terminal velocity

  1. Calculate the terminal velocity of a 250 micron droplet, given the following data:  particle density = 900 kg/m3, Cc = 1, air density = 1.29 kg/m3, air dynamic viscosity = 1.72 x 10-5 kg/m-s. What would be the value if calculated using Stoke’s Law?
  2. NOx is emitted at a rate of 200 g/s from a stack with an effective height of 90 m.  The wind speed at the stack height is 4 m/s, and the atmospheric stability class is B for the sunny day.  Determine the ground level concentration in ug/m3 along the center line at a distance 1 kilometer from the stack.
  3. Download the SCREEN3 Model from the EPA website here: https://www3.epa.gov/ttn/scram/models/screen/screen3.zip Use the SCREEN 3 model to input the following:

A new factory is proposed to be built. The following data is known about the point source and its location:


o    It will emit SO2 at a rate of 100 grams/sec, through a 100m tall stack. The stack has a 2.5 m inside diameter.

o    The SO2 will be emitted at an exit velocity of 25 m/s at a stack gas exit temperature of 450K.

o    The ambient air temperature is assumed to be 20C (293K).

The factory will be located near an existing school (the “receptor”). The following data is known about the receptor and its location:


o    The receptor height above the ground is 0 m (i.e. it is at ground level)

o    It is located in a rural area.

o    There is no building downwash to be considered.

o    The terrain between the factory is not above the stack height, so no complex terrain screen is needed, and no simple terrain screening is needed.

o    The typical meteorology for the site is Class A

Answer the following questions:

1.    Using an automated distance array from 0 to 50000 m, at what distance does the maximum concentration occur, and what is the value of that maximum concentration?

2.    We want to know what the factory emissions impact will be on the school.  If the school is located 6300 m away from the factory, what is the concentration at this discrete distance?

3.    Print out / screen shot your SCREEN3 Model results and attach to your Assignment answer/submission.