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Bartzanas T.,Institute of Technology and Management of Agricultural Ecosystems | Bochtis D.D.,University of Aarhus | Green O.,University of Aarhus | Sorensen C.G.,University of Aarhus | Fidaros D.,Institute of Technology and Management of Agricultural Ecosystems
Computers and Electronics in Agriculture | Year: 2013

The increasing use of silage has resulted in continuous efforts to minimize the quality losses. As a consequence, there is need to develop systems to predict and evaluate quality parameters. The objective of the present study was the development of a computational fluid dynamics (CFDs) model for the prediction of air temperature and oxygen concentration temporal and spatial variations in silage storages. Two experimental semi-cylinder silo stacks were used for the validation of the model. For monitoring temperature and oxygen concentration, a network consisting of 18 wireless sensors was placed in each stack. In order to validate the CFD model for both cases of sufficient and insufficient covering one of the stacks was penetrated to emulate the influx of outside air. A good agreement was found between measured and predicted obtained results. Measured and predicted values for air temperature varied between 3% and 11% and for oxygen concentration between 5% and 14% with correlation coefficients between 0.76 and 0.81, and between 0.91 and 0.97, respectively. The results show the potential for the development and implementation of decision support systems for the prediction of quality parameters in storaged biomasses. With such systems, an early detection of process disturbances can be obtained and making possible preventive measures. © 2012 Elsevier B.V.

Kitta E.,Institute of Technology and Management of Agricultural Ecosystems | Katsoulas N.,University of Thessaly | Savvas D.,Agricultural University of Athens
Applied Engineering in Agriculture | Year: 2012

The aim of this study was to investigate the effects of greenhouse shading on greenhouse microclimate and energy balance, and on crop production. Experiments were carried out in the experimental farm of the University of Thessaly at Velestino, in three similar, plastic-covered greenhouses using hydroponically-grown cucumbers as a test crop. One of the greenhouses was used as a control (without shading); the other two were shaded using two different shade nets (shading intensity of approximately 35% and 50%, respectively). Climatic parameters were measured during two growing seasons from April to June and from September to November 2008 and seven selected days of the above periods are presented. The results showed that shading could not keep greenhouse air temperature and vapor pressure deficit below 30°C and 1.5 kPa, respectively, values that are considered acceptable for cucumber crop growth (Growers Books, 1980; Bakker et al., 1987; Olympios and Hanan, 1992). From the crop production data it was found that shading intensity should not exceed 35%. The analysis of greenhouse microclimate and energy balance showed that shading is necessary from the middle of spring, while even shading of approximately 50% was not sufficient to cool the greenhouse during noon time of summer days in Central Greece and that an additional cooling system was required. © 2012 American Society of Agricultural and Biological Engineers.

Papanastasiou D.K.,Institute of Technology and Management of Agricultural Ecosystems | Melas D.,Aristotle University of Thessaloniki | Bartzanas T.,Institute of Technology and Management of Agricultural Ecosystems | Kittas C.,Institute of Technology and Management of Agricultural Ecosystems | Kittas C.,University of Thessaly
International Journal of Biometeorology | Year: 2010

During the summer of 2007 several Greek regions suffered periods of extreme heat, with midday temperatures of over 40°C on several consecutive days. High temperatures were also recorded on the east coast of central Greece, where a complex sea breeze circulation system frequently develops. The more intense events occurred at the end of June and July. The highest temperatures were observed on 26 June and 25 July, while the sea breeze developed only on 25 July. Meteorological data collected at two sites-a coastal urban location and an inland suburban site that is not reached by the sea breeze flow-as well as pollution data collected at the urban site, were analysed in order to investigate the relationship between sea breeze development and the prevailing environmental conditions during these two heat wave events. The analysis revealed that sea breeze development affects temperature and pollution levels at the shoreline significantly, causing a decrease of ~4°C from the maximum temperature value and an increase of ~30% in peak PM10 levels. Additionally, several stress indices were calculated in order to assess heat comfort conditions at the two sites. It was found that nocturnal comfort levels are determined mainly by the urban heat island effect, the intensity of which reaches up to 8°C, while the applied indices do not demonstrate any significant daytime thermal stress relief due to sea breeze development. © ISB 2009.

Papanastasiou D.K.,Institute of Technology and Management of Agricultural Ecosystems | Melas D.,Aristotle University of Thessaloniki | Lissaridis I.,Aristotle University of Thessaloniki
Atmospheric Research | Year: 2010

Weather Research and Forecast (WRF) model is applied to study the wind field over the east coast of central Greece under typical summer conditions. This study aims at identifying the major features of the sea breeze circulation that is very frequently developing in the area during the warm period of the year and at verifying the model's ability to simulate the complex flow that is strongly influenced by the complicated coastline and very steep terrain. The simulation is carried out for a five-day period, characterized by sea breeze development. It is found that a complex meteorological phenomenon is evolving in the area, as two circulation systems are successively developing, the first over Pagasitikos Gulf, which is overridden by the system that develops later over the Aegean Sea. The major characteristics of the wind patterns and especially the sea breeze systems are identified and discussed. Additionally, the impact of topography and slope on sea breeze circulation is also commented. Model predictions agree fairly well with the observations taken at a near-surface meteorological station. © 2010 Elsevier B.V.

Papanastasiou D.K.,Institute of Technology and Management of Agricultural Ecosystems | Melas D.,Aristotle University of Thessaloniki
Water, Air, and Soil Pollution | Year: 2010

Ambient aerosol concentrations have been implicated in human health effects, in visibility reduction in urban and regional areas, in acid deposition and in perturbing the Earth's radiation balance. The main concern of the air quality managers is to achieve compliance to the established air quality standards (AQS). As AQS are exceeded in numerous sites worldwide, it is essential to reduce the emissions. Having decided which statistical distribution fits well to the PM10 parent distribution, it is feasible to estimate the reduction in emissions that is required in order to meet AQS. In this study, it is verified that the PM10 concentration distribution can be adequately simulated by lognormal distribution, a conclusion drawn by the calculation of several statistical indexes. The study area is the city of Volos in central Greece, which is experiencing an unpleasant situation concerning the levels of PM10 pollution. The probability density function of lognormal distribution is capable to predict the number of days when the European Union (EU) AQS for PM10 concentration are exceeded in Volos area. Furthermore, the minimum reduction in current emission sources of PM10 required in order to meet the air quality regulations that are established by the EU is calculated for the study area and is found to be ~33%. The results could be utilized as reference for air pollution control strategy. © 2009 Springer Science+Business Media B.V.

Fidaros D.K.,Institute of Technology and Management of Agricultural ecosystems | Baxevanou C.A.,Institute of Technology and Management of Agricultural ecosystems | Bartzanas T.,Institute of Technology and Management of Agricultural ecosystems | Kittas C.,Institute of Technology and Management of Agricultural ecosystems | Kittas C.,University of Thessaly
Renewable Energy | Year: 2010

In the present study the transport phenomena occurring inside a ventilated arc type tunnel greenhouse are simulated during a solar day taking into account the optical properties of plants only in the photosynthetic active radiation (PAR) band. The simulation concerns the day of autumn equinox for an area of central Greece. Two cases are investigated: in the first case the external temperature is considered to be constant while in the second is considered to vary during the day. In order to solve the equations describing the transport phenomena inside the greenhouse a finite volume method is used. Tomato crop inside the greenhouse is simulated as porous material while radiation transport is modelled by the Discrete Ordinates (DO) model. Flow is considered to be incompressible, unsteady and turbulent. From the results it comes out that the consideration of external temperature variation is very important since the internal thermal field is determined by the convection induced by the entering stream except the area covered by a big recirculation in the middle of the greenhouse close to the cover and the close to ground corners where the effect of the entering stream is weak. The distribution of PAR is independent of the external temperature and presents symmetrical time behavior ensuring capable amounts of radiation in all the crops during at least 8 h a day. © 2009 Elsevier Ltd. All rights reserved.

Lee I.-B.,Seoul National University | Bitog J.P.P.,Seoul National University | Bitog J.P.P.,Nueva Vizcaya State University | Hong S.-W.,Seoul National University | And 4 more authors.
Computers and Electronics in Agriculture | Year: 2013

Computational fluid dynamics (CFD) is a proven simulation tool which caters to almost any field of study. The CFD technique is utilized to simulate, analyze, and optimize various engineering designs. In this review, the discussion is focused on the application of CFD in the external atmospheric processes as well as modeling in land and water management. With respect to its application in environmental investigations, numerous CFD studies have been done in the atmospheric processes where generally only the fluid flow characteristics are investigated. The application of CFD to soil and water management is still limited. However, with the present demand for conservation and sustainable management of our soil and water resources, CFD application in this field is fast emerging especially in structure designs of dams and reservoirs where CFD offers fast reliable results with less labor and cost. Every CFD model should be validated in order to be considered accurate and reliable. However, a benchmark or standard procedures in validating CFD models is not yet available. This probably answers why the success of the CFD models is still mostly attributed to the user's skills and experience. At present, the degree of application of CFD to the agro-environmental field is limited by the computing power and software used, however, the fast ever computing power of PCs continually expands the potential of CFD and can be generally more flexible at accounting for the unique aspects of every CFD project. This allows easy access to conduct simulation studies from simple to complex models. In this paper, after a state of art analysis of the past and present application of CFD in the agro-environmental applications, its future directions were discussed, in order to potentially serve as a guide for researchers and engineers on what project or investigations can be conducted. © 2012 Elsevier B.V.

Papanastasiou D.K.,Institute of Technology and Management of Agricultural Ecosystems | Kittas C.,Institute of Technology and Management of Agricultural Ecosystems | Kittas C.,University of Thessaly
Theoretical and Applied Climatology | Year: 2012

This paper studies the maximum intensity of the urban heat island (UHI) that develops in Volos urban area, a medium-sized coastal city in central Greece. The maximum temperature difference between the city center and a suburb is 3. 4°C and 3. 1°C during winter and summer, respectively, while during both seasons the average maximum UHI intensity is 2. 0°C. The UHI usually starts developing after sunset during both seasons. It could be attributed to the different nocturnal radiative cooling rate and to the different anthropogenic heat emission rate that are observed at the city center and at the suburb, as well as to meteorological conditions. The analysis reveals that during both seasons the daily maximum hourly (DMH) UHI intensity is positively correlated with solar radiation and with previous day's maximum hourly UHI intensity and negatively correlated with wind speed. It is also negatively correlated with relative humidity during winter but positively correlated with it during summer. This difference could be attributed to the different mechanisms that mainly drive humidity levels (i.e., evaporation in winter and sea breeze (SB) in summer). Moreover, it is found that SB development triggers a delay in UHI formation in summer. The impact of atmospheric pollution on maximum UHI intensity is also examined. An increase in PM10 concentration is associated with an increase in maximum UHI intensity during winter and with a decrease during summer. The impact of PM10 on UHI is caused by the attenuation of the incoming and the outgoing radiation. Additionally, this study shows that the weekly cycle of the city activities induces a weekly variation in maximum UHI intensity levels. The weekly range of DMH UHI intensity is not very large, being more pronounced during winter (0. 4°C). Moreover, a first attempt is made to predict the DMH UHI intensity by applying regression models, whose success is rather promising. © 2011 Springer-Verlag.

Kalogeropoulos N.,Harokopio University | Yannakopoulou K.,Greek National Center For Scientific Research | Gioxari A.,Harokopio University | Chiou A.,Harokopio University | Makris D.P.,Institute of Technology and Management of Agricultural Ecosystems
LWT - Food Science and Technology | Year: 2010

Purified methanolic extracts of Hypericum perforatum (HP) from Northern Greece were very rich in flavonoids. Among simple polyphenols determined by GC-MS, epicatechin, catechin and quercetin predominated, their concentrations being 118.9 ± 20.6, 8.7 ± 1.4 and 5.8 ± 0.8 mg/g extract. LC-MS analysis revealed that the HP extract was mainly consisted of quercetin glucosides, catechin and quercetin. Among anthocyanins, malvidine was present at 1.96 ± 0.2 mg/g. The 1,1-diphenyl-2-picrylhydrazyl radical (DPPH{radical dot}) and the ferric reducing antioxidant power (FRAP) assays showed that the HP extract exerted significant antioxidant activity. The inclusion complex of HP with β-cyclodextrin (β-CD) was prepared by mixing 1:4 mass ratios of its components in aqueous media and subsequent freeze-drying. The encapsulation was verified by differential scanning calorimetry (DSC) and NMR studies, and encapsulation efficiencies were 27.5, 30.0 and 35.0% for catechin, epicatechin and quercetin respectively. DSC after thermal oxidation indicated that the inclusion complex remained intact at temperatures where the free HP extract was oxidized. It is concluded that the encapsulation in β-CD improves the thermal stability of nutraceutical antioxidants present in St John's wort extract, suggesting that the inclusion complex could serve as a flavonoids-rich food supplement or a novel additive to enhance the antioxidant capacity of fresh or thermally processed food. © 2010 Elsevier Ltd. All rights reserved.

Mikulcic H.,University of Zagreb | Vujanovic M.,University of Zagreb | Fidaros D.K.,Institute of Technology and Management of Agricultural ecosystems | Priesching P.,AVL Inc | And 4 more authors.
Energy | Year: 2012

The cement industry is one of the leading producers of anthropogenic greenhouse gases, of which CO 2 is the most significant. Recently, researchers have invested a considerable amount of time studying ways to improve energy consumption and pollutant formation in the overall cement manufacturing process. One idea involves dividing the calcination and clinkering processes into two separate furnaces. The calcination process is performed in a calciner while the clinkering process takes place in a rotary kiln. As this is new technology in the cement manufacturing process, calciners are still in the research and development phase. The purpose of this paper is to demonstrate the potential of CFD to support the design and optimization of calciners, whose use appears to be essential in reduction of CO 2 emission during cement production. The mathematical model of the calcination process was developed, validated and implemented into a commercial CFD code, which was then used for the analysis. From the results obtained by these simulations, researchers will gain an in-depth understanding of all thermo-chemical reactions in a calciner. This understanding can be used to optimize the calciner's geometry, to make production more efficient, to lower pollutant formation and to subsequently reduce greenhouse gas emissions. © 2012 Elsevier Ltd.

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