To evaluate the adequacy of the effective diameter (d(sd) and d(eq)) of non-spherical particles in predicting pressure gradients of upward air/water two-phase flow through well-packed beds, a set of experiments were performed using four kinds of cylindrical particles under isothermal conditions varying the superficial air velocity (0-0.8 m/s) with no water inflow at the bottom. The measured pressure gradients were compared with the existing models and the proposed model from our previous study adopting d(sd) or d(eq) Consequently, the proposed model adopting d(eq) predicts the pressure gradients of two-phase flow through non-spherical particle beds much better than the existing models, which is reducing the uncertainty in evaluating long-term coolability of ex-vessel debris bed composed of irregular shaped particles. (C) 2019 Elsevier Ltd. All rights reserved.