ABSTRACT
We will consider a free isothermal jet for the analysis of impaction theory. Figure 7.1 shows an isothermal free air jet, in which
D
is a characteristic diameter of the air jet and
L
is the distance between the discharging outlet and the interception wall. If the jet is circular,
D
is the diameter. If the jet is rectangular,
D
is the width of the shorter side. One reason for using the shorter side of a rectangular jet for its characteristic length is that the jet is much easier to expand at the shorter side and has behavior similar to a circular jet. An extreme example is a long, narrow slot air inlet, for which the expansion of the jet is primarily the jet width. In practice, most jets are circular, square, or nearly square in shape.
