The results of research into utilizing grinded beech bark in order to substitute commonly used fillers in urea formaldehyde (UF) adhesive mixtures to bond plywood are presented in the present study. Four test groups of plywood with various adhesive mixtures were manufactured under laboratory conditions and used for experimentation. Plywood made using the same technology, with the common filler (technical flour), was used as a reference material. Three different concentrations of grinded beech bark were used. The thermal conductivity of the fillers used, viscosity and its time dependence, homogeneity and the dispersion performance of fillers were evaluated in the analysis of adhesive mixture. The time necessary for heating up the material during the pressing process was a further tested parameter. The produced plywood was analyzed in terms of its modulus of elasticity, bending strength, perpendicular tensile strength and free formaldehyde emissions. Following the research results, beech bark can be characterized as an ecologically friendly alternative to technical flour, shortening the time of pressing by up to 27%. At the same time, in terms of the statistics, the mechanical properties and stability of the material changed insignificantly, and the formaldehyde emissions reduced significantly, by up to 74%. The utilization of bark was in compliance with long-term sustainability, resulting in a decrease in the environmental impact of waste generated during the wood processing.

The potential of using ground birch (Betula verrucosa Ehrh.) bark as an eco-friendly additive in urea-formaldehyde (UF) adhesives for plywood manufacturing was investigated in this work. Five-ply plywood panels were fabricated in the laboratory from beech (Fagus sylvatica L.) veneers bonded with UF adhesive formulations comprising three addition levels of birch bark (BB) as a filler (10%, 15%, and 20%). Two UF resin formulations filled with 10% and 20% wheat flour (WF) were used as reference samples. The mechanical properties (bending strength, modulus of elasticity and shear strength) of the laboratory-fabricated plywood panels, bonded with the addition of BB in the adhesive mixture, were evaluated and compared with the European standard requirements (EN 310 and EN 314-2). The mechanical strength of the plywood with the addition of BB in the adhesive mixture is acceptable and met the European standard requirements. Markedly, the positive effect of BB in the UF adhesive mixture on the reduction of formaldehyde emission from plywood panels was also confirmed. Initially, the most significant decrease in formaldehyde release (up to 14%) was measured for the plywood sample, produced with 15% BB. After four weeks, the decrease in formaldehyde was estimated up to 51% for the sample manufactured with 20% BB. The performed differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and derivative thermogravimetry (DTG), also confirmed the findings of the study. As this research demonstrated, BB as a waste or by-product of wood processing industry, can be efficiently utilized as an environmentally friendly, inexpensive alternative to WF as a filler in UF adhesive formulations for plywood manufacturing.

Biological materials have a complicated structure. This complicated structure is caused by the great variability of their chemical, biological and physical properties (BLAHOVEC 1993). During processing biological materials, concretely nutritive raw materials as corn, wheat and products made from their grains are heated, cooled, dryed, moistured or mechanically handled. It is necessary to know thermophysical properties of nutritive raw materials to choice optimal technological procedures. Nowadays we know many methods of measurement, apparatures and instruments for thermophysical measurements. For our measurements we selected an Isomet instrument made by Applied Precission. It is used for quick and exact measurement thermophysical parameters of various materials. We can use Isomet for measurement of thermophysical parameters such as temperature, thermal conductivity, thermal diffusivity etc. Concretely we used Isomet for measurements of thermal conductivity and thermal diffusivity of corn flour and wheat flour and related thermal conductivity λ, thermal diffusivity a to moisture content and to bulk density. MATERIALS AND METHODSThe Isomet instrument was used for measurements. This instrument is based on the hot wire method. The simple measurement consists in measuring the temperature rise vs. time evaluation of an electrically heated wire embedded in the tested material. The thermal conductivity is derived from the resulting change in temperature over a known time interval.The ideal analytical model assumes an ideal -infinitely thin and infinitely long line heat source (hot wire), operating in an infinite, homogenous and isotropic material with uniform initial temperature T 0 . If the hot wire is heated for the time t = 0 with constant heat flux q per unit wire length, the radial heat flow around the wire will occur. The temperature rise ∆T (r, t) in any distance r from the wire as a function of time is described by the simplified equation (1) (CARSLAV, JAEGER 1959).where: k -the thermal conductivity, a -thermal diffusivity, C = exp(γ) with γ the Euler's constant.The thermal conductivity is calculated from the slope S of the temperature rise ∆T (r, t) vs. the natural logarithm of the time lnt evolution using the formula 4�SSeveral corrections have been introduced to account for the heat capacity of the wire, the thermal contact resistance between the wire and the test material, the finite dimension of the sample and the finite dimension of the wire embedded in the sample (LIANG 1995;ASSAEL et al. 1992).The hot wire method is in accordance with the way of measurement of the temperature increase and the place of the temperature sensor utilized in three main variations, known as the resistance technique (MARDOLCAR, NIETO DE CASTRO 1992), the standard (cross) technique and the parallel wires technique (ZHANG et al. 1991).Heat transport takes place in three ways: conduction, convection and radiation. Heat transport in grain mass is performed by conduction and by convection of air occurring between grains in the depend...

This article deals with thermal properties of selected biodiesel and bioethanol samples (biodiesel No 1, No 2 and bioethanol No 1, No 2). Biodiesel is renewable fuel that can be manufactured from vegetable oils, animal fats, or recycled restaurant grease for use in diesel vehicles. Biodiesel‘s physical properties are similar to those of petroleum diesel, but it is a cleaner-burning alternative fuel. Ethanol (CH3CH2OH) is a clear liquid. Also known as ethyl alcohol, grain alcohol, and EtOH, the molecules in this fuel contain a hydroxyl group (OH-) bonded to a carbon atom. Ethanol is made of the same chemical compound regardless of whether it is produced from starch and sugar-based feedstocks, such as corn grain, sugar cane, etc. The hot wire method was used for thermal parameters measurements. The experiment is based on measuring the temperature rise vs. time evaluation of an electrically heated wire embedded in the tested material. Thermal conductivity is derived from the resulting change in temperature over a known time interval. For two samples of biodiesel and two samples of bioethanol, there were determined basic thermophysical parameters - thermal conductivity and thermal diffusivity. Two series of measurements were made for each sample of biodiesel and bioethanol. In the first series, there were measured the thermal conductivity and thermal diffusivity at constant room temperature 20 °C. Every thermophysical parameter was measured 10 times for each sample. The results were statistically processed. In the second series of measurements, there were measured the relations of thermal conductivity and thermal diffusivity to temperature in temperature range 20-29 °C. It was evident from results that all measured dependencies are nonlinear. Polynomial functions described by polynomial coefficients were obtained for both thermophysical parameters. The type of function was selected according to statistical evaluation based on the coefficient of determination for every thermophysical parameter graphical dependency. All obtained results are presented in Figures 1-4 and in Tables 1-4. The results of thermophysical parameters measurements of biodiesel and bioethanol could be compared with the values presented in literature.

Energy balance of the photovoltaic system is influenced by many factors. In this article the effect of tilt and azimuth angle changes of the photovoltaic system energy production is analyzed. These parameters have significant impact on the amount of solar radiation which hits on the photovoltaic panel surface and therefore also on the energy absorbed by the module surface. The main aim of research was identification of the optimal position of photovoltaic system installation in the southern Slovakia regions. The experimental apparatus had two setups consisting of polycrystalline photovoltaic modules. The first setup was used for identification of the tilt angle changes in the range (0–90°). The second one was focused on the detection of the azimuth angle effect to the energy production. The measurement results were statistically processed and mathematically analyzed. Obtained dependencies are presented as two-dimensional and three-dimensional graphical relations. Regression equations characterize time relations between the tilt or azimuth angle and the energy produced by the photovoltaic system in Southern Slovakia. Obtained simplified mathematical model was verified by analytical model. Presented models can be used for the dimensioning and optimization of the photovoltaic system energy production.