Sirvi Autor "Herák, D." järgi
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Kirje Extraction of oil from rapeseed using duo screw press(2018) Mizera, Č.; Herák, D.; Hrabě, P.; Kabutey, A.This study was focused on the analysis of optimize the pressing process of rapeseeds ( B rassica napus L.) using screw press. For pressing of oil a screw press Farmer 20 – duo (Farmer 20, Farmet a.s., Ceska Skalice, Czech republic) was used. The screw rotation speed 10, 20, 30, 40, 55 and 65 rpm was used. Oil recovery efficiency and specific mechanical energy were decreased when the seed material troughput was increased. It has been found that the optimal operation point for screw press Farmer 20 – duo was at 20 kg h - 1 rapeseed throughput. The specific mechanical energy at the optimal operation point was 0.61 kWh kg oil - 1 Maximum oil recovery efficiency 82.6% was found at the lowest screw speed.Kirje Factors influencing use of fuelwood and its environmental impacts in Tapanuli Utara regency, North Sumatra(2018) Roubík, H.; Mazancová, J.; Brunerová, A.; Herák, D.Deforestation and forest degradation, after burning of fossil fuels, is considered as the second leading cause of anthropogenic greenhouse emissions (accounting for over 17% of global carbon dioxide emissions) and has become an important issue concerning climate change mitigation. The provision of wood energy is generally thought to be a major contributor to forest loss. In Indonesia, more than half of the rainforest there, the third - largest swath in the world, has been felled in just a few years. Further more, permission has been granted to convert the majority of what remains into palm or acacia plantations. The logging and burning of forests to clear land for cultivation has made Indonesia one of the largest emitters of greenhouse gases. Therefore, the o bjective of this study was to assess the current level and influencing factors of the use of fuelwood among the rural population as well as the consequent environmental impacts in the target area in North Sumatra. The questionnaire survey using randomly se lected households (n = 196) was administered in Tapanuli Utara regency from July to August 2014; followed by several field visits from August to September 2016. Obtained data were analysed with descriptive statistics and cross tabulation. The results indic ate that fuelwood is a significant source of energy in the target area. For 31% of respondents it is the major energy source and for 64% it is a supplementary source. The high rate of use of wood as fuel corresponds to the poor financial situation of respo ndents and the easy accessibility of wood, but only from the surrounding area (own garden or adjacent land). Wood resources are often very distant (on average over 1,000 metres) as a consequence of high deforestation. This study reveals that there is a non - sustainable trend of forest conversion resulting in high land degradation in Tapanuli Utara regency.Kirje Linear pressing of coconut copra meal (Cocos nucifera L.) under different temperatures(2019) Mizera, Č.; Herák, D.; Hrabě, P.; Saller, T.Pressing of vegetable oils plays an important role in the food processing. This study described the compression behaviour of copra (Cocos nucifera L.) using the universal compression testing machine and vessel diameter of 60 mm with a plunger. The influence of heat treatment on oil recovery efficiency and specific mechanical energy were determined. Compression tests at the rate of 1 mm s −1 under five different temperatures 20, 40, 60, 80 and 100 °C were performed. The measuring range of force was between 0 kN and 50 kN. It has been found that the amount of obtained oil increased and specific mechanical energy decreased with increased temperature. Measured data were analysed by computer software Mathcad 14 (MathCAD 14, PTC Software, Needham, MA, USA). Mathematical model describing the mechanical behaviour of bulk copra under compression loading was represented.Kirje Mechanical behaviour of Sugar palm (Arenga pinnata) fibres(2018) Hrabě, P.; Mizera, Č.; Herák, D.; Kabutey, A.The tensile strength of Sugar palm ( Arenga pinnata ) fibres was examined. Fibre samples were prepared and tested up to the point of rupture with a deformation rate of 0.05 min - 1 . The tensile device (Labortech, MPTest 5.050, Czech Republic) were used to determine the tensile force. The aim of the paper was to describe a mechanical behaviour of Sugar palm ( Arenga pinnata ) fibres. Measured values can be used as a basis for further research on the application of Sugar palm fibres.Kirje Modelling of hot-air and vacuum drying of persimmon fruit (Diospyros kaki) using computational intelligence methods(2020) Khaled, A.Y.; Kabutey, A.; Mizera, C.; Hrabe, P.; Herák, D.The study evaluated the feasibility of applying computational intelligence methods as a non-destructive technique in describing the drying behaviour of persimmon fruit using vacuum drying (VD) and hot-air-drying (HAD) methods and to compare the results with thin layer mathematical models. Drying temperatures were 50, 60 and 70 °C. Kinetic models were developed using semi-theoretical thin layer models and computational intelligence methods: multi-layer feed-forward artificial neural network (ANN) and support vector regression (SVR). The statistical indicators of coefficient of determination (R2 ) and root mean square error (RMSE) were used to assess the suitability of the models. The thin-layer mathematical models namely page and logarithmic accurately described the drying kinetics of persimmon slices with the highest R2 of 0.9999 and lowest RMSE of 0.0031. ANN showed R2 and RMSE values of 1.0000 and 0.0003, while SVR showed R2 of 0.9999 and RMSE of 0.0004. The validation results indicated good agreement between the predicted values obtained from the computational intelligence methods and the experimental moisture ratio data. Based on the study results, computational intelligence methods can reliably be used to describe the drying process of persimmon fruit.