Abstract: Convective heat transfer between the air and the pipe wall and evaporative heat removal from the surface of the soil bared in the small holes of the pipe wall are two modes of heat transfer in duct-ventilated embankments with perforated ventilation pipe. The effects of perforating ratio, wind velocity and water content on convective and evaporative heat transfer by the wall of the perforated ventilation pipe are analyzed. The formulae for heat transfer coefficients of convection and evaporation in the perforated ventilation pipe are obtained. The total cooling effect in duct-ventilated embankments during winter is mainly dominated by convective heat transfer due to weak evaporative cooling based on smaller unfrozen water in frozen soils. During warm time, the effect of convective heat transfer between the ambient air and the pipe wall may raise the temperature of the embankment soil, whereas the effect of evaporative cooling by the small holes of the pipe wall is significant due to large unfrozen water content in unfrozen soils, thus being able to partially or completely balance out the heating effect in the embankment due to convective heat transfer and to ensure the embankment stability.

Key words: permafrost embankment, perforated ventilation pipe, convective heat transfer, evaporative heat removal, cooling effect