How to choose the correct liquid pump?

[sonhdv]

Dear everybody !

I means that it is the circle ratio.
Who can tell me know how to choose correct this factor?
I know that, it's limit from 1-15.

[US Iceman]

I believe you are looking at a liquid overfeed system (sometimes also called liquid recirculation). The liquid may be pumped by either a mechanical (usually centrifugal) pump or by a process called gas pumping (where a high pressure vapor is used to displace the liquid, which causes it to flow to the evaporator coils).

The circulation ratio (sometimes called the recirculation rate or recirc rate) is based on the need to supply more liquid refrigerant to the evaporators than what boils off in the coil (due to heat absorption).

Here is an example: On a direct expansion system you supply 1 kg/minute of liquid to the evaporator and the evaporator boils all of this liquid into 1 kg/minute of refrigerant gas. The circulation ratio is 1:1.

If you supply 2 kg/minute of liquid to the evaporator and only 1 kg/minute evaporates into vapor then the circulation ratio is 2:1.

There are some reference sources that state the same range you listed. I think it is safe to use 1.5 to 2:1 as the circulation ratio for ammonia or other refrigerants. The evaporator manufacturer needs to know this so that they can properly design the coil circuits (a circuit is a single path through the evaporator).

[smpsmp45]

This is a debatable question, but US ICeman has replied based on the practical considerations.

[sonhdv]

This is my choose way:
1. For Direct expansion valves feeding
This ration : n=1
2. For Gravity direct feeding
n=1-1.5.
3. For liquid pump feeding
n=2-5
Often using n=4.

Example: Block-ice maker system: n=3
IQF (Individual Quickly Freezer), CF (Contact Freezer) or Cold Storage (low temp) n=4 or 5

Is my choosing right?

[US Iceman]

For gravity flooded evaporators the circulation ratio should be higher than 1-1.5. If you notice the connection sizes on evaporators using this liquid feed method the pipes are normally larger than DX. The circulation rates can be lower at low load, however, the ratio at higher loads can be as high as 10. The reason for this is the higher heat flux at high load conditions causes more boiling. Therefore the gas velocity is higher. The circulation rate at high loads balances with the pressure loss due to flow and the available static head from the surge drum overhead.

For mechanical liquid pumps I use 1.5-2.

[sonhdv]

Thanks so much

[Magoo]

Now you tell us that it is gravity supply, the vertical separation is critical for feed ratios during design versus pull-down. Stops killing compressors during pulldown. Talk nicely to US iceman, he can direct you on a path to optimum design.
magoo

[Sandro Baptista]

For mechanical liquid pumps I use 1.5-2.

I would use between 3 and 5.

• It will increase slightly the the capacity of the evaporator (increase internal heat convection transfer - refrigerant side).
• It will guarantee that all evaporators are with good feeding. If you have 1,5 - 2 circulating factor you would need an extra accurate regulation of the REGs valves.

If I have just onle one service, like cold room I would use 3 or even 2.

If I have many I would use 4 or 5.

If I have only a "static" freezing tunnel I would use about 3 or 4 to ensure that at the first hours when the tunnel needs more refrigerant the evaporators is not with lack of refrigerant.

If I have only a "continuos" tunnel (IQF, SPIRAL, etc) then I would use 3 or even 2.

Regards