Airside heat transfer analysis using Wilson plot method of three analogous serpentine tube heat exchangers for aero-engine cooling

This research investigates the design, manufacture and heat transfer characteristics evaluation of three types of heat exchangers (HXs) serving for modern aero-engines. In the field of heat transfer system, previous research has concentrated on large-diameter tubes, whereas estimation for heat transfer in small-diameter tubes commonly relies on correction factors. However, small-diameter heat exchangers offer extensive prospects for incorporation into aero-engines utilizing cooled cooling air (CCA) technology, benefiting from their high heat transfer efficiency and lightweight. Hence, directly investigating compact small-diameter HXs is of crucial significance. In this paper, three analogous serpentine tube bundle HXs with different tube diameters (OD: 2.2/1.8/1.4 mm with 0.2 mm thickness) were designed by logarithmic mean temperature difference method (LMTD). A series of comparative experiments were conducted to explore the effects of the tube diameter and flow rates on heat transfer under different fuel flow conditions. The results indicate that in the case of turbulent fuel flow, decreasing the tube diameter assists in enhancing total heat transfer, whereas the trend is opposite in laminar fuel flow. In addition, during turbulent fuel flow, heat transfer rises with the increase of flow rates on both sides, while variations in air flow rate have minimal impact on heat transfer in laminar fuel flow. Finally, the calculated heat transfer rate exceeds the experimental measured value by no more than 15 %, with this deviation escalating as the reduction of tube diameter. Subsequently, an airside Nu-Re relationship suitable for small-diameter HXs is fitted based on experimental data, with 94.1 % of the data points fall within the 5 % error band, providing guidance for the design and validation of aero-engine HXs in future.