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Adaptive Insulation System based on Thermochemical Actuation for Heat Flux Control in Thermally Activated Building Structures (TABS)
No full textThe increasing demand for energy-efficient buildings has prompted the development of
innovative solutions, including adaptive building envelopes. One such solution is the controllable
insulation layer, which has the potential to significantly reduce building energy consumption.
The working principle of the controllable insulation layer is to adjust the gas pressure in openpored insulation panels to control thermal conductivity along an S-shaped curve (Knudsen
effect). This can be achieved by using thermochemical materials by precisely setting the
temperature of the reaction material and thus the gas pressure can be adjusted reversibly along
the equilibrium line. By coupling the thermochemical reaction with an open-pored panel, an
insulation system with adjustable thermal conductance is realized. Figure 1 gives a schematic
overview.
The approach proposed here is based on a thermochemical metal hydride reactor component that
serves as control unit for the gas pressure and thus for the heat flux which is integrated in a
vacuum insulation panel and steered externally. The contribution will present a novel design of
the thermochemical reactor, along with experimental proof of function as well as an analysis of
power demand and dynamic evaluation of the gas pressure variation and the resulting switching
behavior
Simulation von Strömungs- und Wärmeübertragungsvorgängen in thermischen Energiespeichern mit Phasenwechsel
Get PDFDie Integration von Phasenwechselspeichern in solarthermische Kraftwerke mit Direktverdampfung
oder industrielle Prozesse stellt eine vielversprechende Technologie zur Steigerung
der Anlageneffizienz dar. Im Rahmen dieser Arbeit wird durch numerische 2D-Simulationen
von transienten Strömungs- und Wärmeübertragungsvorgängen die Auswirkung natürlicher
Konvektion auf die Be- und Entladevorgänge thermischer Energiespeicher mit Fest-Flüssig-
Phasenwechseln untersucht. Fokus dabei ist, den Einfluss geometrischer Parametervariationen
auf das Speicherverhalten zu ermitteln. Dazu wird das Modell eines rechtwinkligen
Plattenwärmespeichers mit vertikalen Speicherkammern entwickelt, in dem ein Nitratsalz
(KNO3 − NaNO3) durch ein zweiphasiges Wärmeträgerfluid (Wasser) seitlich beheizt oder
gekühlt wird. Die Kammern sind in Höhe und Breite variabel. Es werden unabhängig
voneinander jeweils drei verschiedene Abmessungen betrachtet, wodurch sich Seitenverhältnisse
(Höhe/Breite) von 4-40 ergeben. Die Ergebnisse der Parameterstudie werden in
absoluter Form sowie anhand einer dimensionslosen Analyse dargestellt. Es kann unter
Verwendung relevanter Kennzahlen, wie Rayleigh- und Fourier-Zahl, ein Zusammenhang für
das Schmelzverhalten in den verschiedenen Speicherkammern gefunden werden. Zudem wird
anhand der Nußelt-Zahl ein Faktor für die Verstärkung des konvektiven Wärmeübergangs
in Abhängigkeit der Speicherabmessungen gegeben
Adaptive insulation layer to enable thermal activation of building structures: Thermochemical reactor as control unit
No full textThermal activation of existing building masses can significantly increase the energy efficiency of buildings by using them as thermal energy storage. To achieve this, it is essential to control the heat transfer across the massive components such as walls or ceilings. This can be achieved by applying a controllable insulation layer, which combines the gas pressure-dependent thermal conductivity of porous structures with reversible gas-solid-reactions.The heat transfer mechanism in porous insulation materials is dominated by the Knudsen effect, which describes the S-shaped thermal conductivity depending on the prevalent gas pressure in the insulation panel. By employing thermochemical materials, the gas pressure in the vacuum insulation panel can be precisely controlled along the equilibr ium line by adjusting the reaction temperature. This allows for precise control of the heat flux through the insulation panel and enables the thermal activation of building masses. The thermochemical reactor is a key component in the integral adaptive insulation system. The contribution will outline a novel reactor concept addressing the central challenges of accurate pressure adjustment, system dynamics and energy efficiency. We will introduce the novel reactor design and present substantial experimental results on the reactor characterization as well as the proof of concept of the controllable insulation layer as an further development of a switchable insulation layer
Manipulating the Thermal Conductance by Utilizing Reversible Gas-Solid Reactions
No full textThe increasing demand for energy-efficient buildings has prompted the development
of innovative solutions, including adaptive building envelopes. One such solution is the
controllable insulation layer, which has the potential to significantly reduce building
energy consumption. The working principle of the controllable insulation layer is to
adjust the gas pressure in open-pored insulation panels to control thermal conductivity
along an S-shaped curve (Knudsen effect). This can be achieved by using
thermochemical materials by precisely setting the temperature of the reaction material
and thus the gas pressure can be adjusted reversibly along the equilibrium line. By
coupling the thermochemical reaction with an open-pored panel, an insulation system
with adjustable thermal conductance is realized. The approach proposed here is
based on a thermochemical reactor that serves as an external component outside the
panel as a control unit for the gas pressure and thus for the heat flux. The contribution
will present a novel design of the thermochemical reactor, along with experimental
proof of function as well as an analysis of power demand and dynamics for gas
pressure variation in the range of 5 to 1000 mbar. Furthermore, the reactor is coupled
with a vacuum insulation panel, and experimental measurements of the thermal
behavior of the overall controllable insulation system – consisting of the porous panel
and the connected metal hydride reactor component - are presented
Thermochemical Reactions to enable Adaptive Building Insulation and Thermal Component Activation
No full textThe thermal activation of existing building masses can substantially enhance the energy efficiency of buildings by utilizing them as thermal energy storage. To accomplish this, it's crucial to manage the heat transfer across the large components like walls or ceilings. This can be realized by applying a controllable insulation layer, which merges the gas pressure-dependent thermal conductivity of porous structures with reversible gas-solid-reactions.
The heat transfer mechanism in porous insulation materials is primarily influenced by the Knudsen effect, which characterizes the S-shaped thermal conductivity based on the prevailing gas pressure in the insulation panel. By using thermochemical materials, the gas pressure in the vacuum insulation panel can be accurately regulated
along the equilibrium line by modifying the reaction temperature. This facilitates precise control of the heat flux through the insulation panel and allows the thermal activation of building masses. The thermochemical reactor is a crucial component in the comprehensive adaptive insulation system. The contribution will present a new reactor concept that addresses the key challenges of precise pressure adjustment, system dynamics, and energy efficiency and furthermore the experimental integration of the reactor in a lab-scale controllable insulation system will be shown
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Natural convection melting in a high temperature flat plate latent heat storage system: Parameter study of enclosure dimensions
No full textThe impact of natural convection melting in a high temperature flat plate latent heat thermal energy storage system is studied numerically. The storage material is the eutectic mixture of sodium nitrate and potassium nitrate (KNO3-NaNO3). A parameter study on storage material enclosure dimensions is conducted for various widths and heights. Low to very high aspect ratios between 0.5 and 40 and Rayleigh numbers from 1.2·10^4 to 1.6·10^6 are obtained. The liquid phase fraction evolution with time is scaled to non-dimensional form and the impact of natural convection on the heat flux is shown with a convective enhancement factor that is the ratio of heat flux to a hypothetical heat flux only by conduction. The results can be used for future design optimizations considering the effect of natural convection
Non-isothermal but temperature-driven static PCI measurement technique: a novel approach for hydrogen sorption characterization at vacuum conditions
No full textBy utilizing the gas pressure dependent thermal conductivity of porous structures, insulation materials can be transformed into thermal barriers with controllable heat flux. Hereby, controllable insulation layers can support, for instance, the thermal management of BEVs or adaptive façades for active conditioning of buildings’ energy management to variable internal and external constraints.
Such a controllable (vacuum) insulation layer requires the specific adjustment of the gas pressure in the insulation panel. Reversible gas-solid reactions such as metal hydrides with hydrogen are predestined to fulfill this task. In the technically relevant temperature range (approx. 0…150 °C), metal hydrides are promising reaction systems to precisely control the gas pressure along the equilibrium line, especially below ambient pressure. For the accurate adjustment of the hydrogen pressure in this kind of application, detailed sorption characterization data of the metal hydride materials are required. Especially under vacuum conditions, measuring the equilibrium data via conventional isothermal static volumetric technique (Sieverts’ technique) turns out to be a challenge. For a reliable determination of the hydrogen charge, huge volumes have to be provided in the desorption process, which is technically hardly feasible.
Therefore, in this work, a temperature-driven approach of the volumetric technique using a Sieverts’ apparatus is presented. Here, the driving parameter for the changing hydrogen charging states is the temperature of the metal hydride bulk, while the corresponding gas pressure is the dependent variable. The hydrogen concentration is fixed during programmed temperature ramps and is then varied stepwise for different initial charging states. This allows the sorption properties to be measured in the vacuum pressure ranges without having to provide large capturing volumes. In the present contribution, this novel pressure-composition-isotherm (PCI) measurement method itself as well as the accordingly built test bench and the measurement procedure is explained in detail.
The method is applied to two different metal hydride materials, each at the end of range of the technically reasonable pressure range for controllable vacuum insulation panels (ca. 0.01-1000 hPa) in the given temperature interval of 0…150 °C. We carried out both absorption and desorption equilibria measurements for LaNi4.1Al0.52Mn0.38 and ZrNi. The resulting PCIs are presented, including repeating and reproduction measurement series to verify the data yielded by the novel approach. To validate the measurement method and system, the gained PCI data is additionally compared to pressure-concentration isotherms provided in the literature
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