Experimental Investigation On Flow And Heat Transfer Characteristics In Abnormal-shaped Mini-and Micro-channels And A Tube Bundle Air-Precooler

Compact mini-and micro-channel air-precooler is the core component of the precooled combined cycle engine,the structural design of which is of significant importance.The abnormal shape of mini-channel is potential to have the heat transfer enhanced.In the present study,the characteristics of flow and heat transfer in abnormal-shaped mini-channels and a tube bundle air-precooler are experimentally investigated.This research can provide theoretical support and data for the optimization design of the precooled heat exchanger structure.An experimental system for multi-phase flow heat transfer in mini-/micro-channels is fabricated.First,the single-phase flow and heat transfer characteristics in a twisted abnormal-shaped mini-channel with high aspect ratios are experimentally investigated.The twisted shape of the channel is found to lead to the increase of the single-phase pressure drop of the channel and the occurrence of laminar-turbulent transition at lower Reynolds number.Besides,the correlations of the single-phase flow friction factor and average nusselt number are developed.Second,the pressure drop characteristics of two-phase flow in abnormal-shaped mini-channels are studied.The twisted shape of the channel leads to the increase of the two-phase average pressure drop at higher mass fluxes.Low-frequency high-amplitude fluctuation and high-frequency low-amplitude fluctuations are indentified.The effects of different flow parameters on the flow boiling heat transfer characteristics are analyzed.The twisted shape of the channel is demonstrated to enhance the two-phase heat transfer capability.A new flow boiling heat transfer coefficient correlation is developed for the twisted abnormal-shaped mini-channel.An abnormal-shaped mini-channel bundle heat exchanger with high aspect ratio is designed and fabricated based on the 3D printing technology.The air precooled experiments are preformed under different working conditions and the heat transfer characteristics of the heat exchanger are analyzed.