14th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Heat Transfer & Cooling
In numerous turbomachinery applications, e.g., in aero-engines with regenerators for improving specific fuel consumption, heat exchangers with low pressure loss are required. Pillow-plate heat exchangers (PPHE) are a novel exchanger type based on a wavy pillow-like plate geometry. They represent promising candidates for high-speed flow applications due to their smooth profiles avoiding blunt obstacles in the flow path. So far, PPHE have been successfully employed for essentially incompressible flows, but very little is known regarding their high-speed flow characteristics.In this work, high-speed flow phenomena in pillow-plate channels were analyzed experimentally, and the outcome of this analysis was compared with recently published numerical and theoretical results. The pillow-plate channel was placed in the test section of a blow-down wind tunnel working with dry air, and the resulting gas dynamics was investigated by means of conventional and focusing schlieren optics; in addition, static and total pressure measurements and surface oil flow visualizations were performed. The focusing schlieren optics was able to resolve in detail the three-dimensional shock structure in the channel. The experiments confirmed the theoretical prediction that the high-speed flow in pillow-plate channels can be described as Fanno-flow. Since only wavy walls with smooth profiles were involved, linearized gas dynamics was able to cover important flow features within the channel. The efffects of the wavy wall structures on pressure drop and Mach number distribution within the flow path were investigated in detail, and a good agreement with theoretical and numerical predictions was found. The present analysis demonstrates that pressure-losses in pillow-plate heat exchangers are rather small although efficient mixing processes occur. Thus, this type of high-speed heat exchangers offers a great potential for future turbomachinery applications.