Development of a Heat Exchanger for Low Pressure Ratio Gas Turbines with the Use of CFD Computations and Thermodynamic Cycle Analysis

Abstract

The performance optimization of energy systems is a field of increased research interest for reasons strongly related with economy and environmental sustainability. In this context, a significant amount of effort is provided in the direction of gas turbines performance enhancement targeting the reduction of fuel consumption and pollutants emissions. A significant contributor in this attempt can be found in the use of heat exchangers in recuperative gas turbine configurations which can exploit a significant part of the, otherwise wasted, hot-gas thermal energy content in order to preheat the compressor discharge air before the combustor, thus reducing fuel requirements and pollutants emissions. For the proper operation of the recuperative gas turbine, the integrated heat exchanger should be carefully designed in order to provide a favourable combination of sufficiently high thermal effectiveness with tolerable pressure losses. In addition, when gas turbines for propulsion applications are considered such as in the case of heli engines, heat exchanger weight and dimensions should also be taken into strong consideration. Such an effort is presented in the current work, where a heat exchanger for heli engine applications was designed and assessed. At the first part of this work, a detailed thermodynamic cycle analysis was performed on a low pressure ratio gas turbine configuration, suitable for heli engine applications, the operational conditions of which were based on open-literature available data. At the next stage, a tubular heat exchanger was designed taking into consideration geometrical constraints and heat exchanger operational conditions while for the heat exchanger sizing, literature based heat transfer correlations were applied. The heat exchanger performance was further assessed through the use of detailed computations on a CFD model of the integrated heat exchanger in the heli engine configuration, based on which the heat exchanger pressure loss and heat transfer characteristics were computed. At the final stage of the present work, the heat exchanger effect was assessed on a thermodynamic cycle analysis model of the recuperative heli engine, in which the previously derived heat exchanger performance characteristics were included. The analysis showed that the use of a heat exchanger can provide 10.6 % improvement regarding cycle thermal efficiency and 9.3 % fuel consumption reduction in the heli engine gas turbine configuration in relation to a non-recuperative heli engine of the same technological level showing the significant optimization potential of this technology targeting the achievement of more environmentally friendly and cost-efficient gas turbines for heli engines.