Coupled Heat and Water Flow in Variably-saturated Porous Media

T. Kamai, and J. W. Hopmans
Department of Land, Air and Water Resources, University of California, Davis, CA, USA

Simultaneous measurement of coupled water and heat transport in variably saturated porous media is achieved with the heat pulse probe (HPP). The heat needle of the HPP generates a heat pulse, whereas at various strategically placed locations the temperature responses are measured at known distances from the heating element.

Although the current probe design provides use for many applications, changes are needed for both increasing the measurable water flux (MWF) to values near 1 cm/day, and for field appliance which requires a more robust probe. However, changing the probe geometry precludes the use of analytical solutions, so that numerical solutions, such as the ones provided by COMSOL, are required.

Simulations include the coupling of heat conduction and convection with water flow in soils. The advantages of 3D simulations are emphasized, while accounting for differences in thermal properties between soil and probe materials, and for different directions of heat and water flow. Analysis of variable heater diameters, thermistor distances from the heater element and heat pulse patterns provide promising opportunities for increasing the measured water flux threshold.