Parameterization of a reactive force field using a Monte Carlo algorithm

Abstract Parameterization of a Molecular Dynamics force field is essential in realistically modelling the physico-chemical processes involved in a molecular system. This step is often challenging when the equations involved in describing the force field are complicated as well as when the parameters are mostly empirical. ReaxFF is one such reactive force field which uses hundreds of parameters to describe the interactions between atoms. The optimization of the parameters in ReaxFF is done such that the the properties predicted by ReaxFF matches with a set of quantum chemical or experimental data. Usually, the optimization of the parameters is done by an inefficient single parameter parabolic-search algorithm. In this study, we use a robust Metropolis Monte-Carlo algorithm with Simulated Annealing (MMC-SA) to search for the optimum parameters for the ReaxFF force field in a high-dimensional parameter space. The optimization is done against a set of quantum chemical data for M gSO 4 hydrates. The optimized force field reproduced the chemical structures, the Equations of State and the water binding curves of M gSO 4 hydrates. The transferability test of the ReaxFF force field shows the extend of transferability for a particular molecular system. This study points out that the ReaxFF force field is not indefinitely transferable

Energy density and storage capacity cost comparison of conceptual solid and liquid sorption seasonal heat storage systems for low-temperature space heating

Sorption heat storage can potentially store thermal energy for long time periods with a higher energy density compared to conventional storage technologies. A performance comparison in terms of energy density and storage capacity costs of different sorption system concepts used for seasonal heat storage is carried out. The reference scenario for the analysis consisted of satisfying the yearly heating demand of a passive house. Three salt hydrates (MgCl2, Na2S, and SrBr2), one adsorbent (zeolite 13X) and one ideal composite based on CaCl2, are used as active materials in solid sorption systems. One liquid sorption system based on NaOH is also considered in this analysis. The focus is on open solid sorption systems, which are compared with closed sorption systems and with the liquid sorption system. The main results show that, for the assumed reactor layouts, the closed solid sorption systems are generally more expensive compared to open systems. The use of the ideal composite represented a good compromise between energy density and storage capacity costs, assuming a sufficient hydrothermal stability. The ideal liquid system resulted more affordable in terms of reactor and active material costs but less compact compared to the systems based on the pure adsorbent and certain salt hydrates. Among the main conclusions, this analysis shows that the costs for the investigated ideal systems based on sorption reactions, even considering only the active material and the reactor material costs, are relatively high compared to the acceptable storage capacity costs defined for different users. However, acceptable storage capacity costs reflect the present market condition, and they can sensibly increase or decrease in a relatively short period due to for e.g. the variation of fossil fuels prices. Therefore, in the upcoming future, systems like the ones investigated in this work can become more competitive in the energy sector.This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. TU/e has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement Nº 657466 (INPATH-TES). The results of this study can contribute to the development of educational material within INPATH-TES

Sorption heat storage for long-term low-temperature applications: A review on the advancements at material and prototype scale

Sorption heat storage has the potential to store large amounts of thermal energy from renewables and other distributed energy sources. This article provides an overview on the recent advancements on long-term sorption heat storage at material- and prototype- scales. The focus is on applications requiring heat within a temperature range of 30–150 °C such as space heating, domestic hot water production, and some industrial processes. At material level, emphasis is put on solid/gas reactions with water as sorbate. In particular, salt hydrates, adsorbents, and recent advancements on composite materials are reviewed. Most of the investigated salt hydrates comply with requirements such as safety and availability at low cost. However, hydrothermal stability issues such as deliquescence and decomposition at certain operating conditions make their utilization in a pure form challenging. Adsorbents are more hydrothermally stable but have lower energy densities and higher prices. Composite materials are investigated to reduce hydrothermal instabilities while achieving acceptable energy densities and material costs. At prototype-scale, the article provides an updated review on system prototypes based on the reviewed materials. Both open and closed system layouts are addressed, together with the main design issues such as heat and mass transfer in the reactors and materials corrosion resistance. Especially for open systems, the focus is on pure adsorbents rather than salt hydrates as active materials due to their better stability. However, high material costs and desorption temperatures, coupled with lower energy densities at typical system operating conditions, decrease their commercial attractiveness. Among the main conclusions, the implementation within the scientific community of common key performance indicators is suggested together with the inclusion of economic aspects already at material-scale investigations.This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. TU/e has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). The results of this study can contribute to the development of educational material within INPATH-TES

Removal of Particles from a Powdery Fouled Surface due to Impaction

Particulate fouling is defined as the unwanted deposition of particles on heat exchange surfaces. The fouling layer reduces the heat transfer rate and leads to inefficient operation. The net fouling rate is the result of the difference between the deposition rate and the removal rate of particles. One of the mechanisms that contribute to the removal of particles from powdery fouled surfaces is the collision of an incident particle with the fouled surface. In the present study, removal of particles from powdery fouled surfaces due to an incident particle impact is studied numerically and experimentally. A numerical model is developed to study the interaction of an incident particle with a bed of particles. The numerical model is based on the molecular dynamic theory of granular matter. The numerical model is tested for an incident copper particle hitting a bed of particles at different impact speeds. The numerical results are verified experimentally. An experimental setup has been built to study the removal of particles from powdery fouling layers due to an incident particle impact. It is shown that depending on the impact speed, zero, one, two or three particles are ejected from the powdery layer. By comparing the numerical results with the experimental measurements it is shown that the numerical results fit in the measured range of impact mentioned above. The numerical model will be used further to characterize the removal of particles from powdery fouling layers as function of particle size, material, incident particle impact speed and the bed of particles porosity

Seascape carbon management beyond wetlands as eligible blue carbon activities

This Issues Paper reviews peer-reviewed scientific evidence on the potential to expand carbon finance methodologies under the Verified Carbon Standard (VCS) to encompass Near Shore Seascape Carbon, beyond current ecosystems considered under such mechanisms, i.e., vegetated wetlands. For this assessment, no evidence was therefore reviewed on tidal wetlands, seagrasses, and mangrove ecosystems, for which carbon offset methodologies already exist. Management of blue carbon ecosystems has become an area of extreme interest in the context of providing nature-based solutions, or nature-inclusive designs for environmental management, that may help to deliver climate change mitigation. Carbon market methodologies for such defined management activities outline procedures that projects must follow to deliver GHG emission reductions or removals that are real, measurable, additional, permanent (>100 years), independently verified, and conservatively estimated. These methodologies must be rooted in scientific understanding of the global carbon cycle so that projects can develop high quality and credible carbon offsets for the carbon markets. Such carbon projects are coming online for tidal wetlands, particularly mangroves. A lack of scientific consensus and in many cases data gaps, amongst other challenges, have prevented the inclusion of other marine ecosystems under carbon market mechanisms thus far. This has limited the ability to harness private finance to further support the growth of ocean carbon conservation. In recent years, science has advanced at pace

A DFT based equilibrium study on the hydrolysis and the dehydration reactions of MgCl 2

Magnesium chloride hydrates are characterized as promising energy storage materials in the builtenvironment. During the dehydration of these materials, there are chances for the release of harmful HCl gas, which can potentially damage the material as well as the equipment. Hydrolysis reactions in magnesium chloride hydrates are subject of study for industrial applications. However, the information about the possibility of hydrolysis reaction, and its preference over dehydration in energy storage systems is still ambiguous at the operating conditions in a seasonal heat storage system. A density functional theory level study is performed to determine molecular structures, charges, and harmonic frequencies in order to identify the formation of HCl at the operating temperatures in an energy storage system. The preference of hydrolysis over dehydration is quantified by applying thermodynamic equilibrium principles by calculating Gibbs free energies of the hydrated magnesium chloride molecules. The molecular structures of the hydrates (n = 0, 1, 2, 4, and 6) of MgCl2 are investigated to understand the stability and symmetry of these molecules. The structures are found to be noncomplex with almost no meta-stable isomers, which may be related to the faster kinetics observed in the hydration of chlorides compared to sulfates. Also, the frequency spectra of these molecules are calculated, which in turn are used to calculate the changes in Gibbs free energy of dehydration and hydrolysis reactions. From these calculations, it is found that the probability for hydrolysis to occur is larger for lower hydrates. Hydrolysis occurring from the hexa-, tetra-, and dihydrate is only possible when the temperature is increased too fast to a very high value. In the case of the mono-hydrate, hydrolysis may become favorable at high water vapor pressure and at low HCl pressure