In the present study an experimental and computational fluid dynamic carried out for entrance length flow in helical coils for single and two-phase flow. Development region length and the detailed characteristics of fluid flow has been investigated by varying coil parameters such as tube diameter, coil diameter and void fraction. The considered Reynolds number is in the range of 10000 ＜ Re ＜ 80000 and the void fraction is in the range of 0.01 ＜ α ＜ 0.09. For CFD simulation the two-phase fluid flow in this article, the Eulerian-Eulerian model was employed. To calculate the turbulent fluctuations, the k-ε realizable turbulence model has been used. The experimental and numerical simulation of the local parameters demonstrates that developing length (L/D) increases with increase Reynolds in the single and two-phase flows. The obtained results showed that the development entrance length increases with the increase of pipe diameter and decreases with the increase of coil diameter. Also, entrance length decrease with increases void fraction. According to the secondary motion in a curved tube, a major difficulty in describing the problem has been recognition of the importance of flow development at the entrance of a helical tube. Therefore, correlation has been suggested to predict the entrance length as functions of various variables of the helical coil.
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