Addressing the adverse cold air inflow effects for a short natural draft dry cooling tower through swirl generation

•A 2-D axisymmetric model for a short natural draft dry cooling tower (NDDCT) is built up and the transient simulation is conducted.•The cold air inflow penetrates into the tower after the start-up process and a short period of pseudo-steady state.•The cold air inflow can be delayed and reduced by introducing swirl inside the tower, and it is explained by the local vortices reduction and the decrease in the boundary layer thickness by the swirl.•The comparison between the energy consumption and the cooling capacity gain of the tower by the swirl source indicates a reasonable industrial applicability.•Increasing the axial velocity near the wall intensifies the boundary layer separation above the tower throat and thus provokes the cold air inflow in advance. Short natural draft dry cooling towers (NDDCTs) are susceptible to cold air inflow. A transient simulation on Gatton tower is carried out to study the time-dependent cold air inflow characteristic. Our results show that, the cold air inflow penetrates inside the tower after a short period of pseudo-steady state, and a steady state with the cold air inflow is finally formed. We also investigate the possibility of inducing swirling motions to counter the cold inflow. The results demonstrate that, by reducing the local vortices caused by the specific tower structure, and thinning the boundary layer thickness, swirl is able to decrease the cold air inflow effect. Finally, feasibility of the suggested approach was verified by comparing the energy required to create the swirl with the extra heat transfer from the heat exchangers in the tower which would have not been materialized because of the cold inflow. It was observed that, an extra 40 kW heat transfer gain can be anticipated if only 1 W is spent to induce the swirl.