The Impact of Water Vapor Diodes on Soil Water Redistribution.

Diurnal soil temperature fluctuations are the prime cause for subsurface water vapor fluxes. In arid and semi-arid areas, water vapor flux is the dominant means of soil water redistribution. The direction of water vapor flux shifts from upward to downward diurnally based on the soil temperature regime. A water vapor diode is a layer using an egg carton shape design, with pores situated at the peaks between cups. In one direction, both water and heat can move through the diode layer; while in the opposite direction, the water flux will be blocked, while the heat can propagate through. Thus, by applying a water vapor diode, it is possible to maintain direction-controlled vapor fluxes. Thus, in principle, water vapor diodes can be used to accumulate or remove water in particular soil layers.

In this study, we discuss four cases of using water diodes to control soil water redistribution. Numerical simulation is used to evaluate the impact of the various water vapor diodes. The results indicate that water vapor diodes can influence the local water contents up to 10%. For a fixed initial water and thermal condition, the effect of a water vapor diode is related to the placement depth. In conclusion, water vapor diodes can be used to manipulate soil water content. The numerical simulation results are encouraging, and field tests should be performed.