Adéla Macháčková

Twist channel angular pressing (TCAP) as a method for increasing the efficiency of SPD

The paper proposes a new variation for the application of SPD methods. Suggested TCAP (twisted channel angular pressing) technology obtains the larger imposed strain more effectively while increasing homogeneity of material. The number of passes needed to obtain the ultra-fine to nano-scale grains in bulk materials can be significantly reduced. Commercially pure copper (99.97%) was used for the experimental verification of the suggested process. The thermal stability of extruded copper was studied after the application of two modes of heat treatment. The deformation parameters of the process were also described using the numerical simulation based on FEM analysis. Predicted value of imposed strain, after a single pass, reached approximately 2.3. Measured strength, determined after four passes, achieved values around 440 MPa homogeneously along the cross-section of the extruded material. The grain size, determined after four passes, averaged out 1.2 μm. Homogeneity of deformation was also confirmed by micro-hardness tests.

FEM simulation of extrusion by ECAP method on magnesium alloy AZ91

The simulation of extrusion process by (ECAP) technique, which involves a simple large shear deformation during passage through two intersecting channels, was applied to the AZ91 Mg alloy to obtain an ultrafine-grained microstructure. For the stress and strain intensity investigation, computer simulation was used. Temperature dependences of extrusion process have been detected along with others. Four pressings were conducted at 250?C, while the fifth pressing was conducted at 180?C. The grain refinement and homogeneity of grain-size distribution increased with pass number. Temperature of process was measured during pass and decreased with respect to the number of pass along with obtaining finer grains. Finite Element Method (FEM) simulation was examined on AZ 91 alloy by practical tests. The experimental result agreed well with that obtained from numerical analyses carried out based on the FEM. Presented paper shows evidences that this forming method is an efficient tool for improving the mechanical properties. [Received 15 March 2006; Accepted 9 March 2007]

Mathematical modeling of gas flow including heat transfer in spiral heat exchanger

Přispěvek prezentuje numericke řeseni prouděni spalin ve spiralovem výměniku tepla, kterým se ohřiva proudici voda. Plynne spaliny jsou ziskany ze spalovani zemniho plynu V mikroturbině, ktera dosahuje výkonu řadově desitky [kW]. V přispěvku je definovan matematický model prouděni spalin ve výměniku vcetně uvažovani přestupu tepla skrz vodive oblasti spiraloveho výměniku. Vodivými oblastmi výměniku tepla jsou jednotlive stěny a vrstva izolace, ktera obklopuje samotný výměnik. Vstupni okrajove podminky pro spaliny a vodu byly ziskany na zakladě experimentalniho měřeni. Definovaný matematický model byl nasledně řesen numericky V programovem prostředi ANSYS Fluent13. Výsledky numericke simulace jsou prezentovany rozloženim zakladnich proudových velicin V jednotlivých řezech výměnikem. Nasledně jsou vyhodnoceny veliciny K stanoveni energeticke analýze výměniku tepla.