January 20, 2017

Science

Science Objectives

The first set of experiments is dedicated to first-class and original science of very broad interest for the world-wide scientific community in the field of near-ambient and high-temperature critical fluids and in the field of material sciences. This research includes for example combustion in supercritical water and the solidification of lamellar eutecticsand is an extension of the programme conducted on board the MIR space station and the Space Shuttle.

ALI
Grid (top) and direct imaging
of two-phase systems.

The main science objectives are to study the coupling phenomena involving hydrodynamics in highly compressible supercritical fluids and forced piston effect. After a series of experiments on board the MIR station in the ALICE facility, the value of continuing such a research programme on the ISS became clear and was prioritized at programme management level.

In the Declic programme the primary science objective is dedicated to directly visualizing the boiling crisis and to phase separation at very low volume fraction. Preliminary observations of critical density fluctuations in the direct space are also expected. These density fluctuations have natural length scales, as the correlation length is around 0.5µm and the time-scale 12milliseconds for a temperature fluctuation of ± 1mk around the critical point. Simultaneously, typical runs are dedicated to the boiling study. For this latter topic, a specific cell with an internal heater is designed to control the heat flux delivered to the gas bubble, in the two-phase domain T Tc.

HTI 

This High Temperature Insert is dedicated to the study of forced piston effect in H2O and coupling phenomena between chemical reactions and hydrodynamics in highly compressible supercritical fluids.

The scientific objectives are: study of the heat and mass transfer in near-critical water submitted to pulse heating and/or mechanical quenching, with observation of the critical behaviour of water.

The experiment will necessitate critical temperature (Tc) search and balancing steps with measurement of temperature and density gradient relaxation.

This experiment has led to the study of new technological issues linked to high temperature and use of high pressure.

The design is intended to withstand temperatures up to 600°C and high pressure up to 500 bars. The sample cell body and the corresponding optical windows are submitted to an aggressive environment that must to be closely controlled. Recent achievements have evidenced the technical difficulties in this high-temperature, high-pressure experimental cell, observed through a wide transmission diameter (around 12 mm), designed taking into account a reduced volume and NASA safety constraints.


Starting Fire in Water © NASA

DSI
Top-view image of the solid-liquid interface during columnar growth showing a large number of grains with different morphologies, varying from deep cells to dendrites of different growth directions. (Succinonitrile - 0.1 wt% acetone).


Interferogram of dendrites

The DECLIC solidification programme on board the ISS is targeting both fundamental physics and materials processing.

  • Basic fundamental physics is related to:
    • Self-organization in far-from-equilibrium systems
    • Growth and patterns in non-linear physics
    • Dynamics of extended 3D-systems
  • Materials processing with active control is related to:
    • Microstructure engineering for specific in-use properties of materials
    • Well-defined model experiments on technical alloys, and on model transparent systems to be achieved with the DECLIC facility.
    • Physical modelling and numerical simulation at the microstructure and fluid flow scales.
    • Comparative studies involving microgravity benchmarks under diffusion transport and 1g-experiments effected by fluid flow caused by Earth's gravity.

The Directional Solidification experiment is performed in a dedicated insert, which ensures dedicated conditioning of sample material encapsulated in a cartridge.

Using a succinonitrile-based alloy has led the designers to take into account the safety aspects that were considered critical due to the toxicity of the sample in certain conditions.

Main science objectives:

  • Onset of morphological instabilities
  • Dynamics of formation and selection of cellular/dendritic array
  • Recoil of the front in initial solidification transient
  • Coupling effects between solidification front and convection.