HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Heinse, R. Articles by Or, D. Search for Related Content PubMed Articles by Heinse, R. Articles by Or, D. GeoRef GeoRef Citation Agricola Articles by Heinse, R. Articles by Or, D. Related Collections Macroporous/Aggregated Media Variably Saturated Fluid Flow Soil Physics

ORIGINAL RESEARCH

Measurements and Modeling of Variable Gravity Effects on Water Distribution and Flow in Unsaturated Porous Media

^a Dep. of Plants, Soils and Climate, Utah State Univ., Logan, UT 84322-4820
^b Universities Space Research Assoc., Mail Code EC3, NASA/JSC, Houston, TX 77058
^c Dep. of Soil, Water & Environmental Science, The Univ. of Arizona, Tucson, AZ 85721
^d Lab. of Soil and Environmental Physics, Ecole Polytechnique Fédérale de Lausanne, Switzerland
^* Corresponding author (heinse{at}cc.usu.edu).

Received 24 July 2006.

Liquid behavior under reduced gravity conditions is of considerable interest for various components of life-support systems required for manned space missions. High costs and limited opportunities for spaceflight experiments hinder advances in reliable design and operation of elements involving fluids in unsaturated porous media such as plant growth facilities. We used parabolic flight experiments to characterize hydraulic properties under variable gravity conditions deduced from variations in matric potential over a range of water contents. We designed and tested novel measurement cells that allowed dynamic control of water content. Embedded time domain reflectometry probes and fast-responding tensiometers measured changes in water content and matric potential. For near-saturated conditions, we observed rapid establishment of equilibrium matric potentials during the recurring 20-s periods of microgravity. As media water content decreased, the concurrent decrease in hydraulic diffusivity resulted in limited attainment of equilibrium distributions of water content and matric potential in microgravity, and water content heterogeneity within the sample was influenced by the preceding hypergravity phase. For steady fluxes through saturated columns, we observed linear and constant hydraulic gradients during variable gravity, yielding saturated hydraulic conductivities similar to values measured under terrestrial gravity. Our results suggest that water distribution and retention behavior are sensitive to varied gravitational forces, whereas saturated hydraulic conductivity appears to be unaffected. Comparisons between measurements and simulations based on the Richards equation were in reasonable agreement, suggesting that fundamental laws of fluid flow and distribution for macroscopic transport derived on Earth are also applicable in microgravity.

Abbreviations: ESA, European Space Agency • NASA, National Aeronautics and Space Administration • TDR, time domain reflectometry