Susan L. Steinberg

Porous media matric potential and water content measurements during parabolic flight

Control of water and air in the root zone of plants remains a challenge in the microgravity environment of space. Due to limited flight opportunities, research aimed at resolving microgravity porous media fluid dynamics must often be conducted on Earth. The NASA KC-135 reduced gravity flight program offers an opportunity for Earth-based researchers to study physical processes in a variable gravity environment. The objectives of this study were to obtain measurements of water content and matric potential during the parabolic profile flown by the KC-135 aircraft. The flight profile provided 20-25 s of microgravity at the top of the parabola, while pulling 1.8 g at the bottom. The soil moisture sensors (Temperature and Moisture Acquisition System: Orbital Technologies, Madison, WI) used a heat-pulse method to indirectly estimate water content from heat dissipation. Tensiometers were constructed using a stainless steel porous cup with a pressure transducer and were used to measure the matric potential of the medium. The two types of sensors were placed at different depths in a substrate compartment filled with 1-2 mm Turface (calcined clay). The ability of the heat-pulse sensors to monitor overall changes in water content in the substrate compartment decreased with water content. Differences in measured water content data recorded at 0, 1, and 1.8 g were not significant. Tensiometer readings tracked pressure differences due to the hydrostatic force changes with variable gravity. The readings may have been affected by changes in cabin air pressure that occurred during each parabola. Tensiometer porous membrane conductivity (function of pore size) and fluid volume both influence response time. Porous media sample height and water content influence time-to-equilibrium, where shorter samples and higher water content achieve faster equilibrium. Further testing is needed to develop these sensors for space flight applications.

Flow and distribution of fluid phases through porous plant growth media in microgravity: Progress to date

Results from plant growth experiments utilizing particulate growth media during space flight revealed difficulties associated with providing reliable reproducible gaseous and water supply to plant roots. These limitations were attributed to insufficient understanding of liquid configuration and growth media transport processes in reduced gravity. The objective of this NASA-funded research program is to develop a framework for modeling and quantitative characterization of physical processes associated with flow of wetting and non-wetting phases in particulate plant growth media in microgravity. This paper provides an overview of research plans and current status of research activities. Characterization and modeling of substrate water retention and transport properties in microgravity is key to management and control of gas and liquid fluxes within plant root zones. Modeling efforts will focus on both 1) a pore network model for describing discontinuous fluid phase transport (ganglia/blobs) and 2) a statistical distribution model describing water retention and hydraulic conductivity as functions of various pore configurations. Minimizing hydrostatic forces within porous media by using thin samples on earth may provide an approximation to microgravity conditions. In our preliminary study we have used Magnetic Resonance Imaging (MRI) to detect and track the evolution of liquid configuration and dynamics within thin slices of opaque porous media (Aquafoam with mean pore size of 50 μm). Both twoand three dimensional temporal MRI imaging has been performed in thin Aquafoam slices positioned vertically and horizontally (to simulate the effect of gravity). The wetting front exhibited percolation-type patterns and fingering. Preliminary results show that gravity dominates liquid flow even for low Bond numbers. Although the capillary forces are very strong the small hydrostatic pressure built in the initial liquid volume determines the subsequent evolution of the wetting front.

Challenges to understanding fluid behavior in plant growth media under microgravity

Note: SAE Technical Paper 2005-01-2952 Reference LASEP-CONF-2005-012 Record created on 2007-08-24, modified on 2016-08-08

Measurement of Porous Media Hydraulic Properties during Parabolic Flight Induced Microgravity

Bioregenerative life-support systems proposed for longduration space missions require an understanding of the physical processes that govern distribution and transport of fluids in particulate porous plant-growth media. Our objectives were to develop hardware and instrumentation to measure porous-medium water retention and hydraulic transport properties during parabolic-flight induced microgravity. Automated measurements complimented periodic manual operations in three separate experiments using porous ceramic aggregates and glass beads. The water content was adjusted in multiple steps in periods of 1.8g. Continuous hydraulic potential measurements provided information on water retention. The short duration of microgravity limited the occurrence of equilibrium potentials under partially saturated conditions. Measured pressure gradients under fixed flow rates were largely unaffected by gravity force in saturated cylindrical porous-medium-filled flow cells. High resolution video imagery provided details on water imbibition rates into dry and previously wetted porous media. Additional analysis of these data will provide insight into the effects of reduced gravity on porous medium hydraulic properties.

Effects of variable gravity on porous media matric potential and water content measurements

Control of water and air in the root zone of plants remains a challenge in microgravity. Due to limited flight opportunities research aimed at resolving fluid dynamics in microgravity porous media must often be conducted on earth. KC135 flight offers an opportunity for earth-based researchers to study physical processes in a variable gravity environment. The objectives of this study were to obtain measurements of water content and matric potential during the parabolic profile flown by the KC135 aircraft. The flight profile was designed to give 20-25 seconds of microgravity at the top of the parabola, while pulling 1.8-g at the bottom. Temperature and Moisture Acquisition Sensors (TMAS; Orbital Technologies, Madison, WI) use a heat-pulse method to measure water content. Tensiometers were constructed using a porous membrane with a pressure transducer and were used to measure matric potential. The two types of sensors were placed at different depths in a substrate compartment filled with 1-2 mm Turface (calcined clay). The TMAS sensors were unable to monitor bulk changes in water content in the substrate compartment, but were able to track local moisture changes in the soil profile. There were differences in water content data recorded at zero-, one-, and 1.8-g, but these were not significant. Tensiometer readings tracked pressure differences due to the hydrostatic force changes with variable gravity. The readings may have been affected by changes in cabin air pressure that occurred during each parabola. Tensiometer porous membrane conductivity (function of pore size) and fluid volume both influence response time. Porous media sample height and water content influence time-to-equilibrium, where shorter samples and higher water content achieve faster equilibrium. Further testing is needed to develop these sensors for space flight applications.

DISCONTINUOUS PORE FLUID DISTRIBUTION UNDER MICROGRAVITY DUE TO PARTICLE REARRANGEMENT

This paper reports (i) the experimental investigation conducted aboard the NASA’s KC-135 reduced-gravity flights to study possible particle separation and the distribution of discontinuous wetting fluid in porous media under microgravity, and (ii) numerical study of the effect of soil particle rearrangement on the water retention characteristics in zero gravity.

Flow and Distribution of Fluid Phases Through Porous Plant Growth Media in Microgravity

Results from plant growth experiments utilizing particulate growth media during space flight revealed difficulties associated with providing reliable and reproducible water and air supply to plant roots. These limitations have been attributed to insufficient understanding of liquid configuration and growth media transport processes in reduced gravity. This information gap has made it impossible to determine whether culturing technique or microgravity significantly effects water and air transport through particulate media in microgravity. The objective of this NASA-funded research program is the quantitative characterization of physical processes associated with flow of wetting and nonwetting phases in particulate plant growth media that are essential for successful design and control of plant production systems during space flight. Introduction The key to successful plant research or crop production in space is to understand the effect of microgravity on plant physiological functions. Problems with controlling the plant environment have made it impossible to isolate microgravity as a variable of study (Dutcher et al., 1994). Over the last 10 years millions dollars have been spent on flight experiments with plants, with most considered only marginally successful (Steinberg et al., 2002b). Although a number of environmental factors such as light and air quality, and ventilation impact plant growth in microgravity, none have had such a limiting effect as 1 Universities Space Research Association, Mail Code EC3, JSC/NASA, Houston, TX 77058; PH (281)483-8161; FAX (281) 483-2508; email:ssteinbe@ems.js c.nasa.gov. 2 Dept. Mechanical and Aerospace Engineering. Case Western Reserve University, Cleveland, OH 44106; PH (216) 368-6045; FAX (216) 368-6445; email: ida2@po.cwru.edu. 3 Dept. of Civil and Environmental Engineering, University of Connecticut, Storrs, CN 06269; PH (860) 486-2768; FAX (860) 486-2298; email: dani@engr.uconn.edu. 4 National Center for Microgravity Research on Fluids and Combustion, NASA/GLENN, Cleveland, OH 44135; PH(216) 433-3270; FAX (216) 433-3793; Nihad.Daidzic@grc.nasa.gov. 5 Dept. Plants, Soils and Biometerology, Utah State University, Logan, Utah 84322; PH (435)797-2175; FAX (435) 797-2117; sjones.psbdept@mendel.usu.edu. 6 Dept. Civil Engineering, Kansas State University, Manhattan, KS 66506; PH (785) 532-1586; FAX (785) 532-7717; reddi@ksu.edu. 7 Dept. Plant, Soil and Entolological Sciences and Biological and Agricultural Engineering. University of Idaho, Moscow, ID 83844; PH (208) 885-7219; FAX (208) 885-7760; email: mtuller@uidaho.edu. 8 Dept. of Agronomy, Kansas State University, Manhattan, KS 66506; PH (785) 532-7215; FAX (785) 532-6094; email; gjk@ksu.edu. 9 Dept. of Civil Engineering. Kansas State University, Manhattan, KS 66506; PH (785) 532-1837; FAX (785) 532-7717; email: mingxiao@ksu.edu. Flow and Distribution of Fluid Phases Through Porous Plant Growth Media In Microgravity