The amazing Mr. Cap Tube

[shogun7]

Don't ya just love technology? Take the simpilicity of the cap tube I'm always impressed with the the human brain and it's marvilous achevements
The cap tube for example acts as a pressure reducing device. If air or water is pressurized at the inlet, there will be a linear or equal reduction of pressure for each foot of tubing. For example, if water enters a cap tube at 50 psig, the pressure decreases at a constant rate as the water passes through the tube. If refrigerant responded the same way as water, the cap tube could never be used as a refrigerant control. Why not? Because when the head pressure was low, the evaporator would be starved, and when the ambient temperature was high, the evaporator would be flooded with liquid (the flow rate would be greater than the rate of vaporization).
However, if there was a way to increase the flow rate when the head pressure was low, and decrease the flow rate at high ambient temperatures, you would have a refrigerant control. This modulating effect is exactly what happens when a cap tube is installed in a well-balanced system.

[Latte]

Shogun Wrote "Dont Ya love technology" NO!!!!
" " "take the simplicity of cap tube"
" " "Cap tube fitted on a well ballanced system"


1) Technology is OK if use wisely, some manufactures seen these days to go over the top with it, all singing and dancing with nice lights and stats that can tell you to a tenth of a degree whats going on. Keep it simple then there is less to go wrong.
2) cap tube, simplicty to me is somthing that can't go wrong because there is nothing to go wrong. How many jobs have you all been to this week with blocked capillary on R134a

Guess who is not a fan of cap tube


Regards

Raymond

[chemi-cool]

Hi Raymond.

Indeed you are right. R-134a blocks everything. Its such a powerful cleaning agent, much better then good old R-11.

Just changed 15ton TEV on a R-134a system. It was completely blocked with all the dirt from installing the system but I suspect that some of the particles I've found there was from the drier core.

It is defiantly bad refrigerant for cap tube systems.

Chemi

[shogun7]

ERR. Let me guess does he go by the name of Ramon? Gee Ray, You sound like you would like to go back “to the good ole daz”, You must be older then me!
Of course it's not the cap tube it's the refrigerant; never the less it's a wonderful piece of work
“Just changed 15ton TEV on a R-134a system. It was completely blocked with all the dirt from installing the system but I suspect that some of the particles I've found there was from the drier core.” …Chemi try to be more positive and look on the other side, like “boy am I lucky now my system is REALLY clean and look at my pay check, now I can buy the kids some new shoes”

[chemi-cool]

shogun7.

You must re tighten those loose screws!

Whats wrong with you man?
Is this all it comes to? New shoes?

Get your head fixed and come back.
I'm sure you have forgotten to take all your pills today.

This is the last time I'm answering such crap.

Chemi

[shogun7]

Your breakng my heart! Grow up man and get a grip on yourslf what do you do when something really bad happens. This is nothing but just kidding with each other Hay Chemi, who knows, All things are possible until they are proved impossible - and even the
impossible may only be so, as of now. Ya we might even become tight!

[Latte]

Hi Guys,

First of all i am "32" does this count as old, As for going back to the good old days, they are long gone. We would all like to be using R11 & R12 but have to move with the times.

My point was that these days i think technology is used for the sake of it. Controllers costing £100's of pounds when a mechanical stat & time would come to less than £10.
I am not against the new stuff, i just wonder sometimes would it not be better and more reliable to keep things simple.


Regards

Raymond

[shogun7]

Raymond
"My point was that these days i think technology is used for the sake of it. Controllers costing £100's of pounds when a mechanical stat & time would come to less than £10."
By the way this has always been a problem, especially with design engineers
I too like simplicity, and it seems to me that the decision on what to buy for the job is up to you, maybe you need to do more research on ways to achieve a simpler solution ?

[RogGoetsch]

Don't ya just love technology? Take the simpilicity of the cap tube ..... This modulating effect is exactly what happens when a cap tube is installed in a well-balanced system.

Sorry to differ with you Shogun, but I don’t consider a cap tube to be an example of technology as compared to, say, an expansion valve. Simple, yes; technologically advanced? Hmmmmm… Not! But perhaps you were speaking tongue-in-cheek?

I also have to take exception to the idea that the cap tube displays a modulating effect, even in a “well-designed system”.

So, one more time, with feeling!:
(Search earlier cap tube posts if you are not already completely bored with this topic, Dear Readers.)

The simple fact is that capillary systems do not respond well to changes in demand. They only do three things well: cool at design conditions, starve the coil at high demand, and flood the coil if the load drops.

They are used widely because they are effective for many applications and they are cheap. I, too, have found them to be troublesome with R134a, at least with the original POE formulations. Lately, I have not seen so many problems. (Fingers crossed!)

Love & Kisses,

Rog

[shogun7]

Rog:
Technology is the technical means people use to improve their surroundings.( Refrigerator) Technology is people using knowledge, tools, and systems to make their lives easier and better. In the case of the Cap Tube if you wish to get into semantics then I will call it elegant simplicity technology, that is: doing more with less. In the case of the Cap Tube as the temperature of the subcooled liquid at the inlet to the strainer varies inversely with the ambient temperature.So as the ambient temperature rises, and the temperature of the subcooled liquid is reduced.(more flash gas) This is the basic reason why the flow rate modulates in a cap tube. Remember that vapor restricts the flow of liquid. I excuse your lack of knoledge because your so young (lucky). There is another consideration you might think about and that is just because you think you know all about the Cap Tubes there may be others who may not be so informed so all things we discuss may be new to someone reading these posts. Don’t be so selfish Oh.. and I love you too

[Karl Hofmann]

High tech controlers and other such gizmos do not cost hundreds of dollars or pounds, they cost pennies, electronics are far cheaper to make than quality mechanical controlers, its just that we get charged and we pay hundreds

[RogGoetsch]

In the case of the Cap Tube as the temperature of the subcooled liquid at the inlet to the strainer varies inversely with the ambient temperature.So as the ambient temperature rises, and the temperature of the subcooled liquid is reduced.(more flash gas) This is the basic reason why the flow rate modulates in a cap tube.

Hmmmmmm. How exactly does the "subcooled liquid" at the strainer get cooler as the ambient (condensing temp) rises? Now that IS some impressive technology!

Rog

[shogun7]

Rog you seem to misunderstand what I was trying to convey.I said "In the case of the Cap Tube the temperature of the subcooled liquid at the inlet to the strainer varies inversely with the ambient temperature.
So as the ambient temperature rises, the temperature of the subcooled liquid (IN THE CAP TUBE) is reduced.(more flash gas)
Sorry bot tat This is the basic reason why the flow rate modulates in a cap tube. Remember that vapor restricts the flow of liquid.
So as the ambient temperature rises and falls, the temperature of the subcooled liquid in the condenser and cap tube vary directly. It is this variable subcooled temperature that determines the bubble length in the cap tube—which, in turn, modulates the flow rate. This phenomenon in effect transforms the cap tube from a pressure-reducing device to a refrigerant control and that my friend is a wonderful thing

PS about your quesion "How exactly does the "subcooled liquid" at the strainer get cooler as the ambient (condensing temp) rises? Now that IS some impressive technology!

Ans: Thats what I'm talking about WOW what a great technology...and I'm goin to patent it

[Peter_1]

And then, ...we even haven't spoken about the fact that speed in a capillary tube can reach sonic speeds where the common gas laws don't match anymore.

On these moments - sonic speeds - you should need a negative length of capillary tube if U used the formulas.

They call this a choked flow. This is the same reason/phenomena why powerful jet-fighters have on the outlet of there jet-engine a nozzle they can open or close. If this nozzle blocks, then full power can not be reached.

Those who visited air-shows have probably seen already on a F16 that when they go in take-off power - especially when they use the very powerful but fuel consuming afterburners - you can see that the nozzle is going wider and smaller. The computer then calculates the opening diameter for that specific condition of gasflow and temperature.

One of the question on my ATPL exam was: we have this specific engine - it was a GE engine - these are the specs of the engine, mounted on that airplane and the outlet blocks due to a malfunction on diameter x.
To what altitude must the airplane descend to maintain straight and level flight?
I can assure your, it took more than 2 pages to calculate this and it was for me the most difficult question for the course 'Jet engines'
I know, I know,..for some it will be again peanuts, simple maths, simple equations but then... I also had exam-nerves.

This phenomena can be described with the 'Fanno Line'
Fanno line is the locus of all states for frictionless adiabatic flow in a constant-area duct plotted on a T-s diagram.

For those interested: do a Google on 'Fanno Line' and 'Fanno line capillary'.

[RogGoetsch]

Rog you seem to misunderstand what I was trying to convey.I said "In the case of the Cap Tube the temperature of the subcooled liquid at the inlet to the strainer varies inversely with the ambient temperature.

I sure can’t see your reasoning here. As liquid flows directly from the condenser to the strainer inlet, how can it become cooler as the ambient & condensing temperature rise?

So as the ambient temperature rises, the temperature of the subcooled liquid (IN THE CAP TUBE) is reduced.(more flash gas)

Higher condensing temperature = higher pressure so with the captube cooled by contact with the suction line, we have a very subcooled liquid which should only flash at the discharge of the captube.

If you are assuming that there is flash gas forming in the last few inches of the cap tube, you may be correct, but with higher condensing pressure, there should be less flash gas, not more.

Sorry bot tat This is the basic reason why the flow rate modulates in a cap tube. Remember that vapor restricts the flow of liquid.

Where we use the vapor to limit flow is at the entrance to the captube. The system is “critically charged” for this very reason, and the captube usually soldered to the suction line so that it is too cool to allow the liquid to flash. Bubbles entrained at the entrance recondense almost immediately.

So as the ambient temperature rises and falls, the temperature of the subcooled liquid in the condenser and cap tube vary directly.

In a cap tube system, the liquid exiting the condenser should be at saturation all the way to the drier since you don’t get a liquid seal until the captube entrance.

Liquid backed up into the condenser would allow subcooling, but at the cost of condensing surface. This would exact a performance penalty for no purpose since subcooling is accomplished in the captube long before it can flash. The extra liquid in the condenser would delay pressure equalization during the off cycle, requiring a start capacitor, perhaps, and contributing to the amount of liquid in the crankcase on initial start-up.

It is this variable subcooled temperature that determines the bubble length in the cap tube—which, in turn, modulates the flow rate. This phenomenon in effect transforms the cap tube from a pressure-reducing device to a refrigerant control and that my friend is a wonderful thing

DaBit, one of our esteemed posters, has made a captube system jump through hoops. He may have achieved what you believe is possible, but from my own experience, designing units for mass production and manufacturing uniformity, cap tube systems must be optimized for a given set of conditions. For variable loads and conditions, expansion valves were invented.

Shogun, I realize I probably haven’t convinced you, so please don’t take my word for any of this. Test it and let me know if your results vary.

The method I used (I design very small refrigeration systems for bio-med applications, among other things) was to set up my test system with thermistors everywhere tied to a PC, logging temps at every critical point. Combined with pressure gauges installed in several places, I was able to plot the results on a pressure-enthalpy diagram and analyze the performance under different conditions and configurations.

Rog

[shogun7]

“Shogun, I realize I probably haven’t convinced you, so please don’t take my word for any of this. “YOU said this:
I sure can’t see your reasoning here. As liquid flows directly from the condenser to the strainer inlet, how can it become cooler as the ambient & condensing temperature rise?
I said subcooling varies inversely with ambient temp. (Translation in American) is as the temp on the cond goes up the subcooling temp on the refrigerant goes down
You said:
Higher condensing temperature = higher pressure so with the captube cooled by contact with the suction line, we have a very subcooled liquid which should only flash at the discharge of the captube.
I said:
So as the ambient temperature rises, the temperature of the subcooled liquid (IN THE CAP TUBE) is reduced.(more flash gas) because of lower subcooling and pressure drop as the subcooling = PT relationship and starts to flash thereby putting the brakes on the refrigerant mass flow this is called (the bubble point)
You said:
Where we use the vapor to limit flow is at the entrance to the captube.(WRONG) The system is “critically charged” for this very reason, and the captube usually soldered to the suction line so that it is too cool to allow the liquid to flash.( TRUE UP TO A POINT Bubbles entrained at the entrance recondense almost immediately(WRONG < THE ONLY TIME YOU HAVE BUBBLES AT the entrance in a balanced system is if you enter with no sub cooling and are below sat conditions.
I said:
So as the ambient temperature rises and falls, the temperature of the subcooled liquid in the condenser and cap tube vary directly. It is this variable subcooled temperature that determines the bubble length in the cap tube
You said:
In a cap tube system, the liquid exiting the condenser should be at saturation all the way to the drier since you don’t get a liquid seal until the captube entrance ( what the heck does that mean …I’m talking about sub cooling and that certainly means saturation..I Think!!!
YOU said:
Liquid backed up into the condenser would allow subcooling, but at the cost of condensing surface( NOT IN A BALANCED SYSTEM)
This would exact a performance penalty for no purpose since subcooling is accomplished in the captube long before it can flash( this IS SO BAD THAT I’M TOTALLY CONVINCED THAT YOU NEED TO START OVER WITH YOUR STUDIES
The extra liquid in the condenser would delay pressure equalization during the off cycle, requiring a start capacitor, perhaps, and contributing to the amount of liquid in the crankcase on initial start-up. WHY DO YOU INSIST ON TALKING ABOUT SOME CONDITION THAT HAS NOTHING TO DO WITH THE MAIN ISSUE
You said:
The method I used (I design very small refrigeration systems for bio-med applications, among other things) was to set up my test system with thermistors everywhere tied to a PC, logging temps at every critical point. Combined with pressure gauges installed in several places, I was able to plot the results on a pressure-enthalpy diagram and analyze the performance under different conditions and configurations.
Thats really scary!

[Peter_1]

Reading this post without the proper quotes I normally see is almost impossible.
I started reading and stopped it after 4 lines.
Who said what?
Who shouted there very loud and said that someone should start his studies over again. I can't figure out who what said.

Whom who can't quote, who can't solder who said something..??

Anayway, he whos said this...... should first think twice

[Gary]

Shogun, quotations should start with the word quote within square brackets, and end with /quote within square brackets. In the following example, I have inserted spaces within the brackets so that it will appear on your screen:

[ quote]What the other guy said.[ /quote]


If I remove the spaces within the brackets, this is what appears on the screen:

What the other guy said.

[RogGoetsch]

Here is Shogun's post with clarifying separators:

Rog Goetsch: “Shogun, I realize I probably haven’t convinced you, so please don’t take my word for any of this.

Shogun: “YOU said this:

Rog Goetsch: I sure can’t see your reasoning here. As liquid flows directly from the condenser to the strainer inlet, how can it become cooler as the ambient & condensing temperature rise?

Shogun: I said subcooling varies inversely with ambient temp. (Translation in American) is as the temp on the cond goes up the subcooling temp on the refrigerant goes down
You said:

Rog Goetsch: Higher condensing temperature = higher pressure so with the captube cooled by contact with the suction line, we have a very subcooled liquid which should only flash at the discharge of the captube.

Shogun: I said:
So as the ambient temperature rises, the temperature of the subcooled liquid (IN THE CAP TUBE) is reduced.(more flash gas) because of lower subcooling and pressure drop as the subcooling = PT relationship and starts to flash thereby putting the brakes on the refrigerant mass flow this is called (the bubble point)
You said:

Rog Goetsch: Where we use the vapor to limit flow is at the entrance to the captube.

Shogun: (WRONG)

Rog Goetsch: The system is “critically charged” for this very reason, and the captube usually soldered to the suction line so that it is too cool to allow the liquid to flash.

Shogun: ( TRUE UP TO A POINT

Rog Goetsch: Bubbles entrained at the entrance recondense almost immediately

Shogun: (WRONG < THE ONLY TIME YOU HAVE BUBBLES AT the entrance in a balanced system is if you enter with no sub cooling and are below sat conditions.
I said:
So as the ambient temperature rises and falls, the temperature of the subcooled liquid in the condenser and cap tube vary directly. It is this variable subcooled temperature that determines the bubble length in the cap tube
You said:

Rog Goetsch: In a cap tube system, the liquid exiting the condenser should be at saturation all the way to the drier since you don’t get a liquid seal until the captube entrance

Shogun: ( what the heck does that mean …I’m talking about sub cooling and that certainly means saturation..I Think!!!
YOU said:

Rog Goetsch: Liquid backed up into the condenser would allow subcooling, but at the cost of condensing surface

Shogun: ( NOT IN A BALANCED SYSTEM)

Rog Goetsch: This would exact a performance penalty for no purpose since subcooling is accomplished in the captube long before it can flash

Shogun: ( this IS SO BAD THAT I’M TOTALLY CONVINCED THAT YOU NEED TO START OVER WITH YOUR STUDIES

Rog Goetsch: The extra liquid in the condenser would delay pressure equalization during the off cycle, requiring a start capacitor, perhaps, and contributing to the amount of liquid in the crankcase on initial start-up.

Shogun: WHY DO YOU INSIST ON TALKING ABOUT SOME CONDITION THAT HAS NOTHING TO DO WITH THE MAIN ISSUE
You said:

Rog Goetsch: The method I used (I design very small refrigeration systems for bio-med applications, among other things) was to set up my test system with thermistors everywhere tied to a PC, logging temps at every critical point. Combined with pressure gauges installed in several places, I was able to plot the results on a pressure-enthalpy diagram and analyze the performance under different conditions and configurations.

Shogun: Thats really scary!

Does that help?

Rog

[Gary]

BTW, I agree with Rog. In a well balanced, properly designed, and properly charged system, there is a liquid/vapor mixture at the cap tube entrance.

[shogun7]

Gary said and i quote "BTW, I agree with Rog. In a well balanced, properly designed, and properly charged system, there is a liquid/vapor mixture at the cap tube entrance...so Roger(me) asks and I quote me " Gary show me where it says that in a properly charged system with some sub cooing that you have a liquid /vapor mixture".
boy for a guy who sells books and information on this site You seem to be suffering from the same brain drain as Rog!
Peter ,im sorry if you couln't understand my written word, I admit it was a little sloppy and I could say I was pressed for time because I was late my DR. appointmnt or taking my medication or what ever some people think is wrong with me, but I won't other then to say I was in a hurry to get to the gym and workout
(My favorate pass time)

[Gary]

Ever heard of carryover?

If you have ever measured subcooling while filling a system with a sight glass, you would see that the glass clears at 10-15F subcooling, because of carryover. (For much the same reasons, liquid droplets disappear in a suction line at 5-10F superheat.)

And if you have ever seen a cap tube system with a sight glass, you will see lots of bubbles when it is charged properly. And yes, it will be subcooled. That's why they don't put sightglasses on cap tube systems. To avoid confusing you.

Static gas laws only apply when the system is static (no energy applied). When you hit the start button, that all changes.

Technically, saturation only exists at the liquid/vapor interface, thus it is entirely possible and in fact common, for vapor bubbles to coexist with subcooled liquid in the liquid line, and for liquid droplets to coexist with superheated vapor in the suction line.

If this were not so, then all that would be needed is 1F subcooling at the TEV and 1F superheat at the compressor inlet.

[Gary]

Maybe this thread will help to clarify it for you:

http://www.refrigeration-engineer.co...read.php?t=144

[RogGoetsch]

BTW, I agree with Rog. In a well balanced, properly designed, and properly charged system, there is a liquid/vapor mixture at the cap tube entrance.

Oooh, Gary, you are SO diplomatic! You omit saying that I am full of beans about there being no subcooling!

Ever heard of carryover?

If you have ever measured subcooling while filling a system with a sight glass, you would see that the glass clears at 10-15F subcooling, because of carryover. (For much the same reasons, liquid droplets disappear in a suction line at 5-10F superheat.)

Please, oh wise one, explain "carryover" to me. I must confess I have never heard the term, not does my ancient Dossat have it in the index. I have heard of an ASHRAE study that found droplets in highly superheated suction gas. Is that where the term came from?

And if you have ever seen a cap tube system with a sight glass, you will see lots of bubbles when it is charged properly. And yes, it will be subcooled. That's why they don't put sightglasses on cap tube systems. To avoid confusing you.

Proof that you were being too polite earlier!

Static gas laws only apply when the system is static (no energy applied). When you hit the start button, that all changes.

Right again (damn you!) My only (admittedly feeble) defense is that the system I did my testing on was so small that the condenser discharged directly into the drier. But in any system there would have to be cooling in the line between the condenser and the drier, the liquid would have to cool more quickly than the gas, and the saturation principle would only apply after equilibrium in a static system. Ouch!

Thanks for the input. You da Man!

Rog

[shogun7]

[QUOTE=Gary]Ever heard of carryover? (NO) but a nice term.

Just because Gary says it doesn't make it so and I have researched a whole bunch and haven't found where it descrbes flash gas (bubbles if you will) in a balanced system. I ask you again Please show me where that's described in any literature or study Here's ASHRAE's explanation

45.24 2002 ASHRAE Refrigeration Handbook
Theory

A capillary tube passes liquid much more readily than vapor due to the increased volume of the vapor; as a result, it is a practical
metering device. When a capillary tube is sized to permit the desired flow of refrigerant, the liquid seals its inlet. (Where's THE BUBBLES?) If the system becomes
unbalanced, some vapor (uncondensed refrigerant) enters the capillary
tube. This vapor reduces the mass flow of refrigerant considerably, which increases condenser pressure and causes subcooling at
the condenser exit and capillary tube inlet. The result is an increase of the mass flow of refrigerant through the capillary tube. If properly sized for the application, the capillary tube compensates automatically
for load and system variations and gives acceptable performance over a limited range of operating conditions.
A common flow condition is to have subcooled liquid at the entrance to the capillary tube. Bolstad and Jordan (1948) described
the flow behavior from temperature and pressure measurements
along the tube The selection of a capillary tube depends on the application and anticipated range of operating conditions. One approach to the problem involves the concept of capacity balance. A refrigeration system operates at capacity balance when the resistance of the
capillary tube is sufficient to maintain a liquid seal at its entrance WHAT NO BUBBLES?)
Sorry boys ...No mention of BUBBLES!
OH an yes your da man

[shogun7]

Oh, OK Marc whatever you say...NOT!
I think I'll stick with ASHAE, RSES "SAM MANUAL", Priciples of Refrigeration etc, etc..or do you think I should buy Gary' stuff and dump all the other books I have accumlated over the years? By the way, from what I can see from your web page it looks to me that you could use some GYM time...no offence intended

[RogGoetsch]

[QUOTE=shogun7]

Ever heard of carryover? (NO) but a nice term.

Just because Gary says it doesn't make it so and I have researched a whole bunch and haven't found where it descrbes flash gas (bubbles if you will) in a balanced system. I ask you again Please show me where that's described in any literature or study Here's ASHRAE's explanation

45.24 2002 ASHRAE Refrigeration Handbook
Theory

A capillary tube passes liquid much more readily than vapor due to the increased volume of the vapor; as a result, it is a practical
metering device. When a capillary tube is sized to permit the desired flow of refrigerant, the liquid seals its inlet. (Where's THE BUBBLES?) If the system becomes
unbalanced, some vapor (uncondensed refrigerant) enters the capillary
tube. This vapor reduces the mass flow of refrigerant considerably, which increases condenser pressure and causes subcooling at
the condenser exit and capillary tube inlet. The result is an increase of the mass flow of refrigerant through the capillary tube. If properly sized for the application, the capillary tube compensates automatically
for load and system variations and gives acceptable performance over a limited range of operating conditions.
A common flow condition is to have subcooled liquid at the entrance to the capillary tube. Bolstad and Jordan (1948) described
the flow behavior from temperature and pressure measurements
along the tube The selection of a capillary tube depends on the application and anticipated range of operating conditions. One approach to the problem involves the concept of capacity balance. A refrigeration system operates at capacity balance when the resistance of the
capillary tube is sufficient to maintain a liquid seal at its entrance WHAT NO BUBBLES?)
Sorry boys ...No mention of BUBBLES!
OH an yes your da man

Gentlemen, cool your engines.

Before this discussion descends to the level of personal attacks, let’s try to remember that this is supposed to be science. Understanding is the goal, not chest thumping. Empirical evidence is preferred to shouting matches.

If you take it to the level of a pissing contest in a sandbox, you will only find yourselves alone in the sandbox, and covered with piss.

I love a good mystery and Shogun has just given me one. It seems to me, and let me emphasize this: it seems to ME that Shogun has misinterpreted much of the quote. Balance point is precisely that. Designed for, optimized for, and if the system strays, vapor bubbles throttle the flow.

What interests me is that the authors seemed to have it both ways: liquid backed up to the condenser (how else to have condensing pressure rise as the flow is throttled??) as well as a balance point of liquid/vapor at the cap tube entrance.

I’ve got to do some research into this now, not to prove anybody right or wrong, but to understand the phenomenon.

Also, please understand that I did not mean to make a comparison when I told Gary “You da Man”. It is merely an acknowledgement of his contributions to this forum. It was interesting to me that all it took was a simple word from Gary for me to start looking for the errors in my procedures. When someone can have that effect on me, he is indeed “da Man” in my ever-so-humble opinion.

Play nice.

Rog

[shogun7]

[QUOTE=RogGoetsch]Gentlemen, cool your engines.
It seems to ME that Shogun has misinterpreted much of the quote. [ "How much? and what prey tell" ]quote shogun
Balance point is precisely that.
["That was my whole point and no other condition"] quote shogun

What interests me is that the authors seemed to have it both ways: liquid backed up to the condenser (how else to have condensing pressure rise as the flow is throttled??)
as well as a balance point of liquid/vapor at the cap tube entrance.[“ What did he say? Try reading it 10 more times”!]quote shogun

Also, please understand that I did not mean to make a comparison when I told Gary “You da Man”. It is merely an acknowledgement of his contributions to this forum. It was interesting to me that all it took was a simple word from Gary for me to start looking for the errors in my procedures. When someone can have that effect on me, he is indeed “da Man” in my ever-so-humble opinion. ["Oh, you are too humble"]
[Nice recognition!]quote shogun

[“It's for others to theorise. Transition of the system dynamics (instabilities) will play a part, but even considering...”]Marks quote. So shogun says [ Ops, did you say a naughty and get cut off or am I being delusional?]

Marc, as I admire your wit and intelligence, [trying to be polite as Rog suggested] and you say that Gary has seen this then I have no reason not to believe it, however, if this was of any importance I’m sure it would be mentioned somewhere in the literature. So in my mind it's a moot point and of little consequence. In the future I think I will pay more attention to what Gary has to say.

[Peter_1]

, if you half the dP across a cap-tube you would only reduce flow by 1-(0.5)^½ = 0.29 = 29%.

This is only valid I think if you have 100% liquid flowing over the whole lenghth of the tube.

[Gary]

[QUOTE=shogun7]

Ever heard of carryover? (NO) but a nice term.

Just because Gary says it doesn't make it so and I have researched a whole bunch and haven't found where it descrbes flash gas (bubbles if you will) in a balanced system. I ask you again Please show me where that's described in any literature or study Here's ASHRAE's explanation

45.24 2002 ASHRAE Refrigeration Handbook
Theory

A capillary tube passes liquid much more readily than vapor due to the increased volume of the vapor; as a result, it is a practical
metering device. When a capillary tube is sized to permit the desired flow of refrigerant, the liquid seals its inlet. (Where's THE BUBBLES?) If the system becomes
unbalanced, some vapor (uncondensed refrigerant) enters the capillary
tube. This vapor reduces the mass flow of refrigerant considerably, which increases condenser pressure and causes subcooling at
the condenser exit and capillary tube inlet. The result is an increase of the mass flow of refrigerant through the capillary tube. If properly sized for the application, the capillary tube compensates automatically
for load and system variations and gives acceptable performance over a limited range of operating conditions.

If we are going to say that moving the liquid seal down the cap tube regulates flow in one direction, then we must say that moving the liquid seal to the inlet regulates flow in the other direction, with the balance point being in between the two extremes. IOW, theoretically our ideal balance point at design conditions would be to have the liquid seal some short distance from the inlet, allowing compensation for imbalance in either direction.

As far as relying on the books (mine or theirs) the guys over at ASHRAE burp, fart, and scratch their butts just like the rest of us. I would much rather see their test data and draw my own conclusions.

[RogGoetsch]

I have more work to do on this but since I will be gone for a couple of days, here’s an update:

1) A few words got dropped in the referenced quote between the ‘88 edition, when the topic was covered in the ASHRAE Equipment volume and the ’98 ASHRAE Refrigeration volume.
In ASHRAE E19.22, 1988 the same paragraph reads: “…If the system becomes unbalanced, some vapor (uncondensed refrigerant) enters the capillary tube. This vapor reduces the mass flow of refrigerant with little or no change in system pressures. If the opposite type of imbalance occurs, liquid refrigerant backs up in the condenser.
This condition causes subcooling and increases the mass flow of refrigerant.”

Compare to the same paragraph in ASHRAE R45.22 1998: “If the system becomes unbalanced, some vapor (uncondensed refrigerant) enters the capillary tube. This vapor reduces the mass flow of refrigerant considerably, which increases condenser pressure and causes subcooling at the condenser exit and capillary tube inlet. The result is an increase of the mass flow of refrigerant through the capillary tube.”

The 1988 wording also appears in my 1983 Equipment edition. Seems to make more sense.

2) The testing was apparently done with an apparatus that simulated an evaporator with a heater immersed in a vessel of refrigerant. This seems to have provided a supply of refrigerant in excess of system design requirements, which could provide the liquid needed to back up in the condenser. This was not an attempt to study performance of a system but only to test the response of the cap tube to varying conditions.
3) The captube was not soldered to the suction line in the 1948 study.
4) No attempt was made to measure system efficiency at low suction or elevated discharge. The extra flow occurs because the higher the load, the more condenser capacity is reduced! No concern with efficiency since (again) the study was only about cap tube response.

More later.

Rog

[Gary]

I have more work to do on this but since I will be gone for a couple of days, here’s an update:

1) A few words got dropped in the referenced quote between the ‘88 edition, when the topic was covered in the ASHRAE Equipment volume and the ’98 ASHRAE Refrigeration volume.
In ASHRAE E19.22, 1988 the same paragraph reads: “…If the system becomes unbalanced, some vapor (uncondensed refrigerant) enters the capillary tube. This vapor reduces the mass flow of refrigerant with little or no change in system pressures. If the opposite type of imbalance occurs, liquid refrigerant backs up in the condenser.
This condition causes subcooling and increases the mass flow of refrigerant.”

It seems to me that if there is enough refrigerant in the system to back liquid up into the condenser, then there is enough refrigerant to severely flood the compressor on a hot day under light load.

[frank]

In the car the other day I was explaining one of my old theories

That would be on Business Miles then Marc

[shogun7]

45.24 2002 ASHRAE Refrigeration Handbook
Rog/Gary
Again about the bubbles

With subcooled liquid entering the capillary tube, the pressure
distribution along the tube is similar to that shown in the
graph. (see fig 41 ) At the entrance to the tube, section 0-1, a slight pressure
drop occurs, usually unreadable on the gauges. From point 1 to
point 2, the pressure drop is linear. In the portion of the tube
0-1-2,[the refrigerant is entirely in the liquid state],
and at point 2, the first bubble of vapor forms. From point 2 to the end of the
tube, the pressure drop is not linear, and the pressure drop per
unit length increases as the end of the tube is approached. For
this portion of the tube, both the saturated liquid and saturated
vapor phases are present, with the percent and volume of vapor
increasing in the direction of flow. In most of the runs, a significant
pressure drop occurred from the end of the tube into the
evaporator space.

Now this really says it all

[Mikol (1963) and Li et al. (1990) showed that generation of the
first vapor bubble does not occur at the point where the liquid pressure
reaches the saturation pressure (point 2 on Figure 41), but
rather the refrigerant remains in the liquid phase for some limited
length past point 2, reaching a pressure below the saturation pressure.]
This delayed evaporation, often referred to as a metastable or superheated liquid condition, must be accounted for in analytical modeling of the capillary tube, or the mass flow rate of refrigerant will be underestimated (Kuehl and Goldschmidt 1991; Wolf et al.
1995). Now Gary are you sure you didn't hit your head on someting and you were seeing stars instead of bubbles
Rog round file that ASHRAE E19.22, 1988 it’s too old!

[shogun7]

Peter, speaking of GE Jet engines I was a project engineer for a co-generation plant we were installing at the LA downtown Central Plant and I had to go to Houston, Texas to certify that the engine was capable of performing all of the requirements on the punch list. It was very impressive experience. I can’t remember the exact size in HP but it was what is on the DC-10. We installed the engine to generate more electrical power to the downtown buildings and to generate steam from the waste heat to drive 2 new 1800 ton double effect Trane Absorbers Of course we had to rebuild and expand the existing cooling towers. Total plant cap came to 6000 tons. Ahh, those were fun times!

[shogun7]

Marc: Bubbles, bubbles, bubbles that's my focus and I agree that this whole thread is distorted and has gone all over the place. This cap tube discussion is a matter of fact distorted by a lot of opinions. I have not a lot of experience with small systems so I have to rely on what I read and research, but don't ask me to take someones word that he's seen it in deference to what an organization such as ASHRAE says. I can't buy it! Now I know I'm not always right (but most times ) and I can admit if I’m wrong It seems to me that when some people disagree with you they interject some off the wall nonsense and try to confuse the discussion [like that last post from Gary I couldn't gring myself to say anything]and I feel that both Rog and Gary are guilty. Mark Please re-read my posts (if you have the time ) and tell me where I have straid off of the original premice. Oh, and please forgive us for being sooo American. Song: Ho say can you see ..Marc is picking on me..etc,etc

[Dan]

Long time back I promised to find an article in a Danfoss Journal from late 1979.

I was about droplets in the suction gas as a function of the super heat.

I have article with black and white pictures.

All interested please e-mail me at: jbm@danfoss.com

Besr regards

Jorgen Bargsteen Moller
Danfoss Nordborg, Denmark

That's from the discussion in early 2001 that Gary pointed toward. The long time Jorgen referred to was 3 months, and now it is 3 years. LOL. Excellent discussion. Wonderful title too: The Fundamental Myth.

As is: The Amazing Cap Tube.

[RogGoetsch]

I have more work to do on this but since I will be gone for a couple of days, here’s an update:

1) A few words got dropped in the referenced quote between the ‘88 edition, when the topic was covered in the ASHRAE Equipment volume and the ’98 ASHRAE Refrigeration volume.
In ASHRAE E19.22, 1988 the same paragraph reads: “…If the system becomes unbalanced, some vapor (uncondensed refrigerant) enters the capillary tube. This vapor reduces the mass flow of refrigerant with little or no change in system pressures. If the opposite type of imbalance occurs, liquid refrigerant backs up in the condenser.
This condition causes subcooling and increases the mass flow of refrigerant.”

Compare to the same paragraph in ASHRAE R45.22 1998: “If the system becomes unbalanced, some vapor (uncondensed refrigerant) enters the capillary tube. This vapor reduces the mass flow of refrigerant considerably, which increases condenser pressure and causes subcooling at the condenser exit and capillary tube inlet. The result is an increase of the mass flow of refrigerant through the capillary tube.”

The 1988 wording also appears in my 1983 Equipment edition. Seems to make more sense.

2) The testing was apparently done with an apparatus that simulated an evaporator with a heater immersed in a vessel of refrigerant. This seems to have provided a supply of refrigerant in excess of system design requirements, which could provide the liquid needed to back up in the condenser. This was not an attempt to study performance of a system but only to test the response of the cap tube to varying conditions.
3) The captube was not soldered to the suction line in the 1948 study.
4) No attempt was made to measure system efficiency at low suction or elevated discharge. The extra flow occurs because the higher the load, the more condenser capacity is reduced! No concern with efficiency since (again) the study was only about cap tube response.

More later.

Rog

Theory vs. application: aye, there’s the rub!

Hmmmmm. If ASHRAE Handbooks are now Holy Writ, how could the same paragraph differ in meaning from one edition to the next? Blasphemy!

In the ’98 Ref Handbook it says a captube “…gives acceptable performance over a wide range of operating conditions.” But in 2002 the same paragraph reads: “…gives acceptable performance over a LIMITED range of operating conditions.” Perhaps the refrigeration deity is merely testing us to see if we will abandon faith-based science for tawdry experimentation!

By the way, I love ASHRAE, been a member for 28 years so far, and consider it a wonderful information source for all things HVAC. In my early years it wasn’t as much help with refrigeration, per se, as other sources.

And, I have no problem with the theory. Seems pretty straightforward if you have a refrigerator designed like the lab test arrangement demonstrated in ASHRAE: an evaporator consisting of a refrigerant reservoir, an adiabatic cap tube (no heat transferred in or out of cap tube), and a water-cooled condenser with counter-flow (coldest water enters at subcooled end). No problemo.

My problem is with Shogun’s assertion that the cap tube is an amazing modulating device when applied to real applications.

Not to quibble too much, though, let’s assume we have a unit which is properly designed with a capacity balance point based on a 72F ambient in a temperature controlled building at the same temperature. Say we have 10F degrees of superheat at the compressor, liquid seal at the cap tube, and just enough liquid so that an imbalance allows liquid to back up into the condenser to supply our extra pressure and extra subcooling.

Since only one capacity balance point exists for any given compressor discharge pressure, according to ASHRAE (the sacred book lies before me, I blaspheme not!), let’s imagine that the condenser gets dirty. (I know, it never happens, but just for the sake of argument, okay?)

Our feed rate increases, extra liquid goes into the evaporator until we lose our liquid seal and flow is throttled. Since load didn’t change, can we agree our superheat drops? If there is enough extra liquid, we may even have liquid back to the crankcase. Now compressor energy is expended cooling the crankcase. Big efficiency penalty there.

Opposite case: we have the unit operating as described and the load increases: door is opened, perhaps. We have 10 degrees of superheat, but now the refrigerant is boiling sooner as it circuits the evap so superheat increases. But suppose the evaporator is large enough and the refrigerant charge large enough that enough liquid shifts to the condenser to back up and supply the extra pressure and subcooling we need. Great, except that once again we have sacrificed efficiency.

ASHRAE (may Her name be praised) Refrigeration Handbook 2002 page 45.25 describes the method for determining the capacity balance point for a given cap tube and condensing pressure. It provides an example of a capacity balance curve (Fig. 43). When designing the system, the charge is selected for operation at a point on a given cap tube’s curve. The note that accompanies the figure states: “Note: Operation below this curve results in a mixture of liquid and vapor entering the capillary. Operation above the capacity balance points causes liquid to back up in the condenser and elevate its pressure.”

My WHOLE point is that for efficient operation, you would be well advised to design below the curve, not on it. That way you have vapor and liquid always at the cap tube entrance, but you don’t overfeed or lose condensing surface. You won’t find the capacity modulation touted in this thread and elsewhere, but you can match your capacity more exactly to the optimum operating point on the compressor curve. The unit can run longer if it needs to, or it can shut off when the demand is satisfied, but it will be more efficient, using less energy for the same amount of cooling.

You are also less bothered by inconsistencies in manufacturing and the system is a lot easier for the average technician to service. But if you don’t like this advice, by all means ignore it!

Rog

[shogun7]

Marc I have to admit that I don't have a clue as to what all your fancy foot work means as I know not about the SI system so I can't repond to that but please tell me what the hell do you mean by CARYOVER

[shogun7]

Rog:
A cap tube does have some load adjustability don’t you know, but nowhere near what a TXV can do, but as the ambient changes, the degree of sub cooling will change in an air-cooled condenser, and as a result, the bubble point and two phase length will change and although head pressure has an effect on flow rate, it’s the changing two-phase length that counters this action. Sub cooling the refrigerant has the greatest effect on flow rate. For my money the manufacturers’ design engineers have to go through many tests before establishing an optimum bore and length and it may change many times before they achieve the most efficient system. So I think I’ll stick with their values. You seem to believe that you know how to better improve a cap tube system; if that’s the case by all means do so and help the world conserve more energy through your advanced technology

[superheat]

Cap tube are pretty neat. Such a simple device that does so much. You can't blame the cap tube for POE problems. You can blame the manu. for putting out a cheap product that will cost more to maintain in the long run. I do prefer a TEV.

The cap tube can't adjust to load changes. It forces the system to adjust though. It inflates the head pressure, decreases the evap pressure and changes the compressor load to adjust to load changes. TEV would run more eff. in off loads.

[Gary]

Carryover is the coexistance of liquid and vapor in an area that is subcooled or superheated. Specifically it refers to vapor bubbles carried over into the subcooled liquid line or liquid droplets carried over into the superheated suction line.

[shogun7]

Marc That's very cute!. .NOT! so why don't you take Aristotle"s advce? And get off the EGO TRIP you didn't say any thing that is not understood in ASHRAE literature wise guy! Geeezzz your such a Glippy Dork and that last paragraph was totally un called for and just shows what a putz you are!

[RogGoetsch]

This means that when saturated discharge temperatures are higher, in response to higher ambients and higher associated evaporator loads (higher SST's), there will be an overall reduction in capillary pressure drop and so an increase in mass flow by virtue of increases in both volume flow and density of that volume. Of course then, during lower ambients, with the lower associated evaporator loads, there will be an overall increase in capillary pressure drop.

Not that I do a lot with AC, but it seems to me that the load on the system would change only if the user set his thermostat higher on warmer days. Otherwise, the unit starts at the same return air temperature as always.

With the same load and higher ambient, a cap tube would indeed provide increased flow, but a rise in SST (saturated suction temperature) would probably indicate a compressor operating at a less efficient point on its capacity curve due to the higher condensing pressure, and possibly additional load from carryover of some excess liquid refrigerant to the crankcase.

Rog

[shogun7]

This means that when saturated discharge temperatures are higher, in response to higher ambients and higher associated evaporator loads (higher SST's), there will be an overall reduction in capillary pressure drop and so an increase in mass flow by virtue of increases in both volume flow and density of that volume. Of course then, during lower ambients, with the lower associated evaporator loads, there will be an overall increase in capillary pressure drop.

I think what is as important, if not more important, is the fact that if evaporator loads were to increase then with the increased condenser TD occurring in response, the increased capillary dP is assisted quite nicely by way of the refrigerants PT Curves curvature i.e. the changing dP/dT ratio which increases with increasing saturated temperatures. If you consider that to double the volume flow of a fluid through a duct you'd have to quadruple the pressure difference, then it seems rather clever that our refrigerants have this non-linear PT curve that gives natural assistance here by somewhat shadowing this principle.

So, is the "technology" in the capillary tube or in the "refrigerant" that's in the capillary tube?

Well, if you consider that a capillary tube is different from say a TEV in that it has wall length where a TEV does not, then as it follows that the flow rate through a TEV is not nearly as much affected by the ratio of vapour to liquid pressure drops, Shogun might be right in aportioning technological credit to the capillary tube [/I]

In my very first statement I said:
:

If refrigerant responded the same way as water, the cap tube could never be used as a refrigerant control. Why not? Because when the head pressure was low, the evaporator would be starved, and when the ambient temperature was high, the evaporator would be flooded with liquid (the flow rate would be greater than the rate of vaporization).
However, if there was a way to increase the flow rate when the head pressure was low, and decrease the flow rate at high ambient temperatures, you would have a refrigerant control. This modulating effect is exactly what happens when a cap tube is installed in a well-balanced system.:

Seems to me we're saying the same thing. So is a cap tube considered "technlogy"? Well I leave it up to the reader.

[RogGoetsch]

Only on the rare occassion when the system is sized to meet the annual maximum load. Most systems, particularly in the states, are sized to maintain a degree of indoor to outdoor temperature difference, desired indoor temperatures are considered relative, relative to outdoor temperatures. Sometimes this difference is 12K. In these circumstances the stat is being used like a safety.

Nice try.

Rog

[frank]

The Daikin Super Inverter systems we sell compare indoor temperatures to outdoor temperatures and float indoor temperatures relative to outdoor temperatures.

Hi Marc

They didn't mention this on the training course

[shogun7]

Marc “Acute semantic aphasia” back at you pal

You have to think about the explanation as well as the description of a
Phenomenon. Explanation often takes the form of a hypothesis. Therefore, whether or
Not people entertain hypotheses is a useful measure in describing the scientific
discovery processes. So in order to convince us of your entire BS, you have to consider and discriminate among several plausible alternative explanations. Therefore, the extent to which subjects critique other hypotheses or entertain alternative hypotheses can measure how broadly they search the hypothesis space and make up their own minds. Capish!!

[RogGoetsch]

Most systems, particularly in the states, are sized to maintain a degree of indoor to outdoor temperature difference, desired indoor temperatures are considered relative, relative to outdoor temperatures. Sometimes this difference is 12K. In these circumstances the stat is being used like a safety.

The Daikin Super Inverter systems we sell compare indoor temperatures to outdoor temperatures and float indoor temperatures relative to outdoor temperatures.... The one good thing I've noticed about this is the reduction in perceived thermal shock.

They didn't mention this on the training course

They do lots including floating outdoor saturation relative to ambient and indoor saturation relative to deviation from setpoint with outdoor temperatures considered. But then they have EEV's which kinda makes it something of an irrelevenace

Hmmmm. After some of the above, Marc might want to consider a disclaimer of some sort, so as not to confuse the lads. Something at the end of his posts like:

“Notice: Many of the claims in this post are entirely fictional and are intended for purposes of entertainment only. Any similarity to actual systems and practices is purely coincidental.”

That ought to cover it!

Rog

[shogun7]

Hmmmm. After some of the above, Marc might want to consider a disclaimer of some sort, so as not to confuse the lads. Something at the end of his posts like:

“Notice: Many of the claims in this post are entirely fictional and are intended for purposes of entertainment only. Any similarity to actual systems and practices is purely coincidental.”

That ought to cover it!

Rog

Rog that was nice, very nice I give you 2 big grins