Performance evaluation of a micro partial admission impulse axial turbine in a combined ammonia-water cooling and electricity absorption cycle

Abstract

The integration of an expander in an absorption machine allows it to produce cooling and electricity simultaneously. This technology holds great promise for its ability to harness low-temperature heat sources more efficiently than production with separate cycles. The integration of a turbine is currently being studied in an experimental ammonia-water absorption chiller at CEA INES. Given the very small mass flow rate and enthalpy drop, a partial admission impulse axial turbine has been selected for the application. Due to lack of experimental data, a 3D model of the impulse turbine was generated and its functioning studied with CFD simulations using pure ammonia. A compressible real gas 1D model of the turbine was later developed in EES® for the ammonia-water mixture and compared to CFD simulation, adjusting loss term parameters to match CFD results, thus achieving an average discrepancy below 7% in the considered range of operating conditions (inlet pressure 14-10 bar, outlet pressure 5 bar, inlet temperature 120 °C and rotational speed of 10–100 thousand RPM). The tuned 1D expander model was then integrated in a previously developed 0D model of the absorption cycle to demonstrate its robustness and potential to be used in the study of complex combined cycles. An overall energy efficiency is introduced and used to map the performance of the cycle for changing operating conditions. Results show the potential of the combined cycle to produce both power and cooling even at small scale, highlighting at the same time, the constraints imposed by this type of expander on the combined cycle.