The consumption of specialty coffees has been increasing significantly in recent years. Their quality is influenced by several factors and the drying method is the most important. In order to reduce drying time and maintain the quality of the coffee, several techniques have been used, among which the microwave‐assisted convective drying stands out. In this work, a hexagonal microwave dryer was developed using numerical simulation techniques; then some parameters were evaluated in drying of special coffee using air at room temperature and microwaves heating, named hybrid drying. The results showed that the simulations reaches good results, being possible its use in the prediction of the electromagnetic fields and dimensioning of hexagonal cavities. In addition, the prototype performed well in the coffee drying, influenced by the coffee mass, temperature and time, reducing the moisture content from 50.4 to 10 g/100 g wet basis in 5 hr. The hybrid drying was advantageous compared with convective or microwave drying processes.
Practical applications
Special coffees require long drying times so that there is no loss of product quality. The application of hybrid drying by including microwave heating in the drying equipment reduces the energy cost and the processing time, providing an improvement in the processing of specialty coffees. Through this work, it was possible to verify the scale‐up potential of the microwave cavities by simulation and the hybrid drying of special coffees. The use of numerical simulation techniques for the design and scale‐up of microwave cavities will help researchers and the industry to dimension cavities for use in several scientific areas, further spreading hybrid drying via microwave.
The Venturi tube measures the fluid’s flowrate by use of an obstruction in the flow path. As a tool to understand the fundamental principles of Chemical Engineering, an experimental device for flow measurement integrating a Venturi tube was developed in the course of the Chemical Engineering Projects I from the Federal University of Lavras. The system was constructed with materials of low-cost and easy access. The experimental results for the flow and pressure drop were compared with theorical values and with additional data obtained by the use of a numerical and computational method (CFD). The discharge coefficient was 0.680 ± 0.018 [-], an intermediate value of those found in the literature for orifice plate and flow nozzle meters. The numerical method was successfully able to predict the pressure drop in the system.
In simulations, when using multipartitioned computers, the way in which the mesh is partitioned directly affects the average time per iteration, and therefore, the computational cost. This study proposes an analysis of the average time per iteration of 23 different partition methods available for tridimensional mesh in software FLUENT 19.2. For the calculation of the average iteration time, 100 iterations were used. Generally, the best partitioning methods were those in which the mesh division was made perpendicularly to the axis of the equipment. It was stated the choice of an adequate partitioning method can save high costs of computational power. For the hydrocyclone studied, with a computer with 8 cores, approximately 24.56 hours of simulation were saved, representing almost 20% of the total time.
RESUMO-O tubo de Venturi é um medidor de vazão de gases e líquidos por obstrução. Apresenta como vantagens uma baixa perda de carga e uma grande precisão comparada a outros medidores, como a placa de orifício e os medidores bocal. Como ferramenta para a consolidação de conceitos fundamentais de Engenharia Química, um aparato experimental para medição de vazão utilizando um tubo Venturi foi desenvolvido ao longo das aulas da disciplina Projetos em Engenharia Química I, da Universidade Federal de Lavras. O sistema de tubulações interligadas com o tubo Venturi foi construído com materiais de fácil acesso e baixo custo. A medição da vazão foi feita utilizando um cronômetro e um recipiente com capacidade de 15 L. Já a variação da pressão foi obtida a partir da variação de altura de água em manômetros confeccionados com mangueiras de silicone. Os resultados experimentais de vazão e variação de pressão foram comparados com valores teóricos e com os obtidos pela aplicação de um método numérico computacional (CFD). O cálculo do coeficiente de descarga resultou em um valor de 0,68±0,028, valor intermediário entre os encontrados na literatura para medidores de vazão do tipo placa de orifício e bocal. O modelo numérico utilizado foi capaz de prever de forma satisfatória a perda de carga no sistema.
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