Interfacial tension measurements and modelling of (carbon dioxide + n-alkane) and (carbon dioxide + water) binary mixtures at elevated pressures and temperatures

Supercritical carbon dioxide (CO₂) is often used as a process fluid for enhanced oil recovery. The storage of carbon dioxide in underground formations is a potential way of mitigating climate change during a transition period to more sustainable energy sources. Combining injection with subsequent trapping of the non-wetting supercritical carbon dioxide phase in the pores of a depleted reservoir is a promising scheme for allowing the continued use of fossil fuels with minimal environmental consequences. The design of such processes is ultimately linked to the confined behaviour of the fluids in question at reservoir conditions, which is largely controlled by interfacial forces. Measurements of the relevant interfacial tensions for systems containing alkanes, carbon dioxide and water are currently limited and inconsistent while models usually fail to capture the pressure dependence of the interfacial tension. In this work, a density functional theory based on the SAFT-VR equation of state was used to predict the interfacial tension of (H₂O + CO₂ + n-alkane) binary systems over wide ranges of temperature and pressure. The comparison with a new set of reported experimental data of three (n-alkane + CO₂) systems at pressures up to the critical points, as well as with the (H₂O + CO₂) system at pressures up to 60 MPa, for a temperature range of (298-443) K, is discussed.     

Bird-strike simulation for certification of the Boeing 787 composite moveable trailing edge

A validated simulation methodology has been developed to support the bird-strike certification of the carbon fibre epoxy composite, moveable trailing edge (MTE) of the Boeing 787 Dreamliner. The explicit finite element software PAM-CRASH™ was selected to perform the simulations utilising the advanced composite material, fastener and smooth particle hydrodynamic bird models available in the code. The modelling procedures were validated firstly through comparison with existing test data and secondly through the testing and analysis of representative structures. Subsequent use of the validated modelling procedures during the analysis of the MTE facilitated the evaluation of numerous bird-strike scenarios, leading to improved design efficiency and safety, while significantly reducing certification costs.     

Interleukin 1 (IL-1) causes changes in lateral and rotational mobilities of IL-1 type I receptors

To investigate IL-1-dependent interactions of IL-1 type I (IL-1 RI) receptors on intact cells, lateral and rotational mobilities and detergent insolubility were investigated. Lateral mobility was measured by fluorescence photobleaching recovery, using a Cy3-modified, noncompetitive mAb specific for IL-1RI (M5) bound to wild-type IL-1 RI or mutant IL-1 RI with a truncated cytoplasmic tail. Addition of IL-1 causes significant reduction in the mobile fraction of wild-type IL-1 RI for two different transfected cell lines. For the mutant IL-1 RI, no significant decrease in response to IL-1 is observed, indicating that the missing cytoplasmic segment is involved in IL-1-dependent interactions of IL-1 RI that lead to reduced lateral mobility on the cell surface. The rotational mobility of IL-1 RI was assessed with phosphorescence anisotropy decay measurements using erythrosin-labeled M5. IL-1 decreases the rotational mobility of cell surface IL-1 RI on the microsecond time scale and also increases the initial anisotropy, indicating loss in segmental motion. Measurements of resistance to solubilization by Triton X-100 showed that IL-1 binding increases the fraction of IL-1 RI sedimenting with cytoskeletal residues. The IL-1 receptor antagonist protein (IL-1ra) causes partial effects in reducing rotational mobility and increasing detergent insolubility of M5-lableled IL-1 RI, indicating that this ligand causes structural changes in the presence of the dimerizing M5 mAb. These ligand-dependent physical interactions of IL-1 RI on the cell surface may be related to signal initiation by this receptor.     

Modeling and optimization of multi-tubular metal hydride beds for efficient hydrogen storage

This work presents a novel systematic approach for the optimal design of a multi-tubular metal hydride tank, containing up to nine tubular metal hydride reactors, used for hydrogen storage. The tank is designed to store enough amount of hydrogen for 25 km range¹, for a fuel cell vehicle. A detailed 3D Cartesian, mathematical model is developed and validated against a 2D cylindrical developed by Kikkinides et al. [1]. The objective is to find the optimal process design so as to increase the overall thermal efficiency, and thus minimize the storage time. Optimization results indicate that almost 90% improvement of the storage time can be achieved, over the case where the tank is not optimized and for a minimum storage capacity of 99% of the maximum value.     

Dynamic modelling and optimization of hydrogen storage in metal hydride beds

This work presents a systematic approach for modelling, optimization and control of metal hydride beds used for hydrogen storage. A detailed 2-D mathematical model is developed and validated against experimental and theoretical literature results. Based on recent advances in dynamic optimization, the objective is then to find the optimal process design (e.g. cooling systems design) and operating strategy (e.g. cooling fluid profile over time) so as to minimize the storing time, while satisfying a number of operating constraints. Such constraints account for pressure drop limitations, cooling fluid availability, maximum tank temperature, etc. Optimization results indicate that almost 60% improvement of the storage time can be achieved, over the case where the system is not optimized, for a minimum storage capacity of 99% of the total bed capacity. Trade-offs between various objectives, alternative design options and optimal cooling control policies are systematically revealed illustrating the potential offered by modern optimization techniques.     

Numerical implementation of the integral-transform solution to Lamb's point-load problem

The present work describes a procedure for the numerical evaluation of the classical integral-transform solution of the transient elastodynamic point-load (axisymmetric) Lamb's problem. This solution involves integrals of rapidly oscillatory functions over semi-infinite intervals and inversion of one-sided (time) Laplace transforms. These features introduce difficulties for a numerical treatment and constitute a challenging problem in trying to obtain results for quantities (e.g. displacements) in the interior of the half-space. To deal with the oscillatory integrands, which in addition may take very large values (pseudo-pole behavior) at certain points, we follow the concept of Longman's method but using as accelerator in the summation procedure a modified Epsilon algorithm instead of the standard Euler's transformation. Also, an adaptive procedure using the Gauss 32-point rule is introduced to integrate in the vicinity of the pseudo-pole. The numerical Laplace-transform inversion is based on the robust Fourier-series technique of Dubner/Abate-Crump-Durbin. Extensive results are given for sub-surface displacements, whereas the limit-case results for the surface displacements compare very favorably with previous exact results. Received 20 October 1998