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  • 1
    Language: English
    In: Applied Energy, 01 January 2017, Vol.185, pp.1954-1964
    Description: Thermal energy storage technologies are of current interest in order to improve the integration of renewable energy sources as well as energy efficiency. Numerical simulations of thermochemical heat storage are especially challenging and time consuming due to the complexity of the mathematical description of the strongly coupled and highly nonlinear processes characteristics for such systems. These difficulties are exacerbated once practically relevant complex or large geometries are considered as they can occur around heat exchangers or due to internal heterogeneities of the reactive bed. To allow a computationally efficient simulation of such applications, an existing finite element implementation of a thermochemical heat storage model was parallelised using PETSc routines. Input/output, global assembly and the linear solver all work in a distributed fashion. The approach is implemented into the open source framework OpenGeoSys. The performance of the present parallelisation approach is tested by simulating the discharge of a heat store based on calcium oxide and water as a benchmark problem. The algorithm is tested on 2D as well as 3D meshes. The computational time required for the simulation could be reduced significantly. For example, a 3D model running almost 7 days on a single core could be solved in less than 1 h on 120 cores using the developed framework. The results strongly depend on linear solver and preconditioner settings.
    Keywords: Thermochemical Heat Storage ; Finite Element Method ; Petsc ; Parallelisation ; Opengeosys ; Engineering ; Environmental Sciences
    ISSN: 0306-2619
    E-ISSN: 1872-9118
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  • 2
    Language: English
    In: Applied Energy, 15 September 2016, Vol.178, pp.323-345
    Description: Current climate, environmental and energy policies aim at a decarbonisation of the energy sector by a transition to renewable energies on the one hand and at an increased energy efficiency on the other hand. Thereby they stimulate the interest in space-, cost-, and energy-efficient heat storage technologies. Thermochemical conversion is an attractive candidate technology for heat storage fulfilling these efficiency requirements. The design of practically any complex engineered system is accompanied by theoretical analyses based on model representations. Thus, numerical modelling is particularly important for thermochemical heat storage systems to help realise their potential and to advance the technology from the laboratory to a commercial setting. This article reviews modelling work in the context of heat storage and transformation aimed at capturing the coupled multi-physical processes that are relevant to the simulation of thermochemical heat storage in a space- and time-resolved manner.
    Keywords: Thermochemical Heat Storage ; Coupled Problems ; Porous Media ; Multi-Physics ; Numerical Simulation ; Continuum Modelling ; Engineering ; Environmental Sciences
    ISSN: 0306-2619
    E-ISSN: 1872-9118
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  • 3
    Language: English
    In: Applied Energy, 01 January 2017, Vol.185, pp.1965-1970
    Description: The study of water sorption in microporous materials is of increasing interest, particularly in the context of heat storage applications. The potential-theory of micropore volume filling pioneered by Polanyi and Dubinin is a useful tool for the description of adsorption equilibria. Based on one single characteristic curve, the system can be extensively characterised in terms of isotherms, isobars, isosteres, enthalpies etc. However, the mathematical description of the adsorbate density’s temperature dependence has a significant impact especially on the estimation of the energetically relevant adsorption enthalpies. Here, we evaluate and compare different models existing in the literature and elucidate those leading to realistic predictions of adsorption enthalpies. This is an important prerequisite for accurate simulations of heat and mass transport ranging from the laboratory scale to the reactor level of the heat store.
    Keywords: Heat Storage ; Zeolite ; Adsorption ; Dubinin–Polanyi ; Porous Media ; Opengeosys ; Engineering ; Environmental Sciences
    ISSN: 0306-2619
    E-ISSN: 1872-9118
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  • 4
    Language: English
    In: Applied Energy, 01 December 2017, Vol.207, pp.274-282
    Description: Simulating adsorption-based heat storage devices requires knowledge of both the adsorption equilibria and the adsorption enthalpies of the adsorbent materials involved. The Dubinin-Polanyi theory of micropore filling can be used as a tool to reduce the experimental work for the thermodynamical characterization of various adsorption working pairs. In particular it can be used for the deduction of adsorption enthalpies from adsorption equilibrium data. In this work we assess if this theory can be employed to predict the outcome of experiments performed on a lab-scale heat storage device. For that purpose, we present a numerical model of the sorption chamber, which describes the sorption behavior by means of the Dubinin-Polanyi theory. The simulated heat storage densities and water loading lifts are compared to experimentally determined data of two granulated zeolite samples, namely a zeolite Na-X and a zeolite Ca-X, under various humidity conditions.
    Keywords: Thermochemical Heat Storage ; Dubinin-Polanyi Theory ; Zeolites ; Adsorption in Micropores ; Opengeosys ; Engineering ; Environmental Sciences
    ISSN: 0306-2619
    E-ISSN: 1872-9118
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