NH3 recirculation systems

[lraja]

Hi Guys

For a moderate capacity NH3 recirculation plant, say about 300 kW cooling, what is the best arrangement for feeding evaporator coils?, liquid pump based system or gas/compressor driven system …, could anyone guys reason things out for me

lraja

[US Iceman]

I like the mechanical pump version the best. It is more flexible for energy conservation.

The gas driven systems are dependent on constant discharge pressure for pumping the same volume of liquid in the same time frame. If the discharge pressure is allowed to reduce, the transfer rate can decrease.

Secondly, the check valves required in the gas driven system are more prone to problems due to the constant cycles.

I also think the mechanical pumps are more cost effective to operate.

[TXiceman]

I vote for a liquid overfeed or recirculated system using pumps. A number of mmanufacturers make very good canned or semi-hermetic refrigerants. The gas powered or CPR (control pressure receiver) systems are touted as the savior to refrigeration. The controls are more complicated and prone to problems (check valves and solenoid valves). If is also less efficient due to the re-expansion os the gas in the pumper drum or CPR.

On your pump recirculator drum you will need a level control and an oil recovery still or pot.

Ken

[taz24]

liquid pump based system or gas/compressor driven system …, could anyone guys reason things out for me

lraja[/quote]

The heat transfer with the liquid is better han with gas so I would go for the pumped liquid.

Cheers taz.

[nh3simman]

liquid pump based system or gas/compressor driven system …, could anyone guys reason things out for me

lraja

The heat transfer with the liquid is better han with gas so I would go for the pumped liquid.

Cheers taz.[/quote]


Hi taz24
I wonder about this statement. The fluid comes in as a liquid that boils vigorously to a gas. The liquid heat transfer is purely turbulent, so why should this be much better than boiling.

[US Iceman]

The heat transfer with the liquid is better than with gas so I would go for the pumped liquid.

Cheers taz.


I just noticed this comment after nh3simman replied to it as well.

The heat transfer is not appreciably different with gas pumped or mechanically pumped liquid to the evaporators.

The biggest concern is the cost of flash gas on the gas pumped systems and the check valves slamming all of the time. These systems are also dependent on a constant discharge pressure to maintain a constant pumping rate, so this could limit the potential for discharge pressure reduction.

Sorry taz.;)

[cha09]

I have 2 unit ammonia refrigeration system, each has capacity 300 kW, all of the systems use liquid pump, it is looks good.

[taz24]

I just noticed this comment after nh3simman replied to it as well.

The heat transfer is not appreciably different with gas pumped or mechanically pumped liquid to the evaporators.

The biggest concern is the cost of flash gas on the gas pumped systems and the check valves slamming all of the time. These systems are also dependent on a constant discharge pressure to maintain a constant pumping rate, so this could limit the potential for discharge pressure reduction.

Sorry taz.;)

It just goes to show I'm not too old to learn:D

I was of the understanding that flooded evaporator swere used because the heat transfer was greater than saturated liquid vapour evaps (DX).
The reason behind this was the whole evap is used on a flooded system because the need to superheat the vapour was not nessesary.
My understanding of a wet evap was that liquid entered it and saturated liquid left it. Thats why I thought they were more effiecent.

Oh well back to school:)

taz.

[US Iceman]

I was of the understanding that flooded evaporators were used because the heat transfer was greater than saturated liquid vapour evaps (DX).

The reason behind this was the whole evap is used on a flooded system because the need to superheat the vapour was not nessesary.

My understanding of a wet evap was that liquid entered it and saturated liquid left it. Thats why I thought they were more effiecent.


All true...

The original question related to the type of liquid delivery method to the evaporators.

A mechanically pumped liquid overfeed system simply uses a pump to transfer saturated liquid (under pressure) to the evaporators.

A gas-powered system uses high-pressure gas to displace liquid from a tank. Since this liquid is now at a higher pressure, it flows to the evaporator.

There was another thread in the last few days that discussed the coil capacity issue, but I can't remember where it is right now.:o

[taz24]

The original question related to the type of liquid delivery method to the evaporators.




Should have read the question then shouldn't I:D .

Back to School twice for me:) .

Cheers taz.

[Sinke]

...The simply things is the best things...:D
...just buy mechanical hermetic pump and keep on...

[cha09]

I have 300 kW ammonia refrigeration system, I can give you all the spec of equipments if you want it

[Sinke]

I have 300 kW ammonia refrigeration system, I can give you all the spec of equipments if you want it

...I work on system over 1000kw....

[John Hunter]

I For what its worth
Being an ammonia re-circulation Plant your liquid flow to your evaporators will be either via a Flow Control valve or fixed orifice . Assuming the valve is set to handle the total load a fairly constant differential pressure across the valve or orifice is needed. A pump system can deliver a fairly constant delivery head to your distribution system. Gas systems require constant gas pressure to do the same , but to achieve this there will times you would be running compressors to maintain head. The economics doesn't justify this. So use pumps , there are some very reliable Semi- hermetic canned pumps on the market , but I still like my Cornells.

[US Iceman]

...but I still like my Cornells.


Me too! Just started up a new set last week.:cool: