Applying heat pipes to a novel concept aero engine: Part 1 – Design of a heat-pipe heat exchanger for an intercooled aero engine

With the ever-increasing pressure for cleaner and more fuel efficient aero engines, gas turbine manufacturers are faced with a big challenge which they are bound to accept and act upon. The path from current high bypass ratio (BPR) engines to ultra high BPR engines via geared turbo fans will enable a significant reduction in SFC and CO 2 emissions. However, in order to reach the emission levels set by the advisory council for aeronautics research in Europe (ACARE), the introduction of more complex cycles that can operate at higher thermal efficiencies is required. Studies have shown that one possibility of achieving higher core efficiencies and hence lower SFC is through the use of an intercooled recuperated (ICR) core. The concept engine, expected to enter into service around 2020, will make use of a conventional fin plate heat exchangers (HEX) for the intercooler and a tube type HEX as the recuperator. Although the introduction of these two components promises a significant reduction in SFC levels, they will give also rise to higher engine complexity, pressure losses and additional weight. Thus, the performance of the engine relies not only on the behaviour of the usual gas turbine components, but will be heavily dependent on the two heat exchangers. This paper seeks to introduce a heat pipe heat exchanger (HPHEX) as alternative designs for the intercooler and the recuperator. The proposed HPHEX designs for application in an ICR aero engine take advantage of the convenience of the geometry of miniature heat pipes to provide a reduction in pressure losses and weight when compared to conventional HEX. The proposed HPHEX intercooler design eliminates any ducting to and from the intercooler, offering up to 32% reduction in hot pressure losses, 34% reduction in cold pressure losses and over 41% reduction in intercooler weight. On the other hand the proposed HPHEX recuperator design can offer 6% improvement in performance, while offering 36% reduction in cold pressure losses, up to 80% reduction in hot pressure losses and over 31% reduction in weight. An ICR using HPHEX for the intercooler and recueprator may offer up to 2·5% increase in net thrust, while still offering 3% reduction in SFC and up to 7·7% reduction in NO X severity parameter, when compared to the ICR using conventional HEX.