Comparative thermodynamic and frictional characteristics of supercritical LNG in a PCHE with teardrop dimples and protrusions under single and coupled rolling-heaving ocean motions

Efficient supercritical LNG heat transfer in PCHEs is crucial for main LNG gasifiers operating under dynamic ocean conditions, where the complex influence of multi-degree-of-freedom motions is often overlooked. This study investigates how single-degree-of-freedom (rolling/heaving) and coupled multi-degree-of-freedom ocean motions affect the transient thermal characteristics, flow resistance, and turbulence in a PCHE with teardrop dimples and protrusions, aiming to identify optimal designs under these dynamic conditions. Teardrop dimples and protrusions were integrated into a PCHE model, with non-inertial forces from ocean motions incorporated into the Navier-Stokes equations for transient thermal-hydraulic simulations. Analysis focused on heat transfer, Fanning friction, and turbulence energy spectrum, along with comprehensive performance criteria and entropy generation. Coupled motion induces more rapid metric variations and a higher Reynolds positive stress energy spectrum than single motions. Teardrop dimples consistently yield higher time-averaged comprehensive performance (e.g., 1.056 rolling) than protrusions (e.g., 1.024 rolling), exhibiting higher heat transfer entropy generation but lower viscous dissipation entropy generation. Within dimples, shorter periods and larger angles increase turbulence intensity, flow resistance, and the energy spectrum. This comprehensive analysis demonstrates the significant impact of coupled ocean motion on PCHE performance and turbulence, confirming the superior performance of teardrop dimples over protrusions under dynamic conditions.