suction accumulator selection

[Lc_shi]

How to select suction accumulator ? My experience is select capacity to about half of system capacity.
I wonder if there's any rules of thumb about it:)

regards
LC

[US Iceman]

Hi LC,

The capacity of a suction accumulator is first based on the separation capacity of the liquid from the vapor returning to the compressor.

These normally use gravity separation fundamentals where the vapor velocity is allowed to slow down. At some vapor velocity the liquid particles (droplets) will separate by gravity.

Since the liquid has a higher density than the vapor, the liquid is heavier than the vapor.

This is also based on some of the vessel geometry and construction, and liquid droplet size and mass.

There was a good discussion of this in this thread:

http://www.refrigeration-engineer.com/forums/showthread.php?t=2152&page=2

After the accumulator is sized for the cross sectional area required to slow down the liquid, the volume of the vessel is then determined to provide sufficient "holding" capacity.

[US Iceman]

LC,

Here are some additional materials for your review.

http://www.koch-ottoyork.com/downloads/ProductCatalog.pdf

A very nice group of articles (something an engineer would like :cool: ):
http://www.koch-ottoyork.com/downloads/Demystifying.pdf

[bruceboldy]

That Was A Good Description Of How To Size The Vessels

Several Of The Vessel Companies, Have Info For Your Use

My Old Company, Isotherm In The Usa Is Excellent For That Info.

The Site Has Easy To Use Charts For Sizing.

David

[Lc_shi]

thanks for all your good information.
i need the suction accumulator in AC field.
Attached a drawing for yourreview.
How about the oil return mechnism of it?

rgds
LC

[US Iceman]

LC,

The gravity separation mechanisms are the same for refrigeration or AC or hydrocarbons. I am not sure how the capacity was calculated for the accumulators in the picture.

The little accumulators in the picture are listed with a minimum and maximum capacity. I think the minimum capacity is based on maintaining a minimum velocity through the tube to pull oil out of the accumulator.
(The little hole in the tube is the oil return)


My experience is select capacity to about half of system capacity.

If you mean the accumulator is selected to hold one half of the system charge, I would agree. I use a similar logic.

First, the volume of the accumulator should hold about one-half of the refrigerant in the system. Second, the capacity of accumulator should be equal to or greater than the cooling capacity of the system.

I have had some problems on medium sized system using the manufacturers selection charts.

[Lc_shi]

Hi iceman
The chart offer the capacity ton and holding capacity ,select it based on systems cooling capacity and holding capacity 50%. As you said ,the refrigerant vapor flow velocity should meet the gravity separation and oil back requirement.
The oil return hole is at the bottom ,does it mean the oil is heavier than liquid refrigerant, i've not studied it:p

regards
LC

[US Iceman]

If the oil density is greater than the liquid refrigerant density, the oil will have a tendency to sink. But this is not always true as it really depends on the solubility of the mixture.

However, the hole in the tube will also try to vaporize some liquid refrigerant. If the accumulator has liquid refrigerant inside, the hole is exposed to this liquid. During operation the hole acts as an eductor. Some of the liquid will flow through the hole and vaporize.

Wet vapor is better than liquid slugs, so I guess this is better than nothing.

[Lc_shi]

However, the hole in the tube will also try to vaporize some liquid refrigerant. If the accumulator has liquid refrigerant inside, the hole is exposed to this liquid. During operation the hole acts as an eductor. Some of the liquid will flow through the hole and vaporize.
You mean the oil return as the liquid flow through small hole and vaporize and oil return with vapor to compressor. I think you're correct. But is there some oil could be traped in the accumulator?

rgds
LC

[US Iceman]

LC,

I think there will always be a small volume of oil in the bottom. The hole is slightly above the bottom, so the oil level would have to be close to this before it can be sucked out.