Natural convection heat transfer inside an open vertical pipe: Influences of length, diameter and Prandtl number

We investigated the influences of length, diameter and Prandtl number on the natural convection heat transfer inside open vertical pipes. Numerical calculations were performed using FLUENT 6.3 varying the pipe length from 0.2 m to 1.0 m, the diameter from 0.003 m to 0.03 m and the Prandtl number from 0.7 to 2014. The numerical scheme was validated with mass transfer experiments employed to achieve high buoyancy. In large diameter pipes or high Prandtl number conditions, where relatively thin thermal boundary layers formed near the wall, the NuL values were similar to those observed on vertical plates. As the diameter decreased, the length increased, and the Prandtl number decreased, the heat transfer was impaired due to the interactions of thicker thermal boundary layers. The duct flow and chimney effects were analyzed and visualized using the velocity and temperature fields.