End-Of-Use Fly Ash as an Effective Reinforcing Filler in Green Polymer Composites

The aim of this study is to use fly ash powder in an environmentally friendly matrix, in a novel way, addressing environmental and disposal problems. Fly ash/epoxy composites were prepared and studied varying the filler content. An investigation of structural and morphological characteristics was conducted using of X-ray diffraction patterns and scanning electron microscopy images, which revealed the successful fabrication of composites. Thermomechanical properties were studied via dynamic mechanical analysis and static mechanical tests. The composites exhibited an improved mechanical response. Broadband dielectric spectroscopy was used to investigate the dielectric response of the composite systems over the frequency range from 10−1 to 107 Hz and the temperature range from 30 to 160 °C. The analysis revealed the presence of three relaxation processes in the spectra of the tested systems. Interfacial polarization, the glass-to-rubber transition of the polymer matrix, and the rearrangement of polar side groups along the polymer chain are the processes that occur under a descending relaxation time. It was found that dielectric permittivity increases with filler content. Finally, the influence of filler content and the applied voltage under dc conditions was analyzed to determine the ability of the composites to store and retrieve electric energy. Fly ash improved the efficiency of the storing/retrieving energy of the composites

Thermosiphonic Hybrid PV/T Solar Systems

Thermosiphon solar water heaters and Photovoltaic (PV) devices are well known solar systems that provide heat and electricity, respectively. In this work, these two systems are combined into a hybrid hotovoltaic/Thermal (PV/T) solar system which can simultaneously provide electricity and heat, thus achieving a higher conversion rate of the absorbed solar radiation than standard PV modules. When properly designed, PV/T systems can extract heat from PV modules which can be used to heat water or air. By doing so the operating temperature of PV modules is reduced, which is beneficial, as it keeps their electrical efficiency at a sufficient level. In this paper, the design considerations and experimental results of a thermosiphonic hybrid PV/T solar system are presented. The electrical and thermal energy output for a pc-Si PV/T module type under the climatic conditions of Patras are presented

Performance of solar systems employing collectors with colored absorber

Flat plate solar collectors are of black appearance because of the color of the absorber, which is employed to maximize the absorption of solar spectrum. Generally, to avoid the monotony of the black color we can use collectors with absorbers of blue, red–brown, green or other color. These collectors are of lower thermal efficiency than that of the usual black type collectors, because of the lower collector absorptance, but they are of more interest to architects for applications on traditional or modern buildings. In this paper, applications of solar collectors with colored absorbers in a large hot water system suitable for multi-flat residential or office buildings, a house heating system, and an industrial process heat system are presented. The collectors are analyzed with respect to their performance and practical applications, aiming to give guidelines for their wider use on buildings. These systems are simulated on an annual basis at three different locations at different latitudes, Nicosia, Cyprus (35°), Athens, Greece (38°) and Madison, Wisconsin (43°). All simulations are carried out with TRNSYS. The results show that although the colored collectors present lower efficiency than the typical black type collectors, the difference in energy output depends on the absorber darkness. For a medium value of the coefficient of absorptance (α = 0.85), the colored collectors give satisfactory results regarding the drop of the amount of collected energy for the three locations (about 7–18%), compared to collectors with black absorbers (α = 0.95). This implies the use of proportionate larger collector aperture area to have the same energy output as that of typical black colored collectors. Additionally, the economic figures obtained for the systems investigated are very promising

ICS solar water heater study using artificial neural networks

In this paper we present a study in which a suitable Artificial Neural Network (ANN) and TRNSYS are combined in order to predict the performance of an Integrated Collector Storage (ICS) prototype. We use the experimental data that have been collected from outdoor tests of an ICS solar water heater with cylindrical water storage tank inside a CPC reflector trough, to train the ANN. The ANN is then used though the Excel interface (Type 62) in TRNSYS to model the annual performance of the system by running the model with the values of a typical meteorological year for Athens, Greece. In this way the specific capabilities of both approaches are combined, i.e., use of the radiation processing and modelling power of TRNSYS together with the “black box” modelling approach of ANNs. We present the details of the calculation steps of both methods that aim to the accurate prediction of the system performance and we show that this new method can be used effectively for such prediction

Characteristics of the urban heat island effect, in the coastal city of Patras, Greece

The ambient air urban heat island effect (at a height of 4÷4.5 m) is studied in the coastal city of Patras. For this purpose, 11 fixed temperature stations have been placed in chosen representative locations to monitor the ambient air temperature variations. Temperature stations are placed in urban places: at the center of the city (intense traffic), around the center (moderate traffic), and in a rural region outside the town (at ∼10 km). Collected data for June, July, August and September 2018 are examined statistically and results are extracted indicating that urban heat island effects are not very intense. An analysis of air temperatures in transverse and longitudinal to sea-line streets has shown some lower air temperatures across transversal streets