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QUANTUM-MECHANICAL STUDY OF INTERNAL STRUCTURAL TRANSFORMATIONS IN Pb-SUPERSATURATED Pb-Sn ALLOYS
Friák, Martin ; Čípek, Petr ; Pavlů, J. ; Roupcová, Pavla ; Miháliková, Ivana ; Msallamová, Š. ; Michalcová, A.
Motivated by a decades-long controversy related to the crystal structure of Pb-supersaturated solid solutions of Pb in Sn, we have performed a quantum-mechanical study of these materials. Focusing on both body-centred-tetragonal beta-Sn and simple-hexagonal gamma-Sn structures, we have computed properties of two alloys with the chemical composition Pb5Sn11, i.e. 31.25 at. % Pb, which is close to the composition of the experimentally found alloy (30 at. % Pb). The 16-atom computational supercells were designed as multiples of the elemental beta- and gamma-Sn unit cells, where the Pb atoms were distributed according to the special quasi-random structure (SQS) concept. Full structural relaxations of both beta- and gamma-phase-based alloys resulted in very significant re-arrangements into structures which do not exhibit any apparent structural features typical for the original alloys, and are, therefore, difficult to classify. The formation energies of the beta- and gamma-phase-originating equilibrium phases are 50 meV/atom and 53 meV/atom, respectively. Therefore, they are not stable with respect to the decomposition into the elemental lead and tin. Moreover, our calculations of elastic constants of both phases revealed that they are close to mechanical instability. Our results indicate that the studied Pb-supersaturated Pb-Sn solid solutions may be prone to structural instability, transformations into different phases and decomposition. Our findings may contribute into the identification of the reason why the subsequent experimental studies did not reproduce the initial published data.
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Steam turbine
Čípek, Petr ; Škorpík, Jiří (referee) ; Fiedler, Jan (advisor)
The aim of the thesis is to design a high-speed steam turbine as a small energy source. Steam turbine consists of a high-pressure, a medium-pressure and a low-pressure part with a removable condensing module. High-pressure part is designed to perform a single-stage radial turbine with axial steam outlet. The work also includes the layout of the modules and sections. To design individual parts are used steam table „X-steam“.
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Heat Exchanger
Čípek, Petr ; Pavlů, Jaroslav (referee) ; Fiedler, Jan (advisor)
Heat exchanger is a device mediating the exchange of heat between two flowing mediums. This exchange can be periodical or continuous. The choice of the type of heat exchanger depends on the usage and parameters of entering medium. This thesis deals with the tube recuperation (recovery) exchanger and calculation of new one. This new heat exchanger is supposed to replace current one produced by Kralovopolska in 1974. These heat exchangers have wide range of application. They are widely used in all fields, from energy related equipment to the pharmaceutical plants. The conversion of current heat exchanger was made according to the CSN EN 13 445 for non-heated pressure vessels. The calculation was made for all pressure load parts, among these are the mantle, beds, throats, tube plates and tube feet. All parts are suitable for all the styles of load.
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Steam turbine
Čípek, Petr ; Škorpík, Jiří (referee) ; Fiedler, Jan (advisor)
The aim of the thesis is to design a high-speed steam turbine as a small energy source. Steam turbine consists of a high-pressure, a medium-pressure and a low-pressure part with a removable condensing module. High-pressure part is designed to perform a single-stage radial turbine with axial steam outlet. The work also includes the layout of the modules and sections. To design individual parts are used steam table „X-steam“.
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Heat Exchanger
Čípek, Petr ; Pavlů, Jaroslav (referee) ; Fiedler, Jan (advisor)
Heat exchanger is a device mediating the exchange of heat between two flowing mediums. This exchange can be periodical or continuous. The choice of the type of heat exchanger depends on the usage and parameters of entering medium. This thesis deals with the tube recuperation (recovery) exchanger and calculation of new one. This new heat exchanger is supposed to replace current one produced by Kralovopolska in 1974. These heat exchangers have wide range of application. They are widely used in all fields, from energy related equipment to the pharmaceutical plants. The conversion of current heat exchanger was made according to the CSN EN 13 445 for non-heated pressure vessels. The calculation was made for all pressure load parts, among these are the mantle, beds, throats, tube plates and tube feet. All parts are suitable for all the styles of load.
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