Modelling phase change in a novel turbo expander for application to heat pumps and refrigeration cycles

Abstract

A novel turbo expander based on the Tesla turbine is proposed to be applied to a heat pump or refrigeration cycle to improve the overall cycle efficiency. Initial numerical modelling of this turbo expander at representative conditions was carried out using the homogeneous relaxation model (HRM) to assess the influence of phase change on performance. The presence of a dense cloud of liquid droplets within the rotor was predicted to produce a significant back pressure on the turbine nozzle postponing the phase change. This was expected to occur in the vicinity at the outlet of the nozzle, but high volume fractions of liquid was predicted to penetrate deeper inside the rotor, especially at higher RPM. The resulting lower velocities of the liquid flow at the inlet of the rotor was predicted to significantly degrades the performance of the turbine. It is thus important for a successful implementation of this concept to remove as much liquid droplets as possible before the flow enters the rotor in order to minimise the back pressure.

Numerical assessment of a two-phase Tesla turbine: Parametric analysis

“…Engelbrecht et al investigated the phase change itself based on a CFD simulation using a homogeneous relaxation mode of ANSYS CFX, in which a high number of computational nodes is exploited [27]. A preliminary investigation on the effect of the gap on the turbine output torque was also performed by Papagianni et al [28].…”