SUMMARY

Air-coupled heat exchangers are widely employed in a variety of engineering applications, including power generation, electronics cooling, air-conditioning, refrigeration, and the automotive, and chemical process industries. Air has poor transport properties, resulting in low air-side heat transfer coefficients and large heat exchanger surface areas. The air side typically presents that governing thermal resistance; therefore, there is a significant need to develop strategies to enhance the air-side heat transfer performance while minimizing parasitic power requirements. The proposed study investigates the enhancement of air-side heat transfer using auto-fluttering reeds between the air-side fins.

A review of the literature on the enhancement of air-coupled crossflow heat exchangers is conducted. Aeroelastically fluttering thin reeds installed inside the fin channels of crossflow air-coupled heat exchangers passively oscillate as the air flows through the heat exchanger, generating vortical structures that disrupt the thermal boundary layer and improve mixing. Heat transfer enhancement and pressure drop penalties due to the use of such auto-fluttering reeds will be investigated in representative heat exchanger geometries. Heat transfer and pressure drop experiments are conducted with and without reed enhancement over a wide range of channel Reynolds numbers under uniform and maldistributed air flow conditions in a temperature- and humidity- controlled wind tunnel facility. Based on these experimental results, a model will be developed to predict the heat transfer and pressure drop for reed-enhanced heat exchangers under different air flow conditions. Insights from these experiments and analyses will guide the future development of more compact air-coupled heat exchangers using this enhancement technique.