Expert system for analysis of casting defects - ESVOD

The powerful tool for defect analysis is an expert system. It is a computer programme based on the knowledge of experts for solving the quality of castings. We present the expert system developed in the VSB-Technical University of Ostrava called 'ESWOD'. The ESWOD programme consists of three separate modules: identification, diagnosis / causes and prevention / remedy. The identification of casting defects in the actual form of the system is based on their visual aspect.Web of Science151201

Preparation and evaluation of properties of cast metallic foams with regular inner structure

Lately we encounter still more new applications of metallic foams, as well as possible methods of their manufacture. These metallic materials have specific properties, such as large rigidity at low density, in some cases high thermal conductivity, capability to absorb energy, etc. The work is focused on the preparation of these materials using conventional casting technology, which ensures rapid and economically feasible method for production of shaped components. In the experimental part we studied conditions of casting of metallic foams with a regular structure made of ferrous and non-ferrous alloys. For thus obtained castings we evaluated the achieved microstructure and mechanical properties, which determine the possible use of these materials. The samples were subjected to compression tests, by which we investigated deformation behaviour of selected materials and determined the value of energy absorption.Web of Science6231646164

Border-crossings as memory sites? The case study of the Czech-Polish border in Cieszyn Silesia

This project evaluates the state borders between Czechia and Poland in the region of Cieszyn Silesia from the perspective of memory studies. Emphasizing the fact that the borders and especially border crossings are sites rich in symbolics, a field observation was conducted to explore whether the border-crossings (can) play a role in memory work. These sites, apart from their apparent function, represent bridges between two states and are usually two national communities. If these groups were in antagonistic relationships in the past (tensions, violence), the border could also become a site of rivalry (e.g., contested border demarcations). In this project, all the border-crossings between Czechia and Poland in Cieszyn Silesia are considered, and the imprints of the past are identified. According to the approach of the SANE framework (Björkdahl et al., 2017), some of these border crossings can be also considered memory sites which means they are (can become) a platform for reconciliation or construction of new and better cross-border relationships. That goal is also valid for Cieszyn Silesia which was divided into two parts after the First World War (Czechoslovak and Polish). Such demarcation did not respect the national and linguistic distribution of populations and left many Poles in Czechoslovakia. The demarcation of the new border was accompanied by events that turned sensitive from a longer perspective (Czechoslovak military campaign in 1919 on Polish territory, Polish occupation of Cieszyn Silesia in 1938). This paper, therefore, explores the reconciling and conflicting narratives the memory sites may have

Parade of the Dolls

https://digitalcommons.library.umaine.edu/mmb-ps/2585/thumbnail.jp

Utjecaj aluminija i titana na mikrostrukturu i kvalitetu željeznih odljevaka s udjelom vermikularnog grafita

The contribution is aimed at study of influence of chemical composition of compacted graphite cast iron (CGI) on microstructure and surface quality of castings, particularly on the occurrence of pinholes. It has been found out that aluminium and titanium in CGI effect the formation of this defect in castings. Aluminium content in the range of 0,02 up to 0,1 % is critical. Increased occurrence of pinholes was also determined with Ti contents above 0,1%. On the same set of experimental castings it has been found out that increased contents of those elements on the other hand support the crystallization of compacted graphite. But the utilization of that method for control of CGI microstructure is limited with a possibility of formation of surface defects in castings – pinholes, but also coldshuts and shrinkage cavities.Rad istražuje utjecaj kemijskog sastava odljevaka čelika s udjelom vermikularnog grafita na njihovu mikrostrukturu i površinska svojstva, osobito pri pojavi poroznosti. Utvrđen je utjecaj aluminija i titana na nastanak pora u odljevcima. Kritičan je udio aluminija između 0,02 i 0,1%. Također, pore su učestalije pri udjelu titana iznad 0,1%. Na istim uzorcima eksperimentalnih odljevaka utvrđeno je i kako povišeni udjeli ovih elemenata istodobno potpomažu kristalizaciju vermikulanog grafita. Primjena metode za kontrolu mikrostrukture odljevaka s vermikularnim grafitom (CGI) limitirana je, uz mogućnost pojave površinskih nedostataka odljevaka u vidu pora, hladnih zavara i šupljina nastalih skupljanjem

A Fresh Look At Vortex Tubes Used As Expansion Device In Vapor Compression Systems

The vortex tube is an intriguing device that separates an incoming high-pressure fluid stream into a two low-pressure streams. Work interaction during the expansion process causes a temperature decrease in of the two exit streams, while the other one experiences a temperature increase. The expansion process in a vortex tube therefore approaches isentropic rather than isenthalpic expansion, and the internal flow separation is achieved without any moving parts, resulting in robust and inexpensive designs. Commercially available vortex tubes are almost exclusively used for spot cooling in industrial applications and use compressed air as the working fluid. In addition, vortex tubes have been gaining lots of attention in air-conditioning and refrigeration research, because of the possibility to replace the expansion valve of vapor compression systems with this low-cost device that can recover expansion work that would otherwise be lost in the isenthalpic throttling process. Most of the work on vortex tubes used for refrigeration have been numerical studies, and many of them predict very optimistic energy efficiency improvements. However, the few papers available that describe experimental validation of vortex tubes in HVAC&R systems are far less optimistic, which is often caused by the selection of cycle architectures that seem inappropriate for vortex tubes. This paper takes a fresh look at vortex tubes used as the expansion device in refrigeration systems. Vortex tube performance is assessed on a fundamental level for different working fluids, including air and R134a. Suitable vortex tube geometries and operating conditions have been identified and actual work recovery effects have been demonstrated experimentally for both air and R134a. Based on these new findings it is possible to devise novel vortex tube cycles that are able to utilize the demonstrated improvement potentials when applied to vapor compression systems

Comprehensive Study of Heat Transfer and Pressure Drop in Regenerator and Optimization of Solid-state Caloric Cooling Cycles Using Realistic Hydraulic Diameter of Regenerator

Many researchers have used very small hydraulic diameters in regenerators of solid-state caloric cooling cycles, because smaller diameters can generate higher cooling capacity and system COP. However, using very small diameters hardly represent the real performance of the caloric cooling cycle, because they cannot be manufactured for a real system. Therefore, this paper has used more realistic hydraulic diameter which is used in commercial heat exchangers. To get the more accurate heat transfer coefficient and friction factor, the model used in this paper incorporates hydrodynamic and thermal developing regions which are usually neglected in other papers. This paper shows that COP is a function of heat transfer coefficient, pressure drop and displacement ratio. Higher heat transfer coefficient, lower pressure drop and the optimal displacement ratio can generate higher COP in magnetocaloric refrigeration cycle. From simple analytical comparison, it is expected that plate type regenerators can generate the highest cooling capacity and COP. The regenerator with smaller hydraulic diameter has higher performance, but 0.3mm hydraulic diameter has been chosen in this paper due to manufacturing limitation. In addition, this paper has investigated the effect of the length of the regenerator, the cycle frequency and the regenerator’s porosity on heat transfer phenomena in the regenerator. The cycle frequency has a large effect on cooling capacity and system efficiency while the effects of length and porosity of the regenerator are marginal. For the plate-type regenerator with 0.3mm hydraulic diameter, the system with 0.2m length of the regenerator, 0.45Hz cycle frequency and 0.5 porosity has the highest COP of 2.3 to generate 100W kg-1 cooling capacity for a temperature lift of 20°C. This paper provides detailed information of heat transfer phenomena in the solid-state cooling cycles, which need to be understood thoroughly in order to efficiently utilize caloric effects

CFD Simulation Of Vortex Flashing Flows In Convergent-Divergent Nozzles

Vortex control is a novel two-phase convergent-divergent nozzle restrictiveness control mechanism by adjustable nozzle inlet vortex. It requires no change to the physical dimensions of the nozzle geometry. A nozzle with inlet vortex was called vortex nozzle (or swirl nozzle). Previous experiments on vortex nozzle with initially subcooled R134a showed that the nozzle becomes more restrictive as the strength of the inlet vortex increases. The maximum vortex control range has been observed to be 42% of maximum choked total mass flow rate through the nozzle. The control range of inlet pressures and mass flow rates that can be achieved by vortex control appears to be large enough to be suitable for numerous technical applications. This novel mechanism can potentially provide flow control with less sacrifice of nozzle efficiency, which is extremely important for ejector cooling cycle performance. It is also less vulnerable to clogging since the flow control is achieved without changing the flow area. However, the underlying mechanism behind the vortex control is still unclear. In this study, 3D CFD simulation of vortex flashing flows in convergent-divergent nozzles has been conducted. The simulation results show increase of nozzle restrictiveness after the application of inlet vortex, which is the same as the experimental results. The vortex control mechanism has also been explained with the insight provided by CFD simulation