题目内容
（请给出正确答案）
[主观题]
A 2-mm diameter raindrop falls at its tenninal velocity through 1000 ft of air that contains 80 μg/m
3of 3-μspherical particles.
(a) How many particles does the drop collect？
(b) What is the percentage increase m mass of the drop due to these particles？
答案
已知ρp=2×103kg/m3，雨滴Db=2mm，查表得到雨滴终端沉降速度为=9.0m/s，
因此，碰撞参数
从Figure 9.18读出ηt=0.25。
故
=0.0188μg=1088×10-8g
(a)每个雨滴下降过程中可以捕集的颗粒数
(b)雨滴本身
M/M'= 0.0188μg/4.19×103μg=4.49×10-4%
另，如果查表得到雨滴终端沉降速度为Vt=7.3m/s，
M/M'=0.0136μg/4.19×103μg=3.25×10-4%
