Thermal and Hydraulic Performance of Enhanced Rectangular Tubes for Compact Heat Exchangers
The thermal and hydraulic performance of rib-roughened, dimpled and offset strip fin tubes has been investigated experimentally. Results from measurements on commercially manufactured tubes have shown that rib-roughened tubes have best potential for heat transfer enhancement with moderate pressure drop increase. Therefore, the performance of various rib-roughness geometries have been further investigated including flow visualization and LDV measurements of the flow fields in the tubes. Parallel ribs, V-shaped ribs and multiple V-shaped ribs (Swirl Flow Tube) were considered as roughness geometries in rectangular tubes of aspect ratio 1 to 8. It has been found that the Swirl Flow Tube provides the highest heat transfer enhancement for Reynolds numbers from 1 000 to 2 000, while V-shaped ribs pointing against the flow direction provide the highest heat transfer enhancement for Reynolds numbers from 4 000 to 15 000.
Correlations of j and f factors for the Swirl Flow Tube have been determined taking into account the influence of Reynolds number, rib height, rib pitch and rib angle. It was found that a rib angle of 45° provide the highest j/f ratio, while increasing the rib height or decreasing the rib pitch lowers the j/f ratio.
From measurements on a fullscale radiator, it has been found that the j and f factors obtained for air flow in single tubes can be used to predict the pressure drop and heat transfer on the liquid side of radiators with good accuracy.
The thesis also includes a paper on the influence of tube diameter on pressure drop characteristics and a paper on simulation of the flow in a smooth rectangular duct using a linear and a non-linear k-.epsilon. model.
enhanced heat transfer