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Scott A. WellsDepartment of Civil and Environmental Engineering
Portland State University
OverviewWhy develop a compressible model?Example application ‐ Dead SeaSpecial features of a model for hypersaline systemsModel development assuming incompressiblity and compressiblity in 2DModel results and comparisonsConclusions
Why use a compressible model for hypersaline systems?
Issues: Incompressible assumption
Typically less than 0.01‐0.03 ‐ hypersaline systems can be as high as 0.4
Related issues:Equation of state as a function of chemical componentsEvaporation as a function of water activityChemical equilibrium model including precipitation of solidsDouble‐diffusion
1<<Δρρ
Examples Dead Sea, Israel/West Bank/Jordan [350+ g/l TDS] Elevation: ‐420 mGreat Salt Lake, UT, USA [100‐230+ g/l TDS] Mono Lake, CA, USA [50‐100 g/l TDS]Ocean [32 g/l TDS]Lake Tahoe, CA/NV, USA [0.06 g/l TDS]
The Dead Sea
The Dead SeaIsrael/West Bank/Jordan
Inflows: Jordan River, saline and freshwater springs, return brines from mineral processing
Outflows: evaporation, pumping for mineral processing
Dead Sea water level changes over last 100 years
Water level decline
Impacts:Sink Holes
Saving the Dead Sea
Rescue Plan
“Peace Conduit”
“Valley of Peace” Video
Possible Environmental IssuesChange in chemical composition of Dead SeaPrecipitation of gypsum
Ca + SO4 + 2H2O ===> CaSO4•2H2ONo longer will people be able to ‘float like penguins’ !
stratification
Mixing experiments and microbial blooming
100% DS brine 85% DS brine + 15% SW
70% DS brine + 30% SW70% DS brine + 30% SW + 10 μMPO4
Possible Environ‐mental Issues
Algal blooms + secondary production in surface layer
Model unique theoretical issuesCompressibility Equation of state based on chemical components and temperature rather than salinity and temperatureEvaporationChemistry
Na, K, Ca, Mg, Cl, Br, SO4, HCO3
Precipitation of halite, gypsum, carnallite (KMgCl 3 ∙6H2O)
Growth of algae and bacteria as a function of salinity
Compressible
∂∂
∂∂
∂∂
ux
vy
wz
+ + = 01 1 0ρ∂ρ∂ ρ
ρt
q q+ ⋅∇ +∇⋅ =v v v v
Momentum equations: the Boussinesq approximation
ρρρρρρρ οοο
Δ+=≈Δ+
= where111
Continuity
2D x‐z governing equationsEquat‐ion
Governing equationincompressible fluid
Governing equationcompressible fluid
x‐mom‐entum
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛+
+−
=++
∫
zB
xB
dzx
gBx
gB
zwuB
xuuB
tuB
xzxx
z
∂τ∂
∂τ∂
ρ
∂∂ρ
ρ∂∂η
∂∂
∂∂
∂∂
η
1⎟⎟
⎠
⎞
⎜⎜
⎝
⎛+
+−
=++
∫
zB
xB
dzx
gBx
gB
zwuB
xuuB
tuB
xzxx
z
∂τ∂
∂τ∂
ρ
∂∂ρ
ρ∂∂η
ρρ
∂∂
∂∂
∂∂
η
η
1
2D x‐z governing equationsEquat‐ion
Governing equationincompressible fluid
Governing equation compressible fluid
Contin‐uity
Freesurfaceequation
qB = zB +
xB
∂∂
∂∂ wu
inBqzwB
xuB
tB ρρρ∂ρ∂
=∂
∂+
∂∂
+
∫∫ −=hh
qBdzBdzuxt
Bηη
η ∂∂
∂∂η
dzBq
dzuBx
dzt
Bt
B
h
in
hh
∫
∫∫
−
∂∂
+∂∂
=∂∂
η
ηηηη
ρ
ρρρη
2D x‐z governing equationsEquat‐ion
Governing equationincompressible fluid
Governing equation compressible fluid
z‐mom‐entum
Conser‐vation ofheat
BS +
Bq = z
zBD -
xxBD
- z
+ x
B + t
B
zx
c
c
TT
TwBTuT
∂
⎟⎠⎞
⎜⎝⎛
∂∂
∂
∂
⎟⎠⎞
⎜⎝⎛
∂∂
∂
∂∂
∂∂
∂∂
BS + Bq
= z
zBD -
xxBD
-
z +
xB
+ tB
zx
p cp c
pp
ppp
cc
TcTc
TwBcTucTc
ρρ
ρρ
ρρρ
∂
⎟⎟⎠
⎞⎜⎜⎝
⎛∂
∂∂
∂
⎟⎟⎠
⎞⎜⎜⎝
⎛∂
∂∂
∂∂
∂∂
∂∂
01
= −gPzρ
∂∂ 0
1= −g
Pzρ
∂∂
Equation of State),,f( = olidsSuspendedSTDSeTemperaturρ
Traditional
Unique for Dead Sea – developed by Hebrew University and GSI, Jerusalem
EvaporationEvaporation rate now a f(chemical composition) or computed water activity
ChemistryPrecipitation of gypsum/halite salts
Algae Growth a f(density)
No growth
Growth not affected by salinity
Dead Sea GridCE‐QUAL‐W21 km X 1 m grid70 km vs about 300 m
Typical Model ResultsWater Level 1998
Typical Model Results
Return brine tracer
Compressible vs Incompressible Models
1 l fresh 1 l “brine”
2 l
Compressible vs Incompressible Models
Summary and ConclusionsFor hypersaline systems must use compressible form of governing equationsUnique waterbodies unique equation of stateChemical equilibrium model precipitation effects
Application of ‘typical’ models are not adequate for hypersaline systems
Next tasks: refining boundary conditions and basic science, model simulations for long‐term effects of Peace Conduit