Fluid film characteristics over horizontal multi-faceted tube and the augmentation of thermal performance

A two-dimensional numerical model of a multi-faceted tube is established to investigate fluid film's kinematics and thermal performance on various surface geometries on the same fluid film path. Such surface condition is commonly encountered inside cooling tower fill. The model was solved using the volume of fluid method while the spatial discretization of volume fraction through the compressive method. The results show that the vertical flat and tilted flat surface components contribute most of the thermal performance augmentation with signifi-cantly higher fluid film thickness than the circular tube. The film thickness is uniquely characterized by the wall shear stress and the fluid average velocity, V-avg. The maximum fluid film thickness is produced on the leading edge of the tilted flat surface where the wall shear stress decreases due to flow separation that reduces the time rate of strain, dV/d (y) over bar . The highest dV/d (y) over bar is located on the vertical flat surface where the maximum wall shear stress is produced at the trailing edge capitalizing on gravity force. The multi-faceted tube also performs rela-tively better than the equivalent circular tube, producing a higher heat transfer coefficient and Nusselt number.

Automated summary

The study found that the vertical flat and tilted flat components on the surface of the multi-faceted tube contribute the most to the enhancement of thermal performance, with significantly higher fluid film thickness than a circular tube. The thickness of the fluid film is uniquely characterized by wall shear stress and fluid average velocity.