Heat transfer in a U-Bend pipe: Dean number versus Reynolds number

The performance of ground source and surface water heat pumps relies greatly on the heat transfer efficiency throughout the ground loop configuration. Typically these are vertical loops and consist of two pipes connected by a U-Bend at the bottom end. The U-Bend section generates vortical structures and turbulence, enhancing the heat transfer process. Two parameters that affect the flow turbulence and vortical structures are the Reynolds number and the Dean number. The isolated effects of the Reynolds and the Dean number are studied. It was found that while the Reynolds number has the greater effect on the average heat flux of the system; the Dean number's influence on the heat flux is greater in the curved section of the pipe. The large vortex structures can last for many diameters downstream of the U-Bend. For the high Reynolds number flow it was shown that increasing the Dean number significantly enhances the longevity of vortex structures. This indicates that enhancing the Dean number in an already turbulent flow will further augment the heat transfer process.