fluid mechanics in liquid nitrogen vessel
I am attempting to use differential pressure to measure the level within a small cryogenic container which automatically fills and maintains it's own preset pressure. There is an inlet for liquid nitrogen to enter the vessel, as well as a vent gas exit orifice. When the system is static, the measurement works well, even though the differential measurement is quite small. I am only dealing with approximately 10 inches of LN2. The problem is that when the system vents, or fills, the differential readings become unreliable. Since my automation system is dependent upon this measurement system, I have a situation which can result in an overfill condition. I have tried pressure snubbers in the differential sensor location, with no significant improvement. I believe that the velocity of the fluid moving through either path is creating a small siphon pressure at the sensor which, due to the fact that the total pressure being compared is so slight, is causing major fluctuation in my level measurement. Could someone please offer advice on dynamic systems and differential pressure. I fully understand that in this case, diff. pressure is not the ideal method of level measurement, but I am not in a position to totally rework the system at this time. I need a "patch" method for temporary fix. Any suggestions would be appreciated.