Experimental study on friction factor and numerical simulation on flow and heat transfer in an alternating elliptical axis tube

This paper focuses on the experimental study on friction factor and the numerical simulation on the periodic fully developed fluid flow and heat transfer in an alternating elliptical axis tube (AEAT). The experimental results show that in the laminar flow regime fRe = 84.7, and the transition from laminar to turbulent flow occurs at an earlier Reynolds number about 1000. The predicted cycle average Nusselt numbers from the standard k-ε model and RNG k-ε model are quite close to each other, which are appreciably higher than that of elliptic tube and round tube. Heat transfer performance comparisons are made under identical pumping power constraint, showing the obvious superiority of AEAT over a round tubes. In addition, the complicated multi-longitudinal vortex structure of the flow is detected in detail from the numerical simulation results, which improves the synergy between velocity field and temperature gradient in a large extent, hence, greatly enhancing the convective heat transfer.