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To describe the performance as well as the thermodynamic behaviour of a multiphase screw pump, also operating at very high gas volume fractions up to 100 %, a new thermo- and fluid dynamic model was developed. The model, which will be presented in this paper, takes the time-dependent gas-liquid heat transfer, the compressibility and acceleration effects of the multiphase gap flow as well as the possibility of critical flow conditions into account. For the simulation of the mutual phase heat transfer, the solution of the gap flow conservation equations and the optimisation of the gap inflow velocity, different numerical techniques were used. The model as such gives important information of the pressure and the temperature distribution, the multiphase leakage flows through the chamber connecting gaps as well as the effective flow rate or the volumetric efficiency of the pump near the conveyance break-off at very high gas volume fractions.

The multiphase application of screw pumps, especially at high pressures and gas volume fractions implicates thermal loads for the solid components of the pump. For the evaluation of these loads and their consequences, a finite volume heat transfer model for the screws, as the main parts of a screw pump, was developed to describe and simulate the transient and 3-dimensional heat transfer process. The time-dependent heat transfer is mainly influenced by convection and thus by the rotational speed of the screws and by the tempera-ture distribution of the multiphase fluid along the screw surface.