Figure 7. The ratio (d_j/r^*) is almost independent of η for η < 1, meaning that the r^* could be an appropriate scale for the jet diameter at low flow rates.

The ratio (d_j/R^*) decreases with η for η < 1 but varies slightly when η > 1. The proper scale for the jet diameter at high flow rates is R^*. By definition r^* = R^* at η = 1. The jet diameter is measured for three different voltages at each η and the lines represent the mean values trend.