Vertical header/collector

[herdian]

Hi all,
I have a design of pumped evaporator, it uses R22. The evap. has a vertical collector and header [the reason is; we can design less pass/more lines for the evap. without making the evap. too thick instead of using a horizontal header]
Would someone give me a suggestion, what is the best position for the inlet pipe and outlet pipe for the evap. [which is connected to the header/collector] ???
Thanks

[US Iceman]

HI,

I have a feeling this is going to be a long thread.

The first thing to describe is how the direction of air flowing over the fins affects the LMTD.

Are you using parallel air flow or counter-flow? By this I mean, is the air flow parallel with the direction of refrigerant flow, or is the air flow direction counter-flow to the flow of refrigerant?

Ideally, I think you would want the greatest LMTD to gain additional capacity.

Having said that, on a pumped liquid refrigerant system or a flooded coil I don't think it makes a difference. The refrigerant evaporation temperature is constant.

If this was for a direct expansion evaporator, the direction of air flow would matter. That should determine where your suction and liquid headers are placed.

If the evaporators are used for hot gas defrost also, then you want to make sure you can drain the condensed refrigerant out of the last tube on the last pass.

Another problem is if you are using top feed liquid or bottom feed liquid. And, how you feed hot gas into the coil for defrosting.

Know you now, why I said this might be a long thread.

[herdian]

The first thing to describe is how the direction of air flowing over the fins affects the LMTD.

It is a counter flow type

Another problem is if you are using top feed liquid or bottom feed liquid. And, how you feed hot gas into the coil for defrosting.

I use bottom feed liquid.
For defrosting, I use a bypass into the outlet of the evap using a checkvalve, after it travels to the tray at the bottom of the evap, and then goes to the outlet of the evap, the condensed gas goes out from the inlet of evap.

[herdian]

I want to know what is the best position for the suction/outlet pipe position at the collector, is it better to place it at the bottom of the collector or at the upper side of the collector..and also for the inlet pipe at the header in evap. is it better to place to the middle area of the header in. evap???

[US Iceman]

Well, if the coil is bottom feed (meaning the liquid enters here) where does the gas go? As the vapor forms, the gas flows through each circuit until it terminates in the suction header, right?

What does gas want to do naturally? It rises.

Therefore the suction connection on the header would be at the top.

And the liquid connection would be on the bottom of the liquid header to allow the condensed refrigerant to drain.

Are you using orifices in the entrance of the circuits?

[mohamed khamis]

Hi all,
I have a design of pumped evaporator, it uses R22. The evap. has a vertical collector and header [the reason is; we can design less pass/more lines for the evap. without making the evap. too thick instead of using a horizontal header]
Would someone give me a suggestion, what is the best position for the inlet pipe and outlet pipe for the evap. [which is connected to the header/collector] ???
Thanks

Hi herdian

Firstly i don not know what does it mean by pumped evaporator? what is the position of the evaporator it self?

Secondly;

the position of the evaporator header and collector is identified by the position of the evaporator either horizontal or vertical i.e. the horizontal evaporator should has horizontal header (unless there is distributor) and collector and so on.

thirdly;

the position of the header or collector has no relationship with the evaporator thickness, it is assigned by the evaporator capacity and proper pressure drop for the evaporator.

In addition, the number of passes and circuits are determined by the proper required pressure drop in the refrigerant side.

Lastly;

the best position for the pipeline which makes the air in counter flow with the refrigerant inlet direction unless there is no superheat region it does not matter the direction in counter or in parallel as US iceman said. And this in case of the liquid overfeed or flooded type evaporator.

Cheers

[herdian]

Yeah, that's exactly my thought. The vapor refrigerant will fill the upper side of the circuit. But will the gas pumped as well as the liquid to the suction line? So would it become a problem if i place the suction line at the lower side of the header [would the gas refrigerant trapped inside and not returning to the compressor???]


For the liquid header i have fixed my question, it will be placed at the bottom, that's for sure [as well as those with horizontal headers]

Yes Iceman i use orifices at the header.

[herdian]

Im sorry guys, its time for me to make a prayer here in Indonesia, Im hoping so much that u guys will still in this thread...sungguh2 ak membutuhkan this discussion LOL
Ill be back after an hour an a half from now...see u...
Im hoping so much that u guys will still in this thread...mmuuuaach..

[herdian]

Firstly i don not know what does it mean by pumped evaporator? what is the position of the evaporator it self?

Its a liquid overfeed evaporator, but using a vertical collector/header

Secondly;

the position of the evaporator header and collector is identified by the position of the evaporator either horizontal or vertical i.e. the horizontal evaporator should has horizontal header (unless there is distributor) and collector and so on.

Usually i learn aboyt vertical pumped evap. using a horizontal header

thirdly;

the position of the header or collector has no relationship with the evaporator thickness, it is assigned by the evaporator capacity and proper pressure drop for the evaporator.

the evap will be slimmer if we use vertical header. rather than the horizontal one, for the same no of passes

So could u give me another clue mohamed? Pliiiizzzzz...

[mohamed khamis]

Its a liquid overfeed evaporator, but using a vertical collector/header

ok I got it but i want to confirm

Usually i learn aboyt vertical pumped evap. using a horizontal header

I don not have knowledge about this concept but i think if u use horizontal header with vertical evap will cause uneven refrigerant distribution. Otherwise u have multiple evaporators and the horizontal header distributes the refrigerant in all around them. this is another issue

Or U have multiple-circuits evaporator each circuit has its own solenoid valve for the sake of cooling capacity control. so u have to use horizontal header to use row-by-row control.

the evap will be slimmer if we use vertical header. rather than the horizontal one, for the same no of passes

So could u give me another clue mohamed? Pliiiizzzzz...

As U know the liquid has the bigger density than the gas so it makes sense to get the liquid from the bottom of the header to feed the circuiting pump to reduce the probability of pump caviation.

And collect the saturated refrigerant vapor into the collector and let the vapor exit from the top to prevent the liquid accompanies the gas and are sucked to the compressor.

I am afraid u r asking about something else, it sounds u r asking about the refrigerant feeding to the evaporator from highest tube ( down-feed) or lowest tube (up-feed) , u need to know that or not?

kind regards

[herdian]

I don not have knowledge about this concept but i think if u use horizontal header with vertical evap will cause uneven refrigerant distribution. Otherwise u have multiple evaporators and the horizontal header distributes the refrigerant in all around them. this is another issue

The distribution will be even by using orifices [drilling a small hole on the header which is smaller than the connesction tube]

Or U have multiple-circuits evaporator each circuit has its own solenoid valve for the sake of cooling capacity control. so u have to use horizontal header to use row-by-row control.

I accept this as an information for me, thank u

I am afraid u r asking about something else, it sounds u r asking about the refrigerant feeding to the evaporator from highest tube ( down-feed) or lowest tube (up-feed) , u need to know that or not?

The refrigerant feeding is from the lowest tube, but im still confuse about, where should i connect the suction connection on the collector/header out, is it on the lower side of the collector or the upper side [im thinking about vapor trapped if i connect the suction at the lower side of the collector, or should i connect it at the middle side of the collector]

[mohamed khamis]

T

The refrigerant feeding is from the lowest tube, but im still confuse about, where should i connect the suction connection on the collector/header out, is it on the lower side of the collector or the upper side [im thinking about vapor trapped if i connect the suction at the lower side of the collector, or should i connect it at the middle side of the collector]

Of course from the upper side of the collector to allow the vapor to release and is drawn off to the compressor suction and the liquid is separated from the vapor and recirculated to the evaporator.

If u feed the refrigerant in the lower or the middle side u will allow to pump suction to have vapor and causes caviations. U want to have a sufficient area to allow the vapor to expand and the separation between the vapor and liquid is done efficiently. And this sufficient area is found on the top of the vessel (above the liquid level).

Furthermore the refrigerant liquid which is settled inside the collector can be vaporized owing to the suction (evacuation) action from the compressor and cause erratic behavior for system control particulary at partial load operation.

I wish it could help and u'r welcome at any time "Selemat datang"

Cheers

[herdian]

What does "Selamat Datang" mean??? LOL
Just Kidding...Terima Kasih yah bapak...
I wonder where does my Grandpa go...he left me...without further answer...hikz..hikz..

[mohamed khamis]

Sorry there is no influence on the pump cavitation in ur case because ur have two vessels header and collector and the pump will be in the header side.

Terima Kasih yah bapak....

"Sama Sama" U'r welcome my daughter !!!

Cheers

[mohamed khamis]

Yes I think it is fair to call me bapak "father" and US iceman as Grandpa....

[US Iceman]

herdian, I'm in a different time zone that you. It was late last night when I replied to your questions.

But will the gas pumped as well as the liquid to the Suction Line?

The gas is not pumped! The liquid is. The pump pushes the liquid refrigerant to the expansion valve, which reduces the pressure of the liquid down to almost the evaporating pressure.

The orifices reduce the pressure again to balance the flow of liquid into the circuits. As the liquid begins to boil, vapor forms and flows up. After the liquid flows through the orifice the compressor is pulling the vapor out of the evaporator coil. The pump does NOT push it.

mohamed, the evaporator header design has nothing to do with the refrigerant pump or cavitation. This is a completely different problem in a very different part of the system. I don't understand how you think cavitation occurs because of an evaporator???

The distribution will be even by using orifices [drilling a small hole on the header which is smaller than the connection tube]

Since I do not have a picture of how you are building this coil, I have to assume you did mean drilling a hole in the header? How are you connecting the circuits to the header? And, in which header are you placing the orifices?

[mohamed khamis]

mohamed, the evaporator header design has nothing to do with the refrigerant pump or cavitation. This is a completely different problem in a very different part of the system. I don't understand how you think cavitation occurs because of an evaporator???

Yes it is perfectly correct US Iceman and i had caught it and i corrected it immediatly in the following post of the mistake.

The picture for liquid overfeed in my mind ususally has one vessal feeds the pump from the bottom and this pump feeds the evaporators and the above of this vessal the rerfigernat vapor is accumlated and sucked to the compressor suction side. However in her case there are two vessals separtely. So i corrected my speaking once i had remebered that.

I did not mention the cavitation occurs because of an evaporator but i mentioned if there is the dischagre refrigernat from the evaporator is feeded to the bottom of the vessal (the system has one vessal) the pump might suck liquid and gas becuse there is possiblty for the gas to be entraped in the vessal. So this will hasten the possiblity of cavitation to occur. However, i think it is also impossible to occur becasue the liquid which is already settled in the vessal has a pressure of condensing pressure the dischage refrigernat from the evaporator is at evaporating pressure. so at this case the settled liquid refrigerant can flood back to the evaporator so it is not possible for the discharge to enter the vessal from the bottom or the middle for the vessal as she wanted to do.

This also

[mohamed khamis]

mohamed, the evaporator header design has nothing to do with the refrigerant pump or cavitation. This is a completely different problem in a very different part of the system. I don't understand how you think cavitation occurs because of an evaporator???

Yes it is perfectly correct US Iceman and i had caught it and i corrected it immediatly in the following post of the mistake.

The picture for liquid overfeed in my mind ususally has one vessal feeds the pump from the bottom and this pump feeds the evaporators and the above of this vessal the rerfigernat vapor is accumlated and sucked to the compressor suction side. However in her case there are two vessals separtely. So i corrected my speaking once i had remebered that.

I did not mention the cavitation occurs because of an evaporator but i mentioned if there is the dischagre refrigernat from the evaporator is feeded to the bottom of the vessal (the system has one vessal) the pump might suck liquid and gas becuse there is possiblty for the gas to be entraped in the vessal. So this will hasten the possiblity of cavitation to occur. However, i think it is also impossible to occur becasue the liquid which is already settled in the vessal has a pressure of condensing pressure the dischage refrigernat from the evaporator is at evaporating pressure. so at this case the settled liquid refrigerant can flood back to the evaporator so it is not possible for the discharge to enter the vessal from the bottom or the middle for the vessal as she wanted to do.

Cheers

[US Iceman]

However in her case there are two vessels separately.

I don't think so.

I believe she is simply talking about the suction and liquid headers for the evaporator coil. These are as herdian mentioned simply "collectors" for the evaporator circuits.

At least this is my understanding.

[US Iceman]

Where did everyone go???

[mohamed khamis]

Where did everyone go???

I have just finished the VIVA exam of my PhD Grandpa

I believe she is simply talking about the suction and liquid headers for the evaporator coil. These are as herdian mentioned simply "collectors" for the evaporator
circuits.
At least this is my understanding.

Yes it is correct but why did she ask about the connection of the pipeline with collector in the middle or in the bottom?

So it does not matter in the collector where is its entrance as long as a way off the compressor suction.

Each circuit exit port in connected anywhere in the collector than the total discharge of the collector exits from its top to the top of the low pressure vassal.

cheers

[herdian]

Bit i read an article there is a picture of a liquid overfeed evaporator that has an outlet connection placed at the bottom of the collector?? is it really works?

Please find at [triplew.parker.com/RS/90-11a.pdf]
Couldnt send a link

[mohamed khamis]

Bit i read an article there is a picture of a liquid overfeed evaporator that has an outlet connection placed at the bottom of the collector?? is it really works?

Please find at [triplew.parker.com/RS/90-11a.pdf]
Couldnt send a link

The link is not valid ...otherwise if u can upload the article by attached file it will be greatly appreciated.

Cheers

[herdian]

Ive tried it, the file is too large. The link is valid, i only write "www" as "triplew", change it in ur browser...