<p>Usavršavanje aerodinamike privrednim motornih vozila putem optimizacije aerodinamičkih dodataka u svrhu postizanja boljih aerodinamičkih performansi u vidu umanjenja sile otpora vazduha. Prostiranje vazdušne struje oko modela je unapređeno optimizacionim dodacima što se sve ogleda u smanjenoj potrošnji goriva privrednog motornog vozila. Osim virtuelnih simulacija računarske dinamike fluida, u radu je prikazana validacija rezultata putem eksperimentalnog merenja u vazdušnom tunelu.</p> / <p>The improvement of commercial motor vehicle&#39;s aerodynamics through optimization process of aerodynamic equpments in order to achieve better aerodynamic performance in the form of drag force reduction. The expansion of the air flow around the model is enhanced by optimization accessories, which is all reflected in the reduced of fuel consumption of the commercial motor vehicle. In addition to virtual simulations of computational fluid dynamics, the paper presents the validation of results by experimental measurement in the wind tunnel.</p>

<p>U radu se na osnovu eksperimentalnih podataka analizira konvektivno su&scaron;enje jedne sorte<br />jabuke u laboratorijskoj &scaron;aržnoj kondenzacionoj su&scaron;ari vlastite konstrukcije. Istražuju se uticaj<br />procesnih parametara na kinetiku su&scaron;enja i kvalitet su&scaron;enih proizvoda. U tu svrhu izabrana je &scaron;iroko<br />rasprostranjena sorta &bdquo;crveni deli&scaron;es&ldquo;, rezana na kolutove, početne relativne vlage oko 87% su&scaron;ena na<br />konačnu oko 7,5 - 8,5 %.<br />Relevantnost pojedinih faktora i njihov uticaj na vreme trajanja procesa i parametre kvaliteta<br />su&scaron;enih proizvoda određivani su metodom planiranog eksperimenta.<br />Cilj primene procedure faktorskih planova eksperimrenta je dobijanje matematičkih modela i<br />grafičkih prikaza uticaja procesnih parametara na promenu merenog svojstva.<br />Temperatura vazduha menjala se od 40 do 600C, uz brzinu strujanja od 1 do 2 m/s i relativnu<br />vlažnost vazduha od 55 do 75%. Utvrđene su krive kinetike su&scaron;enja a kvalitet su&scaron;enih jabuka ispitan<br />je instrumentalnom analizom i ocenom potro&scaron;ača o prihvatljivosti proizvoda. Dobijeni su su&scaron;eni<br />proizvodi visokog kvaliteta. Regresionom analizom eksperimentalnih podataka dobijeni su<br />matematički modeli koji opisuju zavisnost izlaznih veličina od procesnih parametara koji defini&scaron;u<br />režim su&scaron;enja. Izlazne veličine koje se prate (odzivi) i označavaju stanje sistema su: vreme trajanja<br />procesa su&scaron;enja, sadržaj ukupnih kiselina izražene kao jabučna i sadržaj ukupnih &scaron;ećera.<br />Na osnovu matematičkog modela prove&scaron;će se detaljna parametarska analiza istraživanog<br />procesa, uticaj pojedine ulazne veličine na sam proces i omogućiti predviđanje svojstava su&scaron;enog<br />proizvoda u različitim kombinacijama procesnih parametara.<br />Rezultati istraživanja potvrđuju da se povećanjem temperature i smanjenjem relativne<br />vlažnosti agensa su&scaron;enja (vazduha) značajno smanjuje vreme procesa su&scaron;enja kolutova jabuke. Na<br />sadržaj ukupnih kiselina dobijen je značajan uticaj brzine srujanja vazduha, interakcije brzine<br />strujanja i temperature, temperature i relativne vlažnosti vazduha.<br />Očekujemo da će rezultati ovih istraživanja proizvesti dovoljno dobre matematičke modele<br />za dobijanje kvalitetnih su&scaron;enih proizvoda koji će se moći primeniti kao osnova za optimizaciju i<br />upravljanje procesima su&scaron;enja u poluindustrijskim i industrijskim razmerama.<br />Značaj predloženog istraživanja je, uz očekivani naučni doprinos, dobijanje su&scaron;enih<br />proizvoda ciljanih svojstava, uvažavajući kriterijum očuvanja kvaliteta, očuvanja energije i za&scaron;tite<br />okoline.</p> / <p>The thesis analyzes, on the basis of experimental data, convective drying of a sort of apple in<br />a laboratory batch condensation drying plant designed especially for the laboratory researches. The<br />influence of process parameters on drying kinetics and quality of dried products is examined. For this<br />purpose a widespread sort of apple called &bdquo;Red Delicious&ldquo; is chosen. It is cut into slices with the<br />starting and final moisture being about 87% and 7,5-8,5%, respectively.<br />The relevance of certain factors and their effect on the duration of the process and parameters<br />of the quality of dried products is determined by the method of planned experiment.<br />The procedure of factor plans of the experiment is applied in order to obtain mathematical<br />models and graphical illustrations of the influences of process parameters on the change of measured<br />characteristic.<br />Air temperature varies from 40 to 60&ordm;C, while the flow speed is from 1 to 2 m/s and relative<br />moisture of air is in the range from 55 to 75%. The curves of drying speed are identified and the<br />quality of dried apples is tested by instrumental analysis and consumers&rsquo; evaluation on the product<br />acceptability. The obtained dried products are of high quality. Regression analysis of experimental<br />data results in mathematical models describing dependance of output values on process parameters<br />which define drying mode. Output values (responses) which are monitored and which represent the<br />state of the system are: duration of drying process, content of total acids expressed as malic acid and<br />content of total sugars.<br />On the basis of mathematical model, a detailed parameter analysis of the process is carried<br />out as well as the influence of individual input value on the process itself and it will provide the<br />prediction of characteristics of dried products in various combinations of process parameters.<br />Research results confirm that the increase of temperature and decrease of relative moisture of<br />drying agents (air) significantly reduce the process of drying apple slices. The content of total acids is<br />significantly influenced by the speeds of air flow, interaction of flow speed and temperature,<br />temperature and relative air moisture.<br />The results of the research work are expected to produce mathematical models which are<br />good enough to achieve high quality dried products which can be applied as a basis for optimization<br />and control of drying processes in semi-industrial and industrial scopes.<br />In addition to expected scientific achievement, the presented research is significant for<br />obtaining dried products having defined qualities with regard to criteria of quality preservation,<br />energy conservation and environment protection.</p>