PUMP MOTOR SIZE DUE TO FLUID TEMPERATURE OF ABOVE 40 DEG C

[Askarel27]

Can someone explain the effect of fluid temperature to the motor size.
Mostly, Vendor provided to size of motor at 40 deg C to be 112kW (150hp).
However, as per our client the fluid temperature shall be used is 60 deg C. Again, the pump vendor have size the motor to 160kW (200hp).

My question are?
Is their an derating factor that if the fluid is above the normal temperature the pump motor also increase the kW (hp)?
What is the reference or table to this derating factor as per standard?

 

[electricpete]

Within a given fixed system and speed, increasing temperature decreases density which decreases BHP drawn by the pump.

Increasing temperature also decreases viscosity, which again decreases BHP drawn bu the pump (for a fixed system and speed).

Neither of above suggests a reason to increases BHP with speed.

Maybe the motor is in somewhat intimate contact with the fluid and the client specifies higher motor rating as means to compensate for the higher temperature. That would be an indirect way of doing it but you never know. All I can do is swag guess. Maybe someone else has better ideas.

=====================================
(2B)+(2B)' ?

 

[electricpete]

typo alert

Neither of above suggests a reason to increases BHP with speed.

should've been

Neither of above suggests a reason to increases BHP with temperature..

=====================================
(2B)+(2B)' ?

 

[BrianPetersen]

It would help to know what kind of "fluid" we are talking about here.

It doesn't sound like a power-demand-related issue, but it could very well be a reserve-cooling-capacity issue.

 

[Askarel27]

The fluid is industrial waste water, TDH = 30 m, Duty = 885 m3/hr, Sunction = Flooded, Fluid temp = 60deg C, Sump depth = 3m , Motor Voltage 460V, 3ph, 60HX, Exd, IE3 efficiency.

The vendor calculated at fluid temp at 40degC, the selected motor rating is 112kW (150hp).However, when he changed the fluid temp to 60degC, the selected motor is 160kW (200hp).

 

[ScottyUK]

The ATEX rating may be a factor - what temperature class is the motor? Heat gain from ambient or from process can make it harder to get a motor designed to run at Class F or Class H internal temperature limits to pass the surface temperature tests for a T3 or T4 class. The only option open may be to use under-utilise a much larger motor, which will reduce the I²R losses and thus reduce the rise above ambient.