Δημοσιεύσεις σε συνέδρια

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Open Access
Air flow characteristics in an industrial wood pallet drying kiln
(2010-07-21T09:52:17Z) Tzempelikos, Dimitrios; Filios, Andronikos; Margaris, Dionisios; Τζεμπελίκος, Δημήτριος; Φίλιος, Ανδρόνικος; Μάργαρης, Διονύσιος
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχαν. (Δημοσ. Π.Π. σε συνέδρια)
The improvement and optimization of air-distribution systems in drying kilns contributes to the preservation of the quality, safety and shelf life of perishable products. The present study reports on the numerical solution of airflow within a two dimensional drying kiln enclosure loaded with wooden pallets. The performance of air flow field is examined with and without supply of wooden pallets. Different arrangements of the supplied wooden pallets are investigated as well as the use of a screen in order to improve the airflow filed. The steady state RANS equations that formulate the flow problem are solved along with a turbulence model that is the standard k-εor the rng k-ε. The effect of the turbulence modeling is distinguished through direct comparisons of the derived airflow patterns. The results obtained show the presence of stagnant zones inside the pallets columns and above of them and the presence of recirculation regions in different zones of the drying kiln with the two turbulence models.
Open Access
Air flow characteristics in an industrial wood pallet drying kiln
(2013-07-30) Tzempelikos, Dimitrios; Filios, Andronikos; Margaris, Dionissios; Τζεμπελίκος, Δημήτριος; Φιλιός, Ανδρόνικος; Μάργαρης, Διονύσιος
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχαν. (Δημοσ. Π.Π. σε συνέδρια)
The improvement and optimization of air-distribution systems in drying kilns contributes to the preservation of the quality, safety and shelf life of perishable products. The present study reports on the numerical solution of airflow within a two dimensional drying kiln enclosure loaded with wooden pallets. The performance of air flow field is examined with and without supply of wooden pallets. Different arrangements of the supplied wooden pallets are investigated as well as the use of a screen in order to improve the airflow field. The steady state RANS equations that formulate the flow problem are solved along with a turbulence model that is the standard k-ε or the rng k-ε. The effect of the turbulence modeling is distinguished through direct comparisons of the derived airflow patterns. The results obtained show the presence of stagnant zones inside the pallets columns and above of them and the presence of recirculation regions in different zones of the drying kiln with the two turbulence models.
Open Access
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.
Open Access
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.
Open Access
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.
Open Access
Industrial drying of wooden pallets - CFD analysis of air flow
(2013-07-30) Ghiaus, Adrian; Filios, Andronikos; Margaris, Dionissios; Tzempelikos, Dimitrios; Φιλιός, Ανδρόνικος; Μάργαρης, Διονύσιος; Τζεμπελίκος, Δημήτριος
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχαν. (Δημοσ. Π.Π. σε συνέδρια)
This paper presents the results of the airflow 2D numerical simulation inside an industrial unit designed for drying of wooden pallets. The airflow field profile was examined in different operation conditions by plotting velocity vector distribution, path lines and pressure contours for both loaded with the wooden pallets and unloaded drying room. The analysis of the obtained results shows the presence of stagnation zones between and above the pallet columns and recirculation regions in different zones of the drying room. Further work will focus on validation of the predicted CFD results by means of local measurements that will be taken on a full scale dryer.
Open Access
Use of virtual instrumentation and computational fluid dynamics in an undergraduate research project
(2013-07-30) Xanthopoulos, Efstathios; Tzempelikos, Dimitrios; Filios, Andronikos; Margaris, Dionissios; Ξανθόπουλος, Ευστάθιος; Τζεμπελίκος, Δημήτριος; Φιλιός, Ανδρόνικος; Μάργαρης, Διονύσιος
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχαν. (Δημοσ. Π.Π. σε συνέδρια)
The current paper demonstrates how to introduce a combination of CFD (Computational Fluid Dynamics) and virtual instrumentation to undergraduates in a research setting in the framework of a fluid mechanics course. A laboratory research project has been developed to enable students to compare and analyze pressure and velocity measurements obtained experimentally in a “Venturi tube” setup to those generated using a commercial CFD software package. An old but proven laboratory setup has been retrofitted with computer data acquisition system and custom written software has been developed to suit the experimental module. Pressure measurements received along the tube for five Reynolds numbers are directly compared with corresponding predictions using CFD code and all are contrasted with the 1-d inviscid flow solution. It is shown that, although undergraduate students may have limited knowledge in the underlying theories and equations used by CFD codes to solve flow problems, they are capable of using the code in solving classical and more complex problems with supervision by a faculty member. The developed project provides a cost-effective means for laboratory improvement in addition to educational benefits derived by the students since they have the opportunity to explore first-hand the various capabilities of CFD as an analysis tool and additionally to familiarize using modern measurements techniques such as pressure and temperature transmitters, experimental data acquisition and processing.

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