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Example_05_16 - Chapter 5 418 Example 5.16 Formaldehyde...

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Chapter 5 418 Example 5.16 - Formaldehyde from Methanol - Fueled Vehicles in Tunnels Given : Methanol-fueled autos receive increasing attention because of their potential to reduce ozone levels in urban areas. While methanol combustion produces fewer unburned hydrocarbons that ultimately produce ozone, combustion of methanol produces more formaldehyde than does combustion of gasoline. The PEL for formaldehyde is currently 0.75 PPM (920 µ g/m 3 ), but the EPA is concerned that outdoor concentrations as low as 150 µ g/m 3 may cause irritation for some individuals. One may assume that the conditions given by Chang and Rudy (1990) apply to roadway tunnels under severe conditions of traffic congestion, poor tunnel ventilation, and engines with high rates of formaldehyde emission. Four tunnels are analyzed, as shown in Table E5.16. The diameter and amount of traffic are the same in each tunnel, but the tunnels are of various lengths; each tunnel also employs a different type of ventilation: (a) a short tunnel with natural ventilation (b) a moderate length tunnel with uniform make-up air ventilation (c) a long tunnel with balanced transverse ventilation (d) the same long tunnel, but with unbalanced transverse ventilation To do : Estimate the formaldehyde concentration in the four tunnels listed above.
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Chapter 5 419 Table E5.16 Parameters for the four tunnels of Example 5.16. parameter (units) (a) natural (q m = q e = 0) (b) uniform make-up air (q e = 0, q m = constant) (c) balanced transverse (q m = q e ) (d) unbalanced transverse (q m q e ) L (m) 300 1000 2000 2000 D (m) 7.57 7.57 7.57 7.57 U(0) (m/min) 60. 60. 60. 60. q m (min -1 ) 0 0.20 0.20 0.20 q e (min -1 ) 0 0 0.20 0.18 c m ( µ g/m 3 ) 5.0 5.0 5.0 5.0 c(0) ( µ g/m 3 ) 7.4 7.4 7.4 7.4 n c (autos/km) 100 100 100 100 v c (km/hr) 8.0 8.0 8.0 8.0 (EF) c [mg / (auto km)] 100 100 100 100 k (min -1 ) 0.020 0.020 0.020 0.020 Solution : The source term (s) is common to several of the equations above, and can be calculated from Eq. (5-76), using Eq. (5-71), c c c c c c 2 2 c (EF) n v L 4(EF) n v S s A L D D L 4 = = = π π which upon substitution of the values provided in the table yields ( ) 2 3 mg auto km 4 100. 100. 8.0 hr 1000 g km g auto km km hr s 2 60 min mg 1000 m m min 7.57 m µ µ = =
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