Influence of two-phase flow on the performances of thermogravimetric heat pumps

A non-conventional heat pump, the so-called Thermogravimetric Heat Pump TGHP, fundamentally based on an isothermal compression of a gas-liquid two-phase flow is analysed. The operating fluid couple consists of a carrier fluid constantly in liquid phase and of a working fluid that undergoes a thermodynamic cycle with a phase transition. Thermodynamic aspect of a TGHP is definitely more convenient compared to a conventional compression HP; conversely, the partial evaporation of carrier fluid and fluid dynamic dissipative effects reduce the thermodynamic benefit and such reduction can amount up to few percent even if homogeneous model is considered. The prevision of the energetic performances of TGHP is rather critical in that no correlation of void fraction are at present available for large duct diameters and for the range of gas fractions of volume flow typical of thermogravimetric heat pumps. In the present paper, the impact on TGHP performances due to uncertainties ensuing from different types of extrapolations regarding some experimental tests have been considered.