This Demonstration shows convective, steady-state heat transfer from a bank of tubes to cross-flowing air. This depends on the configuration of the tubes and when the inlet air velocity changes. Two tube configurations are considered: aligned and staggered. The aligned configuration has flow lanes for the air, whereas the staggered configuration disrupts these flow lanes. The air enters at 15 °C at a constant velocity, with the tubes at a constant temperature of 70 °C. When the air velocity increases, the rate of heat transfer increases and the outlet air temperature decreases. An average Nusselt number is calculated for the entire tube bank, and that number is used to calculate the outlet air temperature and the heat rate per length of tube. Radiation effects are assumed negligible and the air properties are assumed independent of temperature. The sliders can adjust the arrangement of the tubes, but for a ratio of transverse pitch to longitudinal pitch less than 0.7, aligned tubes should not be considered due to ineffective heat transfer. The tube diameter does not change when the tube arrangement changes, but the diameter displayed in the tube configuration figure changes so that all tubes can be shown.