluded that they worked by magic.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Hi guys,
Sorry it took a year to get back.
Great answers. I now understand. Paul and Erick's answers made it click. Now I get at least the ideas of it, one part recovers water from the steam supply and the other made the vacume to evaporate for cooling.
Is it safe to say these were a dry climate unit best suited for the southwest deserts or did they wokk in the humid southeast.
Thanks for all the replys.
The system must have worked in the Southeast, for it was the one preferred by Southern for its cars. If you walked by the cooling unit on a car you could get spray from it.
Quoting Paul Milenkovic--"Steam is also used to provide chilled water for air conditioning in many large commercial buildings. There, something called "absorption cycle" air conditioning is used. The steam supplies heat that provides the motive power to a refrigeration cycle without any mechanical compressor -- I believe it involves ammonia being "absorbed" into water. There are refrigerators for RVs working on the absorption cycle driven by a butane flame, but that is not how the A/C on trains had worked."--As to the use ammonia in refrigerators, about 100 years ago, my mother was in a school in Northfield Massachusetts, and she spoke of occasional ammonia leaks in the kitchen.
Also, for a few years, about fifty years ago, I had the use of a natural gas-powered refrigerator. It worked--but not as fast as an electric powered-one, especially for freezing water.
The ammonia that your mother smelled could have been from a mechanical (i.e. compressor driven) or absorption cycle unit. Ammonia is about the best refrigerant with the annoying side effect of being toxic in high concentrations and annoying in low concentrations. The natural as powered fridge (Servel?) used the absorption cycle. BTW, my incle had a natural gas powered chiller for a number of years for his house.
The absorption cycle make use of the fact that ammonia likes to dissolve in water and the heat is used to free the ammonia from water.
DeggestyQuoting Paul Milenkovic--"Steam is also used to provide chilled water for air conditioning in many large commercial buildings. There, something called "absorption cycle" air conditioning is used. The steam supplies heat that provides the motive power to a refrigeration cycle without any mechanical compressor -- I believe it involves ammonia being "absorbed" into water. There are refrigerators for RVs working on the absorption cycle driven by a butane flame, but that is not how the A/C on trains had worked."--As to the use ammonia in refrigerators, about 100 years ago, my mother was in a school in Northfield Massachusetts, and she spoke of occasional ammonia leaks in the kitchen. Also, for a few years, about fifty years ago, I had the use of a natural gas-powered refrigerator. It worked--but not as fast as an electric powered-one, especially for freezing water.
When I had my Mini-motorhome with the LPG fired absorbtion refrigerator/freezer - the main requirement was to have the frig level - I had multiple levels on the motorhome to assist in getting it level. (flame burns up - and if the flame doesn't hit the proper area, the cooling is less than effective.
Never too old to have a happy childhood!
Forty nine years ago I was on board Her Majesty's Australian Ship Melbourne, an aircraft carrier built as HMS Magnificent in 1943 but incomplete at the end of WWII. I had visted the ship in 1956 on its arrival in Australia, the ship's first Commander Air being our next door neighbour. It had been used to test the steam catapault for subsequent RN carriers and had a fairly nominal angled deck fitted, all of which used up the twelve or so years.
Anyway, the ship had steam ejector air conditioning. The ejectors were quite large as I recall now around six feet long and maybe eight inches across at the inlet. While I didn't know much about the theory the steam inlet pipes were hot and there were inches of ice on the ejectors just past the nozzle. This convinced me that the theory of steam cooling actually worked.
Peter
I probably should have described the house, built in 1931, which was next door to the Naval Aviator mentioned above. In the early 1950s, there were relatively frequent electric power cuts due to a series of strikes by coal miners seeking better conditions and pay. For some reason not clear to me, this didn't affect the supply of gas, then produced by burning coal.
Anyway, the house had an all gas kitchen, gas stove, gas water heater and gas refrigerator. The laundry had a gas fired "copper" where washing was boiled and a spin dry tub driven by a water turbine connected to the cold water tap.
Heating, such as there was, was by an open fireplace in the lounge room and a portable kerosene heater.
So when the power was cut, all we lost was the lights and the radio....
And there was a good supply of candles.
M636C Anyway, the ship had steam ejector air conditioning.
Anyway, the ship had steam ejector air conditioning.
One of the points brought up in the 1917 Electric Journal article on steam ejector cooling was that it did not involve either open flame or toxic chemicals and thus was safe for use on ships.
The technology would make for an interesting example in an engineering thermodynamics text, combining boiling, condensation and supersonic flow.
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