Discharge coefficient behaviour in presence of four perforated plates flow conditioners - Numerical investigation Part 1 -

Abstract

This paper present a part 1 of numerical experimentation of the behaviour of the discharge coefficient and the effect of four perforated plates flow conditioners on the discharge coefficient for flow measurement accuracy. Three of the plates are described by the Standard ISO5167 and the fourth one is proposed for study. In this part 1, the disturber used is 90° double bend in perpendicular planes while in the part 2 the flow is subject to disturbers namely 30% and 50% closed valves. The turbulent flow is examined in conduit with an inner diameter of D=100mm. The diameter of orifice meters are respectively d=50, 60, 70 and 75mm which done for β=d/D respectively the values of 0.5, 0.6, 0.7 and 0.75. The orifice meters are located in conduit at different stations z/D downstream the disturber. The flow is examined with air at Reynolds number Re=2.5x105 . The software used for this simulation is ANSYS package with k-e like turbulence model. A numerical investigation was done before (CIM 2013) with the same conditions but without perforated plates and the results showed that when the diameter of the orifice meter increases the shifts deviation of the discharge coefficient increases this causes a great error in flow measurement. Contrary, when the diameter of the orifice meter decreases the shifts deviation in the discharge coefficient decreases and the error in flow measurement is reduced. These results are the same with the two disturbers 90° double bend and 50% closed valve used separately in conduit. In this paper the results showed that the perforated plates have significantly reduced the error on the discharge coefficient. Indeed, the errors recorded downstream disturbers are superior to 2%. Downstream the perforated plates used separately the errors on the discharge coefficient are reduced to a value inferior to 1% for the four plates. It is noted that the standards ISO5167 and AGA3 stipulate that the error on the discharge coefficient Cd must be less than ±0.5% for better flow measurement accuracy. By comparing our results with this condition we found that the results obtained with the four plates are substantially reduced especially downstream station z=25D (z=20.5D downstream flow conditioners). However the fourth proposed plate with its high porosity produces less losses pressures than those of the other three plates. This is good condition of exploitation for some installation where high losses pressures are not tolerated.