Papers by Andronikos Filios
Comput., 2021
In the present case study, a moisture diffusion model is developed to simulate the drying kinetic... more In the present case study, a moisture diffusion model is developed to simulate the drying kinetics of Lavandula x allardii leaves for non-stationary convective drying regimes. Increasing temperature profiles are applied over the drying duration and the influence of temperature advancing rates on the moisture removal and the drying rate is investigated. The model assumes a one-dimensional moisture transfer under transient conditions, which occurs from the leaf center to the surface by liquid diffusion due to the concentration gradient developed by the surface water evaporation caused by the difference of water vapor partial pressure between the drying medium and the leaf surface. A numerical solution of Fick’s 2nd law is obtained by an in-house code using the finite volume method, including shrinkage and a variable temperature-dependent effective moisture diffusion coefficient. The numerical results have been validated against experimental data for selected cases using statistical in...
Προσδιορισμός θερμοκρασιακού πεδίου γύρω από κάθετο γεωθερμικό εναλλάκτη
Evaluation of multilayer perceptron neural networks and adaptive neuro‐fuzzy inference systems for the mass transfer modeling of Echium amoenum Fisch. & C. A. Mey
Journal of the Science of Food and Agriculture, 2021
BACKGROUND Multilayer perceptron (MLP) feed-forward artificial neural networks (ANN) and first or... more BACKGROUND Multilayer perceptron (MLP) feed-forward artificial neural networks (ANN) and first order Takagi-Sugeno type adaptive neuro-fuzzy inference systems (ANFIS) are utilized to model the fluidized bed drying process of Echium amoenum Fisch. & C. A. Mey. The moisture ratio evolution is calculated based on the drying temperature, airflow velocity and process time. Different ANN topologies are examined by evaluating the neuron number (3 to 20), the activation functions and the addition of a second hidden layer. Respectively, different number (2 to 5) and shapes of membership functions are examined for the ANFIS, using the grid partitioning method. The models with the best performance in terms of prediction accuracy as evaluated by the statistical indices, are compared with the best fit thin-layer model and the available data from the experimental cases of 40, 50 and 60°C temperatures at 0.5, 0.75 and 1 ms-1 airflow velocity. RESULTS The best performed ANFIS model, comprised by 5-2-2 of π-shaped and triangular membership functions for time, temperature and airflow velocity inputs respectively, was able to describe the moisture ratio evolution of Echium amoenum more precisely than the best ANN topology with R2 =0.9992, RMSE=0.0078 and SSE=1.06·10-2 . Best thin-layer model involving six adjustable parameters, managed to describe experimental data with R2 =0.9996, RMSE=0.0057 and SSE=7.3·10-4 . CONCLUSION The results of the comparative study indicate that empirical regression models with increased number of adjustable parameters, constitute a simpler and more accurate modeling approach for estimating the moisture ratio of Echium amoenum Fisch. & C. A. Mey under fluidized bed drying. This article is protected by copyright. All rights reserved.
CFD Modeling of Convective Drying of Cylindrical Fruit Slices
Computational Fluid Dynamics in Food Processing, 2018
Techno-economic evaluation of large energy storage systems used in wind energy applications
Interest in employing renewable energy sources has significantly grown during the last few years,... more Interest in employing renewable energy sources has significantly grown during the last few years, mainly as a reaction to the concern about environmental impacts from fossil and nuclear fuels, along with rate-instability in the international oil market. However, due to the periodic or even stochastic behaviour of the renewable energy sources (e.g. wind speed), the corresponding contemporary electricity generation systems cannot provide firm capacity to an electrical power system. Additionally, these fluctuations can -in some cases- cause problems to a distribution network related to stability, harmonics or flicker. Such issues present serious obstacles to the substantial penetration of wind energy, mainly into weak (medium or even large sized) power grids. On the other side, an energy storage system, when sized appropriately, can match a highly variable power production to a generally variable and hardly predictable system demand, remarkably limiting the energy production cost (e.g....
Airflow patterns in a laboratory batch-type tray air dryer
The batch-type dryer is one of the most popular equipment for fruit drying. However, the optimiza... more 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 an...
Use of virtual instrumentation and computational fluid dynamics in an undergraduate research project
The current paper demonstrates how to introduce a combination of CFD (Computational Fluid Dynamic... more 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, the...
Influence of a circular exit wall boundary on the axisymmetric jet flow
In the frame of “engineering education” activities, the Laboratory of Fluid Mechanics and Turboma... more In the frame of “engineering education” activities, the Laboratory of Fluid Mechanics and Turbomachinery (FMTULAB/ASPETE) is continuously targeting to create links between education and basic research activities in fluid mechanics/dynamics. This task is expected to attract and motivate young engineers and scientists to join the fluid dynamics sector, which significantly contributes to the improvement of efficiency of applications relating clean energy sources and air pollution control. For this purpose computational and experimental studies are combined mainly in fundamental topics, while innovative results are produced to improve the knowledge of additional effects rising from the adoption of alternative flow configurations. Axisymmetric jet flow constitutes a subject of research from the origins of fluid dynamics; however it remains a subject of interest due to the new findings regarding the influence of flow and geometry conditions utilized in configurations that diverge from the...
The Use of CFD for Flow Analysis and Performance Prediction of Centrifugal Pumps
This paper presents some user experience in using the commercial CFD code Fluent for pump flow fi... more This paper presents some user experience in using the commercial CFD code Fluent for pump flow field calculations. It demonstrates the use of the code with respect to simulating the flow within an industrial centrifugal pump and predicting the corresponding head-capacity curve. Throughout the paper, the CFD model of the selected pump is discussed. The pump with backward curved blades is modeled and meshed with unstructured grid. Quasi-steady calculations utilizing the k-ε turbulence model and the multi reference frame technique are performed for the design point as well as for a range of volume rates with a deviation of 50% from the design value but with similar flow patterns. The data obtained allow the analysis of the main phenomena existent in the pump, such as: pressure changes in the volute for different flow rates; and the incidence at the leading edge of the blade with different flow conditions.
The effect of the blade geometry geometry in the velocity profile in a radial pump impeller
In the present paper, the evolution of the velocity field in the blade passages of two radial pum... more In the present paper, the evolution of the velocity field in the blade passages of two radial pump impellers with different curvature and outlet blade angle (β2= 20 and 50 degrees) is reported. The study is based on computational modelling. The numerical solution of the discretized three-dimensional, incompressible Navier-Stokes equations over a structured grid is accomplished with a commercial CFD finite-volume code. For each impeller, pressure and relative velocity distributions are presented and analyzed. The flow patterns in the blade passages are monitored, and the mechanisms that dominate the flow field in the different regions of the impeller geometry are discussed.
Thin-layer drying models critical evaluation based on laboratory scale convective dryer experiments
A laboratory scale convective dryer equipped with advanced instrumentation was developed in order... more A laboratory scale convective dryer equipped with advanced instrumentation was developed in order to study the drying kinetics of quince slices. Experiments were carried out for air temperatures 40 o C, 50 o C and 60 o C and 2 ms -1 bulk velocity. The whole process occurred within the falling rate period. Results showed that a temperature increase from 40 to 60 o C produced a decrease of the total time of drying of about 54%. Eight thin-layer drying models were incorporated to fit the time evolution of the moisture data using non-linear regression analysis. Among the various models, the Weibull formula was best fitted to measurements. For the range of the drying temperatures examined, Fick's law of diffusion was used to determine the effective moisture diffusivity, which varied between 3.23 × 10 -10 m 2 s -1 and 7.82 × 10 -10 m 2 s -1 . Assuming an Arrhenius type model for the drying process, a value of 38.291 kJmol -1 was estimated for the activation energy.
Design and implementation of a three axis digitally controlled traverse system for flow surveys in a drying chamber
International Journal of Engineering & Technology, 2014
Case studies on the effect of the air drying conditions on the convective drying of quinces
Case Studies in Thermal Engineering, 2014
Determination of the thermal and cooling needs of the broader region of Athens
Renewable Energy, 2008
An original method to determine the thermal and cooling loads of the broader region of Athens is ... more An original method to determine the thermal and cooling loads of the broader region of Athens is presented in the present work. The buildings in the area are classified in various categories related to their energy behaviour, year of construction, and geometrical characteristics. ...
Wind Energy, 2006
Autonomous wind power systems are among the most interesting and environmentally friendly technol... more Autonomous wind power systems are among the most interesting and environmentally friendly technological solutions for the electrification of remote consumers. In many cases, however, the battery contribution to the initial or the total operational cost is found to be dominant, discouraging further penetration of the available wind resource.This is basically the case for areas possessing a medium-low wind potential. On the other hand, several isolated consumers are located in regions having the regular benefit of an abundant and reliable solar energy supply. In this context the present study investigates the possibility of reducing the battery size of a stand-alone wind power installation by incorporating a small photovoltaic generator. For this purpose an integrated energy production installation based exclusively on renewable energy resources is hereby proposed. Subsequently a new numerical algorithm is developed that is able to estimate the appropriate dimensions of a similar system. According to the results obtained by long-term experimental measurements, the introduction of the photovoltaic panels considerably improves the operational and financial behaviour of the complete installation owing to the imposed significant battery capacity diminution.
Applied Thermal Engineering, 2007
A new computational algorithm for the calculation of maximum wind energy penetration in autonomous electrical generation systems
Applied Energy, 2009
ABSTRACT
Modeling and optimization of non-isothermal convective drying process of Lavandula × allardii
Information Processing in Agriculture
Determination of the thermal and cooling needs of the broader region of Athens
Renewable Energy, 2008
An original method to determine the thermal and cooling loads of the broader region of Athens is ... more An original method to determine the thermal and cooling loads of the broader region of Athens is presented in the present work. The buildings in the area are classified in various categories related to their energy behaviour, year of construction, and geometrical characteristics. ...
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Papers by Andronikos Filios