Help with discharge line

[luissandoval]

Hi everybody:

I have a system with the following characteristics:

Single stage
Ammonia
Screw compresors
T evap = -21 ªC
T Cond. = +35ºC
Compressor's capacity = 1395Kw
Condenser's Capacity = 2047 Kw
The actual discharge line is 4" and I was thinking to change it for 5". i would like to know your opnion about this. somebody could tell me if there are some rule for sizing the discharge line or what happens if i don't change nothig. i hope you can help me

Best Regards.

Luis Sandoval.

[taz24]

Hi everybody:


I have a system with the following characteristics:

Single stage
Ammonia
Screw compresors
T evap = -21 ªC
T Cond. = +35ºC
Compressor's capacity = 1395Kw
Condenser's Capacity = 2047 Kw
The actual discharge line is 4" and I was thinking to change it for 5". i would like to know your opnion about this. somebody could tell me if there are some rule for sizing the discharge line or what happens if i don't change nothig. i hope you can help me

Best Regards.

Luis Sandoval.


I would ask why?

Why do you want to change the discharge line.
Is the ststem not working?

Cheers taz.

.

[US Iceman]

The rule is: how much pressure drop is there and can you live it? Each value of pressure loss translates into an equivalent temperature loss. The temperature loss affects the saturated condensing temperature.

Therefore, if you keep the saturated discharge temperature (at the compressor) at say 95°F (35°C) the condensing temperature will be lower. Is the condenser heat rejection rated for the lower condensing temperature?

On the other hand, if the condensing temperature is 95°C (35°C), then the saturated discharge temperature will be higher. The latter one is how I look at this. Otherwise, the condenser must be larger for the lower condensing temperature.

[luissandoval]

i'm worry about the velocity in the discharge line because it's so so 22.5 m/s i don't sure if this pipe will work ok with this velocity.

Luis

[US Iceman]

Two concerns.



High velocity = higher pressure loss.
Higher velocity = greater concern for liquid hammer if condensate is inside pipe (gas condensing).

If you can ensure you will not have gas condensation in the discharge line then the main concern is the pressure loss and affect it has on saturation temperatures.

[gwapa]

Luis
I think you should figure out the pressure drop and temperatura drop.
I made a preliminare calculation with 20 m long pipe/4 elbow, 2 Globe valve and a I get 0,133 bar pressure loss and 0,344 ºC (no condenser pressure drop).
Look in the compressor curve how much power you will low with 5 in pipe.
The next question will be: will the power reducction payback the new pipe?

Hope this help take a desition
regards
Gwapa