Buoyancy Effect on Developing Turbulent Flow and Heat Transfer in a Helical Pipe with Finite Pitch
by
M.A. Ebadian
Florida International University - Hemispheric Center for Environmental Technology
Coauthors: B. Zheng, Ph.D. (Florida International University - Hemispheric Center for Environmental Technology), C.X. Lin, Ph.D. (Florida International University - Hemispheric Center for Environmental Technology)

This paper describes a fully elliptic numerical study performed to investigate the buoyancy-affected, three-dimensional turbulent flow and heat transfer in a helical pipe with uniform wall temperature. The renormalization group (RNG) k~e model was used to simulate the turbulent flow and heat transfer in the pipe. The emphasis of this analysis was focused on the interactive effect of centrifugal force and buoyancy force on the mixed convective turbulent flow and heat transfer. The governing equations were solved by a control volume method with second-order accuracy. Assuming that the fluid entered the pipe with a uniform temperature and velocity profile, the wall was kept at constant temperature, and the flow and thermal boundary layers developed simultaneously downstream in the helical pipe. The O-type non-uniform structure grid system was adopted to discretize the computation domain.

The working fluid in this study (saturated water) was considered as incompressible fluid. With the exception of density, all physics properties were set to constant. The Bossinesq approximation was applied to deal with the buoyancy effect caused directly by density difference. The numerical results revealed turbulent flow and heat transfer characteristics in a helical pipe. The developments of streamwise velocity and temperature distribution visualized by contours, and local friction and Nusselt numbers at different sreamwise positions, were given to demonstrate the developments of mixed turbulent flow and temperature fields in the helical pipe. The developments of peripherally averaged friction factors and Nusselt numbers were given to reveal the effect of Groshof numbers on the developments of mixed turbulent flow and heat transfer in a helical pipe.

The computed results revealed that the buoyancy force affected flow and temperature fields more with increasing Groshof numbers; the local friction factors and Nusselt numbers were also affected significantly by buoyancy force. The peripherally averaged friction factor and Nusselt number exhibited an oscillatory behavior in the entrance region of the helical pipe. In addition, the buoyancy effect on the average Nusselt number and friction factor was greater at the entrance region of the helical pipe, but it gradually became weaker further downstream.

Date received: July 30, 1999