A non-isothermal kinetic analysis of kaolinite dehydroxylation was carried out using thermogravimetric analysis on powder samples with heating rates from 1 to 30 °C・min-1 in a dynamic air atmosphere. The mechanism of the reaction, values of overall activation energy and pre-exponential factor were determined from a series of thermogravimetric experiments by the Coats- Redfern method. The results show that the dehydroxylation of kaolinite is controlled by the rate of the third-order reaction (F3) with the mean values of overall activation energy (EA) 255 kJ・mol-1 and pre-exponential factor (A) 25.56 × 1014 s-1.

Three filtration systems using the tractor hydraulic circuit were proposed and verified during the tractors operation. Using the tractor-implement hydraulic system and filter body with accessories the universally useful filtration systems were designed. The designed filtration systems are the second stage of universal oil filtration whereas the first stage is the standard tractor filter. The decrease in the content of iron reached the values 25.53 %, 32.95 % and 41.55 % and the average decrease in oil contamination characterized by average value of decrease in content of iron, copper and silicium reached values 24.3 %, 24.7 % and 35.53 % in dependence on the filtration system and an oil contamination level. The decrease in contamination level verified the ability of designed filtration systems for agricultural tractors.

Abstract. Nowadays the biomass or more precisely biofuel is more and more being exploited as a substitute for fossil fuels for heating as well as for example for heating of drying surroundings. The contribution is focused on reviewing of heat source by the combustion of various kinds of solid biofuels. It is a boiler VIGAS 25 with regulation AK 2,000 for heating the house and boilers VESKO-B and RH 4000. For the measurement of gaseous emissions was used device TESTO 330-2LL and other facilities. Firewood, peat briquettes, briquettes from the bark and hardwood briquettes were burned. Results of experimental measurements of production of gaseous emissions are processed in the tables and graphs depending on the performance of the boiler and the combustion time. Quantity of production of gaseous emissions depends mainly on the amount and uniformity of the fuel, the relative humidity of fuel, type of fuel and keeping the fuel mix prescribed by the manufacturer of the boiler. Found concentrations of gaseous emissions showing compliance with the statutory emission limits.

Vitázek I., Klúčik J., Uhrinová D., Mikulová Z., Mojžiš M. (2016): Thermodynamics of combustion gases from biogas. Res. Agr. Eng., 62 (Special Issue): S8-S13.Biogas as a respected source of renewable energy is used in various areas for heating or in power cogeneration units. It is produced by anaerobic fermentation of biodegradable materials. The utilization of biogas is wide -from process of combustion in order to obtain thermal energy, combined heat and power production, gas combustion engines, micro turbines or fuel cells up to trigeneration. Biogas composition depends on the raw material. The aim of this paper was to develop a new methodology; according to this methodology, by means of gas mixture thermodynamics and tabular exact parameters of individual gaseous components, all the necessary thermodynamic and operating values of biogas composition were calculated. The mathematical model of biogas combustion was elaborated. For an accurate realization of calculation, a computing program was designed.

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This work contains the results of measuring the electrical properties of sunflower achenes. The interest in electrical properties of biological materials resulted in engineering research in this field. The results of measurements are used for determining the moisture content, the surface level of liquid and grainy materials, for controlling the presence of pests in grain storage, for the quantitative determination of mechanical damage, in the application of dielectric heating, and in many other areas. Electrical measurements of these materials are of fundamental importance in relation to the analysis of quantity of absorbed water and dielectric heating characteristics. It is a well-known fact that electrical properties of materials, namely dielectric constant and conductivity, are affected by the moisture content of material. This fact is important for the design of many commercial moisturetesting instruments for agricultural products. The knowledge of dielectric properties of materials is necessary for the application of dielectric heating. The aim of this work was to measure conductivity, dielectric constant and loss tangent on samples of sunflower achenes, the electrical properties of which had not been sufficiently measured. Measurements were performed under variable moisture content and the frequency of electric field ranging from 1 MHz to 16 MHz, using a Q meter with coaxial probe. It was concluded that conductivity, dielectric constant and loss tangent increased with increasing moisture content, and dielectric constant and loss tangent decreased as the frequency of electric field increased.

Mojžiš M., Vitázek I., Varga F., Lindák S. (2015): Experimental determination of lethal doses of heat in thermal weed control. Res. Agr. Eng., 61 (Special Issue): S9-S12.Thermal weed control performed by weeders working on physical principles is already commonly used on farms dealing with bioproducts. It helps to reduce strenuous human labour and to effectively control weeds and, to some extent, pests and diseases threatening the crops. It also prevents other weeds from spreading by destroying them in the early growth stage. In addition, development of weeds is inhibited when the soil is not being ploughed. Effective deployment of these machines in practice is currently addressed by experts in the field, as well as the possibility of rational use of heat energy while achieving the maximum effect on weeds. This method in particular helps to reduce costs of thermal treatment, which are the key factor limiting widespread deployment of weeders. The paper introduces long-term research based on laboratory and field experiments, which is intended to broaden the knowledge regarding this issue.

Nowadays, biomass or more precisely biofuel is more and more being exploited as a substitute for fossil fuels for heating as well as for example for heating a drying environment. This contribution focuses on assessing a heat source by combusting various types of solid biofuels. It is a boiler VIGAS 25 with AK 2000 regulation for heating a family house. Gaseous emissions were measured using a device TESTO 330-2LL. Firewood, peat briquettes, bark briquettes and hardwood briquettes were burnt. Results of experimental measurements concerning the production of gaseous emissions are processed in tables and graphs depending on boiler performance and combustion time.