Flooded Systems

[bernard]

Was introduced to a huge water chiller recently ,the system is a lot larger than I normally work with but I found it fasinating.It was a flooded system ?? Please can someone explain this, it had a very large suction accumulator and a flow con valve.They have a problem from time to time where liquid gets trapped in the suction accumulator and the only way to get it out is to add more gas then recover it again????This does not sound correct, why would this happen,what is the advantages with a flooded system.


Regards Bernard

[Brian_UK]

A flooded system provides a more constant (if that is the right word?) cooling surface as the refrigerant is not in a superheated state when in contact with the secondary cooling medium.

[JERRYCOOL]

The liquid recover system seems not econmical but simple. The hot gas enter the accumulator to boil the liquid. if so, this is the cheapest way to solve the problem. sometimes people will install a liquid pump or another tank to pipe the liquid to high side. And maybe you can lower the level of the chiller to to get some superheat and see what happens.

[Peter_1]

.. The hot gas enter the accumulator to boil the liquid.

This beed some explanation for me.
I always thought that the return mix of gas and liquid came into the accumulator.

[Snowman123]

Might need a enconomizer fitted after expansion valve. What make of chiller are you working on?

[wambat]

Sounds like you have an economizer with a hi presure float thats 'Hanging up If this is an air conditioning chiller I don't see a need for an accumulator.

[TXiceman]

Flooded systems are generally used in larger systems where you can not get a thermal expansion valve sized large enough. Also with large DX units you do get into problems with liquid distribution in the tubes. Another case where you would use a flooded exchanger is certain fluids do better with them being cooled in the tubes. Such as fluids which are prone to high fouling rates. Also, corrosive fluids where it is cheaper to build an exchanger with stainless steel tubes, tube sheet and channel as opposed to an expensive stainless steel shell.

Is the flooded system you are looking at one with the liquid in the shell of the evaporator and is it controlled by a high side float as in a critically charged system or is it low side float or orifice plate controlled? Is it on a water chiller or on a lower temperature industrial process system.

My primary concern is that in a properly designed flooded system the suction accumulator should run dry and is there as a safety device to protect the compressor from process upsets and liquid slugs. If it routinely gets flooded with liquid, they are either creating a process upset and slopping over liquid, the evaporator is not properly designed or they have the liquid level too high.

Another type of stem refereed to as "flooded" is a coil or unit cooler that is fed by a gravity drum (or thermosiphon drum). These are typically used in larger industrial cooled warehouses. In these, the drum runs wet and acts as a suction accumulator as well as a liquid supply drum.

When I design a system with a suction accumulator, I generally take the warm condensed liquid through a "boil-out coil" in the bottom of the accumulator. This supplies a small heat source to get the refrigerant to boil out in the event of a liquid flood over.

I do hope that they have an oil recovery system attached to the accumulator to get oil back to the compressor (probably will not on a centrifugal compressor).

The ASHRAE Handbook has a good explanation of flooded evaporators. Another book that is a good source of refrigeration data and design is Refrigeration Fundamentals by Wilhelm Stoecker.

Ken

[Lc_shi]

Attachment is a sketch from ASHRAE handbook for your ref.

[ferretman]

Dear Bernard

The reason for the large suction accumlator is that the system as you know is flooded,any liquid that does not boil off through heat transfer then returns to the accumlator,inside the accumlator passes the liquid line the heat from the liquid line boils off the returned liquid from the evap then the vapour is then drawn off the top to the compressor.the system will run with a high level switch on the accumlator so if the level raises the switch will make and drop out the compressor to stop any damage.If this happens then liquid will need to be decanted from the accumlator and the problem repaired i.e solinoid valve passing.Hope this helps.

[Lc_shi]

why can't upload,try again.