Presented paper is focused on comparison of certain physical properties of selected vegetable oils. Physical properties, such as density, dynamic, kinematic viscosity and fluidity, were experimentally determined. All experiments were conducted on two samples of vegetable oils: sunflower and extra virgin olive oils with approximate temperature range of 5–32 °C. Density of oils was determined by oscillation method utilizing digital densimeter Anton Paar DMA 4500M at different temperatures. Dynamic viscosity was measured by means of rotational viscometer Anton Paar DV-3P. The rest of rheological parameters were determined on the basis of their definitions. Obtained results are depicted as graphical dependencies of rheological parameters and density on temperature. These dependencies of vegetable oils on dynamic and kinematic viscosity showed decreasing exponential shape, which is in compliance with Arrhenius equation; temperature dependencies on fluidity showed an increasing exponential shape for both samples. Density dependencies of samples on temperature were characteristic with decreasing linear function within measured temperature range. Similar results were achieved by other researchers. On the basis of measured values, it is evident that dynamic viscosity of extra virgin olive oil shows higher values than sunflower oil viscosity, which is a result of different composition of oils.

The physical properties of any fuel are of significant importance to determining its suitability for a particular engine. The prediction of various properties of biodiesel or biodiesel blends with gasoline is vital to the design of different diesel engines. Therefore, the purpose of this paper is to examine the characterization of biodiesel density according to the standard testing methods employed in the present study. On the basis of the experimental material research in the field of biofuels, the effect of gasoline addition to biofuel on the biofuel properties was studied. The density of biofuel was found to decrease linearly with an increase in the blending ratio. Based on the data obtained, = 0.8838 g/cm 3 for 100 % biodiesel is not fully acceptable according to the referenced standards, and thus cannot be used in the United States without blending. However, this value is still within the acceptable range for use in the EU.

Due to expansion of utilisation of photovoltaics in ordinary households, the question arises how this phenomenon affects the electric power of photovoltaic modules. The article deals with the electric power analysis of photovoltaic modules as a function of two very important factors. The first examined factor was partial shading, and the second factor was the intensity of reflected radiation. In order to determine the dependence of module power on the aforementioned parameters, a measurement system under laboratory conditions has been prepared. For identification of the reflected radiation effect on the power of the photovoltaic module, a series of measurements was performed on 7 different surfaces with the same radiation source. It is evident from obtained experimental result that the ratio of reflected irradiation on the solar module power is 1.29%. By simulation of partial shading of photovoltaic module, the decrease of 86.15% in its output power was identified.

The aim of the present study was to determine the physico-chemical properties (dry matter content, combustion heat, electrical properties, total protein, ash, fat and crude fibre contents, selected amino acids, and trace elements), antioxidant content, and sensory profile of Linz biscuits. They were enriched by the addition of powdered carrot, nettle leaves and elderberry fruit, which is 3% of the product. For comparison of results, a control variant without the addition of these components was also prepared. The enriched biscuits showed slightly higher total ash and crude fibre contents in comparison to the control samples. Results for the antioxidant activity and total polyphenol, flavonoid, and phenolic acid contents of the enriched biscuits were higher in all observed parameters than in the control sample with the best results obtained for Linz biscuits enriched with elderberry and nettle powder. In enriched biscuits, higher contents of iron, zinc, and manganese were measured, especially in biscuits with nettle. Linz biscuits with nettle had higher combustion heat values than control samples; the other two sample types had lower values. We found that the resistance, capacitance, and relative permittivity of the enriched biscuits decreased with frequency according to the power regression function. On the contrary, the conductivity increased with an increasing frequency. Electrical properties were mainly influenced by the water content but also by added components.

The density of materials can be used for assessing their quality. The density of food materials depends on temperature and is caused by thermal expansion during heating. The density of a material is defined as a ratio between the mass of the material and its volume at the same temperature. One of the most exact methods for measuring liquid density is the pycnometric method. Measurements of materials density could also be performed using hydrometers or densimeters, where the exact value of density can be discerned on the hydrometer scale or on the display of measurement devices. During our experiments, we used two methods of density determination: pycnometric method and determination by a densimeter Mettler Toledo DM 40. Measurements were performed in the approximate temperature range (0 -30) °C. The effect of various parameters (such as temperature, fat content, alcohol content and short storing time) on the density of the material was analysed in this paper. A linear decreasing character was applied for temperature dependencies of the sample density in the measured temperature range. The highest fat content of milk caused the lowest density, whereas lower fat contents (less than 1.5 %) were not consistent with this proportion due to different amounts of proteins in the measured samples of milk. The effect of the alcohol content on density had to be investigated alongside the material composition (wine, whisky and piña colada). The density values obtained were a bit higher after a short storage period due to the water loss during storage. REZIME Gustina materijala može se koristiti za procenu njegovog kvaliteta. Gustina prehrambenih materijala zavisi od temperature i izazvana je toplotnom ekspanzijom tokom zagrevanja. Gustina materijala je definisana kao odnos mase materijala i zapremina pri istoj temperaturi. Jedna od najtačnijih metoda merenja tečnosti je piknometrijska metoda. Merenje gustine materijala, takođe, može se obaviti pomoću hidrometara ili densimetara , pri čemu se tačna vrednost gustine može očitati na skali hidrometra ili na displeju mernih uređaja. Tokom eksperimenata korišćene su dve metode određivanja gustine: piknometrijska metoda i određivanje denzimetarom Mettler Toledo DM 40. Merenja su obavljena u približnom temperaturnom opsegu (0 -30) °C. U radu je analiziran efekat različitih parametara (kao što su temperatura tečnosti, sadržaj masti, sadržaj alkohola i kratko vreme čuvanja) na gustinu materijala. Linearno smanjenje karaktera je primenjeno za zavisnost gustine od temperature u mernom opsegu temperature. Najveći sadržaj masnoće u mleku uzrokovao je najmanju gustinu, dok sadržaj masnoće (manje od 1,5%) nije bio u skladu sa ovim sadržajem, zbog različitih količina proteina u izmerenim uzorcima mleka . Efekat sadržaja alkohola na gustinu moraose ispitati uz sastav materijala (vino, viski i pina kolada). Dobijene vrednosti gustine su bile malo veće nakon kratkog vremena skladištenja usled gubitka vode tokom skladištenja.