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Abstract

Potential sources of rare earth elements are sought after in the world by many researchers. Coal ash obtained at high temperatures (HTA ) is considered among these sources. The aim of the study was an evaluation of the suitability of the high temperature ash (HTA ) formed during the combustion of bituminous coal from the Ruda beds of the Pniówek coal mine as an potential resource of REY . The 13 samples of HTA obtained from the combustion of metabituminous (B) coal were analyzed. The analyses showed that the examined HTA samples varied in their chemical composition. In accordance with the chemical classification of HTA , the analyzed ash samples were classified as belonging to the following types: sialic, sialocalcic, sialoferricalcic, calsialic, fericalsialic, ferisialic. The research has shown that the rare earth elements content (REY ) in examined HTA samples are characterized by high variability. The average REY content in the analyzed ashes was 2.5 times higher than the world average (404 ppm). Among rare earth elements, the light elements (LREY ) were the most abundant. Heavy elements (HREY ) had the lowest share. A comparison of the content of the individual rare earth elements in HTA samples and in UCC showed that it was almost 20 times higher than in UCC. The distribution patterns of REY plotted for all samples within their entire range were positioned above the reference level and these curves were of the M-H or M-L type. The data presented indicate, that the analyzed ash samples should be regarded as promising REY raw materials. Considering the fact that in 7 out of 13 analyzed ash samples the REY content was higher than 800 ppm, REY recovery from these ashes may prove to be economic.
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Abstract

Performance assessment of ejector-expansion vapor compression refrigeration system with eco-friendly R134a alternative refrigerants (R152a, R1234yf, R600a, R600, R290, R161, R32, and propylene) is presented for air-conditioning application. Ejector has been modeled by considering experimental data based correlations of component efficiencies to take care of all irreversibilities. Ejector area ratio has been optimized based on maximum coefficient of performance (COP) for typical air-conditioner operating temperatures. Selected refrigerants have been compared based on area ratio, pressure lift ratio, entrainment ratio, COP, COP improvement and volumetric cooling capacity. Effects of normal boiling point and critical point on the performances have been studied as well. Using ejector as an expansion device, maximum improvement in COP is noted in R1234yf (10.1%), which reduces the COP deviation with R134a (4.5% less in basic cycle and 2.5% less in ejector cycle). Hence, R1234yf seems to be best alternative for ejector expansion system due to its mild flammability and comparable volumetric capacity and cooling COP. refrigerant R161 is superior to R134a in terms of both COP and volumetric cooling capacity, although may be restricted for low capacity application due to its flammability. Słowa kluczowe
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Abstract

Induction surface hardening means the hardening of a thin zone of the material only, while its core remains soft. The paper deals with the modelling of the Consecutive Dual Frequency Induction Hardening (CDFIH) of gear wheels and its validation. For gear wheels with modulus m smaller than 6 mm a contour profile of hardness distribution could be obtained. The investigated gear wheel is heated first by a medium frequency inductor to the temperature approximately equal to the modified lower temperature Ac1m. It means beginning of the austenite transformation. Then the gear wheel is heated by the high frequency inductor to the hardening temperature making it possible to complete the austenite transformation and immediately cooled. In order to design the process it is necessary to identify modified critical temperatures and to obtain expected temperature distribution within the whole tooth.
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