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Measurement of Hydraulic Characteristics of Porous Media Used to Grow Plants in Microgravity

Hernandez Engineering, Mail Code C77, Johnson Space Center, National Aeronautics and Space Administration, 2101 NASA Parkway, Houston, TX 77058

View larger version (37K): [in a new window]   Fig. 1. Diagram of hanging water column system. One or both water columns were used to control inflow/outflow from the porous medium. Horizontal steady flow was induced by maintaining a 1-cm height difference between h1 and h2. Transient flow was induced by changing the h of one water column from 0 to –15 or –25 for 1- to 2- or 0.25- to 1-cm porous medium. Continuous pumping from the supply reservoirs to water columns and overflow from the water columns back to supply reservoirs maintained a constant head. P = pressure transducer.

View larger version (27K): [in a new window]   Fig. 2. Water retention characteristics of baked ceramic aggregate. Upper: 0.25 to 1 mm; lower: 1 to 2 mm. Static water retention: • = drying curve; = wetting curve. Data are means ± SD. Predicted by the Van Genutchen (Van Genuchten, 1980) water retention model: drying (—), wetting (- - -). Dynamic water retention (drying curve) = .

View larger version (39K): [in a new window]   Fig. 3. (A), (C): Measured matric potential gradient during steady state flow. For each imposed matric potential, the difference in water tension within microporous membranes on either side of the porous medium sample was 1 cm. (B), (D): Matric potentials measured at the same vertical depth, 7 cm apart, during approach to steady horizontal flow in a 3-cm depth of porous medium. Imposed suction within porous membranes on either side of the sample: –19 to –20 or –7.5 to –8.5 cm H2O suctions for 0.25- to 1- or 1- to 2-mm porous medium.

View larger version (40K): [in a new window]   Fig. 4. Water transport and matric potentials in 0.25- to 1-mm (left) or 1- to 2-mm (right) porous medium during horizontal transient flow. (A) Cumulative outflow (•) or volumetric water content () () as a function of time. (B) Matric potential gradient across a 7-cm section of medium during transient drainage. (C) Matric potential () as a function of position for different times during transient flow across a 15.24-cm length of porous medium.

View larger version (33K): [in a new window]   Fig. 5. Measured and interpolated hydraulic conductivity function (K) for 0.25- to 1-mm and 1- to 2-mm porous medium.

View larger version (26K): [in a new window]   Fig. 6. Comparison of the hydraulic conductivity function (K) measured by steady state and instantaneous profile methods and predicted by the van Gentuchen/Mualem models.