Δημοσιεύσεις σε συνέδρια

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Browsing Δημοσιεύσεις σε συνέδρια by Author "Bardakas, Achilleas"

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    Airflow patterns in a laboratory batch-type, tray air dryer
    (2013-07-30) Tzempelikos, Dimitrios; Vouros, Alexandros; Bardakas, Achilleas; Filios, Andronikos; Margaris, Dionissios; Τζεμπελίκος, Δημήτριος; Βούρος, Αλέξανδρος; Μπαρδάκας, Αχιλλέας; Φιλιός, Ανδρόνικος; Μάργαρης, Διονύσιος
    Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχαν. (Δημοσ. Π.Π. σε συνέδρια)
    The batch-type dryer is one of the most popular equipment for fruit drying. However, the optimization of the air distribution inside the drying chamber remains a very important issue, due to its strong impact on efficient drying and uniformity of moisture content of products. A new scale laboratory batch-type, tray air dryer has been designed, constructed and evaluated for drying several horticultural and agricultural products. The flow field inside the dryer is studied through computational fluid dynamics (CFD). A three-dimensional model for laboratory dryer has been created and the steady state incompressible, Reynolds-Averaged Navier-Stokes (RANS) equations that formulate the flow problem are solved, incorporating standard and RNG k-ε turbulence models. The simulations are conducted for testing chamber average velocity of 2,9 m/s at ambient temperature. The CFD models are evaluated by comparing airflow patterns and velocity distributions to measured data. Numerical simulations and measurements convince that the new scale laboratory batch-type dryer is able to produce a sufficiently uniform air distribution throughout the testing chamber of the dryer.
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    An experimental study on convective drying of quince
    (2013-08-06) Tzempelikos, Dimitrios; Bardakas, Achilleas; Vouros, Alexandros; Tsepenekas, Dionysios; Filios, Andronikos; Margaris, Dionissios; Τζεμπελίκος, Δημήτριος; Μπαρδάκας, Αχιλλέας; Βούρος, Αλέξανδρος; Τσεπενέκας, Διονύσιος; Φιλιός, Ανδρόνικος; Μάργαρης, Διονύσιος
    Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχαν. (Δημοσ. Π.Π. σε συνέδρια)
    A laboratory convective drying unit (LCDU) has been designed, constructed and equipped with an integrated measurement and control instrumentation, in order to evaluate the essential drying characteristics of various horticultural and agricultural products. The current paper presents experimental results from tests with quince slices. Drying kinetics was investigated as a function of drying conditions. Experiments were conducted at air flow temperatures of 40, 50 and 60oC and average velocities of 1, 2 and 3 m/s. Temperature changes of the drying quince samples, the relative humidity and the temperature of the drying air were measured during the drying processes and finally the moisture ratio (MR) was calculated. The experimental MR data were fitted with three mathematical models available in the literature and a good agreement was observed. In the ranges measured, Fick’s 2nd law of diffusion was used to fit the experimental data for the determination of the effective moisture diffusivity. The activation energy was determined, assuming an Arrhenius type temperature relationship with moisture diffusivity.
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    Design, construction and performance evaluation of a new laboratory convective dryer
    (2013-07-30) Tzempelikos, Dimitrios; Bardakas, Achilleas; Vouros, Alexandros; Tsepenekas, Dionysios; Christoloukas, Dimitrios; Filios, Andronikos; Margaris, Dionissios; Τζεμπελίκος, Δημήτριος; Μπαρδάκας, Αχιλλέας; Βούρος, Αλέξανδρος; Τσεπενέκας, Διονύσιος; Χριστολουκάς, Διονύσιος; Φιλιός, Ανδρόνικος; Μάργαρης, Διονύσιος
    Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχαν. (Δημοσ. Π.Π. σε συνέδρια)
    Aiming to overcome the lack of experimental data in the open literature and the necessity to validate numerical models which are an essential tool for optimization and increase the efficiency of the drying process, a laboratory convective (LC) dryer has been designed, constructed and equipped with an integrated measurement and control instrumentation. The main sections of the LC dryer, which can be arranged for operation in a closed or open circuit mode through manually controlled dumpers, are the vertical flow drying chamber, the heat exchanger, the boiler and the fan - motor with smooth speed control unit. The experimental facility is under operation for testing and monitoring the hydration of horticultural and agricultural products. The current paper outlines the methodology applied for the design and optimization of the LC dryer which it has been achieved through the analysis of the flow field by means of computational fluid dynamics (CFD). The prediction of the three – dimensional flow problem is accomplished through the solution of the steady-state incompressible, Reynolds-Averaged Navier-Stokes (RANS) equations with the incorporation of standard turbulence model. The measurement and control instrumentation with the inclusion of the innovative, pc-controlled, 3d traverse system that serves detailed surveys of temperature and velocity inside the drying chamber, are discussed. The performance test and evaluation of the LC dryer is conducted using quince as a test material at an average temperature of 60oC and air of 2 m/sec into the drying chamber.