flooded evaporators and surge drums

[stan1488]

GREAT SITE !!! I was wondering if someone can explain how the pressure drop occurs in a surge drum , ( example being a blast freezer nh3 or r22) ,as far as I can tell there is no expansion devices, so does this occur through the metering of float device into drum controlling the pressure or through flashing in drum , Im am really confused on this application , I do understand that coils are gravity fed, my only question is" how" for example the low pressure temperature conditions are met , any info is greatly appreciated !! stan

[Andy]

Hi Stan,
check thru the industrial section, there is a post on flooded NH3, this covers most of what you want to know.
Every fridge system has four main components.
[list=1][*]Compressor[*]Condenser[*]Expansion device[*]Evaporator[/list=1]

This does not change from a domestic to a blast freezer.
On a flooded system you can have basically two types of expansion valve/control type.

• High side float/control
• Low side float/control

With high side control, liquid is metered into the vessel/ coolers by a control (float/needle valve/ solinoide with oriface plate) the liquid is basically dumped into low side as it is condensed in the condenser. If you make 1kG of liquid in the condenser you dump (give or take a small differential)1 kG of liquid to the low side.

With low side control you are simply maintaining a level in the low side, (give or take a differential) similar contols are used, just the function changes, ie you are now controllinga level in the low side not a level in the high side.

Hope this helps, please read the industrial section for more info.
Regards. Andy