Date: Mon, 13 Apr 1998 12:06:54 -0700
Reply-To: "Chao, Harvey" <harvey.chao@LMCO.COM>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: "Chao, Harvey" <harvey.chao@LMCO.COM>
Subject: Propane fired refrigerators
Content-type: text/plain; charset="iso-8859-1"
I have been off the Vanagon list for some months, (still am off of it too)
due to workload and am sending this out "in the blind" to the group. Please
share it with our air cooled brothers and sisters too.
I have two comments on the two messages I am about to append to this -
1) They come via a mailing list devoted to mechanical devices that generate
music - such as player pianos, music boxes, "hurdey gurdey" boxes,
calliopes, etc - that somehow raised the topic (off subject of course) about
absorption refrigerators and I thought you all might be interested in how
the beasts work as used in your campers.
2) The second message is from a fellow named George Goebel at Purdue Univ.
in Indiana. How he ties in is a demonstration in how much our world
shrinks. I know of him due to his web page about igniting charcoal
briquettes using liquid oxygen(VERRRY Spectactular!) . It seems that the
editor/moderator of the Mechanical Music Digest also knows him
Hope you are all weathering El Nino well. The '82 Vanagon Bunker Burner is
still churning along.
Harvey
From: rollreq.geentroep (Jody Kravitz)
To: rrhodes, neilson@pagesz.net (Peter Neilson)
Date: Sat, 11 Apr 1998 22:33:11 -0700 (PDT)
Subject: Absorption Refrigerants
Peter Neilson wrote to me:
> Ammonia plus hydrogen is still used in gas-flame refrigerators,
> of which Servel is the best-known maker. It's a curious cycle,
> lacking a mechanical compressor. I understand a lot of weird
> things, but still don't know how gas refrigerators work.
These are referred to as "absorption" refrigerants. There are two
common absorption cycle refrigerants -- actually, they are always
pairs. One is ammonia/water, and the other is lithium-bromide/water.
In the case of ammonia/water, ammonia gas is separated from and
ammonia/water solution by heating. The ammonia gas is then cooled to
produce liquid ammonia. The liquid ammonia is allowed to boil at a low
pressure in the evaporator where it absorbs heat from the food.
This is not where the word "absorption" comes from, however. In a
separate part of the refrigerator, cool water (I don't recall if they
actually condense water vapor) is allowed to "absorb" ammonia gas from
the evaporator. If you recall from chemistry, ammonia _really_ likes
to be absorbed into cool water. This is how the low pressure is
maintained so the ammonia (the refrigerant) will boil and absorb heat.
This refrigerant being absorbed into the water is where the word
"absorption" comes from. This cycle will operate with only gravity
helping it. There's lots of finned pipes. ;-) It's used mostly in
small refrigerators and freezers. (Yes, I saw a propane fired chest
freezer recently.)
The water/lithium-bromide cycle is often used in large air-conditioning
applications where there's plenty of steam available, such as any place
where there's co-generation of steam and electric power. In this case,
water is the refrigerant. It is allowed to boil at a low pressure (at
temperatures above 0 C., obviously). The water vapor is "absorbed"
into a lithium-bromide brine. The diluted brine is later concentrated
by using steam, via a heat exchanger, to boil off the unwanted water.
50 to 100 ton chillers (1 ton = 12,000 BTU/hour) built on this cycle are
not uncommon in institutional buildings. I saw many of these at the
University of Illinois.
>
> H2S is poisonous, more so than cyanide. It's treacherous, too,
> because it's a nasal anesthetic; you think it's gone, but it's merely
> become concentrated enough to kill off your nose. I've never heard
> of H2S in a fridge.
>
> CO2 (Dry Ice [a trade-mark]) is a refrigerant, but it's evaporated in
> air, not in coils.
>
> Freon(tm) is used for reasons of safety. It is far less reactive,
> under household conditions, than NH3 or SO2.
>
> Peter Neilson, straying pretty far from mechanical music.
For further reading see the web site of Ammonia Refrigeration
Technicians Association, Danville IN:
http://www.nh3tech.org/abs.html
Jody Kravitz
[ Would you believe: Jody is a computer engineer !! ;) -- Robbie
--------------------
From: ghg@ecn.purdue.edu.geentroep (George Goble)(fwd)
To: rollreq@foxtail.com
Date: Sat, 11 Apr 1998 10:22:22 -0500 (EST)
Subject: Refrigerants
[ Jody asked his friend, George Goble, at Purdue University, for
[ further information about refrigerants. ]
--- forwarded message, please reply to sender and MMD ---
[ In Digest 980410 Richard Vance wrote: ]
> Prior to [using] Freon(tm) in the late thirties, SO2 was usually used
> in small refrigerators because liquefied NH3 (ammonia) gas is very
> hazardous, as opposed to the liquid ammonia NH3OH (ammonia water) we
> are familiar with.
>
> If it gets on the skin, or is breathed, it causes terrible burns by
> leeching out the H2 and O2 from organic material. Also, it can break
> down and burn in certain circumstances. SO2 only stinks if it leaks
> out.
Freon was invented in 1929-1930 era, but didn't get widely commercial-
ized for another 10 years. Ammonia requires all steel pipes/parts that
must be welded, not soldered or brazed. No copper allowed. I think
methyl chloride was also used then. Along with DME (dimethyl ether)
and butane/propane and other flammable hydrocarbons, methyl chloride
is pretty toxic.
> NH3 is still the best refrigerant, but it is impractical for small,
> isolated units. In large installations, the chiller unit is usually
> in a safe, isolated area. The liquefied gas is evaporated in a heat
> exchanger, which cools a brine that is piped to the various cold
> rooms, ice machines, or freezers throughout the plant.
>
> Richard Vance
This is correct. Purdue Univ. closed it's ice rink because the
physical plant could not keep the ammonia system running, due to
lots of leaks in the compressor room.
George H. Goble
[ I have known George for years and would describe him as having a
[ passion for materials that boil at low temperatures. He holds a
[ patent for a non-ozone-depleting substitute for R-12 which is
[ approved for automotive use:
[
[ http://www.autofrost.com/
[
[ George is also known for his exploits with liquid oxygen at the
[ Purdue engineering fraternity's annual barbecue:
[
[ http://ghg.ecn.purdue.edu/
[
[ Thanks for writing to us, George!
[
[ Jody
