Differences between external and internal flow External flow Boundary layer develops freely without constraints Free strea olx Velocity boundar Internal flow: boundary layer is constrained and eventually merges #4 Heat Transfer Su Yongkang School of Mechanical EngineeringHeat Transfer Su Yongkang School of Mechanical Engineering # 4 Differences between external and internal flow • External flow: Boundary layer develops freely, without constraints • Internal flow: Boundary layer is constrained and eventually merges