Highly curved helical pipes offer attracting potentialities for intensified mass/heat transfer performances as they generate intense Dean-type vortices. The evaluation of friction factor in such geometries is necessary for assessing the trade-offs between the increase of transfer efficiency and the associated specific energy requirement. Unfortunately, such data are lacking for highly curved helixes, probably due to the difficulty to manufacture these geometries through traditional manufacturing techniques. In this paper, CFD simulations are carried out for determining the laminar flow friction factor in helical pipes, particularly highly curved ones. For an experimental validation of the numerical results, a highly curved helix was built by 3D-printing. Existing correlations are shown to fail for the accurate prediction of the friction factor in highly curved helixes. A new correlation is thus proposed. An excellent agreement is obtained between the experimental pressure drop measurements and the proposed correlation predictions. (C) 2019 Elsevier Ltd. All rights reserved.