Direct Expantion Ammonia Plate Heat Exchanger

[gwapa]

Dear Friends
I am curious for the performanse of a ammonia PHE when working with under ammmonia expantion system.
Normally a heat exchanger shell and tube or evaporator has a distributor to fill evenly all pipes
The proposal I have received do not show any distributor.

How it really work? How the expanded ammonia fill all the plates?
Thanks in advance
Gwapa

[alphi]

Gwapa, these might help you understand how PHE works

kind regards,
alphi

[gwapa]

Thanks Alphi
I is a good article.
For me it is very clear how the ammonia in a PHE flow when it is working overfeeded or gravety feeded. However when it work in a expantion system I am not very clear how the ammonia flows inside the PHE. As pointed before most of the expantion Heat Exchaanger have a distributor to garantee al tubes get the same amount of liquind. But what happen in a PHE ? How does the refrigerante distribute inside?
Thanks again
Gwapa

[mazbut]

useful link , alphi. However, I had been using Vertical surge drums linke to a liquid pump instead to operate my series of Kino****a plate freezers and never had any problem. contrarily on the older model Amerio or Jackstone Froster contact plate freezers a huge surge drum came installed with the freezer and there was no pump. regardless it did fine ,,,

In a flooded system it is necessary to flood all the tubes through an accumulator or a surge drum as it is called for effective performance. If the level of the liquid in the plates is not maintained (through a solenoid operated float valve, etc) it will never give the desired cooling in a certain time. The same applies in case of heat rejection,,,,,

[RANGER1]

gwapa,
Too the best of my knowledge you have to order it for that type of service. Alfa laval heve an inbuilt ditributor like you describe otherwise common sense says it will not work.

[alphi]

Hi Gwapa,

That type of PHE you'd encountered, is it semi-weld or compact brazed type?

Addition info that may help you.

For some installation like for evaporator, direct expansion of Ammonia in the PHE is done by TEV(thermostatic expansion valve). The refrigerant enters the TEV, where it partly vaporizes and therefore cools down.The valve is controlled by superheat at the evaporator exit. Two phase refrigerant mixture that leaves the expansion valve directly enters the evaporator. There, it evaporates completely and the vapour leaves slightly superheated. At the end of the evaporation when the vapor content approaches 100% heat transfer in gas phase that returns to the separator.

For some design of PHE like Compact braced PHE, the inlet side for the refrigerant have equalancer. The equalancer functions to equal distribution of refrigerant in the plate channels. But the disadvantages of equalancer system is that, not applicable to single phase flow.

alphi

[Cold Down Under]

Both Alfa-Laval and APV are offering different approaches on DX ammonia plate heat exchangers. In their large plates Alpha Laval have rudimentary distribution tube in their heat exchanger and a liquid/suction HX that fits into the suction port of the exchanger to provide final superheating if wet gas was leaving the top of the HX. APV have a more sophisticated distribution system on their inlet ports, which is based on carefully calibrated expansion orifices into the bottom of each pair put in the port gaskets to ensure even distribution.

[gwapa]

Dear Alphi

I am refering to twin PHE.
I think that our friend Cold Down Under is right
There should be a special distributor at the inlet port of the PHE in order all two phase flow ammonia goes evenly to all the plates.
I have not seen it yet but I am very courius
thanks
gwapa

[winfred.dela]

Dear Friends
I am curious for the performanse of a ammonia PHE when working with under ammmonia expantion system.
Normally a heat exchanger shell and tube or evaporator has a distributor to fill evenly all pipes
The proposal I have received do not show any distributor.

How it really work? How the expanded ammonia fill all the plates?
Thanks in advance
Gwapa

Check this out. . .

[alphi]

Hi winfred,
you still have my gift to you.................

Gwapa,

check the pdf copy sent by winfred. I used to work with this cool guy.

Twin plate is what we call semi-weld plates (cassettes for short in Alfa Laval term)

kr,
alphi

[winfred.dela]

Hi alphi,

so your now working abroad. . .

keep in touch, PM me when your free.

Regards. . .

[rajgulati]

In Nh3 Dx system there might be chance of oil chocking problem. Be careful while installing.
regards

[gwapa]

wilfred.dela
It is a very good documents. Everything is clear to me now
thanks a lot
regards
gwapa

[US Iceman]

winfred.dela,

Do you have a link to the entire pdf you referenced?

This appears to be a very good source of material.

Thank you.

[winfred.dela]

winfred.dela,

Do you have a link to the entire pdf you referenced?

This appears to be a very good source of material.

Thank you.

Hi US Iceman,

I have posted the link (Alfa Laval Technical Manual) under the Refrigeration Books.

Regards,
winfred

[US Iceman]

Found it and have already downloaded it.

Thanks again. I'm sure others will appreciate it also.