The aim of this study was to provide a characterization of non-symmetrical operation in two counter-flow primary surface exhaust gas recuperators installed in parallel flow loops. The hybrid system emulator test rig and facility designed and operated by the Department of Energy, National Energy Technology Laboratory located at the West Virginia (USA) campus was used for the study. Various tests from the past years often resulted in non-symmetrical operation, indicated by significantly variant temperature measurements at the outlets of the recuperators. Some specific tests have been carried out in order to identify the possible cause of this flow unbalance. The isolated effects of bleed air, cold air and hot air valve on the heat exchangers flow unbalance have been studied. Also, the impact of load bank changes on flow distribution has been considered in this study. Each test has been carried out in close loop fuel valve speed control. The influence of each independent variable in the study on parallel recuperator flow distribution has been quantitatively characterized using temperatures and a heat balance. Both the bleed and the cold air compressor bypass valves showed an appreciable impact on the heat exchangers flow unbalance, while hot air valve and load bank changes had minimal effect.
