Skytherm: an approach to year-round thermal energy sufficient houses

The skytherm system, a roof covered with water filled plastic bags equipped with moveable insulation, is studied and a model is presented to predict its thermal behavior. A computer program is written to calculate hourly cooling and heating load requirements of a building and is validated by comparison with field data taken from an actual house in Shiraz, Iran. This program is then used to simulate metal and concrete skytherms. It is shown that for a 140.55 m² one story house, the skytherm system is capable of reducing heating demands by 86% and cooling loads by 52%.     

Microstructure and Multiwall Carbon Nanotube Partitioning in Polycarbonate/Acrylonitrile-Butadiene-Styrene/Multiwall Carbon Nanotube Nanocomposites

The multiwall carbon nanotube (MWNT) partitioning and its impact on morphology and electrical properties of Polycarbonate (PC)/Acrylonitrile-Butadiene-Styrene (ABS)/MWNT nanocomposites were studied. The rheological and TEM results indicated that the MWNT partitioning and state of dispersion of MWNT were determined by the affinity between MWNT and the blend components and MWNT concentration. In the PC/ABS (70/30: w/w)/2 wt.% MWNT sample the MWNTs were preferentially located in the ABS droplets and the interface due to the greater affinity between MWNT and ABS compared with PC. In the PC/ABS (30/70: w/w)/MWNT samples, however the MWNTs were mostly located in the ABS matrix.     

Site-specific atomic scale analysis of solute segregation to a coincidence site lattice grain boundary

A site-specific method for measuring solute segregation at grain boundaries in an Aluminum alloy is presented. A Σ7(Σ7=38°〈1 1 1〉) grain boundary (GB) in an aluminum alloy (Zr, Cu as main alloying elements) was evaluated using site-specific Local Electrode Atom Probe (LEAP). A sample containing a Σ7 GB was prepared by combining electron backscatter diffraction (EBSD) and focused ion beam (FIB) milling to locate the GB of interest and extract a specimen. Its composition was determined by LEAP, and compared to a general high angle GB (HAGB). Zr was the only alloying element present in the Σ7 GB, whereas the general HAGB contained both Cu and Zr. This site-specific LEAP method was found to be an accurate method for measuring GB segregation at specific GB misorientations. The method has advantages over other methods of measuring chemistry at GBs, such as spectroscopy, in that GB structure can be assessed in three dimensions.     

Environmental,technical and financial feasibility study of solar power plants by RETScreen,according to the targeting of energy subsidies in Iran

In this study, based on new electricity tariffs, three scenarios have been developed with The RETScreen International Photovoltaic Project Model, according to the targeting of energy subsidies in Iran. We have also dedicated one of our scenarios to the reduction of greenhouse gasses.In the first case the electricity price was set to 3.75 Cents/kWh (450 Rial/kWh) and no credit was assigned to the reduction of greenhouse gasses (GHG), therefore equity payback (Return positive cash flow) has been 12.1 year. In the second case the electricity price was set to 17.5 Cents/kWh, therefore equity payback (return positive cash flow) was 8 year. Finally in the last scenario by considering a credit to the reduction of greenhouse gasses and electricity price being 175 Cents/kWh and applying solar panels with high efficiency and suitable batteries (DOD = 60%), equity payback (return positive cash flow) reached within 6 years.     

Simulation of an orifice scrubber performance based on Eulerian/Lagrangian method

A mathematical model based on Eulerian/Lagrangian method has been developed to predict particle collection efficiency from a gas stream in an orifice scrubber. This model takes into account Eulerian approach for particle dispersion, Lagrangian approach for droplet movement and particle-source-in-cell (PSI-CELL) model for calculating droplet concentration distribution. In order to compute fluid velocity profiles, the normal k− turbulent flow model with inclusion of body force due to drag force between fluid and droplets has been used. Experimental data of Taheri et al. [J. Air Pollut. Control Assoc. 23 (11) (1973) 963] have been used to test the results of the mathematical model. The results from the model are in good agreement with the experimental data. After validating the model the effect of operating parameters such as liquid to gas flow rate ratio, gas velocity at orifice opening, and particle diameter were obtained on the collection efficiency.     

Effect of Ti-ion non-stoichiometry on microstructure and microwave dielectric characteristic of Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript> ceramics

This paper studies the microwave dielectric properties, microstructure, vibration and densification of Li₂ZnTi_3+xO_8+2x (\(- 0.04 \le {\text{x}} \le +0.06\)) ceramics, manufactured via a conventional mixed oxide route. The X-ray diffraction and Raman spectroscopy revealed the unit cell parameter and cation ordering in LZT non-stoichiometry in their vibrational modes. The densification and phase composition were characterized by the EDX and SEM methods. It was found that a slight Ti vacancy can improve the relative density to the maximum value (96.2%). The XRD results showed that the second phase of TiO₂ in the Li₂ZnTi_3.06O_8.12 composition is formed. The sintered samples were detected in the microwave frequency range by using the resonance technique. The \({\text{~}}{\tau _f}\) values of the ceramics within Ti excess adjusted to near zero. The Li₂ZnTi_2.96O_7.92 ceramic showed the best relative density, single phase and best microwave dielectric \({\varepsilon _r}~={\text{ }}25.98\), Q?×?f?=?61,000 GHz, \({\tau _f}={\text{ }} - 17.4{\text{ ppm/}}^\circ {\text{C}}\) sintered at 1100 °C for 4 h.     

Shape memory response of porous NiTi shape memory alloys fabricated by selective laser melting

Porous NiTi scaffolds display unique bone-like properties including low stiffness and superelastic behavior which makes them promising for biomedical applications. The present article focuses on the techniques to enhance superelasticity of porous NiTi structures. Selective Laser Melting (SLM) method was employed to fabricate the dense and porous (32–58%) NiTi parts. The fabricated samples were subsequently heat-treated (solution annealing?+?aging at 350?°C for 15?min) and their thermo-mechanical properties were determined as functions of temperature and stress. Additionally, the mechanical behaviors of the samples were simulated and compared to the experimental results. It is shown that SLM NiTi with up to 58% porosity can display shape memory effect with full recovery under 100?MPa nominal stress. Dense SLM NiTi could show almost perfect superelasticity with strain recovery of 5.65 after 6% deformation at body temperatures. The strain recoveries were 3.5, 3.6, and 2.7% for samples with porosity levels of 32%, 45%, and 58%, respectively. Furthermore, it was shown that Young’s modulus (i.e., stiffness) of NiTi parts can be tuned by adjusting the porosity levels to match the properties of the bones.

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Modeling and simulation of photovoltaic (PV) system during partial shading based on a two-diode model

This paper proposes accurate partial shading modeling of photovoltaic (PV) system. The main contribution of this work is the utilization of the two-diode model to represent the PV cell. This model requires only four parameters and known to have better accuracy at low irradiance level, allowing for more accurate prediction of PV system performance during partial shading condition. The proposed model supports a large array simulation that can be interfaced with MPPT algorithms and power electronic converters. The accurateness of the modeling technique is validated by real time simulator data and compared with the three other types of modeling, namely Neural Network, P&O and single-diode model. It is envisaged that the proposed work is very useful for PV professionals who require simple, fast and accurate PV model to design their systems.