Distributor & Capillary tube position

[MrReds]

Hallo to everybody !

I’d like to make you a question concerning the position of distributors and capillary tubes in the air coolers.
I am wandering if somebody can clarify me this issue.


Very often the position of the distributor in DX coils is “top down” .
With this definition I am meaning:
- the direction of refrigerant passing through the distributor is from top to down (the holes for capillary tube face at the earth), as "from sky to earth".



Sometimes the capillary tubes leave the distributor in down direction and enter directly into the coil.
Sometimes I have seen, in the same position of distributor (“top-down”), that capillary tubes go down, then up, then down into the coil, like an S.
In some cases I have seen the distributor in the position “down up”,
- the direction of the refrigerant through the distributor is from "earth to sky".

In this case I have seen capillary tubes go up, then down into the coil, like a reversed U.


I hope to have made a clear description.


Please, do you know if this is due to manufacturing or technical reasons ?
If there are technical reasons, is there somebody who can kindly explain them to me ?

Thanks in advance !

[Dan]

Sometimes the capillary tubes leave the Distributor in down direction and enter directly into the coil.
Sometimes I have seen, in the same position of Distributor (“top-down”), that capillary tubes go down, then up, then down into the coil, like an S.
In some cases I have seen the Distributor in the position “down up”,
- the direction of the refrigerant through the Distributor is from "earth to sky".

In this case I have seen capillary tubes go up, then down into the coil, like a reversed U.

First, I want to be sure we are using the same terminology. When you say "capillary" tubes, I am assuming you are seeing the smaller piping coming out of a distributor after a thermostatic expansion valve.

The purpose of the distributor is to insure ahead of the distributed tubing or capillary tubing that each tube receives an equal amount of refrigerant. This makes it possible for manufacturers of coils to bend or turn the capillary tubing with some freedom now that gravitational distribution has been overcome. Check the following link:

http://www.sporlan.com/refrigerants.shtm

[US Iceman]

One of the reasons for the top-down position of the distributor I have always heard is that gravity helps to distribute the liquid through the distributor. Having said that, I personally don't think the position of the distributor has any preference.

The velocity & mixture of the liquid and vapor exiting the TXV could be considered uniform so that each distributor tube receives equal gas and liquid.

The reason for the "S bends" is because of the equal length required for the distributor tubes. These tubes have to be bent like this because they are all the same length.

[Dan]

An industrial refrigeration system is a perfect example of not being able to see the forest for the trees.

US Iceman, pardon me if I am repeating the question, but what do you mean when you say this?

[US Iceman]

I'm sure you have heard the old saying about being to close to the problem to see the forest from the trees, right?

My tongue-in-cheek take on it was a way to explain there are so many variables and factors to take into consideration, that it is easy confuse the issues.

Many people tend to get lost in large complex systems and let this simple fact override logic in finding problems. I have seen this with supermarket systems too. The first rack system someone sees, they get overwhelmed with all of the parts and pieces.

To restate the phrase, you might say it is easy to get lost if you think of how many trees there are, instead or worrying about the problems first.

It's another way of saying it is sometimes easy to forget your original purpose was to drain the swamp, if you get overwhelmed by the quantity of alligators!

Stick with the basics and the problems will solve themselves.;) Large problems are usually just a lot of small problems combined...

[Dan]

Can't see the forest for the trees.


Used when expressing that a person is focusing too much on specific problems and is missing the point

Certainly an industrial refrigeration system cannot be held responsible for this. :)

Perhaps it is a type of person?

[lana]

Hi MrReds,

Everything said so far.
I would like to add something.

As the name indicates, distributors are for distributing the liquid refrigerant EQUALLY into the evaporator circuits. For doing this, the length and the diameter of the cap tubes must be exactly the same. If one cap tube is shorter than the others, the pressure drop in that tube will be less and therefore, more liquid will pass through that tube.
In design we take the required capacity and evaporating temperature and number of circuits and then the best distributor arrangement is designed.

About the direction. Sporlan uses another orifice inside the distributor which helps the distribution , if you like. With this arrangement, Sporlan suggest that you can place it as you like.
But experience showed me that if this orifice is not used then the best way is up to down.

Producing the distributor also is very important. If the holes are not made with correct angle then the distributor will be useless.

Also, Danfoss suggest the correct orientation for TEV. There you see that TEV also is placed upside down for best performance.
Hope this helps.

[DeB]

The best position is distributor outlet facing down.This gives the best homegenised mixture of liquid/vapour.Although some will work at other angles, face down is best practice.

[MrReds]

many thanks Mrs. Lana, Mr. Us Iceman, Mr Dan, Mr DeB.

It seems that everybody agrees that best solution is having distributor in position of flow up - down.

Concerning capillary, do you think that it should be better that they first go up at the same height and then go down into the coil ?

Do you know, by the way, any calculation software for dimensioning the right length of the capillars ?

Thanks in advance !

[lana]

Hi there,



Do you know, by the way, any calculation software for dimensioning the right length of the capillars ?


Danfoss software "DanCap" is available from Danfoss site.

Cheers

[Peter_1]

The tunes coming out the distributor aren't in fact capillary expensions devices which can't be calculated with software.
You just have to make as Lana said that each have exact equal length, so the longest circuit/length determines how long every tube have to be.

[yorkie]

Gravity is great for refrigeration distributors to ensure even distribution.

If you dont have equal distribution through a coil /or poor air distribution accross a coil. you may find that the stream with poor heat transfer will shut down the expansion device.. will see a cold temperature. This will reduce the refrigeration effect and performance.
sporlan valves have a great document about this.

[Samarjit Sen]

For calculating the dimension of the distributor tube, orifice etc. Sporlan bulletin 20-10 is vey good.

While on the subject, I would like to mention that we are using Roller Evaporator for the first time. In this we find that the distributor entry is from bottom to top. We have located the TEV horizontally and with a bend have connected the same to the distributor. Is it correct?