Effects of viscosity on the performance of Hydraulic Power Recovery Turbines (HPRTs) by the means of Computational Fluid Dynamics (CFD) simulations

Centrifugal pumps are used for increasing the energy content of a liquid: this technology is used in chemical processes with liquids having specific chemical and physical characteristics. Most of the processes are closed-loop, meaning that the liquid is reused after a proper physical or chemical washing treatment is performed. Therefore, the pressure of the liquid has to be decreased by means of a lamination valve or a Hydraulic Power Recovery Turbine (HPRT) with the advantage of recovering energy. HPRTs are generally tested in both pump and turbine modes using water as working fluid. The technical report ISO/TR 17766 indicates the procedure to evaluate the performance of centrifugal pumps handling viscous liquids by supplying correction factors with respect to water, but no indications are given in turbine mode. This work provides correction factors able to evaluate also the performance of HPRTs handling viscous fluids in turbine mode by varying the proposed formulae in the technical report. Computational Fluid Dynamics (CFD) simulations of two tested HPRTs are performed using, at first, water as working fluid for validating the experimental results and, subsequently, the SELEXOL® solvent. Results show that the original correction factors are still valid for the HPRT B that has a parameter B, which is the main one to be involved in the evaluation of the correction factors, lower than 1. A better accuracy, instead, is achieved by modifying the correction factors of the HPRT A, having a value of B higher than 1.