Enhancement of air-side heat transfer in crossflow heat exchangers using auto-fluttering reeds

Thin film aeroelastically fluttering reeds are investigated as a mechanism to enhance air-side heat transfer in an industry relevant crossflow heat exchanger that can reject over 10 kW of heat. Nusselt number and friction factor measurements are made in a temperature- and humidity- controlled wind tunnel over a range of air inlet temperatures and flow rates spanning an air-side Reynolds number range of 800 < Re < 6000 without the reeds and 1200 < Re < 3400 with the reeds installed in the heat exchanger fin channels. Experiments are conducted with a set of 1440, 50.8-mm long, 15.9-mm wide, rectangular Mylar reeds installed in the heat exchanger fin channels. The fluttering reeds enhanced heat transfer by up to 60% with a maximum friction factor penalty of 200%. Two different reed thicknesses are investigated, 0.013 mm and 0.025 mm. Increasing the reed thickness yielded similar heat transfer performance while decreasing the friction factor penalty, indicating that it may be possible to decrease the pressure drop penalty through geometric optimization. Correlations for the reed Strouhal number and the reed-enhanced Nusselt number and friction factor are developed as a function of relevant dimensionless parameters.