An experimental study using the Laser Doppler Anemometery (LDA) has been carried out to investigate fully developed laminar Newtonian fluid flow inside a helicoidal pipe. A corresponding experimental setup was designed and built. In the test section made of helicoidal pipe, the curvature ratio of the centerline of the coil diameter to the pipe diameter, Dc/d, and the pitch ratio of the centerline of the coil diameter to the pitch of the coil, Dc/b, are 13.6 and 4.0, respectively. The experimental uncertainties of the current experimental system were evaluated. The uncertainties of velocity, the friction factor, the Reynolds number, and the Dean number were under 1.52%, 3.41%, 2.37% and 2.60%, respectively. The friction factor for the helicoidal pipe was measured in the present investigation. It was found that the flow remains laminar until Re ≈ 8,000, which is much higher than the critical Reynolds number for the straight pipe (Recr ≈ 2,500). In addition, the ratio of the friction factor of the current helicoidal pipe (fc) to the friction factor of the straight pipe (fs) was compared with the previous investigations, and a good agreement was obtained. Furthermore, the axial velocity distributions at two different cross-sections of a helicoidal pipe for different Reynolds numbers (1,800, 2,500 and 4,300, corresponding to Dean numbers, 480, 700 and 1,100, respectively) are measured and reported. Inspection of velocity contours, it is observed that the fully developed axial velocity profile shifts toward the outer wall of the helicoidal pipe as a result of the fluid flow in the helicoidal pipe. From the experimental results, it is also observed that the symmetry of the axial velocity distributions is destroyed as an effect of finite pitch or torsion. Finally, it is concluded that in the present investigation the torsion effect is very small compared to the curvature effect in the current investigation, but it is evident.
