since diffusion argumenrs show that the gas rapidly acquires the wall teaperature.
Furtheraore, there is noc enough gas flowing through the iapactor
to appreciably beat it.
For the lowest elevations (220,000 feet), flow
welocity, according to Eq. 5.5, would exceed acoustic.
In this case the
relation is still used bot, instead of using the total pressure difference,
&@ condition of acoustic flow welocity as it leawes the impactor has been
applied.
Calculation of Impactor Performance.
‘
By use of the laws just discussed,
impactor performance for a wariety of cooditions has been calculated.
these calculations, certain ranges of performance become apparent.
In
First,
for wery samll particles down to the diameter of molecules, the collection
is effected through diffusion which, in nearly all cases, collects all debris
carried by air flowing through the impactor.
Next, for the range of particle
sizes abowe molecular, impaction becomes important and, in most cases, a 100percent impaction efficiency is achiewed for diameters above 5 x 1073 sicron.
There exists between these cases a transition range where collection is effected partly by impacrion and partly by diffusion.
Finally, for still larger
particles of the order of above 10°? micron, a third process becomes important.
This process, which has been termed “gathering,” results from particles
penetrating the stagnation region in front of the impactor and striking the
impactor or crossing streamlines leading to the impactor.
Figure 5.2 shows
the range of these warious phenomena at 250,000 feet, where the sampler rocket
welocity is 2000 ft/sec and ambient conditions are assumed.
In addition to
efficiencies for the various phencmens, a curve representing overall] perfora
ance is also shown.
Impactor performace at 220,000 and 260,000 feet have also been examined
in order to ewaluste the wariation of efficiency with altitude and speed.”
Overall performance curves are presented in Fig. 5.3.
Purther, to exanine
the effect of the ambient teuperature, overall perforaance has been calculated on the assimption that the teuperature is 1000 degrees above ambient
at 250,000 feet, while the pressure is ambient.
overall perforcance is also shown in Fig. 5.3.
The curve representing this
Finally, in order to exanine
tne effect of che constitenrs Of tne gas, it has Deen assumed Coat tne air
The
wa
*mese calculations are based on a rocket apogee of 315,000 feet.
actual expected haighr was abouc 255,000 feet.
LY