Cutting temperature measurement and material machinability

Cutting temperature is very important parameter of cutting process. Around 90% of heat generated during cutting process is then away by sawdust, and the rest is transferred to the tool and workpiece. In this research cutting temperature was measured with artificial thermocouples and question of investigation of metal machinability from aspect of cutting temperature was analyzed. For investigation of material machinability during turning artificial thermocouple was placed just below the cutting top of insert, and for drilling thermocouples were placed through screw holes on the face surface. In this way was obtained simple, reliable, economic and accurate method for investigation of cutting machinability

Numerical simulation of thermo-fluid properties and optimization of hot water storage tank in biomass heating systems

Za potrebe zagrevanja 1 ha plastenika na poljoprivrednom dobru u Padinskoj Skeli, koje se nalazi u okviru PKB korporacije, izgrađen je grejni sistem sa kotlom na biomasu, u kome se toplota dobija sagorevanjem balirane sojine slame. Zbog nestacionarnih efekata zagrevanja pojavila se potreba za uključivanjem akumulatora toplote u sistem grejanja. Ovaj rad ima za cilj numeričku i eksperimentalnu studiju izvršenu sa ciljem optimizacije akumulatora toplote u predmetnom grejnom sistemu, kao i optimizaciju celokupnog grejnog sistema. U akumulatoru toplote kapaciteta 100 m3, u kome se skladišti zagrejana voda, izvršena su merenja u 256 tačaka, kako u stacionarnom tako i u nestacionarnom režimu rada kotla. Analiza optimizacije je izvršena numeričkom simulacijom koja je obuhvatala i stacionarne i nestacionarne režime. Dobijeni rezultati pokazuju dobro poklapanje rezultata dobijenih eksperimentom i numeričkom simulacijom.A 1.5 MW combustion facility burning large bales of soy straw has been built for the purpose of heating 1 ha of vegetable greenhouses located within the complex of Agricultural Plant PKB in Padinska Skela, Serbia. The paper addresses numerical and experimental study of temperature distribution in a cylindrical, 100 m3 (8 m high, 4 m in diameter) hot water storage tank. The water tank optimization, as well as optimization of the heating facility as a whole, were identified as the main goals of the study performed. Water temperature was measured by a temperature probe inserted in the tank. Measurements were conducted in 256 measurement points, both under steady and unsteady water flow conditions. Water tank optimization analysis was carried out utilizing both steady and unsteady state numerical simulation. The results obtained indicated good agreement between the experimental and computational data acquired

Drying processes of lignites with high moisture content in packed and fluidized bed

Уклањање влаге из нискоквалитетних угљева се сматра важним поступком побољшања квалитета угља. У раду је приказан преглед тренутног стања технологија оплемењивања нискоквалитетних угљева, са посебним нагласком на процесе сушења као и одстрањивања влаге (у течном стању). Да би се израчунали значајни параметри процеса уклањања влаге развијен је и представљен модел конвективног сушења угља у флуидизованом слоју, заснован на двофазном моделу мехурастог флуидизованог слоја са гасом и честицама у суспензионој фази и гасом у мехурастој фази. Основна концепција развијеног модела је да се процес сушења у суспензионој фази разматра као за непокретни слој честица, коришћењем концепта "коефицијент сушења", при чему се врши прорачун за елементарне слојеве (запремине) и уопштава за цео слој честица. Мешање честица које се јавља у флуидизованом слоју урачунава се преко дифузионог члана у диференцијалним једначинама. Топлотна проводљивост непокретног слоја коју су дефинисали Zehner, Bauer и Schlünder је коришћена за дефинисање механизама преноса топлоте који се јављају у суспензионој фази флуидизованог слоја. Дискретизација система диференцијалних једначина извршена је нумеричком методом контролних запремина. Добијени систем линеаризованих алгебарских једначина је решаван помоћу ТДМА алгоритма (Три- Дијагонални Матрични Алгоритам). Релације зависне од материјала (пренос супстанције унутар чврсте фазе, равнотежно стање влаге између гасне и чврсте фазе), које се односе на одговарајућу врсту угља (лигнит Колубара), добијене су претходним истраживањима...Removal of moisture from low-rank coals is deemed an important quality upgrading method. An overview of the current status of low-rank coal upgrading technologies is presented in the paper, particularly with respect to drying and dewatering procedures. In order to calculate the significant parameters of the moisture removal process, a model of convective coal drying in a fluid bed, based on the two-phase bubbling fluidization model with gas and particles in suspension phase and gas in bubbling phase, is developed and presented. Basic assumption of the model is that the drying process in suspension phase is considered as for packed bed of particles by applying concept "drying coefficient", where the calculation is performed for elementary layers (volumes) and generalized for the entire bed of particles. The mixing of particles is calculated by means of diffusion term in the differntial equations. Effective thermal conductivity of the packed bed as defined by Zehner/Bauer/Schlünder is used to define heat transfer mechanisms occurring in the suspension phase of the fluid bed. A control volume numerical method is used for discretization of the differntial equations. Discretization equations have been solved by means of TriDiagonal-Matrix Algorithm. Product-specific data (intraparticle substance transfer, gas-solid moisture equilibrium) related to the particular coal variety addressed here (Kolubara lignite) are obtained through preliminary investigations. Тwo series of experimens in fluidized bed and one series in packed bed were performed. A completely new set of experimental results obtained has been successfully used to validate the model additionally. Comparison of obtained numerical simulation results and experimental results and results of other authors from available literature have shown a good agreement..

Characterization of dispersion strengthened copper with 3wt%Al2O3 by mechanical alloying

The copper matrix has been dispersion strengthened with 3wt. %Al2O3 by mechanical alloying. Commercial alumina powder with an average particle size of 0.751 mum was used for alloying. The mechanical alloying process was performed in a planetary ball mill up to 20h in air. After milling all powders were treated in H-2 at 400(degrees)C for 1h, and finally hot pressing was used for compaction (800degreesC, 3h, Ar). Structure observations revealed a lamellar structure (Al2O3 particles largely restricted to interlamellar planes between adjacent copper lamellae) accompanied also by structure refinement. These structural changes were mostly completed in the early stage of milling, and retained after compaction. Micro. hardness was found to progressively increase with milling time. So, after 5h of milling the micro hardness of the Cu+3twt%Al2O3 compact was 1540MPa, i.e. 2.5 times greater than for the as-received electrolytic copper powder (638MPa) compacted under identical conditions, while after 20h of milling it was 2370 MPa. However, after exposing the tested compact at 800degreesC up to 5h, the achieved hardening effect vanished

Effect of Mineral Nutrition on Red Clover Leaf Area Index

The legume red clover (Trifolium pratense) fixes its own nitrogen (N), but requires P and K fertilisation. There are no recent reliable data in the domestic literature, on the amounts of P and K recommended to farmers; present recommendations are often either inadequate or excessive. Red clover mineral nutrition is significantly affected by soil and weather conditions (Taylor & Quesenberry, 1996). The objective of our twoyear study was to enable rational fertiliser application in accordance with soil type and agro ecological conditions

Microstructure and fracture mode of unalloyed dual-phase austempered ductile iron

Dual-phase ADI material microstructure consists of different amounts and morphologies of ausferrite and free ferrite, obtained by subjecting ductile iron to specific heat treatment. Its strength is lower compared to comparable ADI materials but exhibits a higher ductility, the major disadvantage of ADI. In the current study, an unalloyed ductile iron was intercritical austenitized in two-phase regions (??+??) at four temperatures from 840 to 780 ??C for 2 h and austempered at 400 ??C for 1 h to obtain dual-phase ADI with different percentages of free ferrite and ausferrite. Light and scanning electron microscopy was performed for the metallographic and fracture studies, respectively. Microscopy results were correlated to tensile testing results. The results indicated that, as the amount of ausferrite present in the matrix increases, higher values of strength and lower ductility are obtained. The fracture surfaces of dual-phase ADI microstructures with 22.8% of ausferrite in their matrix have regions of quasi-cleavage fracture around last-to-freeze zones, related to the presence of ausferrite in those areas. The specimens with the highest values of ausferrite of 86.8% among the dual-phase microstructure have a dominant quasi-cleavage type of fracture

Pljevlja lignite carbon emission charateristics

The anthropogenic emission of GHG especially CO has to be limited and reduced due to their impact on global warming and climate change. Combustion of fossil fuels in the energy sector has a dominant share in total GHG emissions. In order to reduce GHG emission, European Union established a scheme for GHG allowance trading within the community, and the implementation of the European Union emission trading scheme, which is a key to GHG reduction in a cost-effective way. An important part of emission trading scheme is prescribed methodology for monitoring, reporting, and verification of the emission of GHG including characterization of the local fuels combusted by the energy sector. This paper presents lignite characteristics from open-pit mine Borovica-Pljevlja, which has highest coal production in Montenegro (>1.2 Mt per year), including evaluation of its carbon emission factor based on the laboratory analysis of 72 coal samples. Testing of the samples included proximate and ultimate analysis, as well as, net calorific value determination. In accordance with the obtained results, linear correlations between net calorific value and combustible matter content, carbon content and combustible matter content, hydrogen content and combustible matter content, carbon content and net calorific value, were established. Finally, the non-linear analytical correlation between carbon emission factor and net calorific value for Pljevlja lignite was proposed, as a base for the precise calculation of CO emission evaluation