6 replies to this topic

[asade abiodun]

Hi,

Is there a rule of thumb used in determining the flow required through the recycle line on the pump discharge in case of minimum flow problem in pump? If yes, what percentage of the pump flow is considered to flow through the recycle line.

Responce is highly welcome.

[Chris Haslego]

Seems like the answer would be:

Minimum recycle flow = Minimum flow required by pump - Feed flow to pump

Am I understanding the question correctly? You're using the recycle to maintain a minimum flow at the pump suction...correct?

[asade abiodun]

Admin,

you answer my question rightly. May i ask how can i determine the minimum flow required by the pump since i have the feed flow to pump.

Thanks for your responce.

[pleckner]

I've seen estimates anywhere from 10% up to 50% of the normal flow depending on the size of the pump. Your best bet would be to contact a manufacturer of the pump you have or are considering and they will be able to give you a better answer. If you are sizing the pump then go to the manufacturer website. Many (Goulds, Durco/flowserv) have sizing software on-line. The sizing program will give you an estimated minimum flow required.

[fallah]

In determination of min. flow we must assume that the horsepower at blocked-in conditions turns into heat.
The minimum flow is determined such that carry away this heat at a 15 Deg.of Far.(as a normal value) in its temperature, and you can calculate that by a simple material and energy balance.

Anyway, if you need ,I can present an example for you in this regard.

[AA Mishra]

60.


Regards

[JoeWong]

Fallah has pointed one factor affecting pump minimum flow. There are other factors determining pump minimum flowrate.

3 other points that i can remember.

i) Fluid temperature rise
ii) Minimum system stable flow
iii) Internal recirculation
iv) Thrust capacity

Phil has cleared pointed that 10%-50%. Personally i use 30%-40% for first guess (during basic/conceptual design phase). Somehow this needs to be confirmed during Detailed Design with pump vendor input.

JoeWong