testing oil miscibility/oil return
asc...@mo.net
>For all you experts out there on oil return in R-12 low temp systems.
>
>I built a refrigeration test stand out of a 2-ton med temp R-12
>semi-hermetic Copeland compressor. The goal is to try to force
>oil logging (poor oil return) to occur.
>
>Evaporator is a 50 foot coil of 5/8" refrigeration copper, in free air,
>no fan or fins. The coil diameter is around 14 inches and spread out to
>be about 2 1/2 feet deep. The centerline of the coil is parallel
>to the ground, providing each loop (11 of them) a chance to "trap"
>oil. Sight glasses all over the place. Evaporator heat can be provided
>from direct electric heating of the coil, upto 310 Amps, approx 5V.
>The liquid line has a 1 foot rubber hose (automotive barrier hose)
>segment to block current flow thru the condenser and compressor.
>
>The (hand operated) metering device is a multiturn needle valve,
>approx 4 tons capacity wide open.
>
>The suction line, is a 6 foot piece of 7/8" vertical (straight up)
>copper, followed, by a 6 foot horiz run (also 7/8"). The horizontal
>run has a "low spot", about 1 inch lower than the ends, for oil to
>collect in (and a sight glass). There is also a manual EPR
>(ball valve, with 3/4" opening), with low side gauges on either side
>of the valve.
>
>Operating temps on the evap, with R-12-like refrigerants will be -30 to -40F,
>so the 2 ton med temp compressor will be delivering less than 1/2
>ton effective. This should further magnify the effect of the
>large diameter suction line on poor oil return.
>
George, curious to know what you are expecting to find with this
apparatus. Are you attempting to determine minimum refrigerant
velocities for oil return? I've wondered about 'rules of thumb'
recommendations like 700 ft/min for horizontal runs, 1500 ft/min
for vertical risers. How appropriate are these recommendations?
Should they vary with refrigerant and oil used?
Btw, kudos on your home page mention in the Nov 7th issue of PC
Mag.
Andy Schoen
asc...@mo.net
George Goble
>In <46amuk$h...@mozo.cc.purdue.edu>, g...@cidmac.ecn.purdue.edu (George Goble) writes:
>>
>>Operating temps on the evap, with R-12-like refrigerants will be -30 to -40F,
>>so the 2 ton med temp compressor will be delivering less than 1/2
>>ton effective. This should further magnify the effect of the
>>large diameter suction line on poor oil return.
>>
>
>George, curious to know what you are expecting to find with this
>apparatus. Are you attempting to determine minimum refrigerant
>velocities for oil return? I've wondered about 'rules of thumb'
>recommendations like 700 ft/min for horizontal runs, 1500 ft/min
>for vertical risers. How appropriate are these recommendations?
>Should they vary with refrigerant and oil used?
Thanks for the 'ruls of thumb'. This test stand is for testing
oil return/miscibilities of various refrigerant blends I am
concocting up. Managed to get -50F on the evap, and 4 inch diameter
frost jackets on the evap and part of suction line.
R22 has always had more oil miscibility problems and oil return
problems than R12.. I have heard early R-22 systems often used
R12 line sizes, [which were larger], and thus lower gas velocities,
and oil return problems. By decreasing suction and evaporator
line sizes, gas velocities went up (slight drop in efficiency),
but mineral oil returned well.
I put R22 in the test system, and ran for 8 hours.. whole evap [-40F] and
vertical suction line full of white globs of "solid paraffin wax,
just starting to melt", which was the oil (Suniso 3GS)..New blend
did not do this and left minimal oil in evap after a slow pumpdown
to boil off the refrigerant. Had to wait for a cold day to do the
R22, to keep the compression ratio down, still had about 210F
discharge temps, ambient in the 40's, head approx 100 PSIG. Evap at
18 in vacuum.
Running R-134a (with 3GS mineral oil),
did manage to get SOME oil return, but "by force", formed oil
slugs and "oil bullets" in the suction lines.. and a sudden heat
load in the evap (or cycling on after being off), could easily
oil slug a compressor and bust valves, etc.. I have a ball valve
in the suction line, so when the evap is full of refrigerant & oil,
and compressor is started, this valve is opened slowly, while observing
slugs in the sight glasses. R-134/oil in the liquid line and evap
looks like "milk"..forcibly mixed refrigerant & oil, but not really
"dissolved".
R-12 & R-406A worked well down to the -40 to -50 F range with
no oil return problems.. Have a jug of FX-56 (R-409A) on order,
still looking for FRIGC FR-12..
>
>Btw, kudos on your home page mention in the Nov 7th issue of PC
>Mag.
Thanks.. maybe I should submit the homepage to www.ashrae.org
to see if they assign at an R-number, and classify it A3/A3 :) ?
[starting a BBQ grill in 3 seconds with liquid oxygen]
PC mag listed it under "flammable web sites", part III...
>
>Andy Schoen
>asc...@mo.net
--ghg
http://ghg.ecn.purdue.edu
http://worldserver.com/R-406A
George Goble
>>
>
>George, I doubt you are going to make many friends among the
>compressor manufacturers with your testing. :-)
>
Compressor mfgrs already hate me, for inventing R-406A..
probably means less new 134a compressors for them to sell..
[ghg wrote]
>>R22 has always had more oil miscibility problems and oil return
>>problems than R12.. I have heard early R-22 systems often used
>>R12 line sizes, [which were larger], and thus lower gas velocities,
>>and oil return problems.
>
>Same issue with the many R-12 (and R-502) systems being converted
>to R-22. R-22 is inexpensive, plentiful, and well understood.
>As a result, it is still a popular refrigerant for converting
>systems away from CFCs.
22 has a very high heat of compression (reason 502 was invented)
that low and medium temp will generate refrigerant and maybe
oil brakedown.. and "coke" the valves, discharge line.. failure
being carbonized cap tubes (plugged), "wire drawing" on compressor
discharge valve plates, etc.. Home freezers used to use R22, but
not anymore..
Some method is needed to deal with this, such as liquid injection,
two stages of compression (with cooling between), etc... I think
a lot of converted to R22 systems will fail in a year or so.
I would be willing to take my chances with 10% CO2/ 90% propane
(if conditions permitted a flammable refrigrant), it should
perform well into lowtemp, no breakdown like R22.
>
>>
>>I put R22 in the test system, and ran for 8 hours.. whole evap [-40F] and
>>vertical suction line full of white globs of "solid paraffin wax,
>>just starting to melt", which was the oil (Suniso 3GS)..New blend
>>did not do this and left minimal oil in evap after a slow pumpdown
>>to boil off the refrigerant. Had to wait for a cold day to do the
>>R22, to keep the compression ratio down, still had about 210F
>>discharge temps, ambient in the 40's, head approx 100 PSIG. Evap at
>>18 in vacuum.
>
>Interesting. Waxing problems are normally associated with low temp
>R-502 systems running mineral oil. Older R-12 low temp systems never
>seemed to have waxing problems. With low temp R-22 systems, high
>discharge temperatures causing oil breakdown problems seemed to be
>the major problem. I have not seen major waxing problems with
>R-22 systems.
The "wax" was just partially frozen oil.. it cleared up when
system was turned off (i.e. melted). Good refrigerant miscibility
would impede "wax" formation I would think.
>
>Btw, the reasons why wax forms in a refrigeration system would be a
>great area of study. It is known that filter-driers with activated
>charcoal will remove wax from systems. However, no one has any real
>definitive explanations why wax is more of a problem with one
>refrigerant than another.
R12 is totally miscible in mineral, R22 is only partially miscibile.
>
>The move to POE oils, however, may make this issue irrelevant.
POE's dont foam, so R-12 compressors may have lube problems,
if the foaming was relied on to cover some parts.. steel is
a breakdown agent for POEs, so there must be passivators to
prevent this, etc, etc, etc..
>
>>
>>Running R-134a (with 3GS mineral oil),
>>did manage to get SOME oil return, but "by force", formed oil
>>slugs and "oil bullets" in the suction lines.. and a sudden heat
>>load in the evap (or cycling on after being off), could easily
>>oil slug a compressor and bust valves, etc.. I have a ball valve
>>in the suction line, so when the evap is full of refrigerant & oil,
>>and compressor is started, this valve is opened slowly, while observing
>>slugs in the sight glasses. R-134/oil in the liquid line and evap
>>looks like "milk"..forcibly mixed refrigerant & oil, but not really
>>"dissolved".
>
>This is essentially what I've heard from others who have run
>similar tests with R-134a and mineral oil.
>
>>
>>R-12 & R-406A worked well down to the -40 to -50 F range with
>>no oil return problems.. Have a jug of FX-56 (R-409A) on order,
>>still looking for FRIGC FR-12..
>
>Just found out about FRIGC FR-12. It's a ternery blend of
>R-134a/R-124/R-600 (59/39/2) by weight with a reasonably low
>temperature glide (approx 3F). My guess would test similar to R-134a
>with your tests. Marketed at the automotive market. UHaul seems
>to like it. You can obtain it from Intermagnetics Corp.
FRIGC admitted to me a year ago, that they took the oil miscibility
idea from R-406A. Intermagnetics wont sell us any, wonder why.
I saw the UHAUL yea FRIGC press release.. They said FRIGC had
good performance compared to a R-12 car that had been retrofitted
to 134a. Nothing was said about FRIGC to R-12 comparison.
Only advantage I can see in FRIGC is the raising the critical
temp of the refrigerant compared to 134a.. should help out in
"hot idle" (gridlock).. Their patent 5,425,890 claims the above
3 components..
With all the bitching going on about flammability, even "weak"
flammability, what happens if a car sets parked with FRIGC,
with a vapor leak, at an ambient temp of 15F..BP of
of R-124 is 8.26F and R-134a is -15.07F and BP of R-600 (n-butane)
is 31.03F. All the R-134a and R-124 will leak off, (15F ambient),
and R-600 (BP 31.03) will be left as liquid.. and could
concentrate to "3" flammability??? Wonder why they don't submit
to ASHRAE for an R-number and safety classif? They would have
to do low temp leakdowns?
Jim Calm's June 1995 ARTI Refrigerant Dbase lists the above
formulation also (bet that is where you saw it?), however
there are rumors that FRIGC reformulated some.. changing
the R-600 to R-600a (n-butane to isobutane, BP 10.83).
I have no hard evidence of this though.. Using isobutane
would cause FRIGC to infringe on US patent 4,482,465 (Gray),
which has claims of "bracketing" (by boiling point) a
hydrocarbon with two nonflammable halocarbons.
None of FRIGC's components has a boiling point less than (colder
than) R-12.. (-21.something F), so barring an azeotrope formation,
how is FRIGC going to provide proper suction pressures?
Calculations with NIST REFPROP V4.0 show suction pressure
at 32F would be about 21 PSIG for FRIGC, not 29-30 PSIG
as R-12 would do. That is going to result in low capacity,
and problems with low pressure cutout switches.. so the
compressor would probably cycle off and back on every
few seconds, further reducing delivered capacity, and
causing excessive compressor clutch wear.. Variable displacement
automotive compressors, such as the GM V-5 vary their displacements
to hold suction at 28-30 PSIG.. so when they see 21 PSIG
suction (FRIGC).. they will go to nearly 25% or so displacement,
causing very poor performance and almost no capacity.
Someone might want to suggest to FRIGC (Intermagnetics?) to try
R-600a/124/134a/22 4/28/40/28
That should fix both the low pressure and oil miscibility problems.
>Andy Schoen
>asc...@mo.net
>
--ghg
asc...@mo.net
>>
>>Just found out about FRIGC FR-12. It's a ternery blend of
>>R-134a/R-124/R-600 (59/39/2) by weight with a reasonably low
>>temperature glide (approx 3F). My guess would test similar to R-134a
>>with your tests. Marketed at the automotive market. UHaul seems
>>to like it. You can obtain it from Intermagnetics Corp.
>
>FRIGC admitted to me a year ago, that they took the oil miscibility
>idea from R-406A. Intermagnetics wont sell us any, wonder why.
>I saw the UHAUL yea FRIGC press release.. They said FRIGC had
>good performance compared to a R-12 car that had been retrofitted
>to 134a. Nothing was said about FRIGC to R-12 comparison.
>
>Only advantage I can see in FRIGC is the raising the critical
>temp of the refrigerant compared to 134a.. should help out in
>"hot idle" (gridlock).. Their patent 5,425,890 claims the above
>3 components..
Thus the purpose for using R-124, a low pressure refrigerant,
in their blend?
>
>With all the bitching going on about flammability, even "weak"
>flammability, what happens if a car sets parked with FRIGC,
>with a vapor leak, at an ambient temp of 15F..BP of
>of R-124 is 8.26F and R-134a is -15.07F and BP of R-600 (n-butane)
>is 31.03F. All the R-134a and R-124 will leak off, (15F ambient),
>and R-600 (BP 31.03) will be left as liquid.. and could
>concentrate to "3" flammability??? Wonder why they don't submit
>to ASHRAE for an R-number and safety classif? They would have
>to do low temp leakdowns?
Then you have folks promoting hydrocarbons as a substitute for
R-12, e.g., OZ HC-12a.... Definitely a problem for service
mechanics who like to smoke while they work. :-)
>
>Jim Calm's June 1995 ARTI Refrigerant Dbase lists the above
>formulation also (bet that is where you saw it?),
No, actually, FRIGC notes this and other thermodynamic property
details in their sales brochures.
> however
>there are rumors that FRIGC reformulated some.. changing
>the R-600 to R-600a (n-butane to isobutane, BP 10.83).
>I have no hard evidence of this though.. Using isobutane
>would cause FRIGC to infringe on US patent 4,482,465 (Gray),
>which has claims of "bracketing" (by boiling point) a
>hydrocarbon with two nonflammable halocarbons.
>
So, that's the trick of formulating ternary blends, eh?
Does the patent cover all hydrocarbons whose BP falls
within the BPs of the halocarbons one wants try to make
a blend? How about R-143a + R-134a + cyclopropane?
>
>Someone might want to suggest to FRIGC (Intermagnetics?) to try
>
>R-600a/124/134a/22 4/28/40/28
Well, that would certainly bring suction pressures up. :-)
I would suspect one design criteria used in the development of FR-12
was not to use either CFC or HCFC components. In that way, one can
claim having a long term alternative, and not just a service replacement,
even though R-22 will likely be around for quite some time.
How about using R-143a in place of R-22?
Andy Schoen
asc...@mo.net
George Goble
>In <47497t$9...@mozo.cc.purdue.edu>, g...@cidmac.ecn.purdue.edu (George Goble) writes:
>>
>>Only advantage I can see in FRIGC is the raising the critical
>>temp of the refrigerant compared to 134a.. should help out in
>>"hot idle" (gridlock).. Their patent 5,425,890 claims the above
>>3 components..
>
>in their blend?
R-124 will certainly lower the critical temp of the blend.. It is
not really a "low pressure" refrigerant like R-11, but has a higher
BP than R-12. Unless they form an azeotrope (very unlikely), three
components all with boiling points higher than R-12, will never
get a boiling point to R-12, and will have low pressure problems
in an unmodified (ie. drop-in) system.
>
>>
>>With all the bitching going on about flammability, even "weak"
>>flammability, what happens if a car sets parked with FRIGC,
>>with a vapor leak, at an ambient temp of 15F..BP of
>>of R-124 is 8.26F and R-134a is -15.07F and BP of R-600 (n-butane)
>>is 31.03F. All the R-134a and R-124 will leak off, (15F ambient),
>>and R-600 (BP 31.03) will be left as liquid.. and could
>>concentrate to "3" flammability??? Wonder why they don't submit
>>to ASHRAE for an R-number and safety classif? They would have
>>to do low temp leakdowns?
>
>Then you have folks promoting hydrocarbons as a substitute for
>R-12, e.g., OZ HC-12a.... Definitely a problem for service
>mechanics who like to smoke while they work. :-)
It is possible to have small amounts of hydrocarbons in a blend
(for oil miscibility and oil return), and have the blend be
totally non flammable or very weakly flammable in worst case
scenarios (large vapor leak).. on the order 100X less than
pure hydrocarbons like OZ-12, HC-12a, etc.. Outside of the safety
problem, hydrocarbons are excellent refrigerants.
Take a lit cigarette, and spray butane on it (from an unlit lighter),
and the cigarette will go out, most likely. If you just took a long
drag on the cigarette, it will be hotter and problably ignite the
butane. Cars carry around 100lbs or more gasoline.. and the public
and others get fanatic about 1lb of hydrocarbons in the A/C..
OZ-12 was on 50,000 cars and other things, before somebody wanted to
"make a point", and deliberately, after much trying, blew up cars
with it (letting it loose in the passenger cmpt, getting the air-fuel
mix right and igniting it). In general propane/butane, etc, need
to be roughly 2-8% in air by volume to burn, out side that range,
no fire. There were no reported safety problems with OZ-12
before that. Suddenly bunch of states banned it immediately.
There have been too many movies where the slightest accidents or
cars going off cliffs and exploding (sometimes in midair) to
inflame the public. Take off the gas filler cap on a car, and
drop in a lit match.. what happens..
1) in the movies, the whole car blows up, along with the gas station.
2) in real life, the match goes out, or a small flame forms at the
neck, which can easily be snuffed.
The movies often use waterbeds filled with gasoline in the trunk
and back seat, set off with a stick or two of dynamite..
Safety must be considered, but the flammability I think is
way overblown (due to the movies), and often not considered
in a scientific way
>>
>>Jim Calm's June 1995 ARTI Refrigerant Dbase lists the above
>>formulation also (bet that is where you saw it?),
>
>No, actually, FRIGC notes this and other thermodynamic property
>details in their sales brochures.
>
>> however
>>there are rumors that FRIGC reformulated some.. changing
>>the R-600 to R-600a (n-butane to isobutane, BP 10.83).
>>I have no hard evidence of this though.. Using isobutane
>>would cause FRIGC to infringe on US patent 4,482,465 (Gray),
>>which has claims of "bracketing" (by boiling point) a
>>hydrocarbon with two nonflammable halocarbons.
>>
>
>So, that's the trick of formulating ternary blends, eh?
>Does the patent cover all hydrocarbons whose BP falls
>within the BPs of the halocarbons one wants try to make
>a blend? How about R-143a + R-134a + cyclopropane?
BP -53.23F -15.07F -27.2F
That would not infringe on Gray's patent. Be pretty hard
to keep it non flammable though.. even with large amounts
of R-134a.. Pure R-134a is on the verge of burning in 100C
flammability tests now used by ASHRAE and UL. R-143a
is "weakly" flammable and cyclopropane is highly flammable.
R-134a goes flammable at room temp, at 5PSIG above atmospheric.
Yep..about as broad as a patent on gravity.. what a pisser.
>
>>
>>Someone might want to suggest to FRIGC (Intermagnetics?) to try
>>
>>R-600a/124/134a/22 4/28/40/28
>
>Well, that would certainly bring suction pressures up. :-)
>
>I would suspect one design criteria used in the development of FR-12
>was not to use either CFC or HCFC components. In that way, one can
>claim having a long term alternative, and not just a service replacement,
>even though R-22 will likely be around for quite some time.
HCFCs may be allowed for service until 2029 or such.. we will
all be dead or retired by then..
>
>How about using R-143a in place of R-22?
They already use a huge amount of R-124, chlorotetrafluoroethane, an HCFC..
I suggested R-22, since they already have HCFCs and cannot be vented.
and R-22 is cheap. R-143a, CF3-CH3, trifluoroethane, is weakly flammable,
flammability range around 7-19% in air by vol, slightly more flammable
than R-142b.
>
>
>Andy Schoen
>asc...@mo.net
>
--ghg
Peter Kesselman
> Once a substance is classified as flammable, it becomes a serious
shipping headache.
> We use pentane in our R23 systems, but leave that off the manifest of
materials when
> shipping. Shhh... don't tell anyone. Insurance costs go when up, as do
handling charges.
> All for 2 oz. of pentane.
>
> JIm Sullivan
Hey Jim, why aren't you guys using SUVA-95. No pentane required, just POE
oils. Works better than R13 or R503 ever did. We literally dropped it into
systems that were designed for R13 (with oil change of course) and it
works great. They were 1 HP and 2 HP cap tube systems. We tried R23 but
discharge temperatures were out of this world. What kind of reliability
are you getting with R23 in the field?
--
Peter Kesselman