A comparative analysis between small-scale recuperated parallel-flow Brayton cycles

Abstract

Parallel-flow Brayton cycles developed from commercial turbochargers can present feasibility for providing electricity to regions with poor power infrastructure. To increase the thermal efficiency of these alternative gas turbine cycles, various recuperator geometries are investigated in this work together with three different power turbine split-off points. A novel intermediate-temperature turbine (ITT) layout, a recuperated low-temperature turbine (LTT) layout, and a recuperated high-temperature turbine (HTT) layout are considered. An analytical approach is followed to determine which configuration offers the best thermal efficiency improvement relative to unrecuperated parallel-flow LTT and HTT layouts. The recuperated LTT layout produces the lowest power outputs of the three cycles, over the simulated range of pressure ratios, but offers better thermal efficiency values at most compressor pressure ratios. At a pressure ratio of 1.5, the thermal efficiencies are quantified as 19.2%, 7.1%, and 5.1%, for the recuperated LTT, ITT, and recuperated HTT cycles, respectively. At a pressure ratio of 2.5, where the highest power outputs are obtained, these cycles produce thermal efficiencies of 9.8%, 10.1%, and 9%, respectively. It is recommended that the recuperated LTT layout should be further investigated for implementation due to its high thermal efficiency values at pressure ratios between 1.5 and 2.32.