Selectable Optical Diagnostics Instrument - Diffusion and Soret Coefficient (SODI-DSC) - 09.17.14
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The Selectable Optical Diagnostics Instrument - Diffusion and Soret Coefficient (SODI-DSC) experiment will study diffusion in six different liquids over time in the absence of convection induced by the gravity field.
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Verhaert Design and Development, Antwerp, , Belgium
Sponsoring Space Agency
European Space Agency (ESA)
ISS Expedition Duration
September 2011 - September 2012
Previous ISS Missions
The precursor to SODI-DSC, DCCO was operated on the ISS during Expedition 4.
- The Selectable Optical Diagnostics Instrument - Diffusion and Soret Coefficient (SODI-DSC) measurements for improvement of oil recovery experiment consists of three stages:
- The determination of diffusion data requirements for petroleum reservoir models
- The simultaneous measurement of the Soret diffusion (a major process by which components tend to separate, occurring each time heat flows in a mixture, or each time the regions of a mixture are at different temperatures) coefficients in binary and in tertiary systems
- The refinement of a multi-component transport model applied to petroleum reservoir evaluation.
Diffusive processes are widely present in daily life and in natural processes, and play a key role in the transformation and mixing of fluid mixtures. In this context, the term diffusion is used to describe the relative motion of a species with respect to the other and can be caused by a concentration (isothermal diffusion) or temperature (thermal diffusion) across the mixture or by a potential gradient (as sedimentation).
A very peculiar natural laboratory where mixing processes in fluid mixtures have a high scientific and industrial interest is the one of oil reservoirs, where various effects contribute to the distribution of the component of the mixture that forms crude oils. A role is played by thermal diffusion caused by temperature gradient that develops inside reservoirs, assessing around an average value of 3ºC/100 m.
The prediction of hydrocarbon composition is an important factor that contributes to the reservoirs exploitation strategies. Since the cost of resources increase with depth, the oil companies are interested in reliable thermo dynamical models that allow the characterization of an entire reservoir using a reduced number of exploratory wells. To better model the complex behavior of crude oils, a better prediction of the thermal diffusion or Soret effect could be included. To this extent, there is a need of an experimental determination of the diffusion and thermal diffusion coefficients of crude oils.
The SODI-DSC investigation will provide information to scientist aiming to better understand the behavior of various liquids over time in the absence of convection induced by a microgravity environment, therefore allowing for more successful science to be operated onboard ISS. The microgravity environment is a unique tool for studying the behavior of liquids, since the reduced buoyancy force allows the observation of processes that are masked or biased by normal gravity. In particular, for binary and more complex fluid mixtures, accurate measurements of thermal and isothermal diffusion coefficients in ground based experiments are often perturbed by gravity, especially in the case of thermal diffusion, where the temperature difference applied to the sample may provoke parasitic convective flows.
The SODI-DSC investigation will provide information to scientist which can be used to more efficiently extract oil resources.
Downlink of data is required to quickly assess the integrity of the liquid sample and to characterize the thermal field imposed on the experimental cell. Residual gravity levels will be measured with a companion cell filled with calibrated tracers. The 3D motions of the tracers will be reconstructed by digital holography (a technique for producing an image which conveys a sense of depth).
Crewmembers will install the SODI optical instrument and the DSC experiment cell arrays (2 cell arrays each composed of 5 cells). After installation, the next step involves the optical processing of the liquid binary/ternary solution in two steps. A thermal gradient imposition occurs across the experimental cell followed by a concentration difference created due to the linear temperature profile which is due to the thermo-solutal (i.e. Soret) diffusion effect. After the temperature gradient has relaxed, the liquid system will homogenize due to molecular diffusion processes. These processes should be repeated several times (up to 16 times) to acquire statistically relevant results. After processing the DSC cells, the SODI instrument should be stowed.
Ahadi A, Van Varenbergh S, Saghir Z. Measurement of the Soret coefficients for a ternary hydrocarbon mixture in low gravity environment. Journal of Chemical Physics. 2013; 138(20): 204201.
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