Pressure loss through a straight pipe
 

I have a straight pipe of 0.43" ID. I am trying to determine the pressure loss through a straight pipe of 1 m. I only know the Inlet pressure. I do not know the flow rate or the inlet velocity. I set my gauge pressure/Inlet pressure to 800 Psi. What should my outlet condition be? I tried setting it to outflow but I am getting reversed flow. What is a better boundary condition at the outlet?

Keep it as pressure outlet. Fluent will calculate the pressure at outlet.

There's not enough info.

Knowing only the inlet pressure and pipe length doesn't define the problem. Any mass-flow rate, any pipe length, will satisfy this constraint.