National Aeronautics and Space Administration National Aeronautics and Space Administration The U.S. Government's Official Web Portal National Aeronautics and Space Administration National Aeronautics and Space Administration
NASA Banner spacer Banner Spacer spacer spacer
Advanced Search
Go button
spacer About NASA About NASA Glenn Exploration Systems Mission Directorate
ISS Research Project GRADFLEX banner
ISS Research Project @ ARC
ISS Research Project @ GRC
ISS Fluids & Combustion Facility
FCF Investigations
Microgravity Science Glovebox
Announcement Background spacer
Gradient Driven FLuctuations Experiment

The GRAdient Driven FLuctuation EXperiment (GRADFLEX) involves the investigation of fluctuations induced in simple fluids and in binary mixtures by imposing a macroscopic temperature or concentration gradient under microgravity conditions. Recent experiments have shown that giant nonequilibrium fluctuations are present during diffusion processes in liquid mixtures and in the presence of a heat flux through a fluid. These fluctuations occur at all length scales between the microscopic and a macroscopic scale set by the sample dimensions. The fluctuations are due to corrugations in the diffusing front, whose fractal properties explain the presence of fluctuations involving all length scales. The fluctuations are generated by coupling between velocity fluctuations and the macroscopic gradient (concentration or temperature) which drives the flux. The amplitude of these fluctuations diverges as q-4, where q is the wave vector of the fluctuation. Long wavelength fluctuations are stabilized by gravity, which quenches the q-4 divergence at the smallest wave vectors.

On Earth, gravity suppresses the long wavelength fluctuation below a typical cutoff wave vector. The aim of the GRADFLEX project is to investigate these fluctuations in the absence of gravity, where the long wavelength fluctuations are no longer predicted to be stabilized by gravity, and to compare the results with those obtained on Earth. Many materials science processes (for example, crystallization and growth of materials) are performed in microgravity because of advantages expected from the absence of convection. However, the presence of nonequilibrium fluctuations could lead to the unexpected presence of large scale inhomogeneities that could impair processing under microgravity conditions.

Two prototype systems to guide the engineering of flight hardware have been developed, one in the Optics and Microgravity Laboratory at the University of Milan by the Istituto Nazionale per la Fisica della Materia (INFM) and one in the Physics Department at the University of California at Santa Barbara (UCSB). Both systems use the shadowgraph method to measure the fluctuations. The system developed at INFM is devoted to the investigation of concentration fluctuations occurring during a Soret induced mass diffusion process, while that developed at UCSB is designed to investigate fluctuations induced by a thermal gradient in a single-component fluid. The project is scheduled for flight in 2008 onboard the Russian satellite capsule FOTON M3.

The current sensitivity of the shadowgraph method is now sufficiently developed to measure the scattering from the fluctuations, both on Earth and in microgravity. Samples are contained between parallel sapphire windows to provide the necessary thermal boundary conditions. The fluctuations give rise to phase perturbations in the wavefronts of a beam of light passing through the sample, resulting in measurable intensity modulation a sufficient propagation distance beyond the sample. This intensity modulation is time-dependent, and it can be analyzed to obtain both the mean squared amplitude of the fluctuations S(q), and their power spectrum S(q,ω), for wave vectors as small as 20 cm-1. Thus the method is useful well below the range where small angle light scattering is typically impossible because of stray light and other effects. The resulting data are the product of S(q) and the shadowgraph transfer function T(q) = Sin2 (q2z/2ko).

Objective

  • Study gradient driven density and concentration fluctuations that are strongly enhanced in fluids by the absence of gravity.
  • Achieve a quantitative understanding of gradient driven fluctuations, both on Earth and in the microgravity environment provided during a Foton-M3 mission.

Relevance / Impact

  • In reduced gravity, gradients drive giant fluctuations that may impact processes such as crystal growth.
  • This experiment was featured on the front-cover of the April 1, 2006 issue of Applied Optics.

Development Approach

  • ESA / ESTEC is funding the flight hardware and provides ground-based support in Italy.
  • NASA funding allowed the development of essential prototype hardware and provides ground-based support in the U.S.

Contacts at NASA Glenn Research Center
Project Manager: Dr.William V. Meyer
NCSER at NASA GRC

william.v.meyer@nasa.gov
216-433-5011

Project Scientist:
Dr.William V. Meyer
NCSER at NASA GRC

william.v.meyer@nasa.gov
216-433-5011

Principal Investigator: Professor David Cannell, UCSB


GRADFLEX on frront-cover of Applied Optics
GRADFLEX on frront-cover of Applied Optics
 
Foton-M3 satellite
Foton-M3 satellite
 
Gradient driven fluctuations visible with a shadowgraph
Gradient driven fluctuations visible with a shadowgraph
 
GRADFLEX Sample Degassing Configuration
GRADFLEX Sample Degassing Configuration
 
GRADFLEX Sample Filling
GRADFLEX Sample Filling
 
 
 

Acceleration Measurements
Express Racks
Maintentance Work Area
Expendable Launch Venicle Investigations
GRADFLEX
Telescience Support Center
ISS Research Project @ JSC
ISS Research Project @ JPL
ISS Research Project @ KSC
ISS Research Project @ MSFC

ISS Research Project Links
Space Station Research & Technology  
Space Station Project Links
     
     
Space Flight Systems Links
  Space Flight Systems @ GRC
  Human Research Program  
Acronyms  
Articles
 
Missions  
This Month in Exploration  
   
   
GRC Microgravity and Technology Flight Experiments
Accomplished  
Planned  
   
   
 
GRADFLEX Related Documents
small acrobat icon
 
small acrobat icon   Photon correlation and scattering: introduction to the feature issue  
small acrobat icon   GRADFLEX Press Release
 
 

Adobe Acrobat

 
Footer seperator
FirstGov Logo

+ Freedom of Information Act
+ Privacy Policy and Important Notices
+ Applications and Plugins for Viewing Documents and Media
NASA Logo

Webmaster:
Tim Reckart
NASA Official: Thomas St. Onge
Last Updated: February 8, 2011
Footer spacer
Footer spacer