Інноваційні енерготехнології (Innovative energy technologies)

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https://card-file.ontu.edu.ua/handle/123456789/3420

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Перегляд Інноваційні енерготехнології (Innovative energy technologies) за Ключові слова "evaporation"

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  • Документ
    Experimental modeling of process of water solutions evaporation in the vacuum and microwave field conditions
    (2019) Burdo, O.; Gavrilov, A.; Mordynskiy, V.; Sirotyuk, I.; Sereda, A.
    A comparative analysis of traditional methods for the food solutions concentration is given. The main problem of classical evaporators is identified, which is associated with the impossibility of obtaining high concentrations of the finished product due to a sharp increase in its viscosity and temperature through the formation of a boundary layer. A scientific and technical hypothesis has been formulated, representing a possible solution to this problem by providing a volume supply of energy directly to the moisture of the product. Thermophysical scheme of evaporation processes by traditional and innovative methods is considered. Their fundamental differences are highlighted and the relevance of the development of an innovative evaporation method is substantiated. The scheme of the innovative evaporator is presented, which allows to obtain the finished product in the solid phase with a final concentration of up to 90 °brix. By the example of apple juice, experiments were conducted to study the effect of pressure of the electromagnetic field on the steam output of the apparatus. Dependencies that indicate a constant evaporation rate throughout the entire process, up to a concentration of 80-85 °brix, were built. The product temperature did not exceed 35-40 °C, which may indicate its high nutritional value. The above data confirm the formulated hypothesis about the possibility of transition in the process of evaporation from the boundary conditions of the 3rd type to the boundary conditions of the 2nd type by the using microwave energy. On the basis of the obtained results, a model in the criterial form was obtained, which makes it possible to accurately calculate the performance of a microwave vacuum evaporator in certain ranges of the number of energetic action and the obtained dimensionless complex.
  • Документ
    Experimental studies of boiling heat transfer of food solutions
    (2017) Zykov, A. V.; Reznichenko, D. N.; Bezbah, I. V.
    Vacuum evaporation is widely used in the food technologies. The equipment for this process is well known and methods of calculation and design of vacuum evaporators are described in literature as well. However, in some cases the accuracy of existing methods is not enough. The problem of designing the new, more efficient apparatuses that work in regimes, which are not usual, needs to clarify some dependencies. It concerns the problem of boiling heat transfer coefficient determination for such solutes as food products because of the high or sometimes extremely high viscosity of many food staffs is. To take into account properties of products many authors use the Prandtl number. However, determination of these properties exact values is not always possible especially it concerns the viscosity of Non-Newtonian fluids, which are the most of food staff. For experimental verification of heat transfer coefficient values, an apple juice was chosen. At first, the theoretical value was obtained with Tolubinskiy dependency using. The vapor bulbs grows rate and surface tension coefficient were solved as for water. The dependencies between the heat transfer coefficient and heat flux for apple juice with concentration from 15 to 50 Brix were obtained as result. There are several different equations to calculate the properties of apple juice depending on temperature and concentration and several resulting dependencies that differ from each other were obtained. The comparison with the experimental data that was obtained by authors made possible to choose the right equations for apple juice viscosity determination when the heat transfer calculation error did not exceed 20% that is standard error for used dependency and for many others. To reduce this error on the base of obtained experimental data the correction coefficient was calculated. Therefore, the equation to calculate the heat transfer coefficient for boiling apple juice where maximum error did not exceed 5% was obtained. The experimental research was conducted under atmospheric pressure. To obtain the value of heat transfer coefficient in vacuum condition the Tolubinskiy dependency can be used or addition experiments should be conducted. It depends of required accuracy level.