Grease Filter Efficiency Test Method - Food Service Technology ...

Centerline Velocity vs Flow Rate
2000
1800
Q duct = 0.7239v cl
1600
R 2 = 0.999
Flow Rate (CFM)
1400
1200
1000
800
600
400
200
1000 CFM
1381 ft/min
0
0 500 1000 1500 2000 2500 3000
Centerline Velocity (ft/min)
Figure 4.3. Flow Rate vs. Centerline Velocity using hot-wire anemometer
The results of the spatial uniformity tests showed that for the small particles, near 0.3 µm, the
concentration distribution within the exhaust duct is very uniform both with and without the
filters installed, and regardless of the location of the aerosol source on the griddle. As shown
in Table 4.2, the maximum standard deviation was found to be 5 % or less. For the particles
near 5 µm in size as shown in Table 4.3, the variation was larger but no observable trend was
found, top to bottom or left to right. Slightly more variation was observed when the source
was located at one of the corners rather than at the center. The maximum standard deviation
for these tests was 13 % or less. Plots of particle number counts vs. duct sampling locations
for each aerosol source position on the griddle are given in Appendix C.
The conclusions drawn from these spatial uniformity tests are that no mixing device is
required in the exhaust duct to mix the aerosol, it is well mixed already, and the concentration
distribution is insensitive to the position of the source on the griddle surface. Thus, a sample
probe inlet located at the centerline of the exhaust duct will provide a representative sample
of the effluent in the exhaust. Other quantities measured at the duct centerline, such as
temperature and vapor concentration, will also be representative of the exhaust values as their
diffusion is much higher than for the small aerosol particles that were found to be very well
mixed.
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