Numerical simulation and experimental setup of a multiphase pump application

The topic of this paper is the numerical simulation of a newly developed medium consistency (MC) pulp pump. Pulp of medium consistency (MC) is a three-phase fluid including dissolved and unresolved air, fibres as solid matter and water as the liquid phase. The fluid – although quite highly consistent as compared to normal liquid pumping – may easily provoke blockage effects as the water-fibre mixture can be modeled as Bingham fluid. The paper describes a new way of efficient and reliable stock pumping in modern fibre lines without vacuum pumps – and thus claims to change the rules for MC-pumping by setting new standards for efficiency, maintenance and usability for medium-consistency pulps up to 14 %. Conventional process pumps are not able to pump such solid non-newtonian multiphase fluids with air. In parallel to the test rig development, a complete CFD- model of the pump was generated in order to investigate different effects of the geometry – variations – and to get an impression of the pump’s interior processing this multiphase flow. A RANS-calculation (Reynolds Averaged Navier Stokes) gives detailed information on the degassing process, the fluidization of the pulp into the stand pipe and the efficiency improvement potential for the whole pump configuration. A pulp model being integrated as beta function into the commercial CFD-code, modified pure substances and the above-mentioned Bingham medium were used as fluid models for the solid-liquid components in multiphase calculations with air as a third phase. At the same time, a MC-pump test rig equipped with online air content and other measurement systems was used to carry out a series of more than 1000 test runs for the experimental part of the development process. Thus, systematic variations of different elements were verified.