Numerical and Experimental Study of Flow-Induced Vibrations in Micro-Tube Heat Exchangers

Thermal management presents an increasing challenge in future engineering systems, especially in applications like combined cycle precooling, waste heat recovery, and innovative propulsion systems. These systems face a growing demand for managing higher heat loads while coping with limited heat sink. Central to these thermal management systems is the heat exchanger, with microtube heat transfer emerging as a promising solution for future technologies. Microtube heat exchangers are becoming popular owing to their ability to significantly enhance the heat transfer surface area while maintaining a compact core volume. As the demand for high-performance, lightweight heat exchangers escalates, microtube heat exchangers are being designed to be increasingly compact yet highly loaded. This trend poses significant challenges to their structural integrity, particularly under harsh operational conditions. Flow-induced vibrations, a critical concern in the design of tubular heat exchangers, can lead to tube failures, compromising the safe operation of engineering systems. While the flow-induced vibrations of conventional-sized heat exchangers have been extensively studied, there is a noticeable gap in the research on similar phenomena in microtube heat exchangers. This paper details ongoing research at Reaction Engines Ltd (REL) to aid the design of safe and robust heat exchangers, focusing on the flow-induced vibrations in microtube heat exchangers and utilizing a cutting-edge laser vibrometry test facility. A predictive model, employing an unsteady flow simulation approach and eigenvalue analysis, has been formulated. A key observation is the distinctive coupled transverse-streamwise orbital motion in microtube heat exchangers, differing from the predominantly transverse direction of failures in conventional-sized heat exchangers.