CFD Analysis of Flow through Single and Multi Stage Eccentric Orifice Plate Assemblies

Abstract

Multistage orifice plate assemblies are used as pressure reduction devices in many industrial applications. They have the advantage in the sense that, they are more compact, less noisy and have no moving parts. As compared to valves, higher pressure reductions can be obtained by these devices without chocking. The design of such devices at present is based on empirical correlations derived from experience. It is usual to assume a constant discharge coefficient for all stages during the initial design. In the present work, CFD has been used to analyze the flow through multistage eccentric orifice plate assemblies and thus make the design procedure more accurate. The commercially available software package ANSYS FLUENT is used for the flow analysis. The fluid is assumed to be incompressible and Newtonian as well as flow is assumed to be steady and three dimensional. The CFD methodology has been validated by analyzing the flow through a standard concentric orifice plate assembly having diameter ratio of 0.5. The computed values of discharge coefficient and permanent pressure loss coefficient are in excellent agreement with the values given in ISO-5167 standard. The validated methodology is used for the analysis of flow through eccentric orifice plate. Computations have been made for wide range of parameters like Reynolds number (1 to 106), diameter ratio (0.25 to 0.8). The computed values of discharge coefficient and permanent pressure loss coefficient agreed very well with the values given in BS-1042. CFD analysis has also been carried out for multistage orifice plate assemblies, number of stages considered are 2, 3, 5 and 7. Each stage consisted of eccentric orifice plate having same diameter ratio with successive stages being staggered. The spacing between the stages (X/D) is varied from 0.5, 1, 2, 3, 4 and 5. Analyses have been made with two diameter ratios namely 0.3 and 0.5, Reynolds number is fixed as 105. Discharge coefficient of each stage and overall permanent pressure reduction, permanent pressure loss have been computed. Conclusions on the optimum spacing, value of discharge coefficient as well as pressure reduction ratio have been drawn based on the CFD analysis.