In this paper, we investigated the chilldown process of a horizontal tube by a liquid nitrogen flow with low mass fluxes. The flow patterns and heat transfer characteristics are studied experimentally. Visualization results illustrate the successive states of liquid-wall interaction with different mass fluxes. For a horizontal tube, the liquid filament-wall interaction is an important contributor to the heat transfer on the bottom wall while the upper wall is cooled by forced convection with superheated vapor. A phenomenological model is developed. in which the heat transfer on the bottom wall is composed of film boiling and forced convection while for the upper wall, forced convection is the only mechanism of heat transfer. A good agreement is achieved between the model prediction and the experimental result. (C) 2007 Elsevier Ltd. All rights reserved.