Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Where Does the Fluid Go?

25.02.2010
Revised model will help scientists better understand transport of fluid constituents, with a wide range of applications.

Combined mechanisms of transport have important applications—transport of nutrients across cell membranes in plants and animals, the aeration of agricultural soils, performance of chemical reactors, the design of membranes for desalting brackish water, and the design of clay membranes for retaining dangerous chemicals.

Because mass transport of fluid constituents has important roles in biology, physics, and chemistry, one would assume that such transport would be well understood by the scientific community. However, transport of fluid constituents continues to be a source of confusion, particularly regarding models for combining transport by molecular diffusion and advection.

In a recent article in Vadose Zone Journal, A.T. Corey, W.D. Kemper (both of Colorado State Univ., Fort Collins), and J.H. Dane (Auburn Univ., Auburn, AL) show that the developers of popular models of diffusion have made invalid assumptions. Currently popular models define diffusion of a particular constituent as a flux relative to mass average flux so that diffusive flux of all constituents in a fluid mixture must sum to zero, and self-diffusion of a single-specie fluid cannot exist, contradicting experimental evidence previously reported in the literature. Research conducted and referenced by the authors shows that these assumptions and their models do not provide a satisfactory description of the flux taking place in media with small pores.

The authors provide an improved analysis, based on the principle that driving forces (for both advection and diffusion) are each equal in magnitude (and opposite in direction) to the associated rate of change of momentum. Mass average flux resulting from combined advection and diffusion is shown to be evaluated as the vector sum of advective and diffusive fluxes, rather than diffusive flux being evaluated as a flux relative to a mass average flux. This procedure is necessary because “mean flux” cannot be determined independent of an evaluation of diffusive flux.

Corey et al. describe two experiments with transport of gas constituents through porous media (providing data consistent with their revised model) that contradict widely accepted models. One of the experiments presents previously published data and the other describes new data obtained by the authors. Three additional experiments are presented (one representing new data) showing that self-diffusion of pure liquid water occurs in response to a temperature gradient, contradicting theory that diffusion of a single-specie fluid cannot occur, and showing that the sum of diffusion fluxes do not sum to zero in the general case. The measured diffusion of water was proportional to the gradient of the vapor pressure, which is a well-documented measure of the kinetic energy of water.

The full article is available for no charge for 30 days following the date of this summary. View the abstract at http://vzj.scijournals.org/cgi/content/full/9/1/85.

Vadose Zone Journal, http://www.vadosezonejournal.org/ is a unique publication outlet for interdisciplinary research and assessment of the biosphere, with a focus on the vadose zone, the mostly unsaturated zone between the soil surface and the permanent groundwater table. VZJ is a peer-reviewed, international, online journal publishing reviews, original research, and special sections across a wide range of disciplines that involve the vadose zone, including those that address broad scientific and societal issues. VZJ is published by Soil Science Society of America, with Geological Society of America as a cooperator.

The Soil Science Society of America (SSSA) is a progressive, international scientific society that fosters the transfer of knowledge and practices to sustain global soils. Based in Madison, WI, and founded in 1936, SSSA is the professional home for 6,000+ members dedicated to advancing the field of soil science. It provides information about soils in relation to crop production, environmental quality, ecosystem sustainability, bioremediation, waste management, recycling, and wise land use.

SSSA supports its members by providing quality research-based publications, educational programs, certifications, and science policy initiatives via a Washington, DC, office. For more information, visit www.soils.org.

SSSA is the founding sponsor of an approximately 5,000-square foot exhibition, Dig It! The Secrets of Soil, which opened July 19, 2008 at the Smithsonian's National Museum of Natural History in Washington, DC.

Sara Uttech | EurekAlert!
Further information:
http://www.agronomy.org

More articles from Agricultural and Forestry Science:

nachricht Energy crop production on conservation lands may not boost greenhouse gases
13.03.2017 | Penn State

nachricht How nature creates forest diversity
07.03.2017 | International Institute for Applied Systems Analysis (IIASA)

All articles from Agricultural and Forestry Science >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>