Airside heat transfer and pressure loss characteristics of bare and finned tube heat exchangers used for aero engine cooling considering variable air properties

•The paper deals with bare and finned tube heat exchangers used for aero-engine cooling.•The exchanger airside performance is predicted with consideration of air property variability.•Ignorance of air property variability causes overestimation of heat transfer and pressure loss.•Both overall and local heat transfer and pressure drop characteristics are provided.•The plain finned tube heat exchanger is superior to the bare tube bank heat exchanger.

Numerical studies have been conducted to investigate the airside thermal-hydraulic characteristics of bare tube bank and plain finned tube heat exchangers intended for use in aero-engine cooling. The exchangers use small diameter tubes (3.0 mm) with compact tube layout and operate at high temperatures with large temperature changes over the exchanger depth. Calculations are performed for frontal air velocities between 5 and 20 m/s, yielding tube diameter based Reynolds numbers from 4898 to 19,592. Calculations are implemented using the Realizable k-ɛ turbulence model with consideration of the air physical property variations caused by the air temperature changes. The results show that ignorance of the air property variability leads to overestimations of both heat transfer and pressure loss, with a smaller air velocity yielding a more serious overestimation. The numerical fin efficiency agrees with the Schmidt fin efficiency within 7.0%. The plain finned tube heat exchanger is superior to the bare tube bank heat exchanger if the exchanger performance is evaluated using the heat transfer rate to pressure drop ratio.