View Full Version : Capillary tube size, refrigerant, oil
I would like to discuss capillary tubes in regards to the following technical aspects:
1. Capillary tube size - diameter, length;
2. Refrigerant type;
3. Oil.
The technical aspects that come to mind are as follows (there will be many others):
a. Does each refrigerant have a certain cap tube 'sweet diameter'?
b. Cap tube noise levels;
c. Oil wetting, by refrigerant;
d. When does refrigerant plug-flow occur?
e. What size oil globule forms in each refrigerant (due wetting)?
f. How does the cap tube manage oil?
Basically, let's say, hypothetically, that you have a system that has been originally set up to use R-22 refrigerant. A new system is built, with compressor, filter-drier set up to use R-134a, but using the same diameter cap tube. What could reasonably be expected to happen?
If folks have practical experience in cap tubes, under different refrigerants & oils, I would very much like to hear your experiences.
aabbcc
19-02-2010, 09:05 PM
I would like to discuss capillary tubes in regards to the following technical aspects:
1. Capillary tube size - diameter, length;
2. Refrigerant type;
3. Oil.
The technical aspects that come to mind are as follows (there will be many others):
a. Does each refrigerant have a certain cap tube 'sweet diameter'?
b. Cap tube noise levels;
c. Oil wetting, by refrigerant;
d. When does refrigerant plug-flow occur?
e. What size oil globule forms in each refrigerant (due wetting)?
f. How does the cap tube manage oil?
Basically, let's say, hypothetically, that you have a system that has been originally set up to use R-22 refrigerant. A new system is built, with compressor, filter-drier set up to use R-134a, but using the same diameter cap tube. What could reasonably be expected to happen?
If folks have practical experience in cap tubes, under different refrigerants & oils, I would very much like to hear your experiences.
Well from my litle experience the R-22 'likes' the 1.25mm inner diameter.
The R-134A 'likes' the 1.0mm and in small wattage the 0.8mm.
However the capillary tubes dima selection has to do also with the Wattage of the system. Sorry for my poor english but changing the compressor NEEDS to change the capilary as well.
Also the R-22 has a reacher Condenser comparing R-134A , so there are other to consider.
A chip trick is to keep the condenser but change the fan with a smaller one or change the pitch...
Also the R-22 needs fan controllers (pressure switches) in order to work without problems.
R134A can use the old known klixons or as mentioned again depending on the system can have the fan motor constantly work
THe b,c,d I am not sure if have understood well - poor English- Anyway I wil try what I have ubderstood!
The noise has to do also with the quantity of refrigerant and correct setup of cap and system
Answering to your question what will happen...
I repeat I would be more specific If had the exact system.. Is it a refrigerator, a freezer or a A/C??
Also what is the length of current diam?
Actually there is a terrible BRAINSTORMING of what will happen:rolleyes::confused::confused:
Well you see the R134 works nearly the half Lbs of R-22 or even less. The correct HP for temp 10C ~ 12C is to have a 90Lbs ~ 110Lbs HP with the R-134A, BUT i think with the R22 cap the pressure will be lower. So you will think to charge with Refrigerant and will have the opposite results.. Actually will haveincreased the LP... This is one thought.
The 2nd thought if the current R22 cap has big Length (as I mentioned , depend on the system, so if it is a freezer WILL have bigger Length in order to have better evaporation) SO It might have the correct HP but the evaporation would not be correct and would not have the requested results...
Sorry for my LOOOONNNNNGGGGG TEXT...
aabbcc
19-02-2010, 09:08 PM
Ohhh !! Yes NOT forget...
Capillaries need tremendous RESEARCH... There are no books or programs to give you correct answers. Actually will give you a direction NOT the SOLUTION...
So EVERYONE NEEDS to experiment and try hard for the capillarie.
Thanks for your posts 'aabbcc'. Some very interesting observations & thoughts.
Well from my litle experience the R-22 'likes' the 1.25mm inner diameter.
The R-134A 'likes' the 1.0mm and in small wattage the 0.8mm.
However the capillary tubes dima selection has to do also with the Wattage of the system. Sorry for my poor english but changing the compressor NEEDS to change the capilary as well.
A good starting point. So you're saying that R-134a typically 'prefers' a smaller diameter cap tube, than R-22, for instance.
The noise has to do also with the quantity of refrigerant and correct setup of cap and system
So, quantity of refrigerant & correct cap tube diameter/length.
I repeat I would be more specific If had the exact system.. Is it a refrigerator, a freezer or a A/C??
Also what is the length of current diam?
This is an air-to-water heat-pump.
Well you see the R134 works nearly the half Lbs of R-22 or even less. The correct HP for temp 10C ~ 12C is to have a 90Lbs ~ 110Lbs HP with the R-134A, BUT i think with the R22 cap the pressure will be lower. So you will think to charge with Refrigerant and will have the opposite results.. Actually will haveincreased the LP... This is one thought.
So, with a system originally designed for R-22, the R-134a equivalent system would require far less refrigerant charge. Interesting observation.
The reason I introduced the R-22/R-134a aspect for the particular machine, is that I suspect that this is how the current machine was developed.
The evap & coil condenser were originally set up for R-22. The compressor was replaced by an R-134a equivalent. The cap tube selection still remains a mystery, but, seems to be close to a 'standard' requirement for the compressor operating at the rated performance of Te,sat=7.2'C, Tc,at=54.4'C , for the inner diameter of 1.3973mm.
The odd thing about this setup, is that, under colder ambient weather conditions, the capillary & evaporator expansion noise seems to increase a great deal. This happens across the charge range, from low, to high.
Toosh
19-02-2010, 11:35 PM
Hi desa, this might interest you
http://findarticles.com/p/articles/mi_m5PRC/is_1_115/ai_n32071939/pg_3/?tag=content;col1
Toosh
Hi desa, this might interest you
http://findarticles.com/p/articles/mi_m5PRC/is_1_115/ai_n32071939/pg_3/?tag=content;col1
Toosh
Thanks, Toosh - much obliged. I'm reading through it now. :)
A Google search for "capillary tube r134a R22" brings up links to a number of interesting scientific papers, which can be downloaded free-of-charge.
Quite a broad spectrum of interesting information amongst these.
There are adiabatic & diabatic capillary tubes.
A question:
What are the implications of an adiabatic capillary tube, on the way it is, or should be installed?
Remembering that the definition of the term adiabatic is:
ad·i·a·bat·ic [àddee ə báttik, àydee ə báttik, ày dī ə báttik]
adjective
without change in heat: describes a thermodynamic process that happens without loss or gain of heat
There are adiabatic & diabatic capillary tubes.
A question:
What are the implications of an adiabatic capillary tube, on the way it is, or should be installed?
Remembering that the definition of the term adiabatic is:
I would assume that a cap tube is adiabatic unless soldered to the suction line.
I would assume that a cap tube is adiabatic unless soldered to the suction line.
The diabatic one seems to be the cap tube soldered onto the suction line, according to the article Toosh refered to.
As I recall, a cap tube should not exceed 4 feet in length.
If the chosen diameter requires more than 4 foot, then a smaller diameter should be chosen.
http://www.cubigel.com/java/X?cgi=cubigel.infotecnica.InformacionTecnicaArticulo2.pattern&seccion=informaciontecnica
The Cubigel compressor website has some very useful comparative information on various capillary tubes. Some, for R-134a go up to 5.50 m (2mm ID).
http://www.cubigel.com/java/X?cgi=cubigel.infotecnica.InformacionTecnicaArticulo2.pattern&seccion=informaciontecnica
The Cubigel compressor website has some very useful comparative information on various capillary tubes. Some, for R-134a go up to 5.50 m (2mm ID).
Hmmm... maybe it was 4 meters... been a while. :)
A question:
What are the implications of an adiabatic capillary tube, on the way it is, or should be installed?
Remembering that the definition of the term adiabatic is:
Quote:ad·i·a·bat·ic [àddee ə báttik, àydee ə báttik, ày dī ə báttik]
adjective
without change in heat: describes a thermodynamic process that happens without loss or gain of heat
Progressing the term adiabatic little further. For no loss, or gain of heat, does this imply that an adiabatic capillary tube should be insulated?
Toosh
20-02-2010, 07:00 PM
Hi Desa, Here is another interesting study
http://oriunno.web.cern.ch/oriunno/www-transfer/capillarybasic1.pdf
Toosh
aabbcc
20-02-2010, 08:48 PM
Well I was trying to find this thread as I am new to this forum and lack of Positioning (LOL).
Well I have carefully read all the above and also the very interesting sites the pther memebrs posted about the formulas and cap diameters.
Well before 2 years I did set up a system with 5.5Hp compressor LOW and been able to set uo 14 pieces capillary tubes into one evaporator refrigerant R404A, which is really busting ba**s.
I can say I have read all the thermodynamics (even some times is Korean language LOL) Well anyway I can say from my little experience the formulas and adiabatics CAN ONLY give you a very small indication of what will the system needs.
Concerning the minimum of 4ft of length I disagree as there many set ups from domestic refrigerators to industrial refrigerators with more than 3.5meters or even 5meters of capillary...
Concerning the noise during cols days, well you should use a pressostat switch so it could stop the fan motors to turn when the LP is less 32Lbrs and start again at 42 ~ 45 Lbrs.... So in R22 the fluid would expand and would not have the noise and the same time more efficiency of the system...
Now the R134A with 5.5metres LENGTH and 1.3mm I can say with sure it is not a winner.
Let;s make it a little bit more difficult..
Well I would use a 1.mm cap size and about 3meters of length... But the capilarries would be 2 pieces...
Then you will have better boiling of fluid and enough quantity for the evaporator...
Cappilaries must be of the same size 2x3mmxΦ1.0mm
And lastly something that will help you...
Increasing Length of capilary = decreasing evaporation Temp and of course decreasing the LP.
Decreasing Length of Capilary = increasing the evaporation Temp and of course increasing the LP..
As the increasing and decreasing of the LP, there are many parameters you could twist, change or upgrade as the capilary will perform differently from 10C ~ 40C...
When working wih capilary MUST increase or decreas 10cm maximum of the length in each attempt to make the system to balance.
The MAIN TARGET is to have BALANCE in all the ambient Temperatures... It can be done and this is the magic of the capilary...;)
Just my 2cents.
aabbcc
20-02-2010, 08:59 PM
How can someone correct his post?
Well due my worp speed typing (LOL) please consider the following ammendment (LOL)
Capilaries 2pcs x 3meterLength x Φ1.0mm.
Also the pressostat I mentioned for the R22 should be installed in the High Pressure. But you should be interested for thr Low Pressure.
Toosh
20-02-2010, 10:27 PM
How can someone correct his post?
Well due my worp speed typing (LOL) please consider the following ammendment (LOL)
Capilaries 2pcs x 3meterLength x Φ1.0mm.
Also the pressostat I mentioned for the R22 should be installed in the High Pressure. But you should be interested for thr Low Pressure.
Hi aabbcc, there is an edit button when you make a post just click it and your post will come back
Toosh
ps welcome to the form
Hi Desa, Here is another interesting study
http://oriunno.web.cern.ch/oriunno/www-transfer/capillarybasic1.pdf
Toosh
That's a great find, Toosh - much obliged. :)
Take a look at the rest of the articles on that link - may be a few more useful articles there.
Toosh
21-02-2010, 07:07 AM
That's a great find, Toosh - much obliged. :)
Take a look at the rest of the articles on that link - may be a few more useful articles there.
Hi Des, here is a good experiment
http://spectrum.library.concordia.ca/194/1/NQ25924.pdf
Toosh
Hi Des, here is a good experiment
http://spectrum.library.concordia.ca/194/1/NQ25924.pdf
Toosh
Another great find. Keep them coming. :D
Well before 2 years I did set up a system with 5.5Hp compressor LOW and been able to set uo 14 pieces capillary tubes into one evaporator refrigerant R404A, which is really busting ba**s.
Wow. That must have been something to try & balance.
I can say I have read all the thermodynamics (even some times is Korean language LOL) Well anyway I can say from my little experience the formulas and adiabatics CAN ONLY give you a very small indication of what will the system needs.
Fair comment.
Concerning the minimum of 4ft of length I disagree as there many set ups from domestic refrigerators to industrial refrigerators with more than 3.5meters or even 5meters of capillary...
True. There are some at Cubigel, for R-134a, at 5.5m.
Concerning the noise during cols days, well you should use a pressostat switch so it could stop the fan motors to turn when the LP is less 32Lbrs and start again at 42 ~ 45 Lbrs.... So in R22 the fluid would expand and would not have the noise and the same time more efficiency of the system...
Interesting idea. If you turn off the evaporator fan, surely Te,sat will continue to drop lower? Perhaps stop at a certain value & then re-start if the system pulls down too low?
I've seen the evap fan turned off on a european specification heat-pump operating at low temperatures. Interesting.
Now the R134A with 5.5metres LENGTH and 1.3mm I can say with sure it is not a winner.
Let;s make it a little bit more difficult..
Well I would use a 1.mm cap size and about 3meters of length... But the capilarries would be 2 pieces...
Then you will have better boiling of fluid and enough quantity for the evaporator...
Cappilaries must be of the same size 2x3mxΦ1.0mm (corrected to suit later post)
This is interesting, indeed. Thanks for this. I have seen a few of these dual-capillary systems for R-134a fridges & even R-22 airconditioning systems.
And lastly something that will help you...
Increasing Length of capilary = decreasing evaporation Temp and of course decreasing the LP.
Decreasing Length of Capilary = increasing the evaporation Temp and of course increasing the LP..
Ok. Good points to remember. Thank you.
As the increasing and decreasing of the LP, there are many parameters you could twist, change or upgrade as the capilary will perform differently from 10C ~ 40C...
When working wih capilary MUST increase or decreas 10cm maximum of the length in each attempt to make the system to balance.
The MAIN TARGET is to have BALANCE in all the ambient Temperatures... It can be done and this is the magic of the capilary...;)
Just my 2cents.
Some excellent tips. Thanks you 'aabbcc'. :)
Would it be possible to run two capillaries of different dimensions, to stage the flow across a wider range?
Say for instance, dia 1mm x 3m + dia 1.5mm x 5m?
Has any work been done on stretching the operating range in this way?
aabbcc
21-02-2010, 02:43 PM
Would it be possible to run two capillaries of different dimensions, to stage the flow across a wider range?
Say for instance, dia 1mm x 3m + dia 1.5mm x 5m?
Has any work been done on stretching the operating range in this way?
Well This will not work. Capillaries MUST be ALWAYS same diameter and Length...
Of course in case we need to have a perfectly balanced system and not just to have it work anyhow. I have tried this but never been able to adjust and set up a correct 'behaviour'...
Well I am trying to find a way to upload a photo with the evap of 14cap's
aabbcc
21-02-2010, 02:59 PM
Here is the evaporator with 14Capillary ...
Well It is a nightmare.
Now I am on a work with more cap's and then there is a project with some more and then........ (nightmare)
:rolleyes::rolleyes::confused::confused::confused:
Also a pressure switch for HP . You can find in the market...
aabbcc
21-02-2010, 03:02 PM
Oopss! I made them too small.
Wel I still CANNOT find the edit button.. As said am newbie here and cannot positioning yet...
aabbcc
21-02-2010, 03:07 PM
Still cannot find the EDIT as Toosh advised (thanks) . Maybe it is not allowed to newbies to edit their posts?
^ That is quite a remarkable picture. :D
Can I ask why you are using so many capillaries, & not a TXV?
aabbcc
21-02-2010, 03:42 PM
^ That is quite a remarkable picture. :D
Can I ask why you are using so many capillaries, & not a TXV?
Because of the :
Efficiency
Cost
Efficiency Again - No Valve can match the cappilary in efficiency.
Rapid balance of the system
No malfunctions , No orifice
Well many more ...
And because I have tried the TXV's without having the same results.
But results for each one of us different ... So for me the capillary is the one. :D:D
aabbcc
21-02-2010, 03:45 PM
Well let's say you have a system that defrost's many times per hour.
So the buol of the Valve would be heated as well and would retain the valve close - Correct?
So until the system regains its 'position' the bulp will remain close. This might be from 2minutes up to 10minutes from working condition to working condition.
With the capillary you just switch ON. The system immediately sprays fluid in the evaporator and the 2minutes is a GAIN...
aabbcc
21-02-2010, 04:36 PM
I have just red you other thread with the capilary tube system and the really very interesting analysis you all guys made...
But really for science it is nice to experiment and 'play' . In the real orld unfortunatelly NO PROGRAM or CALCULATION is enough to direct you in the correct diameter and length.
Eventhough there are other parameters to twist or upgrade to a cap system in order to put it down the RIGHT WAY (LOL)
Because of the :
Efficiency
Cost
Efficiency Again - No Valve can match the cappilary in efficiency.
Rapid balance of the system
No malfunctions , No orifice
Well many more ...
Very interesting.
I'm finding the capillary to be very challenging. For small power systems, it's difficult to get a TXV anyway - they are also expensive. It is going to be worth the time & effort to get to understand these fascinating parts of our toolbox.
How do you see the cap tube working for a heat-pump, with the large spread in Tc,sat from cold to hot condition?
Eventhough there are other parameters to twist or upgrade to a cap system in order to put it down the RIGHT WAY (LOL)
Hahaha... I guess I know what you are getting at... :D
aabbcc
21-02-2010, 05:52 PM
Very interesting.
I'm finding the capillary to be very challenging. For small power systems, it's difficult to get a TXV anyway - they are also expensive. It is going to be worth the time & effort to get to understand these fascinating parts of our toolbox.
How do you see the cap tube working for a heat-pump, with the large spread in Tc,sat from cold to hot condition?
I have never tried to work capilary on a heat pump.
However my opinion is the target with the Cap is to make the LOW PRESSURE decreases as possible even in 40C work conditions. As mentioned before the Tcsaturation and/or superheats, subcooling and all the book of thermodynamics can be manipulated else way. As mentioned in previous posts for R22 and R404A this can be done with Presure switches to control the fan. Also the use of more capilaries instead of one, the quantity of refrigerant, a receiver , fan rpm, fan pitch, Diam of fan, condensing unit and many more...
What I am thinking now is that the Cap on a heat pump might and should work different since the system advantages from the HOT PLATE - not the cold.
So the more HP in the Hot plate (that in standard systems is the cold plate) the more of the benefit...
So we are talking for a smaller condenser and bigger in length capillary... Then wll need some more fluid in it, but will change the thermodynamics once more...
So you need a small receiver in order to store the excess of the refrigerant fluid.. Receiver can be a small filter of let say 60gram as the excess of refrigerant should only be a +25gr ~ 50gr.
I refer ,as have in mind an older htread of yours, to the system have in your lab and the rest of the members gave a fantastic analysis and manipulation of DANFOSS programs...
The noise you were listening it is because the system needed those 25~50 grams... BUT in a warmer weather you would have a problem... BUT WHO CARES as in warm weather the HEAT PUMP will be out of work...:D
Again sorry for my LONG TEXT..
I have tried NOT to enter in any formulas or calculation because I would make it with my Greek letter formulas and then we would LOST TO TRANSLATION and more important BECAUSE I STRONGLY believ that formulas CANNOT PREDICT CAPILLARIES...:eek::eek:
aabbcc
21-02-2010, 06:02 PM
Concerning the receiver . You need to make it by your own. You can cut a 3/8 dryer filter and take everything out. Then put the inlet pipe and the outlet pipe - the one will return to suction should be long and suck only gas not liguid... It is common to have liguid returns with a cap system...So you do need a long outlet pipe in the receiver.(sorry for my English Again I think you get the message).
Why the companies DO NOT DO this..
Well is all about the cost and of course they rush to put the product in the market...
For a small heat pump of 11000BTU or 14000BTU (I gues those are the number of what you have in your lab)
the less parts the better. Adn of course you will need to change it after a while...
Research with capillary is never enough and there is the fascination..
mad fridgie
21-02-2010, 08:29 PM
Well let's say you have a system that defrost's many times per hour.
So the buol of the Valve would be heated as well and would retain the valve close - Correct?
So until the system regains its 'position' the bulp will remain close. This might be from 2minutes up to 10minutes from working condition to working condition.
With the capillary you just switch ON. The system immediately sprays fluid in the evaporator and the 2minutes is a GAIN...
TEV will be open not closed.
A cap has its place, and indeed can equal a valve at a fixed point, "Optimum", but there are very few systems where all process variables are constant, thus keeping the system at optimum.
Practically a valve does allow for inperfection in design, as a cap needs to be right. For one off applications, the time spent optimising the cap, (cost) will be greater than the value of the valve installation.
I agree that present software is an aid to cap selection, no a fixed solution.
I have never tried to work capilary on a heat pump.
However my opinion is the target with the Cap is to make the LOW PRESSURE decreases as possible even in 40C work conditions.
With a heat-pump, there is advantage in allowing the LP rise in a controlled way. If the LP s dropped, then compressor pressure-ratio will be stretched, resulting in high compressor discharge temperatures. There is a limit as to how high the discharge temp should be allowed to climb.
As mentioned before the Tcsaturation and/or superheats, subcooling and all the book of thermodynamics can be manipulated else way. As mentioned in previous posts for R22 and R404A this can be done with Presure switches to control the fan.
For a heat pump, the equivalent of your LP manipulation techniques, would be at HP - by adjusting condenser performance eg. speed up water flow.
Also the use of more capilaries instead of one, the quantity of refrigerant, a receiver , fan rpm, fan pitch, Diam of fan, condensing unit and many more...
Can you perhaps tell us more on your ideas here?
What I am thinking now is that the Cap on a heat pump might and should work different since the system advantages from the HOT PLATE - not the cold.
So the more HP in the Hot plate (that in standard systems is the cold plate) the more of the benefit... So we are talking for a smaller condenser and bigger in length capillary...
Yes, the HP side needs to be worked with - but, don't raise the Tc,sat, as this will lower system COP. The condenser heat-transfer efficiency needs to be adjusted.
Then wll need some more fluid in it, but will change the thermodynamics once more...
I'm interested in this comment & why you need more fluid. Is this because of increased cap tube length?
So you need a small receiver in order to store the excess of the refrigerant fluid.. Receiver can be a small filter of let say 60gram as the excess of refrigerant should only be a +25gr ~ 50gr.
I refer ,as have in mind an older htread of yours, to the system have in your lab and the rest of the members gave a fantastic analysis and manipulation of DANFOSS programs...
The lab system has an inline filter-drier, as well as a small suction strainer, before the cap tube.
The noise you were listening it is because the system needed those 25~50 grams... BUT in a warmer weather you would have a problem...
So, you feel that the noise was because the system was short of refrigerant? Can you perhaps explain this further?
Concerning the receiver . You need to make it by your own. You can cut a 3/8 dryer filter and take everything out. Then put the inlet pipe and the outlet pipe - the one will return to suction should be long and suck only gas not liguid... It is common to have liguid returns with a cap system...So you do need a long outlet pipe in the receiver.(sorry for my English Again I think you get the message).
It would be great if you could sketch this & attach the picture. (Upload your pic to www.tinypic.com, then link it in your RE post).
Why the companies DO NOT DO this..
Well is all about the cost and of course they rush to put the product in the market...
For a small heat pump of 11000BTU or 14000BTU (I gues those are the number of what you have in your lab)
the less parts the better. Adn of course you will need to change it after a while...
Very true. Manufacturers seem to cut costs everywhere - sometimes in the wrong places, unfortunately.
Research with capillary is never enough and there is the fascination..
Thanks so much for your input - it is very useful & interesting. :D
TEV will be open not closed.
As I've read, it will be closed on system start, until sufficient SH has been reached, after which it will open.
A cap has its place, and indeed can equal a valve at a fixed point, "Optimum", but there are very few systems where all process variables are constant, thus keeping the system at optimum.
Now, this is something the industry seems to have fixed in our heads regarding a cap tube. Is this actually true, though?
In other words, what process variables, or grouping of variables, needs to remain fixed, in order for a cap tube to work over a wider operating range? If both Te & Pc slide together, is there a group that remains relativley constant? Perhaps it is time we re-think a little more about cap tubes?
Practically a valve does allow for inperfection in design, as a cap needs to be right. For one off applications, the time spent optimising the cap, (cost) will be greater than the value of the valve installation.
I agree that present software is an aid to cap selection, no a fixed solution.
Does the cap tube actually need to be 'perfect'? Perfect at what point in a system? Could a target point in the system be selected & used for nominal cap tube sizing? Does it really need all the laborious cut-&-try efforts we hear about in the received logic?
mad fridgie
22-02-2010, 06:24 AM
Problem with broad statements??
TXV do not close completely.
Depends upon defrost type and method. (how far the valve is open)
As soon as comp starts suction will fall, SH is achieved, in my experience is does not take two minutes, it may take 2mins, to arrive at stable condition.
I should have said cap size and charge need to be correct.
Can i system work if size and charge are wrong, yes as long as you have enough grunt,
Will a cap work over aworking range, yes, is at optimum across the whole range no. Will a TXV, no but the optimum range is extended.
Problem with broad statements??
:D
TXV do not close completely.
Depends upon defrost type and method. (how far the valve is open)
Fair-enough.
As soon as comp starts suction will fall, SH is achieved, in my experience is does not take two minutes, it may take 2mins, to arrive at stable condition.
Actually, for a heat-pump starting off a cold condition, the stabilisation time will actually be a lot longer then 2 minutes - more like 10-15 minutes. The TXV will obviously begin tracking on the start-up trajectory when SH is reached, until a quasi-steeady-state is reached - that could well be around 2 minutes.
The start-up dynamics will apply equally to a cap tube, in this case. It is the thermal cost of heating up a lump of cold metal to an operating condition.
I should have said cap size and charge need to be correct.
Very true. Question, though - with an accumulator inline (filter-drier etc), would the charge be as critical?
Can i system work if size and charge are wrong, yes as long as you have enough grunt,
Could you please elaborate a little more on this?
Will a cap work over aworking range, yes, is at optimum across the whole range no. Will a TXV, no but the optimum range is extended.
In your view, for a system operating over a wide temp range, where should the ideal cap tube be sized? Start, midrange, hot condition?
aabbcc
22-02-2010, 08:52 PM
TEV will be open not closed.
aabbcc wrote:
Actually never is closed , always a small quantity of refrigerant will pass, if that is what you mean...But I do consider this to be closed...
A cap has its place, and indeed can equal a valve at a fixed point, "Optimum", but there are very few systems where all process variables are constant, thus keeping the system at optimum.
aabbcc wrote:
I agree. However there is the opportunity to twist and do things as mentioned before and can balance the cap system, practically in every working temp.
Well please do not misunderstand me. The Neuton's 2nd law actually gives NO margin for ABSOLUTES...:D
Practically a valve does allow for inperfection in design, as a cap needs to be right. For one off applications, the time spent optimising the cap, (cost) will be greater than the value of the valve installation.
aabbcc wrote:
Yes indeed. This reminds me an old say of the PC GURUS ... PROGRAMMERS DO IT ON DOS:D
Yes the Valve DO make the difference on service time. And I would go there too. But there are systems many times that CANNOT WORK with the TXV's and can only work with Caps. Strange enough but this has happened to me.
Lastly at this thread I do not want to downgrade the TXV (how could I?) but just some of personal opinions always...
I agree that present software is an aid to cap selection, no a fixed solution.
I have put my answers within the above quotation:o
aabbcc
22-02-2010, 08:58 PM
DesA .. Thank you for your input and this reat exchange of opinions and ideas.
Well I have to read all the above slowly, since I do speak English and write but I cannot follow all your technical details, but will come back soon. At the moment I am sending in jpg the silly idea of a receiver ...
It is not different of other receivers.
mad fridgie
22-02-2010, 09:13 PM
DesA
Grunt;, if we look at the end result, net cooiling or indirectly net heating (cooling plus motor), if you have enough mass flow (compressor grunt), then diresed results can be acheved, nothing to do with efficiency.
What is ideal sizeing for cap, firstly one that always protects comp, low mid or high, I would look at the combination that gives the best results over a process, even though performance may be poor a some point of the process.
Acc does allow for a an over charge
aabbcc, only done alittle work in fractional comp hp range, where TEV valves are not available, so here caps are good.
in commercial range never came across a system that we could protect, i presume you are taking systems with very low loads, where valves minimum are higher than the low load, you are using the cap as a flooded system. critical charge.
good point to both you
aabbcc
22-02-2010, 09:37 PM
Well My silly receiver...:o
Madfridgie...
I am talking for capacities of 1/8Hp up tp 7Hp...
Being honest I have a project for more than 7Hp and honestly I am not sure if will work... Then eventually we will turn to TXV's ...:o
Else could say in the 80% of the worlds ref systems:D:confused::confused: LOL....
aabbcc
22-02-2010, 09:59 PM
I do not think this will lead to any logical conclusions. But will try...
With a heat-pump, there is advantage in allowing the LP rise in a controlled way. If the LP s dropped, then compressor pressure-ratio will be stretched, resulting in high compressor discharge temperatures. There is a limit as to how high the discharge temp should be allowed to climb.
That was the general idea. The start of my thinking ending in the next sentenses that in a heat pump things should work else way...
For a heat pump, the equivalent of your LP manipulation techniques, would be at HP - by adjusting condenser performance eg. speed up water flow.
Can you perhaps tell us more on your ideas here?
Yes, the HP side needs to be worked with - but, don't raise the Tc,sat, as this will lower system COP. The condenser heat-transfer efficiency needs to be adjusted.
I assume you are talking for the COP ratio of ref capacity and compressor consumption.
The HP will not increase dramatically and will definetely not infect the compressors consumption , but with the longer Length will increase the HP and (Boyle/Marriot) increasing Pressure = increasing Temp..
I'm interested in this comment & why you need more fluid. Is this because of increased cap tube length?
Because of the Length and the Working Temp is below (assume) 10C... The fluid has shrink.
The lab system has an inline filter-drier, as well as a small suction strainer, before the cap tube.
So, you feel that the noise was because the system was short of refrigerant? Can you perhaps explain this further?
As mentioned I assume the Heat pump is working below 10C. The ref is shrinking. Perhaps Cap has been adjusted to work above 10C...
With a small receiver there is the possibility to have the adequate amount in cold days. Over thermodynamics you/we have to calculate again and again with different ambient conditions and different amount of charges...:confused:
Well My silly receiver...:o
By your previous descriptions, I'm thinking this is an accumulator, not a receiver. It goes in the suction line, right? A receiver would be installed in the liquid line.
aabbcc
22-02-2010, 10:31 PM
Actually this is a 3/8 cutted and drilled... It is something for desA's R&D facilities... High stuff...
And personally would install it between suction and evaporator....
Sorry for my English. We call it receiver but will catch up with you.
Thanks for correcting me Gary.
aabbcc
22-02-2010, 10:37 PM
And something that have just remember. desA another practical way to help you more fill a cap system with fluid is the sight glass to be installed in suction line... Between the evaporator and the silly accumulator I draw ... (LOL)
I know is common to put the sight glass in the HP line... But try it and see. Just My 2cents
All this grunting & groaning... :D
DesA
Grunt;, if we look at the end result, net cooiling or indirectly net heating (cooling plus motor), if you have enough mass flow (compressor grunt), then diresed results can be acheved, nothing to do with efficiency.
Ok, so basically with enough compressor over-size, the job can get done, no matter the efficiency. True, but getting harder to justify in these days of price & energy pressures.
What is ideal sizeing for cap, firstly one that always protects comp, low mid or high, I would look at the combination that gives the best results over a process, even though performance may be poor a some point of the process.
Acc does allow for a an over charge
Fair-enough - I'd agree with that viewpoint. What I had in mind is developing a set of simple design rules which target a cap to work at a representative cycle nominal point. This would allow pretty much a one-shot selection process & save a lot of cut-&-try. If the essential process remains consistent & the evap/compressor/cond selection/design philosophy remains consistent, then there is no reason for such a nominal selection procedure to not have a reasonably high accuracy.
aabbcc, only done alittle work in fractional comp hp range, where TEV valves are not available, so here caps are good.
You are correct. Also, the cost of a TXV may not be justified in these applications.
in commercial range never came across a system that we could protect, i presume you are taking systems with very low loads, where valves minimum are higher than the low load, you are using the cap as a flooded system. critical charge.
What do you mean when you say 'protect'? SH control, liquid floodback?
Well My silly receiver...:o
Madfridgie...
I am talking for capacities of 1/8Hp up tp 7Hp...
Being honest I have a project for more than 7Hp and honestly I am not sure if will work... Then eventually we will turn to TXV's ...:o
Else could say in the 80% of the worlds ref systems:D:confused::confused: LOL....
Very nice sketch. Thanks for that. :)
How are you going to get the oil to move out of there, though?
And something that have just remember. desA another practical way to help you more fill a cap system with fluid is the sight glass to be installed in suction line... Between the evaporator and the silly accumulator I draw ... (LOL)
I know is common to put the sight glass in the HP line... But try it and see. Just My 2cents
That is an interesting idea. The sightglass will tell us a tremendous amount about what is really going on in the suction line.
Very good point. :)
I'm interested in this comment & why you need more fluid. Is this because of increased cap tube length?
Because of the Length and the Working Temp is below (assume) 10C... The fluid has shrink.
The lab system has an inline filter-drier, as well as a small suction strainer, before the cap tube.
So, you feel that the noise was because the system was short of refrigerant? Can you perhaps explain this further?
As mentioned I assume the Heat pump is working below 10C. The ref is shrinking. Perhaps Cap has been adjusted to work above 10C...
With a small receiver there is the possibility to have the adequate amount in cold days. Over thermodynamics you/we have to calculate again and again with different ambient conditions and different amount of charges...
A good point. The noise level certainly rises in cold weather.
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