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Compatibility of Phase Change Materials and Metals:Experimental Evaluation Based on the Corrosion Rate
(MDPI, 2020-06-18) Ostrý, Milan; Bantová, Sylva; Struhala, Karel
The construction and maintenance of building stock is responsible for approximately 36% of all CO(2)emissions in the European Union. One of the possibilities of how to achieve high energy-efficient and decarbonized building stock is the integration of renewable energy sources (RES) in building energy systems that contain efficient energy storage capacity. Phase Change Materials (PCMs) are latent heat storage media with a high potential of integration in building structures and technical systems. Their solid-liquid transition is specifically utilized for thermal energy storage in building applications. The typically quite old example is the use of ice that serves as long-term storage of cold. Large pieces of ice cut in winter were stored in heavily insulated spaces and prepared for cooling of food or beverages in summer. In the contemporary use of the principle, the PCMs for building applications and tested in this study must have a melting range close to the desired temperature in the occupied rooms. As the PCMs need to be encapsulated, several types of metal containers have been developed and tested for their thermal conductivity and resistance to mechanical damage, which enhances the performance of these so-called latent heat thermal energy storage (LHTES) systems. Long-term compatibility of metals with PCMs depends, i.e., on the elimination of an undesirable interaction between the metal and the specific PCM. Heat storage medium must be reliably sealed in a metal container, especially if the LHTES is integrated into systems where PCM leaks can negatively affect human health (e.g., domestic hot water tanks). The aim of this study is to evaluate the interactions between the selected commercially available organic (Linpar 17 and 1820) and inorganic (Rubitherm SP22 and SP25) PCMs and metals widely used for PCM encapsulation (aluminum, brass, carbon steel, and copper). The evaluation is based on the calculation of the corrosion rate (CR), and the gravimetric method is used for the determination of the weight variations of the metal samples. The results show good compatibility for all metals with organic PCMs, which is demonstrated by a mass loss as low as 2.1 mg in case of carbon steel immersed in Linpar 1820 for 12 weeks. The exposure of metals to organic PCMs also did not cause any visual changes on the surface except for darker stains, and tarnishing occurred on the copper samples. More pronounced changes were observed in metal samples immersed in inorganic PCMs. The highest CR values were calculated for carbon steel exposed to inorganic PCM Rubitherm SP25 (up to 13.897 mg center dot cm(-2)center dot year(-1)). The conclusion of the study is that aluminum is the most suitable container material for the tested PCMs as it shows the lowest mass loss and minimal visual changes on the surface after prolonged exposure to the selected PCMs.
A dynamical system with random parameters as a mathematical model of real phenomena
(MDPI, 2019-10-30) Diblík, Josef; Dzhalladova, Irada; Růžičková, Miroslava
In many cases, it is difcult to nd a solution to a system of difference equations with random structure in a closed form. Thus, a random process, which is the solution to such a system, can be described in another way, for example, by its moments. In this paper, we consider systems of linear difference equations whose coefcients depend on a random Markov or semi-Markov chain with jumps. The moment equations are derived for such a system when the random structure is determined by a Markov chain with jumps. As an example, three processes: Threats to security in cyberspace, radiocarbon dating, and stability of the foreign currency exchange market are modelled by systems of difference equations with random parameters that depend on a semi-Markov or Markov process. The moment equations are used to obtain the conditions under which the processes are stable.
There Are No Conformal Einstein Rescalings of Pseudo-Riemannian Einstein Spaces with n Complete Light-Like Geodesics
(MDPI, 2019-09-01) Hinterleitner, Irena; Mikeš, Josef; Guseva, Nadezda
In the present paper, we study conformal mappings between a connected n-dimension pseudo-Riemannian Einstein manifolds.
Stabilization of company’s income modeled by a system of discrete stochastic equations
(Springer Nature, 2014-11-15) Diblík, Josef; Dzhalladova, Irada; Růžičková, Miroslava
The paper deals with a system of difference equations where the coefficients depend on Markov chains. The functional equations for a particular density and the moment equations for the system are derived and used in the investigation of mode stability of company-s income. An application of the results is illustrated by two models.
Detection of reinforcement in the non-traditional building structures - historical statues
(IOP Publishing, 2018-07-16) Anton, Ondřej; Vítek, Lubomír; Heřmánková, Věra; Komárková, Tereza; Cikrle, Petr
During restoration and maintenance of historical buildings, statues and sculptures are often neglected elements in the pre-construction condition surveys, especially in case they are not part of the supporting structure but only an ornamental and aesthetic complement of the architectural whole. The condition of a number of such artworks requires restoration or static assessment from the viewpoint of safety and durability. In the case of statues made of stone, artificial stone or concrete, an inseparable part of the pre-construction condition survey is determining the method of their reinforcement with steel elements, which is, considering the often complex spatial aspects of their surface, relatively complicated. The paper offers some possibilities of its solution on three examples. The diagnostic methods were proposed based on the authors’ workplace’s long-term experience with the diagnostics of reinforced concrete structures. During the past 10 years, about 1,000 such diagnostics have been performed. These experiences were subsequently experimentally applied to several historical sculptures with great success.

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