7 results on '"Rudonja, Nedžad"'
Search Results
2. EXPERIMENTAL AND NUMERICAL INVESTIGATION OF THERMAL IMPROVEMENT OF WINDOW FRAMES.
- Author
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GOJAK, Milan D., KIJANOVIĆ, Aleksandar I., RUDONJA, Nedžad R., and TODOROVIĆ, Ružica I.
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THERMAL conductivity ,URETHANE foam ,INSULATING materials ,STAINLESS steel ,VINYL ester resins - Abstract
This article presents experimental and numerical determinations of thermal transmittance performed on three different types of window frames (vinyl, aluminium, and wooden) within the same insulated glass unit. Good agreement between experimental and numerical results was attained. Using the numerical models, thermal improvement techniques of the frames and their influence on thermal transmittance of frames were studied. The first thermal improvement technique was using the insulation materials inserted inside large air cavities. By filling the cavity of vinyl frame with the polyurethane foam, thermal transmittance of vinyl frame was lowered by 10%. The second technique was based on repeating the procedure with materials installed inside frames with the materials that have lower thermal conductivity. This technique can be applied on thermal breaks and on steel profiles inside cavities. The result of this thermal improvement (attained by replacing thermal break material with material that has lower thermal conductivity) was certain reduction of the thermal transmittance of frames, by 9%. Using stainless steel instead of the oxidized steel was reduction of the thermal transmittance of vinyl frame by 3%. For the case of wooden frames the influence of shifting glazing unit deeper into profile upon the thermal transmittance of the frame was analyzed. Installing the glass unit by 5 mm deeper into the wooden frame reduced glass thermal transmittance by 5%. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
3. STUDY OF VACUUM AND FREEZE DRYING OF BEE HONEY.
- Author
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NEDIĆ, Nebojša M., GOJAK, Milan D., ZLATANOVIĆ, Ivan J., RUDONJA, Nedžad R., LAZAREVIĆ, Kristina B., DRAŽIĆ, Milan S., GLIGOREVIĆ, Kosta B., and PAJIĆ, Miloš B.
- Subjects
HONEYBEES ,FREEZE-drying ,DRYING ,HIGH performance liquid chromatography ,COMMON sunflower ,VACUUM ,HONEY - Abstract
The aim of this research is to study the drying kinetics of vacuum-dried and freeze-dried bee honey produced from two different varieties: Sunflower honey (Helianthus Annuus L.) and Acacia honey (Robinia pseudo acacia L.). Vacuum drying treatments were carried out with the honey samples' initial temperatures of +25 °C, -20 °C, and -40 °C. Water content, total soluble solids, as well as the water activity of fresh and dried honey samples were determined. Freeze-drying of bee honey with initial sample temperature of -40°C has resulted in shorter drying time (7-9 hours), moisture content (10%-12%), water activity (0.405-0.427 aW) and effective moisture diffusivity coefficient (8.26·10-7-9.51·10-7 m²/s). The high-performance liquid chromatography method was used when analyzing the impact that drying pre-treatments had on honey quality. The application of pre-treatments has led to an increase in hydroxy-methyl-furfural by 39-71%, and a decrease in diastase activity by 17-36%, all compared to fresh honey samples. The solutions of Verma model proved to be the best fit with the experimental results. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
4. Побољшање преношења топлоте у акумулатору топлоте са фазно променљивим материјалом као испуном
- Author
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Rudonja, Nedžad R., Komatina, Mirko, Banjac, Miloš, Gojak, Milan, Antonijević, Dragi, and Živković, Goran
- Subjects
нумеричко моделирање ,парафин ,phase-change material ,numerical modeling ,акумулатор топлоте ,thermal energy storage ,фазно променљив материјал ,paraffin - Abstract
Отежано преношење топлоте у акумулаторима топлоте са фазно променљивим материјалом као испуном, које се јавља као последица мале топлотне проводљивости фазно променљивих материјала који се користе на температурском опсегу до 200 C° , представља главну препреку у примени акумулатора топлоте у којима се акумулација топлоте остварује на рачун промене фазе радног медијума. Поред типова акумулатора топлоте и прегледа потенцијалних, односно коришћених фазно променљивих материјала, разматране су методе за побољшање преношења топлоте, тј. за превазилажење проблема мале топлотне проводљивости материјала. Као најпоузданији метод за поспешивање преношења топлоте се показало повећање површи за размену топлоте, тј. површи која је у контакту са фазно променљивим материјалом. Као фазно променљиви материјал коришћен је парафин комерцијалног назива Е53. Побољшање преношења топлоте је праћено преко смањења времена топљења парафина, тј. повећања брзине промене фазе, односно временског периода у коме се достиже температура промене фазе парафина. За разлику од досадашњих истраживања, у којима је повећање оствареног побољшања преношења топлоте посматрано у функцији од броја ребара или неке карактеристичне димензије ребра (висина, пречник, дужина и сл.), у овом раду је побољшање доведено у корелацију са фактором оребрења. У оквиру дисертације је осмишљен физички модел акумулатора топлоте испуњеног фазно променљивим материјалом за три вредности фактора оребрења, тј. за три варијанте акумулатора топлоте. Уведени физички модел акумулатора топлоте описан је одговарајућим математичким моделом у који су имплементиране претпоставке неопходне за решавање дефинисаног система једначина... Impaired heat transfer in thermal energy storage (TES) with phase change material (PCM) as a filling, which occurs as a result of low thermal conductivity of the phase-change materials used for storing thermal energy up to 200 C° , represents a major obstacle in the implementation of the TES in which the heat accumulation is realized as a consequence of the working medium phase change. Beside review of present thermal energy storages types and potential one, respectively used PCMs, methods for enhancing heat transfer were considered, i.e. method for overcoming the problem of low thermal conductivity material. As the most reliable method for enhancing heat transfer, the increase of heat transfer surface was found, i.e. the surface that is in the contact with PCM. The commercial paraffin E53 was used as the PCM. The enhancement of heat transfer is accompanied by the decrease of the paraffin melting time, i.e. increase of the phase change rate, respectively the period in which the temperature of the phase change of the paraffin is reached. Unlike previous studies, where achieved heat transfer increase was analyzed as a function of the number of fins or some fin characteristic dimension (height, diameter, length, etc.), in this thesis the heat transfer improvement was into correlated with of the finned surface factor. Within this thesis the physical model of the thermal energy storage filled by PCM was conceived for three values of the finned surface factor, i.e. for the three variants of the TES. The introduced physical model of the TES was described by corresponding mathematical model in which the necessary assumptions for solving the defined system of equations were implemented...
- Published
- 2016
5. GREEN ROOFS AND COOL MATERIALS AS RETROFITTING STRATEGIES FOR URBAN HEAT ISLAND MITIGATION: Case Study in Belgrade, Serbia.
- Author
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LALOŠEVIĆ, Marija D., KOMATINA, Mirko S., MILOŠ, Marko V., and RUDONJA, Nedžad R.
- Subjects
URBAN heat islands ,ROOF gardening ,SUSTAINABLE buildings ,RENEWABLE energy sources ,METROPOLITAN areas - Abstract
The effect of extensive and intensive green roofs on improving outdoor microclimate parameters of urban built environments is currently a worldwide focus of research. Due to the lack of reliable data for Belgrade, the impact of extensive and intensive green roof systems on mitigating the effects of urban heat islands and improving microclimatic conditions by utilizing high albedo materials in public spaces were studied. Research was conducted on four chosen urban units within existing residential blocks in the city that were representative of typical urban planning and construction within the Belgrade metropolitan area. Five different models (baseline model and four potential models of retrofitting) were designed, for which the temperature changes at pedestrian and roof levels at 07:00, 13:00, 19:00 h, on a typical summer day, and at 01:00 h, the following night in Belgrade were investigated. The ENVI-met software was used to model the simulations. The results of numerical modeling showed that utilizing green roofs in the Belgrade climatic area could reduce air temperatures in the surroundings up to 0.47, 1.51, 1.60, 1.80 °C at pedestrian level and up to 0.53, 1.45, 0.90, 1.45 °C at roof level for four potential retrofitting strategies, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
6. HEAT TRANSFER ENHANCEMENT THROUGH PCM THERMAL STORAGE BY USE OF COPPER FINS.
- Author
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RUDONJA, Nedžad R., KOMATINA, Mirko S., ŽIVKOVIĆ, Goran S., and ANTONIJEVIĆ, Dragi Lj.
- Subjects
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HEAT storage , *FINS (Engineering) , *HEAT transfer , *HEAT flux , *NUMERICAL analysis - Abstract
Enhancement of heat transfer over a cylinder shaped thermal energy storage filled by paraffin E53 by use of longitudinal rectangular copper fins was analyzed. The thermo-physical features of the storage material are determined in separate experiments and implemented to FLUENT software over user defined function. Advanced thermal storage geometry comprehension and optimization required introduction of a parameter suitable for the analysis of heat transfer enhancement, so the ratio of heat transfer surfaces as a factor was proposed and applied. It is revealed that increase of the ratio of heat transfer surfaces leads to the decrease of melting time and vice versa. Numerical analysis, employing the 3-D model built in Ansys software, observed storage reservoir geometries with variable number of longitudinal fins. The adjusted set of boundary conditions was carried out and both written in C language and implemented over user defined function in order to define variable heat flux along the height of the heater. The comparison of acquired numerical and experimental results showed a strong correlation. Experimental validation of numerical results was done on the real thermal energy storage apparatus. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
7. Термодинамичка анализа, моделирање и оптомизација динамичког понашања система за климатизацију, грејање и хлађење у јавним објектима
- Author
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Manić, Dimitrije, Komatina, Mirko, Banjac, Miloš, Živković, Branislav, Rudonja, Nedžad, and Vučićević, Biljana
- Subjects
енергетске перформансе зграда, термички омотач, КГХ системи калибрисана симулација, мере за уштеду енергије, емисија гасова стаклене баште ,building energy performance, thermal envelope, HVAC systems, calibrated simulation, energy saving measures, greenhouse gasses emission - Abstract
У контексту повећања ефикасности и одрживости енергетског сектора, један од најзначајнијих проблема представља рационализација и оптимизација потрошње енергије у зградама, јер oко 32% глобалне потрошње енергије је у сектору зграда [1]. Значајни напори на глобалном и ло- калном нивоу улажу се у повећање енергетске ефикасности у зградама, укључујући унапре- ђење индустријских стандарда, међународних уговора, законске регулативе и инвестирање у енергетске санације постојећих зграда и енергетски ефикасне технологије... In contexts of sustainability and energy efficiency, one of the most important topics is rationalization and optimization of building energy consumption, since about 32% of total energy consumption in the world is from the building sector [1]. Significant efforts and resources on global and local level are invested in order to increase energy efficiency of the buildings, including improving industrial standards, international agreements, legislation and investment in energy efficient technology, and energy retrofits of existing buildings...
- Published
- 2021
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