flow of liquids through tubing 1

I am using a computer based model to calculate pressure drops along a tubing line. Sometimes when the input pressure is high and the flow rate is high, I get a negative outlet pressure from my model. That does not make much sense to me. I have checked all the equations (these are simple fluid flow, Re, friction equations that one learns in sophmore fluid flow classes. All seem to be ok. What does it mean when I get a negative outlet pressure? My interpretation is that friction is so high that I cannot get the flowrate I think I am getting and that no flow will occur at the inlet pressure I am pumping.

 

[ghillis]

Your (desired) flow rate cannot be reached using the tubing size you have selected. Try inputing the inlet and outlet pressures and see what the flow rate is. [sig][/sig]

 

[Imagineer]

If you have more than one outlet and the proper conditions, one of them may become a venturi suction. [sig]<p> Imagineer<br><a href=mailto: > </a><br><a href= > </a><br> [/sig]