E. Saatdjian

Bio: E. Saatdjian is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Stokes flow & Heat transfer. The author has an hindex of 14, co-authored 23 publications receiving 618 citations.

Application of CFD in the study of supercritical fluid extraction with structured packing: Dry pressure drop calculations

Abstract: Liquid phase SFE has been carried out in extraction columns, with structured packings particularly of the gauze type. Structured packing performs very well during extractions under these conditions, mainly due to their relatively large surface area and free volume. Nevertheless, there are also important disadvantages such as high cost, low capacities at high flow rates, and premature flooding. The assessment of the real efficiencies of these packings poses extreme difficulties related to the moderately high pressures involved in these processes. Computational fluid dynamics (CFD) can be used to characterize the complex single and multiphase flow inside the packed bed and evaluate the influence of the shape and geometry of the packing on the hydrodynamics and mass and heat transfer rates in the SFE packed column. In this first study, and with a very detailed modelling of the packing geometry, the dry pressure drop is calculated for both laminar and turbulent flow conditions. Results are seen to agree well with the experimental data in the literature.

Computational-fluid-dynamics study of a Kenics static mixer as a heat exchanger for supercritical carbon dioxide

Abstract: The thermal efficiency of a Kenics® KM static mixer used to pre-heat supercritical carbon dioxide, under high pressure conditions, is studied using computational fluid dynamics (CFD). A mesh sensitivity analysis is performed and the CFD model is validated against experimental results on heat transfer with conventional and supercritical fluids. Three turbulent models – standard k–ɛ, RNG k–ɛ, and k–ω – are employed to model the flow and heat transfer under high pressure conditions; the effects of large variations of the physical properties in the pseudo-critical region of the fluid are also studied. The RNG k–ɛ model gives results that are closer to the experimental data than the other two turbulence models. The numerical results show that the static mixer has a thermal efficiency more than three times higher than that of a conventional empty pipe heat exchanger with similar heat transfer area.

A simulation model of a high-capacity methane adsorptive storage system

Abstract: A two-dimensional model is developed to describe the hydrodynamics, heat transfer and adsorption phenomena associated with the adsorptive storage of natural gas (NG) in cylindrical reservoirs. Intraparticle and film resistances to both heat and mass transfer are neglected. In the momentum equation, Ergun's law is considered locally valid and is extended to two dimensions. These assumptions are fully justified in the paper. Numerical results are presented concerning the pressurization and blowdown of an ultra-lightweight 50 litre cylinder, commercially available for the storage of compressed NG, if it were filled with an activated carbon having a good adsorptive storage capacity. A simple formula is also proposed to predict the filling times for fast charges. The predicted temperature changes in the packed-bed are in good agreement with those reported in the literature for an experimental charge/discharge.

Methane storage in flexible metal–organic frameworks with intrinsic thermal management

Abstract: Two flexible metal-organic frameworks are presented as solid adsorbents for methane that undergo reversible phase transitions at specific methane pressures, enabling greater storage capacities of usable methane than have been achieved previously, while also providing internal heat management of the system. Natural gas — methane — is a clean and cheap fuel but its usefulness in transport applications is limited by storage problems, given its low energy density per unit volume under ambient conditions compared with petrol or diesel. One way of increasing methane storage capacity is to use tanks containing porous materials, such as metal–organic frameworks, as a storage medium. However, for every methane molecule adsorbed and desorbed there is an associated thermal fluctuation that could cause overheating or reduce storage efficiency if left unchecked. Here Jeffrey Long and colleagues describe two flexible metal–organic frameworks that undergo reversible phase transitions at specific methane pressures, enabling greater storage capacities of usable methane than have been achieved previously, while also providing internal heat management of the system. As a cleaner, cheaper, and more globally evenly distributed fuel, natural gas has considerable environmental, economic, and political advantages over petroleum as a source of energy for the transportation sector1,2. Despite these benefits, its low volumetric energy density at ambient temperature and pressure presents substantial challenges, particularly for light-duty vehicles with little space available for on-board fuel storage3. Adsorbed natural gas systems have the potential to store high densities of methane (CH4, the principal component of natural gas) within a porous material at ambient temperature and moderate pressures4. Although activated carbons, zeolites, and metal–organic frameworks have been investigated extensively for CH4 storage5,6,7,8, there are practical challenges involved in designing systems with high capacities and in managing the thermal fluctuations associated with adsorbing and desorbing gas from the adsorbent. Here, we use a reversible phase transition in a metal–organic framework to maximize the deliverable capacity of CH4 while also providing internal heat management during adsorption and desorption. In particular, the flexible compounds Fe(bdp) and Co(bdp) (bdp2− = 1,4-benzenedipyrazolate) are shown to undergo a structural phase transition in response to specific CH4 pressures, resulting in adsorption and desorption isotherms that feature a sharp ‘step’. Such behaviour enables greater storage capacities than have been achieved for classical adsorbents9, while also reducing the amount of heat released during adsorption and the impact of cooling during desorption. The pressure and energy associated with the phase transition can be tuned either chemically or by application of mechanical pressure.

Methane storage in metal organic frameworks

Abstract: In this applications article (116 references), the use and viability of metal organic frameworks (MOFs) for natural gas storage is critically examined through an overview of the current state of the field. These smart materials can be tuned to deliver best performance according to demand, as a function of temperature, desired storage pressure and mandated fill/release rates. Whilst the chemistry behind optimising natural gas storage performance in MOFs is highlighted, it is contextualised to the specific application in vehicular transport, and the best means of testing performance parameters are canvassed. Future applications of MOFs with natural gas are also discussed.