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Coupled heat and water transport in the vadose zone
1. 29th February 2012
Coupled heat and water transport in bare soils in semi-
arid and arid regions
Thomas Berends
student Hydrology and Water Quality
Supervisors: Dr. K. Metselaar, Dr. J.C. van Dam and MSc. E. Balugani
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Content
Problem definition
Theory of Philip and de Vries
Data
Calibration
Isothermal and thermal, liquid water and water vapour fluxes
Implementation water vapour flow SWAP
Coupled versus liquid models
Design laboratory experiment
Conclusion
Recommendations
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Problem definition
Water balance Energy balance
Precipitation Evaporation Latent heat flux Net radiation Sensible heat flux
Liquid water Water vapour
Soil heat flow
flow flow
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Problem definition
How important is water vapour movement in coupled
heat and water flux models for bare soils in semi-arid
and arid regions on a daily time scale??
Is the Hydrus-1D model able to simulate the field data?
Can water vapour movement be implemented in the SWAP
model to describe the coupled heat and water movement
on a daily time scale?
How to set up a laboratory experiment to measure
accurately the variables for coupled heat and water
movement models?
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Theory
Philip and de Vries (1957)
The theory by Philip and de Vries couples the mass balance for
water, the Richards equation, with a heat conservation
equation based on Fickian diffusion process.
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Theory
Heat conservation equation (Nassar and Horton, 1992)
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Theory
Limitations of the theory of Philip and de Vries:
Hysteresis with respect to the relation between soil water content and
soil water pressure is not taken into account.
Macroscopically the medium has to be homogeneous and isotropic.
No solutes are present.
Vapour movement by diffusion.
In the gas phase free convection can be neglected.
Total air pressure is uniform and constant.
Thermodynamic equilibrium between liquid and water vapour.
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Data
Soil profile
Soil water content & soil temperature (TDR probe)
Soil water pressure (MPS-1 sensors & POT sensor)
Atmospheric conditions
Air temperature & relative humidity (2 and 6 meter above surface)
Wind speed (2 meter above surface)
Short and long in- and outgoing radiation (2 meter above surface)
Rain fall (Tipping buckets)
Soil surface temperature (infrared sensor)
Measurement time and interval
2nd of May till 28th of September
Hourly
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Calibration
The data from the month May used:
Time series h & θ
h versus θ
No POT data
Soil profile divided in four layers
Calibrated parameters: α, n and l
Mean, standard deviation and correlation matrix
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Design laboratory experiment 25 cm
Soil column 100 cm
Coarse sand (largest difference coupled-liquid & quickly drying out)
Boundary conditions
Mass balance for water
• Top boundary condition: Ep is 10 mm/day for warm period, 0 mm/day for cold period
• Bottom boundary condition is free flow
Heat conservation equation
• Top boundary condition: 12 hours of 40 degrees Celsius, 12 hours of 15 degrees
Celsius
• Zero soil heat flux is assumed as bottom boundary conditions
Measurements
Soil water pressure head, soil water content, soil temperature??
Amount of measurement??
Measurement depths??
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Conclusion
1. Thermal vapour flow is the important component of
water vapour flow;
2. During daytime thermal vapour flow is downward,
during nighttime vapour flow is upward; on a daily
basis these fluxes compensate each other;
3. Coupled heat and water transport models don’t
differ significantly from water transport models on a
daily time scale.
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Recommendations
Data from several soil profiles
Use for heat conservation equation flux in stead of state boundary conditions
Convective water vapour flow
Including airflow in the coupled mass and heat transfer, a third balance for the total
gas phase
No thermodynamic equilibrium between liquid water and water vapour