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Influence of hydrodynamic parameters on transfer of Disinfection By-Products in ambient air of indoor
swimming pool: use of Residence Time Distribution approaches on a reference basin
Philippe Humeau*, Nicolas Garandel**, Julien Guilhot*, Monem
Masri Idlibi*, Nicolas Cimetière** * Centre Scientifique et Technique du Bâtiment, AQUASIM, 11 rue Henri Picherit, BP82341, 44323 Nantes Cedex 3, France
** Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, Av. du Général Leclerc, CS 50837, 35708 Rennes Cedex 7, France
2
Context
Health impact of the presence of trichloramine in the air surround the pools
Airborne concentrations above 0.5 mg.m-3
Duration of exposure
Trichloramine concentrations in the air
Renewal of ambient air
Potential of trichloramine emission by the water of the swimming pool
Water concentration
Agitation by swimmers…
Recommendations to limit the presence of Disinfection by-products in water
Larger adding water in the swimming pool
Implementation of dechloramination processes on the recirculating water loop
3
Analyse of emission processes
nAz = NAz × a × S × dz
NAz = KG × (H.CLi – CG
iE)
Specific surface area (m-1)
Presence of swimmers Surface agitation
+
Swimming pool surface (m2)
Specificity of the volatil DBP
Water temperature Air temperature
+
- Air renewal
Overall transfer coefficient in gas phase (m.s-1)
Bustle due to toboggan, backwash, bubbles…
+
DBP concentration in water
Attendance Precursor concentrations Chlorine concentration
+
- Dechloramination processes Water renewal Volume of the pool? Recirculation rate of water?
It is necessary to set specific operating conditions on the issue of NCl3 in the ambiant air
4
Methodological approach
Formation kinetics of disinfection by-
products
Degradation kinetics of disinfection by-
products
Hydrodynamic behaviorof the referenceswimming pool
Hydrodynamic behaviorof air on the reference
swimming pool
Liquid/Gas transferkinetics
Disinfection of swimming pool
Liquid/Gas transfer
Estimate of emission potential of disinfection by-products in ambient air of pool reference
Sanitary objectives:- Regulatory threshold- Sanitary risks
Indoor air quality
Analysis of chlorinatedby-products in air and
water phases
Legend
Literature data: text in italicsExperimental data :
Chemical engineering approaches
5
Presentation of the hydrodynamic study
Experimental hydrodynamic study
Hydrodynamic characterization of a reference swimming pool
3 water recirculation rates: 15 m3.h-1 ; 25 m3.h-1 ; 40 m3.h-1
3 air velocities: 0 m.s-1 ; 2 m.s-1 ; 8 m.s-1
Numerical study of water flow (CFD methods)
Hydrodynamic characterization of a reference swimming pool: validation of calculation methods
Modelisation of hydrodynamic behavior with ideal reactors
Extrapolation ability of the method to a real pool
Location of the flow characteristics (dead volumes, short-circuits…)
6
Material and methods: the swimming pool
Reference swimming pool
Possibility to install a dechloramination device
Possibility to inject a tracer
Characteristic Value
Useful volume Lenght Width Water height Number of injections Water recirculation rate Air velocity Water treatment Water temperature management
42,24 m3 8 m 4 m
1.32 m 4
15 m3.h-1 to 40 m3.h-1
2 m.s-1 0.2 m.s-1 to 8 m.s-1 0.4 m.s-1
Filtration with sand filter, chlorine disinfection, pH regulation
Option
7
Residence Time Distribution (RTD)
The liquid flow has been represented by a tanks-in-series with or without mass exchange model (DTS Pro 4.20 software – Progepi, Nancy)
Q
V.JuaT 1
1
2
V
VK
Q.
Vt 2
m
J
V2
V1
Q Q
Q
Pulse-injection of a non transferable tracer (lithium chloride) at the inlet of the swimming pool
RTD curve obtained by recording the concentration-time of tracer leaving the swimming pool
Residence Time Distribution curve
Numerical study of water flow (CFD method)
The swimming pool is discretized with a Hexahedral mesh type, and includes about
900 000 cells
Turbulence Model: RNG k-ε • Cμ = 0.0845 • C1ε = 1.42 • C2ε = 1.68
Two-phase Model: • DPM (Discrete Particule Motion) • Turbulent dispersion taken into
account • Passive tracer
Material: water • Density: ρ = 998.2 kg/m3
• Viscosity : μ = 0.001003 kg/m.s
Schemes : • Pressure and velocity are coupled with the
SIMPLE scheme • Spatial resolution : Upwind First order method
Boundary conditions: • uniform velocity with a 5%
turbulent intensity at the inputs • Free pressure outlet conditions • 5 mm roughness for the walls of
the pool • smooth walls for the rest (gutter,
pipe, and the water surface)
Simulations Fluent 14.5
Reference : Cloteaux et al. (2013), Influence of swimming pool design on hydraulic behavior: a numerical and experimental study, Engineering, Vol. 5, pp. 511-524
Numerical study of water flow (CFD method)
Hydrodynamic behavior of the water phase
RTD curves of water in the swimming pool for a water flow rate of 40 m3.h-1, and 3 different air velocities (0, 2 and 8 m.s-1)
0
0,5
1
1,5
2
2,5
0 20 40 60 80 100 120
Série1
Série2
Série3
Uair = 0 m.s-1
Time (minutes)
Lith
ium
co
nce
ntr
atio
n
(mg.
L-1)
Uair = 2 m.s-1
Uair = 8 m.s-1
The air flow seems to have a significant influence over the pool on the hydrodynamic behavior of the water phase in the pool
Experimental Residence Time Distribution
RTD curves of water in the swimming pool for a water flow rate of 40 m3.h-1 (Uair = 0 m.s-1)
Deconvolution method on the experimental RTD curves with a compartment model (tanks-in-series) developed by INRS (France)
RTD curves of water in the swimming pool for a water flow rate of 40 m3.h-1 (Uair = 8 m.s-1)
Mean Residence Time t = 1 h 13 min Mean Residence Time t = 1 h 10 min
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5
E (
)
Uair = 0 m.s-1
Uair = 8 m.s-1
Experimental Residence Time Distribution
RTD curves of water in the swimming pool for a water flow rate of 40 m3.h-1 with 2 air velocities (Uair = 0 and 8 m.s-1)
The air velocity has no significant effect on hydrodynamic behavior of the water phase in the swimming pool
Air velocity
Space time
Mean residence time
/ Observation
0 m.s-1
8 m.s-1
1 h 03 min
1 h 03 min
1 h 13 min
1 h 10 min
1.1617
1.1193
Short-circuit
Short-circuit
CFD: Velocity magnitude
Visualizations of water flow in the pool
Water flow rate = 40 m3.h-1
Uair = 0 m.s-1 (not taken into account)
Numerical Residence Time Distribution
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5
E (
)
Experimental RTD
Numerical RTD
RTD curve of water in the swimming pool for a water flow rate of 40 m3.h-1 (Uair = 0 m.s-1)
Comparison of experimental and numerical RTD curves of water in the swimming pool for a water
flow rate of 40 m3.h-1 (Uair = 0 m.s-1)
The experimental Residence Time Distribution is correctly represented by the numerical Residence Time Distribution
Numerical mean residence time t = 1 h 07 min
The hydrodynamic parameters (as the mean residence time) are well-estimated by numerical approaches
Influence of operating conditions on
hydrodynamic behavior of the water
0
0,002
0,004
0,006
0,008
0,01
0,012
0,014
0,016
0 3600 7200 10800 14400 18000 21600 25200 28800 32400 36000
Trac
er p
rop
ort
ion
at
the
ou
tlet
of
the
po
ol
Time(s)
inj1
inj2
inj3
inj4
total
0
0,002
0,004
0,006
0,008
0,01
0,012
0,014
0,016
0 3600 7200 10800 14400 18000 21600 25200 28800 32400 36000
Tra
cer
pro
po
rtio
n a
t th
e o
utl
et
of
the
po
ol
Time(s)
inj1
inj2
inj3
inj4
total
RTD curve of water in the swimming pool for a water flow rate of 15 m3.h-1 (Uair = 0 m.s-1)
RTD curve of water in the swimming pool for a water flow rate of 25 m3.h-1 (Uair = 0 m.s-1)
Water flow rate
Space time
Mean residence time
/ Observation
15 m3.h-1
25 m3.h-1
40 m3.h-1
2 h 49 min
1 h 42 min
1 h 03 min
3 h 32 min
1 h 59 min
1 h 07 min
1.2544
1.1647
1.070
Short-circuit
Short-circuit
Short-circuit
Disrupting flows of water (short-circuits) increase with the reduction of water flow recirculation rate in the swimming pool
Modeling of the hydrodynamic
behavior of the swimming pool
Réacteur Q (m3.h-1) Volume (m3)
J Tm K Pe
1 0,4 0,0875 - - - 0,5
2 0,4 0,875 - - - 0,5
3 0,4 1 - - - 1
4 0,4 1 - - - 1
5 3,35 0,2333 - - - 1
6 3,35 0,2333 - - - 1
7 3,35 0,4258 - - - 1
8 3,35 0,4258 - - - 1
9 3,35 19,679 1 10 0,2048 -
10 3,35 19,679 1 10 0,2048 -
11 3,35 38,574 1 10 0,2048 -
12 3,35 38,574 1 10 0,2048 -
Hydrodynamic parameters of the flow model of the liquid phase in the reference basin (Q = 15 m3.h-1, Uair = 2 m.s-1)
Determination of the influence of operating conditions and pool water features on liquid/gas transfer performance of Disinfection By-Products
Sensitivity analysis of the transfer model according to the hydrodynamic parameters
Perspectives
17
Liquid/Gas transfer modelisation
References : Humeau et al. (2004), Optimization of bioscrubber performances: experimental and modeling approaches, J. Environ. Eng.-ASCE, Vol. 130 n°3, pp. 314-321
Prediction model of the emission of disinfection by-products in the air atmosphere of the reference basin
Gerardin et al. (2014), Modeling of variations in nitrogen trichloride concentration over time in swimming pool water , Process Safety and Environmental Protection , 11 p. http://dx.doi.org/10.1016/j.psep.2014.10.004
V 1
V 2
Q
V 1
V 2
Q
V 1
V 2
Q
V 1
V 2
Q
1 n n + 1 J
Fresh air Polluted Air
Water recirculation
18
Liquid/Gas transfer: equations
J
Z.pxe1.CC.'HCC i
GiL
1iG
iG
1iG
iG
iL
1iL CC.CC
Gas :
Liquid :
Partial mass balance equations, for an elementary volume of compartment i :
:
:
The resolution of the mass balance equations is obtained using an iterative method
Plug flow
Plug flow with dispersion
Transfer without reaction
Transfer with reaction
(dissociation model)
G
G
Q
S.a.K
2G
aG
a
G
U
D.a.K.411.
D.2
U
1
23
21
3
2
L
G
OH
K.K
OH
K1.
Q.
S.a.K
L
G
Q.
S.a.K
Conclusion
19
Characterization of the hydrodynamic behavior of the water in the reference basin
Impact of operating conditions on hydrodynamic parameters
Experimental Residence Time Distribution
Numerical Residence Time Distribution Validation of the method by comparison with experimental data obtained on the reference basin
Modeling the hydrodynamic behavior of a real pool according to its geometry and operating conditions
Prediction of Liquid/Gas transfer of Disinfection By-Products Relevant method for the estimation of the impact of operating conditions on the potential of adverse gaseous emissions and the measurement of the performance of the water treatment devices
Thank you for your attention
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