The 3-D freezing of water in a vertical tube cooled by air flow is investigated by means of a numerical analysis for a useful knowledge to protect the tube destruction on freezing. Air flows normal to the tube axis. Several parameters, air flow temperature T-a, air flow velocity u(a) and initial water temperature T-ini are selected considered in winter season actually encountered. The numerical results present the onset of freezing and development of ice layer. Especially, a new natural convection of water is seen in the range larger than 16 degrees C of initial water temperature. (C) 2019 Elsevier Ltd. All rights reserved.