[en] Numerical work is performed to study the effect of air inlet angle on heat transfer coefficient and pressure drop of the plate-fin heat exchangers. Two special air inlet angles which are in the horizontal plane and in the longitudinal plane are simulated on 7 fin channel meshes with different fin parameters. The numerical results show that the different flow fields of the two special air inlet angles cause different effects on heat transfer coefficient and pressure drop. When the air inlet angle is in the horizontal plane, the air inlet angle effect is strongly related with the entrance region flow flied. When the air inlet angle is in the longitudinal plane, the air inlet angle effect is related with the whole fin channel flow field because the vortex size is much larger and comparable to the fin length. The effects of the two angles have different variation laws, which are greatly influenced by fin parameters. Finally, a prediction model is established to calculate the heat transfer coefficient and pressure drop of an arbitrary inlet angle. The comparison of prediction results and simulation results for 5 air inlet angles shows good agreement. The maximum prediction error is within 10%. - Graphical abstract: Three-dimensional simulations are performed to investigate the effect of air inlet angle on heat transfer coefficient and pressure drop. Two special air inlet angles which are in the horizontal plane and in the longitudinal plane are studied first. When the air inlet angle is in the horizontal plane, the air inlet angle effect is mainly in the entrance region and strongly related with the flow flied. When the air inlet angle is in the longitudinal plane, the air inlet angle effect is related with the whole fin channel flow field because the vortex length is much larger. The heat transfer coefficient increases with the air inlet angle increasing, while the total pressure drop increase is much larger than heat transfer. The increase ratios are defined to describe the effect of air inlet angle on heat transfer and pressure drop. The variation laws are obtained from the simulation data of different fin parameters. The flow fields on the cross sections show that it is applicable to assume that the effect of the air inlet angle (both α and β are nonzero) can be regarded as a combination of the effects in the two special cases (α ≠ 0, β = 0, and α = 0, β ≠ 0). Thus prediction model is established to predict the heat transfer coefficient and pressure drop when both the horizontal angle α and the longitudinal angle β are nonzero. The comparison of prediction results and simulation results for 5 pairs of α and β shows good agreement. The maximum error is less than 10%. - Highlights: • Heat transfer coefficient and pressure drop increase as inlet angle increasing. • The pressure drop increases much larger than heat transfer coefficient. • The effects of inlet angles in horizontal and longitudinal plane are different. • Increase ratios are defined to compare the effects of different fin parameters. • The prediction model agrees well with the simulation results.