AbstractThe swelling and shrinking of Newtonian jets issuing from circular orifices or slits are examined. Equations predicting the die swell ratio and downstream flow characteristics are developed. It is found that the cause of swelling at low Reynolds numbers is related to a negative pressure (below the free stream pressure) at the slit exit. The scatter of experimental data has been studied and the factors contributing to this phenomenon are discussed. The die swell ratios and jet shapes versus Reynolds number for Newtonian liquids issuing from tubes are empirically shown.