Numerical and analytical modeling of pressure drop through a geothermal two-phase orifice plate

Abstract

Measurement of the total mass flow rate of two-phase (steam and brine) geothermal fluid using sharp-edge orifice plates is gaining wide acceptance by the geothermal industry. Computational fluid dynamics (CFD) simulations using the ANSYS™ Fluent software were tested and validated with pressure drop data from the field experiments in Ulubelu, Sibayak, Lahendong and Bukit Daun geothermal fields, Indonesia. A mixture method was used to simulate the combination of steam and liquid in the geothermal flows. The selection of appropriate numerical methods is discussed in detail along with the results of the simulations including pressure, velocity and discharge coefficients. A new analytical correlation to predict the net pressure drop and mass flow rate is proposed and compared with the CFD models and the field test data. Good agreement has been observed between CFD predictions, the proposed correlation and the experimental data for net pressure drop across the orifice plate. This should help when sizing a suitable orifice plate at minimum pressure drop in future implementation.