Hi sirs
I've heard that some manufacturers apply flooded evaoprator design in their screw chillers. It's said that the COP is higher than DX system. But how about the pro and cons of flooded evaporator?
regards
LC
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Hi sirs
I've heard that some manufacturers apply flooded evaoprator design in their screw chillers. It's said that the COP is higher than DX system. But how about the pro and cons of flooded evaporator?
regards
LC
Hi LC,
For flooded units the following comments are applied:
Pros
- Higher heat transfer
- Potentially lower approach temperature with same surface area
- Almost no evaporator superheat that can increase vapor density and mass flow, hence increased capacity
- Liquid/vapor separation incorporated into design
- Easier ability to reduce discharge pressure
- Less low load operating problems (better turndown)
- Cooled fluid flows through tubes (easier cleaning if needed)
Cons
- More refrigerant is required
- Added cost for liquid/vapor separator
- Oil recovery method required
Hi Lc,
Most of my equipment is screw compressor & flooded type,some are shell & tube eveporator, but mostly PHE.
Better COP.
Guapo
Hi,
The item which you should be most concerned about is a loss of water flow condition. In flooded evaps, the tube bundle freezes and ruptures very easily if a loss of water flow condition occurs. We always suggested redundant proof-of-flow switches. We even had freeze-ups when the charge was blown, even though accepted practice [and instructions] was to operate the water pumps during this period.
If it is a R134a machine, once water gets into EVERYTHING, huge trouble as the oil is highly hygroscopic. Very difficult to clean eveything out to acceptable levels.
Good luck, bigJohn
P.S. not to worry anyone, "Blow the charge" is a factory term in current usage. Of course, nowadays, it is recovered.
HI guapo
Use plate heat exchanger as flooded evaporator? I don't know how to control the liquid level? pls teach me :)
rgds
LC
LC,
If you go to this post: http://www.refrigeration-engineer.co...9&d=1147285803
You will find a sketch of a flooded PHE.
The liquid level is maintained in the vessel above the PHE. A simple float switch controlling a solenoid valve will work nicely. The flow rate into the vessel is controlled by a hand expansion valve.
Hi Lc,
US ICEMAN is correct, simple as that.:) You can also control the level by electronic level controller for better performance. I think most of the packaged chiller now they use PHE.:)
Regards,
Guapo;)
hi guapo,
understand what you say:)
Where is the key tech of this type machine? Oil return \ level control or liqiud vapour separator? Could you offer me a system sketch of your screw machine. How about the COP bigger than DX evap?
thanks and regards
LC
Hi Lc,Quote:
Originally Posted by Lc_shi
The unit has oil separator right after discharge, and on the top of the PHE there is a what we call surge drum. Surge drum we maintain the level of refrigerant, around 1/4. Since the suction line is on the top of the surge drum, only vapor will go to the compressor.
The PHE is full of refrigerant because the level is 1/4 on the surge drum which located on the top of the PHE, unlike the DX evaporator you have to left some space for your super heat.
Regards,
Guapo
Is it possible to use PHE as flooded evaporator, I doubt it!Quote:
Originally Posted by Lc_shi
How we get the oil return to the compressor, that's what I concern.Quote:
Originally Posted by US Iceman
That all depends!Quote:
Originally Posted by wilsoncheung
The chillers I work on use a "gas pump" fitted under the evaporator that uses suction pressure to get the oil back to the compressor by opening and closing two solenoid valves.
Attached the principle of a screw chiller!
hI ICEMAN,
CAN U TELL ME, HOW TO SELECT DX AMMONIA EVAPORATOR.If i select the pumped system evaporator and convert in to ammonia dx,will there change in the capacity?
Quote:
Originally Posted by US Iceman
can anyone tell me how to select DX ammonia evaporator. If i select Pumped system evaporator and convert in to DX System , will there be any changes in the capacity.
srini
It can be done, and works very well.Quote:
Originally Posted by wilsoncheung
Just needs a surge drum or LPR and you'll have a very efficient system.
We have hundreds of systems like this in UK working off a high side float switch.
Quote:
Originally Posted by Lowrider
We use a similar system, but with 1 solenoid valve and a motorised valve.
The best way to do this is donn't do it at all. Gravity flooded or pumped ammonia systems ar far more reliable and efficient. Unless you have a small medium temperature system, you're asking for trouble by using DX.Quote:
Originally Posted by srini742
We are building flooded PHE chillers using R-22 and R-717. Our factory is bnear Beijing. Come and visit us some time.Quote:
Originally Posted by Lc_shi
Sorry for reviving this old thread. Can you possibly explain to me how this pump works. I can't understand the principle... ThanksQuote:
Originally Posted by Lowrider
What's the problem? If you can read PID's you'll be able to locate the screw compressor, oil seperator, condensor and evaporator!Quote:
Originally Posted by NoNickName
Of course I can, but what is inside what you call "GAS PUMP"? Are the solenoids interlocked and how are they managed? How is the geometry of the oil pipe in the evaporator vessel?
the dotted line in the evaporator is there to indicate the level,not a pipe, maybe that helps! The solenoids help to suck in and push out the oil.
Quote:
Originally Posted by Lowrider
:o
Good to know. :confused:Quote:
Originally Posted by Lowrider
As for the controls, it's managed by a CH530. (That's trane)
Hi Guapo,Quote:
Originally Posted by guapo
I've read this interesting topic. I'm just studying a ammonia chiller with flooded evaporator. I've understood the surge drum function but how can I design it or choose in a manufacturer's range?
Many thanks in advance
Ice Wombat