Kathleen Smits, Ph.D., P.E.

Assistant Professor

Department of Civil & Environmental Engineering

Smits Research Group - Research (Land/Atmospheric Interactions)

Land/Atmospheric Interactions

The Effect of Wind Speed on Evaporation

In this work we are investigating the effect of wind speed on evaporation from soil through integrated modeling of atmospheric boundary layer and shallow subsurface

Davarzani et al., 2014, WRR

Modeling of single-phase (two-component) transfer in atmosphere and two-phase (two-component) transfer in porous media

Experimental Methods

  • Water table initially at top surface of column
  • Bottom boundary prevented water flow
  • Uniform temperature distribution established at upper boundary using an infrared heater
  • Evaporation induced at soil surface (Drying) upper boundary open
  • 8 test cases under varying wind conditions from 0.5 m/s to 3.5 m/s wind speed
Continuously Monitor:
  • Soil Moisture
  • Temperature (soil and air)
  • Relative Humidity (soil and air)
  • Tank Weight
  • Wind speed

Experimental Setup

Model results: Influence of the wind speed on the evaporation processes (Vw: maximum wind speed in free medium)

Davarzani et al., 2014, WRR

This graph shows that the coupling concept can predict the different stages of the drying process in porous media. Increasing the wind speed increases the evaporation rate at low velocity values; at high values of wind speed the evaporation rate becomes independent of flow in free fluid

Influence of the wind speed on the evaporation processes (Vw: maximum wind speed in free medium)

Davarzani et al., 2014, WRR

Evaporation less dependent on flow in free fluid at high wind velocities

Boundary Layer Development Above Porous Media

In this work, we are investigating the effects of momentum, mass, and energy exchange at the land-atmosphere interface on subsurface transport processes

Three measurement locations along length of wind tunnel tank where vertical momentum, concentration, and temperature profiles are measured

Trautz et al., 2014, in preparation

The figure above shows the turbulent boundary layer velocity profiles under varying wind velocities

Evaporation from Soils Under Thermal Boundary Conditions

In this work, we are evaluating evaporation from soils under different thermal boundary conditions, labeled below as approach 1-2

Boundary condition for water vapor flux at the soil surface

Approach #1

Yamanaka et al., 1997, WRR

Approach #2

van de Griend and Owe, 1994, WRR

Existing continuum models of water and gas flow in soil represent evaporation either by a known time-dependent function as model input or by empirical approaches

Adapted from Smits et al., 2012, WRR

Experimental Set Up

Initial condition:

  • Fully saturated everywhere
Boundary conditions:
  • Bottom and side boundaries - no-flow
  • Upper boundary (infrared heater and fan)
    • Soil surface RH = 80-95%
    • Soil surface temp = 23-26°C
  • Ambient air
    • Temp = 21°C
    • RH = 35%
    • Avg wind velocity = 2.5 m/s

Smits et al., 2012, WRR

Comparison Between Approaches

  • None of the approaches predict Stage 1 evaporation well
  • Approach based on depth of evaporative front (Approach #1) better predicts drying rate than approaches simply based on water contents (Approach #2) or vapor concentration (Approach #3) for dry soil

Equilibrium and Nonequilibrium Phase Change Comparison of Different Modeling Approaches

In this work, we examined the limitations of the equilibrium assumption (Chemical equilibrium among the phases common assumption in soil) and related modeling approaches for vapor transport

Smits et al., 2011, WRR

Equilibrium and nonequilibrium model simulated and observed cumulative evaporation as a function of time

Adapted from Smits et al., 2011, WRR