1. 4. Sampling and Measurement of Concentration
Isokinetic sampling
- Velocity entering the sampling probe is equal to free stream velocity.
- No particle loss at inlet.
- Does not insure no particle loss elsewhere.

2. is the sampling flow rate
is the flow rate of aerosol
is the probe diameter
is the duct diameter

3. Anisokinetic sampling
Misalignment
Superisokinetic
Subisokinetic

4. Case 1: Miasalignment Maximum error is concentration in the probe
is concentration in free stream

5. Effect of misalignment of the sampling probe

6. Case 2 & 3: Superisokinetic & subisokinetic
Maximum error

7. Superisokinetic and subisokinetic sampling (q = 0)

8. Superisokinetic and subisokinetic sampling (q = 0)

9. Case 4: Velocity mismatch and misalignment
Maximum error

10. Sampling from still air
Two sources of error
1. Settling
- sampling tube facing upward-> overestimation of concentration.
- sampling tube facing downward-> underestimation of concentration.
2. Inertia
- Same as superisokinetic case->loss of large particles.

11. Criteria to avoid settling error
Davies’s criteria
For standard condition
in mm
in m3/hr

12. Criteria to avoid inertia error
Davies’s criteria
For standard condition
in mm
in m3/hr

13. Davies’s criteria for upper and lower limits of probe diameter.

14. Maximum air velocity that still-air sampling criteria can be used
Agarwal & Liu’s criteria: less restrictive with less than 10% error
No restrictions for particle smaller than 100 micron.

15. Maximum ambient air velocity that still-air sampling criteria can be used

16. Transport losses: in tubing and fittings

17. 1. Settling loss is the tube length is the inclination of the tube
in radians

18. 2. Inertia loss at the bend
Laminar flow
Turbulent flow
is the bend angle

19. 3. Other losses
- Diffusion: Previous chapter
- Interception: small
- Electrostatic: will be discussed later
- Thermophorsis: sample of hot aerosol stream in a cooler tubing.
Will not be discussed.