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Pump Min. Flow Recycle Heat Gain

Pump Min. Flow Recycle Heat Gain

Pump Min. Flow Recycle Heat Gain

(OP)
Hello All,

I have a question I was hoping you guys could help out with.  

I'm installing a new 5300barrel/hr pump that will be used for two services.  The first will have a required flow of 5300barrel/hr and the second will have a required flow of 1500barrel/hr.  We are limited on nozzles off the tank, so we are planning to route the min flow recycle line back to the pump suction.  Since we are recycling 3800 barrel/hr through the min flow line for the second service, I am worried about heat gain though the recycle line since we can not use the fluid in the tank as a heat sink.  How would I go about calculating what the potential heat gain will be?  They will only use the pump for the second location during outages, however, this could be for a period of 1-2 days.

Thanks

RE: Pump Min. Flow Recycle Heat Gain

You did not mention what type of pump and the operating head.
If it is centrifugal, you will not need to recycle the 3800Barrel/hr  You can throttle the discharge valve until the minimum allowable flow of the pump. If it is still too much, then you recycle the difference.
 

RE: Pump Min. Flow Recycle Heat Gain

If a pump is rated 60% efficient, that means that 40% of the power is being converted to heat. In a normal temperature stabilized pump, running at its best efficiency point, (B.E.P.) the temperature rise within the pump is calculated from the following formulas:


Centigrade Rise:

((BkW-WkW)*14.34)/ (Flow in l/m*Specific Heat)

Where:
BkW = Break kW from pump curve
WkW = Water kW = (Meters * Liters/Min)/6000
14.34 = Conversion from kW to kilocalories

http://www.mcnallyinstitute.com/01-html/1-04.html

The lowest flow that a pump can operate at without compromising mechanical reliability is the "Minimum Stable Flow". For most pumps, this is more of a limiting factor than minimum thermal flow. Minimum thermal flow often does become a critical factor, especially when dealing with volatile liquids , and it should always be checked when evaluating a pump system.

Calculating Minimum Continuous Thermal Flow

http://www.lawrencepumps.com/newsletter/news_v03_i1_Jan06.html

RE: Pump Min. Flow Recycle Heat Gain

You're not going to want to pump at absolute minimum flow for more than 15 to 20 minutes.  Look for minimum stable flow, probably around 20% of pump's BEP flow.  Calculate temperature gain via bimr's links to see if you can dump back into suction, or have to go back to the tank, or ... add a cooler.

From "BigInch's Extremely simple theory of everything."

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