Silly question re closed loop circuit

[KevinNZ]

If I connect a pump discharge to the suction, fill it will water and seal then turn on the pump does the pressure in the pipe rise or does the temperature just go up.

If the pressure rises due to the pump head them where does it stop?

 

[hydtools]

The pump generates just enough pressure differential to make the water flow. The temperature will rise too since there is no dissapation of the heat generated by the flow losses.

Ted

 

[BigInch]

1) There is a minimum pressure in a closed system corresponding to the vapor pressure P_v of the fluid, which corresponds to the fluid's temperature.

2) The pressure in the system will vary from P_v at suction, to P_v plus whatever the pressure equivalent is of the differential head being produced by the pump at any given time corresponding to its instantaneous flowrate (see pump curve), at the pump's discharge.

3) Continued heat input will warm the fluid, raising its temperature, causing the vapor pressure to raise, and in turn, the pressure at all points in the loop will also rise.... goto item #1.

 

[BigInch]

Note: The minimum pressure is P_v. The minimum pressure in the system could be increased above P_v by adding any amount of surcharge pressure over that.

 

[NGLENGR]

In that case, there's only so much hydraulic resistance in the circuit so you'll be running an extremely high flow rate. The pump will heat due to the loss of efficiency because of that high rate of flow.

BigInch's post details the fun unbounded heat rise until failure results!

We have a circuit which pumps liquid ethane into a pipeline. On this circuit is a minimum flow/maximum pressure controlling spillback, which goes to an accumulator on the suction of the pump.

If the pipeline shuts in, the recycle takes over, and we can see our pumpage temperatures rise quite quickly. There's no way to cool the pumpage, and there is only minor hydraulic loss in the system. Eventually, the ethane reaches a near vapor condition and the pumps vapor lock.

Of course, ethane is a different animal than water, but it still illustrates how fun recycle systems can be!

 

[BigInch]

Same - same, but different.