Advances in polybenzimidazole-based membranes for uses in fluid separations and energy conversion

ConspectusNanoporous frameworks are a large and diverse family of supramolecular materials, whose chemical building units (organic, inorganic, or both) are assembled into a 3D architecture with well-defined connectivity and topology, featuring intrinsic porosity. These materials play a key role in various industrial processes and applications, such as energy production and conversion, fluid separation, gas storage, water harvesting, and many more. The performance and suitability of nanoporous materials for each specific application are directly related to both their physical and chemical properties, and their determination is crucial for process engineering and optimization of performances. In this Account, we focus on some recent developments in the multiscale modeling of physical properties of nanoporous frameworks, highlighting the latest advances in three specific areas: mechanical properties, thermal properties, and adsorption.In the study of the mechanical behavior of nanoporous materials, the past few years have seen a rapid acceleration of research. For example, computational resources have been pooled to create a public large-scale database of elastic constants as part of the Materials Project initiative to accelerate innovation in materials research: those can serve as a basis for data-based discovery of materials with targeted properties, as well as the training of machine learning predictor models.The large-scale prediction of thermal behavior, in comparison, is not yet routinely performed at such a large scale. Tentative databases have been assembled at the DFT level on specific families of materials, such as zeolites, but prediction at larger scale currently requires the use of transferable classical force fields, whose accuracy can be limited.Finally, adsorption is naturally one of the most studied physical properties of nanoporous frameworks, as fluid separation or storage is often the primary target for these materials. We highlight the recent achievements and open challenges for adsorption prediction at a large scale, focusing in particular on the accuracy of computational models and the reliability of comparisons with experimental data available. We detail some recent methodological improvements in the prediction of adsorption-related properties: in particular, we describe the recent research efforts to go beyond the study of thermodynamic quantities (uptake, adsorption enthalpy, and thermodynamic selectivity) and predict transport properties using data-based methods and high-throughput computational schemes. Finally, we stress the importance of data-based methods of addressing all sources of uncertainty.The Account concludes with some perspectives about the latest developments and open questions in data-based approaches and the integration of computational and experimental data together in the materials discovery loop.

Laser-matter interactions with metal target cause plasma explosion and shock accelerated variable density flow instabilities in the Semiconfined Configuration (SCC). Their study gives deeper insight into the flow instabilities present in all microchannel devices. Blast wave motion along the SCC microchanel causes the Kelvin–Helmholtz (KH) instability and formation of vortex filaments for the critical Reynolds number. Appearing in all shear layers—it affects the fluid transport efficiency. Shear layer acceleration causes a Raleigh-Taylor instability (RTI). Oriented bubble growth by discrete merging indicates anisotropic RTI mixing. Similar RTI flame instability appears in the conversion of chemical energy into electricity affecting microcombustion efficiency. Another case of anisotropic RTI is the flow boiling for cooling of chips and microelectronic devices. The RTI boiling which appears for the critical heat flux is based on rising surface vapor columns (oriented bubble growth) with liquid counterflow (spike prominences) for the critical wavelength at density interface. The RT bubble merging graph trees determine turbulent mixing which affects the heat transfer rates. Bottom-wall turbulent flow in the SCC microchannel causes streaks of the low momentum fluid and formation of hairpin vortex packets with lattice organization. This makes possible to quantify parameters responsible for the evolution of hairpin vortex packets in the microchannel devices. Appearing from the low to the high Reynolds numbers they affect the transport properties, control of the fluid motion, enhancement of mixing, or the separation of fluids. Fluid particle ejecta—thin supersonic jets - evolve into long needle-like jets which start spiraling, helical pairing and swirling in the field of thermal gradients. Such instabilities appear in the microcombustion flame instability and in the space micropropulsion systems. Oscillating and spiral flames appear in the presence of thermal gradient in the microchannel, due to the combined effects of thermal gradient fields and the mixture flow rates.

We present initial results from a three-dimensional magnetohydrodynamic (MHD) solar wind model that treats solar wind protons, electrons, and interstellar pickup protons as separate fluids and incorporates transport of turbulence and eddy viscosity. Numerical steady-state solutions of mean-field Reynolds-averaged solar wind equations coupled with turbulence transport equations are obtained by the time relaxation method in the corotating with the Sun frame of reference in the region from 0.3 to 100 AU (but still inside the termination shock). The model equations include the effects of electron heat conduction, Coulomb collisions, photoionization of interstellar hydrogen atoms and their charge exchange with the solar wind protons, turbulence energy generation by pickup protons, and turbulent heating of solar wind protons and electrons. The turbulence transport model employs the eddy viscosity approximation for the Reynolds stress tensor and turbulence phenomenologies to describe the conversion of fluctuation energy into heat via a turbulent cascade.

The performance of solar thermal power plants is strongly affected by the radiation intensity, which is subject to large variations depending on the weather conditions and on the time of the year. The control system of the solar thermal energy conversion plant must take into account such variable conditions, introducing correct thermodynamic relations pursuing the minimization of exergy destruction. The advantage of introducing direct-steam solar collectors with respect to the use of a separate heat transfer fluid in the primary circuit is also demonstrated. The model simulation predicts a performance improvement - compared to traditional control laws - ranging from 10 to 20% depending on the reference month.

Results from experimental studies of a solar cogeneration system with linear photovoltaic modules of a fundamentally new design are presented. The Ʌ-shaped frontal walls are installed face-to-face at an angle to each other and mutually shield their own thermal radiation, which decreases the radiation heat losses by 27% compared with linear photovoltaic modules of the known designs. The photocurrent generated by cooled solar cells is directed to a system for charging chemical batteries and the thermal energy released is transmitted to the unconsumed intermediate heat-transfer fluid and then, through the surface of coil pipes of counter-current heat exchangers, to the consumed process water of the outer circulation circuit. The further transportation of thermal energy to the storage system occurs by natural circulation of the consumed process water through the temperature gradient formed by the control system over the height between the heat source, the heat exchanger, and the heat receiver, an insulated container (a heat accumulator). For the first time, efficient controlled transportation of heat has been implemented without using a circulation pump owing to the excess thermal energy released during the conversion of solar energy by the solar cells and a photo-selective film installed in the focal spot of the optical concentrator. Thus, a possibility of increasing the temperature of the heat-transfer fluids at the cogeneration system outlet has been offered. A two-circuit circulation system allows for separation of unconsumed heat-transfer fluids (antifreezing solutions) and the consumed fluid (the process water) by the pressure in the channels and installation of a linear counter-current heat exchanger that performs the functions of a supporting platform’s mechanical axis along the rotational axis of the optical concentrator. The system uses a dual-axis solar tracking concentrating system comprised of flat mirrors installed at an angle to the horizon. The arrangement of the Ʌ-shaped photovoltaic modules on the supporting framework in series along the heat-transfer-fluid path allows for a reduction in the overall dimensions of the channels, an increase in the total efficiency of the solar cells, and simplification of the encapsulation technology. A method for calculating the output of the cogeneration plant is provided. The method is based on the experimentally measured characteristics of silicon solar cells and heat losses in the channels of the linear photovoltaic modules.

Energy loss and mechanical efficiency forecasting model for aero-engine bevel gear power transmission

Liquid metal magneto-hydrodynamic-energy-conversion (LMMHDEC) systems have been a matter of great interest and research & development since 1960. The various states of design and development of such systems go through a step-by-step progress with time. This paper highlights the phenomenon of direct thermal energy conversion systems using liquid metal as an electrodynamics fluid and gas/vapour as a thermodynamic fluid. An analysis of the technological drawbacks responsible for low efficiency of these LMMHDEC systems along with possible R & D solutions have been discussed in this technical research paper. The separation of electrodynamics fluid from thermodynamic fluid at various stages of MHD conversion remained an efficiency challenge of the various types of systems. To meet this challenge, a Dual-cycle MHD system has been designed in this paper. Both the fluids viz. thermodynamic and electrodynamics go through a phase change in this cycle. The thermal efficiency is optimized when one fluid goes into a phase change during a cycle and another fluid does not experience any phase change. The information covered in this paper enables an overview of concepts and the background to choose a cycle for a given temperature range.