280
D Dispersion Models
Fig. D.1 Graphical representation of the model for heavy gas propagation. ˙
M
=
emission mass flow; u = wind speed; t = time
• z-direction: the thickness of the heavy gas layer in the z-direction (H (x))
decreases as the distance from the point source (x) increases. This assumes a
stable layering without any air entrainment.
• Ground: plane and fully reflective with no adsorption
Propagation in the y-direction (at a velocity of v g ) can be described by the
Bernoulli equation (where g is the acceleration due to gravity):
v g =
2 × ρ
ρ Air
× g × H
1
2 =
dy F
dt
(D.1)
At the same time, the law of mass conservation applies to the compartment of width
dx with M = ˙
M dt = 2 × y F × H × dx × ρ Gas :
H (x) =
1
2 × y F
×
˙
M
ρ Gas
×
dt
dx
=
˙
M
2 × u × y F × ρ Gas
(D.2)
D Dispersion Models
Fig. D.1 Graphical representation of the model for heavy gas propagation. ˙
M
=
emission mass flow; u = wind speed; t = time
• z-direction: the thickness of the heavy gas layer in the z-direction (H (x))
decreases as the distance from the point source (x) increases. This assumes a
stable layering without any air entrainment.
• Ground: plane and fully reflective with no adsorption
Propagation in the y-direction (at a velocity of v g ) can be described by the
Bernoulli equation (where g is the acceleration due to gravity):
v g =
2 × ρ
ρ Air
× g × H
1
2 =
dy F
dt
(D.1)
At the same time, the law of mass conservation applies to the compartment of width
dx with M = ˙
M dt = 2 × y F × H × dx × ρ Gas :
H (x) =
1
2 × y F
×
˙
M
ρ Gas
×
dt
dx
=
˙
M
2 × u × y F × ρ Gas
(D.2)