The influence of various process parameters on the deep drawing process is a current research topic in sheet metal forming technology. Starting from the application of the previously constructed ...original testing device, an original tribological model was developed based on the process of sheet metal strip sliding between flat contact surfaces under variable pressures. A complex experiment was executed using an Al alloy sheet, tool contact surfaces of different roughness, two types of lubricants and variable contact pressures. The procedure included analytically pre-defined contact pressure functions based on which, for each of the mentioned conditions, the dependencies of the drawing forces and friction coefficients were obtained. The pressure in function P1 constantly decreased from a high initial value until the minimum, while in function P3 the pressure increased until the minimum value at the halfway point of the stroke, after which it increased up to the initial value. On the other hand, the pressure in function P2 constantly increased from the initial minimum value until the maximum value, while in function P4 the pressure increased until reaching the maximum value at the halfway point of the stroke, after which it decreased to the minimum value. This enabled the determination of the influence of tribological factors on the process parameters of intensity of traction (deformation force) and coefficient of friction. The pressure functions starting with decreasing trends produced higher values for the traction forces and the friction coefficient. In addition, it was established that the roughness of the contact surfaces of the tool, especially those with titanium nitride coating, has a significant influence on the process parameters. For surfaces of lower roughness (polished), a tendency of the Al thin sheet to form a glued-on layer was noticed. This was especially prominent for lubrication with MoS
-based grease under conditions of high contact pressure (functions P1 and P4 at the beginning of the contact).
Influence of the contact pressure in the deep drawing processes is a very actual research topic in the metal forming technology. Within this research the tribological model of the strip sliding in ...the flat die was developed. The original experimental computerized apparatus for testing of the strip sliding in the variable contact pressure conditions was developed, as well. The complex, multi-factor experiment was performed by application of the Al thin sheet, with the contact elements of various roughnesses, with different lubricants application and with the variable contact pressure. Besides the description of the developed apparatus, the theoretical way for determination of the pressure dependences was also presented. Based on the theoretical changes of pressure, set in advance, the real influence of the contact pressure was obtained, for each of the given conditions. That makes possible to determine the influence of the tribological factors on the actual pressure. The obtained real contact pressure has verified the reliability of the experimental apparatus, namely the degree of the theoretical pressure dependences deviation from the real ones.
The use of solar dish thermal collectors is a promising choice for designing
sustainable energy systems. The use of nanofluids is a new way for enhancing
the thermal performance of solar collectors ...because of their improved thermal
properties. The objective of this study is to investigate the use of mono and
hybrid nanofluids in a solar dish collector in order to determine which kind
of nanofluids leads to higher performance enhancements. The analysis is
conducted with a developed thermal model in Engineering Equation Solver and
the collector is studied thermally and exergetically. The examined hybrid
nanofluid has as base fluid syltherm 800 with 1% Cu and 1% TiO2. Moreover,
the examined mono nanofluids are the syltherm 800 with 2% Cu and syltherm 800
with 2% TiO2. The investigated solar dish collector has a spiral absorber and
it is examined for inlet temperatures from 25?C up to 300?C with a flow rate
of 200 L/h. According to the final results, the use of hybrid nanofluid leads
to higher thermal efficiency enhancement compared to the mono nanofluids
because of the higher increase in the Nusselt number in the flow. More
specifically, the use of the hybrid nanofluids leads to 0.99% mean thermal
efficiency enhancement compared to the pure oil case, while the use of Oil/Cu
and Oil/TiO2 lead to 0.42% and to 0.56% mean thermal efficiency enhancement,
respectively. Moreover, the exergy efficiency is found enhanced with the use
of all nanofluids. The mean exergy efficiency enhancement is 1.21% with the
hybrid nanofluid, while it is 0.73% with Oil/TiO2 and 0.53% with Oil/Cu.
Oranges and snow Simic, Charles; Simic, Charles
2010., 20101101, 2010, 2011-01-01, Letnik:
3
eBook
Pulitzer Prize-winning poet Charles Simic has done more than anyone since Czeslaw Milosz to introduce English-language readers to the greatest modern Slavic poets. InOranges and Snow, Simic continues ...this work with his translations of one of today's finest Serbian poets, Milan Djordjevic. An encounter between two poets and two languages, this bilingual edition--the first selection of Djordjevic's work to appear in English--features Simic's translations and the Serbian originals on facing pages. Simic, a native Serbian speaker, has selected some forty-five of Djordjevic's best poems and provides an introduction in which he discusses the poet's work, as well as the challenges of translation.
Djordjevic, who was born in Belgrade in 1954, is a poet who gives equal weight to imagination and reality. This book ranges across his entire career to date. His earliest poems can deal with something as commonplace as a bulb of garlic, a potato, or an overcoat fallen on the floor. Later poems, often dreamlike and surreal, recount his travels in Germany, France, and England. His recent poems are more autobiographical and realistic and reflect a personal tragedy. Confined to his house after being hit and nearly killed by a car while crossing a Belgrade street in 2007, the poet writes of his humble surroundings, the cats that come to his door, the birds he sees through his window, and the copies of one of his own books that he once burnt to keep warm.
Whatever their subject, Djordjevic's poems are beautiful, original, and always lyrical.
An emergency caused by the COVID-19 pandemic affected the rethinking of existing healthcare systems. The increased need for hospital beds appeared short after the outbreak of the pandemic and the ...solution was to adapt the existing buildings, primarily public ones. Among all, sports buildings, i.e. sports halls were successfully used around the globe for conversion into hospitals. Topic of the paper was to investigate whether sports halls in Serbia, which were also used as temporary hospitals, are suitable for conversion in terms of energy consumption needed for achieving thermal comfort. Two case studies were analysed. The energy simulations were done using the DesingBuilder software. The results of thermal comfort summary and energy consumption led to the conclusion that this building type in Serbia could be successfully used for hospital purposes. Although the multiple increase in energy consumption was noted during the heating period, the results were within the limits required by both national and international standards.
The Archimedean spiral coil made of a transversely corrugated pipe represents the radiant heat absorber of a parabolic dish solar concentrator. The main advantage of the considered design is the ...coupling of two passive methods for heat transfer enhancement: coiling the flow channel and changing the surface roughness. The aim of this numerical study is to assess the capability of RANS models of different complexity (realizable k-?, SST k-?, and RSM linear pressure-strain) to adequately represent the heat transfer phenomena in the considered complex flow geometry for wide ranges of Reynolds and Prandtl numbers. The obtained results indicate that the realizable k-? model with enhanced wall treatment is inadequate to simulate the heat transfer for all flow conditions, while both SST and RSM slightly overestimate experimental data in the turbulent region and are able to predict laminarisation at low Reynolds numbers. The SST model predictions are more accurate in the transitional and at the beginning of the turbulent region, irrespective of the curvature ratio. The RSM predictions are generally more accurate in the turbulent region. Numerically obtained circumferential distributions of local Nusselt number reveal that considered turbulence models are unable to completely anticipate the interactions between the complex flow in the basic section of the pipe and the vortex flow within the corrugations.
A polygeneration system is an energy system capable of providing multiple
utility outputs to meet local demands by application of process integration.
This paper addresses the problem of pinpointing ...the optimal polygeneration
energy supply system for the local energy demands of a livestock farm in
terms of optimal system configuration and optimal system capacity. The
optimization problem is presented and solved for a case study of a pig farm
in the paper. Energy demands of the farm, as well as the super-structure of
the polygeneration system were modelled using TRNSYS software. Based on the
locally available resources, the following polygeneration modules were chosen
for the case study analysis: a biogas fired internal combustion engine
co-generation module, a gas boiler, a chiller, a ground water source heat
pump, solar thermal collectors, photovoltaic collectors, and heat and cold
storage. Capacities of the polygeneration modules were used as optimization
variables for the TRNSYS-GenOpt optimization, whereas net present value,
system primary energy consumption, and CO2 emissions were used as goal
functions for optimization. A hybrid system composed of biogas fired internal
combustion engine based co-generation system, adsorption chiller solar
thermal and photovoltaic collectors, and heat storage is found to be the best
option. Optimal heating capacity of the biogas co-generation and adsorption
units was found equal to the design loads, whereas the optimal surface of the
solar thermal array is equal to the south office roof area, and the optimal
surface of the PV array corresponds to the south facing animal housing
building rooftop area.
Polypropylene is a widely used linear hydrocarbon polymer with diverse applications due to its exceptional physicochemical characteristics and minimal changes during the recycling process. Numerous ...studies have focused on factors influencing the mechanical properties of polypropylene and its application in composites. However, despite their significance in the agricultural industry, there is limited research on polypropylene baling twines. This study analyses the behaviour of polypropylene baling twine under tensile loading, exploring the influence of fibre friction and twisting angle on the material’s tensile strength. Experimental investigation indicated that tensile strength increases with twisting angle, but only until the angle reaches a critical value. Further increase in the twist angle led to a decrease in tensile strength. The increase in tensile strength is attributed to the rise in the coefficient of friction between fibres in the twine. An experimental approach was employed to evaluate the mechanical characteristics of the twine, including the effect of prestressing by twisting. Understanding these characteristics is crucial for enhancing the quality of polypropylene baling twines and optimising their application in the agricultural industry.
A polygeneration system is an energy system capable of providing multiple
energy outputs to meet local demands, by application of high process
integration. In this paper, optimal configuration and ...capacity of a
polygeneration system for an indoor swimming pool building is determined by
application of a method based on TRNSYS simulation and GenOpt optimization
software. Based on the applicability, a superstructure of the polygeneration
system is integrated, consisting of the following polygeneration modules: an
internal combustion engine cogeneration module, a vapor compression chiller,
and adsorption chiller, a ground source heat pump, flat plate solar thermal
collectors, photovoltaic collectors, and heat storage. Annual behavior of
energy loads of the public swimming pool building during a typical
meteorological year and the polygeneration system are modeled and simulated
using TRNSYS software, whereas techno-economic optimization is performed by
GenOpt optimization. The results indicated the optimal con-figuration of the
polygeneration system for the modelled energy demands, as well as the optimal
capacity of the polygeneration modules, thus defining the optimal capacity of
the polygeneration system for the energy demands of the public swimming pool
building.
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