Topics in Current Chemistry (2019) 377:22
1 3
3.2 Pollutant Degradation Results
For isothermal systems, the modeling of photocatalytic wall reactors includes
the simultaneous resolution of the momentum, radiation transfer, and mass balance equations with heterogeneous reactions. The motion equation for Newtonian
non-compressible fluids with constant properties and laminar flow becomes the
Navier–Stokes equation. Mass balance equations also include the continuity and
species conservation equations [28].
These equations can be solved numerically applying commercial computational
fluid dynamics (CFD) software. CFD has been used to solve different configurations
and designs of wall reactors, including continuous flat-plate photoreactors [30, 31,
37, 44, 45], annular photoreactors [44, 46, 47], corrugated-plate photoreactor [23,
24, 48], continuous multitubular wall photoreactors [36], cylindrical and rectangular
photoreactors with the photocatalytic wall placed in the bottom [49], and submerged
photocatalyst-coated plates in tank reactor [50].
As previously mentioned, the set of differential equations solved by CFD modeling at steady state are as follows:
where ρ is the fluid density, v is the velocity vector, P is the pressure, is the viscous stress tensor, g is the gravitational acceleration, C i is the molar concentration of
species i, J i is the diffusion flux vector for i, and R i is the homogeneous reaction rate
of species i. For heterogeneous photocatalytic systems, the homogenous reaction
rate is normally null.
The boundary condition at the photocatalytic wall for the species conservation equation can be written as:
Here, r i is the heterogeneous photocatalytic reaction rate of the main (X) or secondary (Y i ) pollutant, and D i-f is the molecular diffusivity of compound i in the fluid (liquid
or gas). For the remainder of non-active walls, the mass flux equals zero.
Passalía et al. [23, 24, 48], working with a continuous corrugated-plate photocatalytic reactor to treat air contaminated with formaldehyde, applied CFD modeling using
ANSYS Fluent commercial software. However, the radiation field was solved externally using a surface lamp emission model and applying a radiation flux balance in the
catalytic wall and a view factor of the corrugated plate. The resulting LSRPA profile
is shown in Fig. 6a. The kinetic expression employed, previously derived from a flatplate photoreactor [22], has the form of Eq. (19) in Table 3. It should be noted that
this mechanistically kinetic approach considers that water vapor acts as a competitor
(32)
Continuity equation: ∇ ⋅
v
= 0,
(33)
Momentum equation: ∇ ⋅
vv
= −∇P + ∇ ⋅
+ g,
(34)
Species i conservation equation: ∇ ⋅
vC i
= ∇ ⋅ J i + R i ,
(35)
n ⋅ J i
|
|
|A cat
= n ⋅
−D i−f ∇C i
|
|
|A cat
= r i
276
Reprinted from the journal
1 3
3.2 Pollutant Degradation Results
For isothermal systems, the modeling of photocatalytic wall reactors includes
the simultaneous resolution of the momentum, radiation transfer, and mass balance equations with heterogeneous reactions. The motion equation for Newtonian
non-compressible fluids with constant properties and laminar flow becomes the
Navier–Stokes equation. Mass balance equations also include the continuity and
species conservation equations [28].
These equations can be solved numerically applying commercial computational
fluid dynamics (CFD) software. CFD has been used to solve different configurations
and designs of wall reactors, including continuous flat-plate photoreactors [30, 31,
37, 44, 45], annular photoreactors [44, 46, 47], corrugated-plate photoreactor [23,
24, 48], continuous multitubular wall photoreactors [36], cylindrical and rectangular
photoreactors with the photocatalytic wall placed in the bottom [49], and submerged
photocatalyst-coated plates in tank reactor [50].
As previously mentioned, the set of differential equations solved by CFD modeling at steady state are as follows:
where ρ is the fluid density, v is the velocity vector, P is the pressure, is the viscous stress tensor, g is the gravitational acceleration, C i is the molar concentration of
species i, J i is the diffusion flux vector for i, and R i is the homogeneous reaction rate
of species i. For heterogeneous photocatalytic systems, the homogenous reaction
rate is normally null.
The boundary condition at the photocatalytic wall for the species conservation equation can be written as:
Here, r i is the heterogeneous photocatalytic reaction rate of the main (X) or secondary (Y i ) pollutant, and D i-f is the molecular diffusivity of compound i in the fluid (liquid
or gas). For the remainder of non-active walls, the mass flux equals zero.
Passalía et al. [23, 24, 48], working with a continuous corrugated-plate photocatalytic reactor to treat air contaminated with formaldehyde, applied CFD modeling using
ANSYS Fluent commercial software. However, the radiation field was solved externally using a surface lamp emission model and applying a radiation flux balance in the
catalytic wall and a view factor of the corrugated plate. The resulting LSRPA profile
is shown in Fig. 6a. The kinetic expression employed, previously derived from a flatplate photoreactor [22], has the form of Eq. (19) in Table 3. It should be noted that
this mechanistically kinetic approach considers that water vapor acts as a competitor
(32)
Continuity equation: ∇ ⋅
v
= 0,
(33)
Momentum equation: ∇ ⋅
vv
= −∇P + ∇ ⋅
+ g,
(34)
Species i conservation equation: ∇ ⋅
vC i
= ∇ ⋅ J i + R i ,
(35)
n ⋅ J i
|
|
|A cat
= n ⋅
−D i−f ∇C i
|
|
|A cat
= r i
276
Reprinted from the journal