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herefishy
27-05-2003, 06:32 PM
Any tool (online) available to calculate cap tube size/lenght for specific application.

I've got my 100' roll of BC-1 on it's way for the -40F+ R-409A 100w video card chiller application on its way, but I'd rather not have to cut the dern tube down fourteen times before I am happy with it.

:\

herefishy
29-05-2003, 03:01 PM
I called SUPCO, they couldn't help me. I need to determine cap tube length (preferrably for .031" cap tube I.D.) for approx. 250BTUH @-40F R-409A.

:)

Gary
29-05-2003, 04:42 PM
How long is the cap tube on the Prommie?

herefishy
29-05-2003, 05:04 PM
How long is the cap tube on the Prommie?

I'd guess about 48". The actual suction line is about 3' total length, and the way it's wrapped it......


47" of .031" cap tube (according to the SUPCO info) is applicable to a 1/4 HP LBP (-10 SST). SUPCO couldn't give me any recommendations fo <-40.

I asked the guy if he had the equations to determine the cap tube length required. He said that the guy that had those equations retired.... and took 'em with him!!!!! :eek:

Gary
29-05-2003, 06:01 PM
I wonder if Chipcon (mfg of prommie) would be willing to share that info?

herefishy
29-05-2003, 06:20 PM
Are you going to call them?..... or should I?

:rolleyes:

Gary
29-05-2003, 06:33 PM
Which of us is getting paid for this job?

herefishy
29-05-2003, 06:59 PM
Originally posted by Gary
Which of us is getting paid for this job?

Well, 'ought dern it! I don't feel like calling Denmark. :(


I think I'll start with 60" of .031. :)

Gary
29-05-2003, 07:36 PM
There's a new thing called "email". :)

http://www.chip-con.com/index.php?pageid=35


I think I'll start with 60" of .031.

I was thinking 120". Easier to cut than to add.

Dan
31-05-2003, 12:57 AM
I think cap tubes are a guess and bygosh arrangement.

Lol. To some extent, Dan, you are correct. But there has been decent tables set up over the years which make it relatively simple for the design engineer to zero in on a proper capillary tube sizing. Also, the Prof has noted some interesting papers published in recent years describing refrigerant flow thru capillary tubes, so there are still some people studying the subject.

Posted by the prof in March of 2001. LOL.

Perhaps the prof would share one of these tables with Herefishy! Recently I posted in another discussion that the subject was discussed in the Fridgetech pages, but it wasn't there. Who would think to search this site? Now all I have to do is recall what that discussion was so I can search the Refrigeration-Engineer website. I bet that's where it lies!

On a lighter note, when you dig up a discussion 2 years ago and see Gary's picture. He was holding the same grandchild.:) Maybe it is not so much a bitch getting old.

Prof Sporlan
31-05-2003, 02:46 AM
The Prof suspects that there hasn't been extensive study on cap tube sizing for the R-12 service replacement refrigerants... other than charge the system till is works right... :D :D :D

When he gets back to the office, he'll look up low temp R-12 cap tube sizing in his Harry Busby reference, and see if it provides a suggested cap tube size.

herefishy
31-05-2003, 05:10 AM
thanks, Prof. It is a real honor to have you get off the bench for me. LOL!!!! :)

Yeh, Gary.... after thinking about it some more... I was thinkin' about starting at 10' too! (we must be phsychotic) :D

Particularly since I'm welding one end of this cap tube into a small copper block.... I don't want to be doing and undoing that connection..


see ya'

:)

frank
01-06-2003, 03:42 PM
I've just been looking up cap tube sizing in one of my reference books and came across some info under "Expansion Devices". The calcs are quite prolonged and complicated to post but the book is by McGraw-Hill - Refrigeration & Air Conditioning (ISBN 0-07-061619-1).

It also states that there are some selection charts in the Ashrae Manual - can't seem to find my Ashrae CD so I can't verify this :(

Frank

DaBit
03-06-2003, 10:09 AM
I do have a few scanned pages from the ASHRAE handbook, with a few covering captube sizing. I won't post them here in public, but I am willing to share them through E-mail.

herefishy
03-06-2003, 02:37 PM
Hi DaBit,

Since you mentioned it, I just pulled my ASHRAE handbook off the shelf, and found the information you reference. I am reviewing it now.

Thanx :)

Prof Sporlan
03-06-2003, 02:54 PM
The Busby reference suggests 12 ft of 0.031" capillary for an R-12 low temp (-10°F evaporator) system using a 1/6 hp compressor. Doesn't provide a Btu/hr rating, though.

It also suggests 12 ft of 0.026" capillary for an R-12 low temp 1/12 hp compressor, which probably better matches your application.

The reference doesn't give a conversion from 0.026" capillary to 0.031", but the Prof would estimate 24 ft of 0.031" capillary would be equivalent to 12 ft of 0.026".

The 2002 ASHRAE Refrigeration Handbook provides capillary tube capacities for R-134a and R-410A.

R-409A at 100°F liquid and -40°F evap will have a net refrigerating effect of about 55.5 Btu/lb. For a 250 Btu/hr load, we will need 250 / 55.5 = 4.5 lb/hr flow rate thru the capillary.

According the the ASHRAE Handbook, R-134a at 150 psi liquid line pressure, zero subcooling, and 130" of 0.034" capillary will give us a 9 lb/hr flow rate. And according to ASHRAE, 200" of 0.030" capillary will give us a correction factor of 0.65, giving us 9 * .65 = 5.85 lb/hr.

Mmmm... this should put us in the ballpark... :)

Gary
03-06-2003, 03:51 PM
I've found sizing tables at this site under technical infomation, but I think we will need an interpreter, as it's written in metric technospeak. I have enough problems trying to figure out SI technospeak.

Perhaps Prof could explain it to us. :D

http://www.cubigel.com/english/frprod.htm

herefishy
03-06-2003, 04:12 PM
Most excellent, Professor. :)

I had determined a required flow rate of approximately 5 lbs./hr.

In conversation with the dude at Supco, we figured an equivalent of 1/8hp (for cap tube purposes) capacity out of the 1/4 horse compressor @-50F.

In reviewing the chart for Pressure-Drop for Capillary Liquid, If I reference the 5LB PER HOUR line, and hit the .031 ID department, the indicated pressure drop per foot = 3.0

If I assume a condensing pressure of about 170 R-409a, and a suction of 10"Hg vaccum (-5 psig?), at 175 psi pressure drop, I would require 58 feet?

__________________________________________________

I went through an example in the book.

I determined:

flow rate = 5lb/hr
absolute inlet pressure = 175psia
mass flow rate from a chart 38 = 72lb/hr
flow factor (5/72) = .07

and using this information, referencing a chart 39 (the book was saying reference chart 42... but that was an error) I come up with about 375" of .031.

...or 31.25' of .031" I.D. cap tube...

if we change the enthalpy to the prof. suggested 55.5 btu/lb and the 4.5 req'd lbs/hr that changes the flow factor to .06.... that would make the cap tube longer (4.5/72).

hmmmmm. 24'..... or ...... 31' :rolleyes:

Prof Sporlan
03-06-2003, 06:54 PM
In reviewing the chart for Pressure-Drop for Capillary Liquid, If I reference the 5LB PER HOUR line, and hit the .031 ID department, the indicated pressure drop per foot = 3.0
What chart might this be? If this chart estimates pressure drop for liquid flow only, it would underestimate pressure drop for a capillary tube used as the expansion device, as it will see two-phase flow somewhere along its length.


If I assume a condensing pressure of about 170 R-409a, and a suction of 10"Hg vaccum (-5 psig?), at 175 psi pressure drop, I would require 58 feet?
In the Prof's humble opinion, 58 ft won't be necessary here... :)


and using this information, referencing a chart 39 (the book was saying reference chart 42... but that was an error) I come up with about 375" of .031.

...or 31.25' of .031" I.D. cap tube...
Not too far from the Prof's guesstimate... :)


hmmmmm. 24'..... or ...... 31'
It will always be easier to shorten the capillary... :D


Perhaps Prof could explain it to us. :D
The ASHRAE Refrigeration Handbook has a rather complicated eight term correlation to predict capillary tube flow rate... It includes the refrigerant's vapor and liquid specific volume, vapor and liquid viscosity, surface tension, specific heat, among other variables. This model apparently have been found to work well with R-22, R-134a, and R-410A. Other than the surface tension variable, the Prof has an Excel spreadsheet capable of generating the necessary thermodynamic data for this correlation. Mmmmm.... But it would hardly be appropriate for the Prof to be developing a cap tube selection program.. :D :D

herefishy
03-06-2003, 07:08 PM
Originally posted by Prof Sporlan
What chart might this be? If this chart estimates pressure drop for liquid flow only, it would underestimate pressure drop for a capillary tube used as the expansion device, as it will see two-phase flow somewhere along its length.


The chart to which I refer Fig 43 of section E19.29 of my....1988.... Ashrae handbook (equipment). Whose title is "Pressure-Drop Chart for Capillary Liquid (R-12 and 22)".

on the "x" axis is Mass flow - lbs per hour, and the "y" axis indicates pressure drop per foot - psi. The linear relationship of the cap tube size if charted for .20" to .020" I.D. :)

And now, if I look at it closer, a more accurate estimation of the reference point would be more like 1.5 psi per foot.

so 175psia pressure drop would be more like 262.5". or 21.875'

I think I'll start with 24' of .031. I have a 100' roll, and I seem to have two or three sources, now that point to around the 24' department.

Prof Sporlan
03-06-2003, 09:32 PM
The chart to which I refer Fig 43 of section E19.29 of my....1988.... Ashrae handbook (equipment).
The Prof will have to root around the Sporlan archives for that Handbook sometime... :D

herefishy
04-06-2003, 01:46 AM
DOH!!!!

Now, if I determine Mass flow, and required flow rate (5 lbs/hr) and the pressure drop is 1.5 psi per foot, I require 175 psia pressure drop.... maybe I should divide :rolleyes:

175 psia / 1.5PD/FT = 9.72' of cap tube.... :confused:

This makes things scary... :(

Previously I had multiplied, not divided...

Maybe Gary is back in the running with his 12' figure... :D

....

PS.. Ihave digital pictures of my heat sink construction.... but I would have to have non-disclosure statements from anyone, before viewing.. hehehehehehe :D

Gary
04-06-2003, 02:21 AM
PS.. Ihave digital pictures of my heat sink construction.... but I would have to have non-disclosure statements from anyone, before viewing.. hehehehehehe

That good... or that bad? :D

I'll show ya mine if you'll show me yours.

Gary
04-06-2003, 03:43 AM
I think this might work for sizing cap tubes:

http://www.gatecom.com/~tmethod/captest.jpg

Sections of cap tube separated by access tees. Altogether 10ft. Connect A to B bypasses 1 ft. Connect B to C bypasses 2 ft. And so on.

When you get the right length, pull the testing rig out and install the right length cap tube.

Gary
04-06-2003, 03:50 AM
Hmmmm... should add a 5ft section to make it more versatile.

Could make those sweat tees, run a piece of tubing between each, with a shut off valve for each section.

Gary
04-06-2003, 05:35 AM
http://www.gatecom.com/~tmethod/captest2.jpg

There... that's better. :D

DaBit
04-06-2003, 09:50 AM
Originally posted by Prof Sporlan
But it would hardly be appropriate for the Prof to be developing a cap tube selection program.. :D :D [/B]

Put some effort in developing small 1/16 ton valves which operate down to 10% of rated capacity first :D

But Prof, as usual I am very interested in that Excel sheet and the correlations used. I might be willing to write the captube selection program....

Also a useful tip: Tecumseh / L'unite Hermetique has a compressor selection program which was also capable of calculating captube sizes given a certain compressor, condensing temp, subcool, superheat and load. The program was called DISK UH (DISK_UH.ZIP). A quick Google seach did not show the link, but with some browsing it should show up.

What I did: I selected a compressor that matched the one I was using and ran the captube calculations. When it came up with some odd diameter, I used a mapping table to convert ID #1 to ID #2.

DaBit
04-06-2003, 09:55 AM
Originally posted by Gary
image (http://www.gatecom.com/~tmethod/captest2.jpg)
There... that's better. :D

Make it a binary system by doubling the lengths of the captube. Thus: 1ft, 2ft, 4ft, 8ft, 16ft.
This allows selection of the tube lengh up to 31ft with increments of 1ft. Say we need 5 ft, we would dial in the 4ft and 1ft section. If we need 27ft, we would dial in the 16ft, 8ft, 2ft and 1ft section.

Gary
04-06-2003, 01:31 PM
Make it a binary system by doubling the lengths of the captube. Thus: 1ft, 2ft, 4ft, 8ft, 16ft.

Yep. That works. :D

herefishy
04-06-2003, 02:24 PM
I thought that you could not "break" the cap tube in such a manner, that it must be one continuous tube to even represent proper operation. :confused:

Gary
04-06-2003, 06:03 PM
I suppose the turbulance in the breaks could cause some small friction-like loss, but that would seem very minimal. I could be wrong.

herefishy
04-06-2003, 06:14 PM
I NEVER repair a broken expansion capillary tube (splice with 1/4" copper say), I always replace the entire critter. :)

Gary
04-06-2003, 06:26 PM
Me too. But we are not talking about repair, we are talking about saving countless hours of trial and error sizing adjustments.

Perhaps Prof Sporlan could provide some insight here :D

Gary
04-06-2003, 07:21 PM
Hmmmmmm...

http://www.gatecom.com/~tmethod/captest3.jpg

Lose the handles. Recessed allen stems. 1/4 flare cap for each. Wrap the cap tubes around a piece of tubing. Insulate.

Voila!!! The universal cap tube w/ suction/liquid HX.

Wanna hire me, Prof? I think I can take this idea one or two giant steps further. :D

Prof Sporlan
04-06-2003, 10:20 PM
Voila!!! The universal cap tube w/ suction/liquid HX.

Wanna hire me, Prof? I think I can take this idea one or two giant steps further.:D

The problem the Prof sees with this device is it will probably cost more to make than a TEV, and OEMs who use capillary tubes aren't generally keen with TEV prices as it is. :)

Gary
04-06-2003, 10:46 PM
Maybe. Maybe not. A TEV is far more complex. If you built one by hand it would cost a fortune. :D

Brian_UK
05-06-2003, 10:25 PM
Sorry to come in late on this one, I've been out of the loop for a while.

Looking back over an old thread on cap tubes reminded me of the Electrolux site which has some data on cap tube sizing which may be of use...

It also has some tables for R12/22/134a/404a.

Try this link -
Electrolux (http://www.cubigel.com/english/tecinf3.htm)

herefishy
06-06-2003, 03:41 AM
Well, now Mr Brian_UK......... "JUST WHERE IN THE H*LL HAVE YOU BEEN?" :mad:

This darn thread has been goin on for a WEEK!!! :p

That link is most very highly appreciated...... :)

My cuthtomer left with his prototype thrown together video card chiller.

Hey, Gary..... just to let you know... I ended up putting about fourteen inches of 1/4" tubing in the 64' of .031" cap tube and put 27 crimps in it......... LOL!!!!!!! ROFL!!!!!!!!! :p

I had a 205psig discharge, 5"Hg vacuum, and the screwed up thermometer we were using (not my fluke) that is mounted into the evaporator was reading -50F to -53F.

We had a card attached to my evaporator block, so I kinda conclude that we loaded up the system just a bit.

Also, I had three coils of 20' each cap tube which I tie-wrapped all together..... which I think helped.

We know the compressor really sucks for the application...... so we're just going to overclock the video card and let the compressor fry!!!! LOL

While Donebalp is having fun blowing the thing up, I am going to research a proper compressor/expansion device application for our new set-up. :)

Gary
06-06-2003, 04:07 AM
Hey, Gary..... just to let you know... I ended up putting about fourteen inches of 1/4" tubing in the 64' of .031" cap tube and put 27 crimps in it......... LOL!!!!!!! ROFL!!!!!!!!!

Have you thought about a hand expansion valve??


While Donebalp is having fun blowing the thing up, I am going to research a proper compressor/expansion device application for our new set-up.


I think I would go for a 1/2-3/4hp methanol chiller with a TXV. Maybe a modified window A/C. Then run waterblocks to everything.

For a second project, I would build a small cascade low stage with a direct die block for the CPU. The chiller would be the high stage for the cascade unit in addition to cooling everything else.

DaBit
06-06-2003, 09:08 AM
A bit offtopic, but for me it is great fun to see you guys breaking your heads over the problems of such small-scale refrigeration.

When I came here first, many of you thought I was insane, and recommended me to just buy a faster processor.

Herefishy: you might want to check out phase-change.com. For professionals it is always good for a good laugh and a bit of head-shaking, but you might find some useful information about overclocking related refrigeration.
Not to mention that a second knowledgeable professional could prevent Gary from getting overworked ;)

Brian_UK
06-06-2003, 09:57 PM
Originally posted by herefishy
Well, now Mr Brian_UK......... "JUST WHERE IN THE H*LL HAVE YOU BEEN?" :mad:

Sorry,... family illness, having to work for a living doing assorted hours.

Oh you know what we're like, whinge, whinge, whinge.

Anyway, glad to be of help.

Brian

Gary
08-06-2003, 02:29 PM
Apparently, the prommie uses roughly 68" of .7mm cap tube.

Going by the electrolux chart for R134a, they are aiming for just under 150 watts of cooling.

Switching to the R404a chart, we would need about 3 meters of .7mm cap tube for the same wattage (at a lower temperature).

The .7mm cap tube equates to just slightly larger than .026 inches (.0276), therefore to achieve the same effect we would want to go slightly shorter in length using .026 cap tube.

In any case, 64 feet of .031 just doesn't make sense.

herefishy
09-06-2003, 11:08 PM
I just bought 100' of .028" cap tube. ;-)

Gary
09-06-2003, 11:26 PM
I wonder if a small needle valve (hand expansion valve) wouldn't be just the thing to fine tune it with. :D

Henry Valve Co makes a 1/4 ODS hand expansion valve. 6291N is the number.

herefishy
10-06-2003, 12:52 AM
The "manual" expansion valve "is" an idea. I'm starting with 12' of .028 (got a vacuum on it as we speak).

Gary, I might have to buy some of your books! (for the input)

LOL.

(I've got a good apprentice who needs it). :)

see ya'

Gary
10-06-2003, 02:39 AM
175 psia / 1.5PD/FT = 9.72' of cap tube....

I think I may have found a problem:

175 / 1.5 = 116.67

Better buy some math books, too :D

herefishy
10-06-2003, 04:09 AM
DOH!!!!!!!!! :p

.... and you thought 64' was crazy...............

This compressor sucks (for the application) My swing was too high with the R-404A.... I charged R-401A and kept a card temperature (other side of the processor on the video card ) of minus 3C to +1C. very stable, and properly charged with up to 142 fps on the 3D benchmark program..... however, I think we're looking for better than that... tommorow I'm buying a Danfoss NFX10.... :)

see ya'

Gary
11-06-2003, 02:34 PM
Correction on information provided earlier:

The uncoiled and measured length of the prommie cap tube is 96 inches (of .7mm ID).

herefishy
11-06-2003, 03:36 PM
Hi Gary,

I hooked up 12' of .028". That copeland 1/4 horse rated at -40 R-12 250btuh was just not doing the job.

My vendor with the Danfoss NF10FX compressors couldn't sell one to me, because the pallets of compressors were already sold to Coca-Cola. DOH!

I selected a Tecumseh rated at about 870btuh @-10FSST R-134A, and employed it with the 12' cap tube and R-404A. The compressor was very happy. :D

whilst running the benchmark program, the backside of the video card never got over 15degF and I had a suction return temp of about -34F running around a 5"Hg vacuum. :)

Before booting the computer, I had chilled through to the other side of the card (other side from the evaporator/processor) to -18F

Gary
11-06-2003, 04:35 PM
That's much better. I'm beginning to think that about 8' of .026 with R404a is the ideal for these.

Your superheat is 23F under full load. I wonder if it might flood back a little under minimum load?

BTW, did you get those cheap guages calibrated yet? :D

RogGoetsch
29-06-2003, 07:30 AM
If you've serviced many cap tube systems, you've probably discovered that there are only two kinds: oversized and undersized! (Okay smartypants, maybe you happened once to look at a system that was behaving perfectly under its own particularly perfect conditions. All I can say is, what are you doing messing around with a system that ain't broke?)

If I recall correctly, fluid flow analysis doesn't easily apply to capillary tubes since pressure drop and viscosity are of less significance than the capillary action between the walls of the tube and the liquid surface.

Therefore, phase change before the end of the cap tube is a no-no, hence all the cap tubes out there soldered to suction lines. (No, that's not to reduce floodback!) Gas restricts big time, and that is very handy, if you read on.

It helps me to think about a refrigeration system as an equilibrium system. That is, under any set of operating conditions, the system will seek its equilibrium or steady-state point where everything is balanced: fluid flow, heat flow, etc. If anything changes, the whole system shifts to a new set of operating conditions.

For example, if one of several evaporator fans fails, airflow will be reduced through the evap coil, air will circulate backwards past the stalled fan, crippling the effectiveness of adjacent fans, suction temperature will drop a bit, condensing temp & motor amps will drop, etc. For any change, there is a domino effect until a new equilibrium point is reached.

Since a cap tube has a very limited range of responses (kind of like me when she asks: "Does this make me look fat, Honey?" "No, Dear, you ARE fat." Wait, that was my first marriage. I mean those three words every woman wants to hear from her man: "You're not fat." But I digress.) You have to optimize the critter for one set of conditions right about the middle of your normal expected operating range and hope for the best.

But maybe you're making it more difficult than it is. Because it's not the fluid flow through the cap tube that alone must properly restrict. The tubing must be sized to allow enough flow under design conditions, the size of the refrigerant charge determines the limits of that capacity.

So you could say the first step is to make sure your selection ALLOWS enough flow with a small extra capacity as a safety factor, and then select the volume of charge to fine-tune to the desired capacity.

That is why it is important to angle the drier down toward the cap tube. It is so that all of the liquid will be directed to the cap tube with the uncondensed refrigerant gas acting as the final flow restricter.

In the old days, when venting was normal, we charged cap tube units till we saw the frost line emerge from the box under as nearly as possible design conditions, then bled some off, watching the frost line recede back into the box.

You may have discovered the truly undersized cap tube where the addition of refrigerant has no effect on the capacity, but backs up into the condenser until the loss of condensing surface raises the condensing pressure so high that we can get a little more flow. That is a design to fear!

In any event, even the ASHRAE method will only get you in the ballpark. I use the tables published with the cap tubes and adjust for blends.

I have fine-tuned on my bench (using 6% Ag alloy so I can test, measure, recover, unsweat, lop off and try again) but for field repairs I select for extra capacity, adjust by carefully limiting and recording refrigerant charge, and get on to the next job.

I will cut a cap tube shorter if damaged but if I have to patch, for instance where removal will take more time than the case is worth, (don't get me started on unserviceable designs!) I will shorten or replace the accessible section with a larger size to compensate for the added restriction of the patch.

Rog

herefishy
29-06-2003, 03:59 PM
Pointing the drier down, toward the cap tube inlet certainly does not hurt anything. I expect condensed liquid to be emitting from my condenser, and my condenser actually partially full of liquid, a couple of passes, perhaps.

The drier is referred to as a "liquid" drier, not a "vapor" drier, or a "saturate" drier for that matter. If you have vapor at your filter- drier, and are pointing the drier outlet down so that gravity will assure that liquid (where ever it may be coming from) drips to the bottom (outlet) of the drier, I just consider to be a misnomer. :confused:


I'd say that if you have vapor in your drier, you got other problems, Bub.

condenseddave
29-06-2003, 06:01 PM
Originally posted by herefishy
I'd say that if you have vapor in your drier, you got other problems, Bub.

I generally would want to make certain that my drier was full of liquid, also.

So, what I gather from the previous post, his exwife is fat, and his current wife probably is also, but he won't tell her.:o :D

DaBit
30-06-2003, 09:27 AM
A well-designed captube system has a good ability to adapt itself to various operating conditions. But designing a captube system well is quite a job.

For example: the load range to which a captube can adjust can be broadened by picking the right size condenser. The condenser should be just large enough to heat up when load increases. The resulting higher condensing temperature increases the pressure drop over the captube, and therefore the massflow, compensating for the higher load.

With a too small condenser, pressure rises too much resulting in flooding of the evaporator. A too large condenser doesn't heat up enough, resulting in a starved evaporator.

Too small hurts, and so does too large.

In my previous captube based chiller, I found that adding an accumulator helped a lot. With an accumulator it is possible to adjust the captube to the highest load that occurs instead of the lowest load. When floodback occurs, the excess refrigerant gets stored into the accumulator, resulting in an increased vapour content at the captube entrance, restricting massflow to the point where massflow matches the load.

The price paid is less efficiency at partial load since at partload we are feeding the captube with a vapour/liquid mixture. Not a big deal; full load perfromance is what counts for me.

Though, your mileage about this 'trick' may vary.

RogGoetsch
01-07-2003, 04:44 PM
Originally posted by herefishy
Pointing the drier down, toward the cap tube inlet certainly does not hurt anything. I expect condensed liquid to be emitting from my condenser, and my condenser actually partially full of liquid, a couple of passes, perhaps.

The drier is referred to as a "liquid" drier, not a "vapor" drier, or a "saturate" drier for that matter. If you have vapor at your filter- drier, and are pointing the drier outlet down so that gravity will assure that liquid (where ever it may be coming from) drips to the bottom (outlet) of the drier, I just consider to be a misnomer. :confused:


I'd say that if you have vapor in your drier, you got other problems, Bub.

Interesting theories. But don't take my word for it. The Prof (Sporlan) may want to weigh in on the drier issue, but for the rest, there is no substitute for testing.

The method I originally 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, including embedded at regular intervals along my heat exchanger. 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.

I know it is possible to build a working system without going into this kind of analysis, but from the posting to this thread, it seems that going back to some theory would simplify the struggle a bit. In my work, it is also important to create a system which can be manufactured with uniformity and serviced by the average technician.

Two drawbacks to liquid backed up into the condenser: subcooling the liquid in the condenser has no advantage in a CAP TUBE system if you have designed it correctly because you can accomplish it so much easier in the cap tube and if you test it, you will find that the loss of condensing surface exacts a penalty in performance. Second, excess charge lengthens time required for equalization and may require a start capacitor for the compressor.

My most important comment, which you are free to ignore if it offends you, is that your restriction is too great if excess charge backs up into the condenser instead of overfeeding the evaporator. not that you want to overfeed.

Again, don't take my word for it, test it yourself.

Rog

Peter_1
04-11-2003, 09:31 PM
[QUOTE]Originally posted by herefishy
[B]Any tool (online) available to calculate cap tube size/lenght for specific application.

try the free selection software available on
http://www.tecumseh-europe.com/M5/UK/p50.htm

Perhaps this may usefull for other members.
Let me know