Tag Archives: model

1072–1083 M. Linda, G. Künzel and M. Hromasová
A dynamic model of electric resistor’s warming and its verification by micro-thermocouples
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A dynamic model of electric resistor’s warming and its verification by micro-thermocouples

M. Linda, G. Künzel and M. Hromasová*

Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamýcká 129, CZ165 21 Prague, Czech Republic
*Correspondence: hromasova@tf.czu.cz

Abstract:

The object of research is a resistor, a real electronic component, loaded by constant or impulse power. As a first approximation, resistor follows 1st order dynamic system, i.e. heating of the hottest spot on its surface is exponential to the power increase. The validity of this model is confirmed by measurements in a constant power loading regime. In an impulse power loading, it is only valid when the pulse duration approaches time constant of the resistor. The aim of this article is to show more credible model warming of the resistor, which is valid even for the case of pulse duration (ms) much shorter than the time constant of the resistor. The model can reveal an overload which does not lead to destruction of the resistor. Dynamic model of the resistor is based on its construction. Typically, an insulating ceramic rod is coated with a resistive layer connected with outlet wires on both sides, all being coated with insulating lacquer layer. The resistive layer is a source of heat flow. Formulation of the model comes from general power balance in a form of three differential equations and it is solved using Scilab. The input variable is the impulse power and the outputs are temperature changes in the ceramic rod, the resistive layer and the lacquer layer, compared to the ambient temperature. The simulation allows to determine solutions for various parameters including very short power pulses, which are confirmed experimentally.

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1299–1305 D. Herak
Image analysis of the shapes and dimensions of Teff seeds (Eragrostis tef)
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Image analysis of the shapes and dimensions of Teff seeds (Eragrostis tef)

D. Herak

Czech University of Life Sciences Prague, Faculty of Engineering, Department of Mechanical Engineering, Kamycka 129, CZ 16521 Prague, Czech Republic e-mail: herak@tf.czu.cz

Abstract:

 With aid of the image analysis using trio ocular microscope the dimensions, circumferences and areas in two perpendicular planes of Teff seeds were measured and based on this information the new ellipsoid model of the seed’s shape was derived and compared with measured values. From statistical analysis implies that this model on probability 0.95 is significantly identical with measured values of the Teff seeds. Determined model can help more accurately set up and developed accurate mathematical model for describing mechanical behaviour of individual seeds as well as bulk seeds.

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5-13 A. Aboltins and J. Palabinskis
Fruit Drying Process Investigation in Infrared Film Dryer
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Fruit Drying Process Investigation in Infrared Film Dryer

A. Aboltins* and J. Palabinskis

Latvia University of Agriculture, Institute of Agricultural Machinery, Cakstes blvd. 5, Jelgava, LV – 3001, Latvia:
*Correspondence: aivars.aboltins@inbox.lv

Abstract:

The work analyzes three different product (apple slices, banana slices and grape halves) drying process in the infrared film dryer. Such drying takes place at low temperatures (to 40 °C), allowing to keep the maximum value of fresh products. The drying process is analyzed in detail in the first 8 hours. The quantity of water runoff, drying product temperature changes and flowing air humidity changes during drying were analyzed. It demonstrates the impact of the product placement on the drying progress. Using the experimental data, average diffusion coefficients are obtained for each product group. The results showed that diffusion coefficients were changing during the drying process. Using mathematical modelling and experimental data, the concentration-dependent diffusion coefficient for apple slices was obtained. The study finds that apple and banana drying using the infrared film is comparatively successful, but the drying process of the half of grape berry is slower. This can be explained by the impact of grape peel on the water diffusion.

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215-222 A. Aboltins, and P. Kic
Forced convection in drying of poultry manure
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Forced convection in drying of poultry manure

A. Aboltins¹,* and P. Kic²

¹Latvia University of Agriculture, Institute of Agricultural Machinery, Cakstes blvd. 5, Jelgava, LV–3001, Latvia; *Correspondence: aivars.aboltins@inbox.lv
²Czech University of Life Sciences Prague, Faculty of Engineering, Kamycka 129, 165 21, Prague 6, Czech Republic

Abstract:

Pollution of environment by animal waste can be problem of intensive animal production in many countries with high density of animal farms. The aim of this paper is to inform about the experimental and theoretical investigations of moisture content reduction from poultry manure by forced convection. The experimental data created the background for calculation and modelling, which resulted in definition of the theoretical drying coefficient, useful for description and modelling of the drying process. The theoretical model has been verified and compared with experimental results obtained from the measurement. The laboratory equipment was used for test the forced convective drying of poultry manure due to vertical air streams going from bottom through supporting trays with holes and therefore through the manure up. Changed opened area of trays with different density has been used for definition of main parameters, which can serve especially in designing and construction of the new equipment for housing of poultry or improvement of the use of drying tunnel or in similar applications. The experimental data show that the air flow significantly increase the amount of moisture carried away from the material. Holes´ size does not significantly affect water runoff by convection without additional air flow.

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