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Corrugation parameter design seeks to maximize the thermal-hydraulic comprehensive performance (THCP) of corrugated tubes as much as possible. Among them, composite corrugations composed of simple corrugations are proposed to strengthen the THCP of corrugated pipes. However, the rule and mechanism regarding the impact of composite corrugations on the THCP of corrugated tubes, particularly when those composite corrugations are composed of simple asymmetric corrugations, are not well understood. Therefore, in this work, the effect of composite corrugations consisting of two simple droplet-shaped corrugations on THCP is assessed numerically, where the first composite corrugation is concave-convex (CTCC1) and the second composite corrugation is concave-concave (CTCC2). In addition, the effect of traditional corrugation (CTSC) on THCP is also examined to further highlight the advantages of composite corrugation in enhancing the THCP of corrugated tubes. The results of the study indicated a 49 %, 55 %, and 61 % increase in THCP at a Reynolds number (Re) of 5000 for CTSC , CTCC1 , and CTCC2 , respectively, compared to a smooth tube, indicating that the combination of composite corrugations in CTCC2 is superior to that in CTCC1. In addition, a smaller corrugation width on the upstream side of CTCC2 is more conducive to enhancing THCP. Furthermore, it should be ensured that the corrugation depth on the upstream side of CTCC2 is not greater than the depth on the downstream side to achieve better THCP. The work confirms the advantages of composite corrugations over traditional corrugations in enhancing THCP and guides the selection of composite corrugation combination forms and the design of composite corrugation width and depth distribution. [ABSTRACT FROM AUTHOR]

[Display omitted] • A Tube-to-Tube sliding wear test rig is developed. • Sliding wear volume of Inconel 690 tube increases with increasing cycle number. • Sliding wear volume of Inconel 690 tube is larger under larger contact force. • Wear volume is smaller under lubrication of water, especially at beginning. • Water reduces oxidative wear due to lower oxygen concentration. A Tube-to-Tube sliding wear test rig was developed in the current work. The reciprocating sliding wear behaviors on Inconel 690 heat transfer tubes were experimentally studied under various conditions. The sliding amplitude and frequency have little influence on wear, and the wear volume is in general positively proportional to the sliding cycle number and the contact force. Therefore, the Archard wear equation can be adopted to calculate the macroscale wear volume of the heat transfer tubes. Based on the results obtained by optical microscopy and scanning electron microscopy, the main wear mechanisms of the tube are the adhesive wear, abrasive wear and oxidative wear. Under the water environment, the wear rate is evidently lower than that of the dry condition and the wear mechanisms were not altered. [ABSTRACT FROM AUTHOR]