Combination of Flat-plate Solar Collectors of Different Performance

The collector most frequently used in solar plants is of the flat-plate single cover type; however its field of use is limited owing to the low temperatures reached with this type of installation. Collectors with a greater number of covers produce higher temperatures, thus broadening their field of use

The analytical model presented in this paper makes it possible to obtain the optimum combination of differently performing flat-plate collectors ( collectors with different numbers of glass covers), in order to maximize the economic benefit of liquid heating solar plants at different temperatures and under different operating conditions

The results obtained justify the assertion that combined flat-plate collector systems present better techno-economic performance at high temperatures than single systems with single cover collectors.     

Preparation and characterization of CuOAl2O3 catalyst for dimethyl ether production via methanol dehydration

In the present study, a CuOAl₂O₃ catalyst with CuAl₂O₄ spinel structure was prepared by a co-precipitation method and used for dimethyl ether (DME) production via methanol dehydration at 50 bar and different reaction temperatures (150, 250, and 350 °C). Upon XPS analysis of the copper and aluminum species in the fresh and used CuOAl₂O₃ catalyst, CuAl₂O₄ was found to be the dominant species with more than 50% of total composition. Three reductive reactions and temperatures for the formation of CuH (102.3 °C), the interaction between Cu²⁺ and Al atoms (356.6 °C), and the reduction of CuO (520.1 °C) were analyzed by H₂-TPR. Furthermore, the copper oxidation state in the fresh and used catalyst was Cu(II), as determined by the XANES spectra. The fine structural parameters revealed that the coordination number of Cu changed from 2.75 to 2.44 during the catalytic reaction, and that the CuO bond distance increased from 1.94 to 1.98 Å due to strengthened Cu²⁺Al interactions. On-line FTIR spectra revealed that the optimum temperature for the formations of HCOOH (by-product) and DME (product) were 150 and 250 °C, respectively. The catalytic reactions in the duration of DME synthesis were found that included methanol decomposition, methanol/formic acid formations, and methanol dehydration occurring at CuO, Cu, and Al₂O₃/CuAl₂O₄ active sites, respectively. The highest methanol conversion (67.3%) and DME yield (40.6%) were obtained at 250 °C and 50 bar, as demonstrated by the catalyst performance. In addition, optimum DME formation (equilibrium constant 1.76 × 10^?2 L mol^?1 h^?1 and activation energy 5.14 kJ mol^?1) occurred at 250 °C, as determined from the linear regression of the second order model with a high R² value (0.98). The exothermal and non-spontaneous nature of DME formation at high temperature was evaluated through thermodynamic calculations of the reaction enthalpy, entropy, and Gibbs energy.     

Survey on the P.V. Generator of Castellina in Chianti (Italy)

The aim of this study was the definition of low-cost solutions to optimise and maintain a satisfactory cost balance in the medium-long term between the different sub-systems and components of P.V. power generators.

In particular, the long-term objective is to keep the cost of support structures below about 20% of the total system cost.

A unit of about 200 modules was investigated in the Chianti Region of Castellina and in this paper results will be presented on the following topics

-the feasibility study of the most appropriate solution of a low-cost, simple, light-weight (0.3 kg/Wp), flexible and continuous array support structure (made of timber and steel wires).

-The study of the soil and of the site including site preparation by simple machines.

-The design of the solution retained valid after the imposed limitations for the plant approval.

-The construction and assembling of the entire P.V. plant.

-The measurements' campaigns carried out on the main structural components and the discussion of these results compared with design assumptions.

-The extrapolation of the real costs to larger P.V. units.

-The conclusive remarks on the experience acquired during the implementation of the project, its realization, its testing and operation over more than 18 months of life-time.     

Experimental research for biomass steam gasification in a fluidized bed

A fluidized bed gasification system was built to investigate the biomass steam gasification performance in different conditions. Medium heating value syngas with 34% H₂ content and no more than 20 g/Nm³ tar content could be obtained under 800°C with a S/B (steam vs. biomass ratio) of 0.9 by using olivine as bed material. The results indicated that syngas quality (including H₂ content, gasification efficiency, tar reduction, etc.) is in a positive correlation with temperature and S/B, but has a negative correlation with fluidization number (FN). Compared with quartz sand and dolomite, olivine is more suitable for fluidized bed because of its catalytic ability and good abrasion performance for fluidized bed gasifier. As a result, a set of optimum parameters is recommended with S/B of 0.9~1.0, FN of 1.4, and temperature of 800°C in this study.

Tar is a by-product from the gasification process, which will cause the pipeline congestion, reduce the gasification efficiency, and deteriorate the working condition. According to this experiment, the temperature and S/B both have a negative effect on tar content, while tar content increased with increase in the FN. Dolomite and olivine both have an inhibition function on tar, and the olivine is considered the best choice of bed material because of its good anti-wear properties.     

Parabolic trough collector with rhombus tube absorber for higher concentration ratio

In the present study, the concentration ratio of the parabolic trough collector using rhombus tube absorber has been estimated. An analytical technique has been developed to determine the optimum size of the rhombus tube absorber for given trough dimensions. The optimum size of the rhombus tube absorber is 13.8% smaller than the circular tube absorber for the LS3 trough with no change in intercept factor. The maximum improvement in the concentration ratio is found to be 31.5% for the troughs with rim angle 90° in comparison to circular tube absorber. Results also indicate that rhombus tube absorber can be employed for a range of rim angle 75 to 90 degree.

Abbreviations: CR: concentration ratio; CSP: concentrated solar power; MCRT: Monte Carlo ray tracing; PTC: parabolic trough collector     

Combustion characteristics of solid waste biomass,oil shale,and coal

In this study, a developed two-dimensional mathematical model was used to represent the physical model of the combustion process of olive cake and date seed, and solve the governing equations using finite-volume method. The simulation was performed using ANSYS/Fluent software in order to estimate maximum temperature, heating values and pollutants concentrations. The obtained results were compared with experimental results, and corresponding values of oil shale and coal. The experimental work of direct burning of olive cake and date seeds was performed using an existing circulated fluidized bed (CFB) unit.

It was found that the adiabatic flame temperatures were 1380 K and 839 K for olive cake and date seed, and 2260 K and 1080 K for coal and oil shale, respectively. The experimental results showed that the maximum temperatures were 1126 K and 723 K for olive cake and date seed, respectively. The lower heating values were 19,500 kJ/kg and 16,400 kJ/kg for olive cake and date seed, and 29,000 kJ/kg and 7000 kJ/kg for coal and oil shale, respectively.

Thus, biomass such as date seed and olive cake may be used as an alternative fuel in electrical power plants in olive- or date-producing countries, which may save 40% of fuel cost.     

Case study: Comparison of enhanced heavy-oil recovery by CGI,WAG, and GAGD

Continuous gas injection (CGI) in the conventional horizontal flooding patterns leads to severe gravity segregation and poor reservoir contact (sweep) volumes. To improve the sweep efficiency, the Water-Alternating-Gas (WAG) process has been widely practiced in the industry. However, the WAG process has not measured up to expectations, as evidenced by the low recoveries observed in several field cases.

The Gas-Assisted Gravity Drainage (GAGD) process is designed and practiced based on gravity drainage idea and uses the advantage of density difference between injected gas and reservoir oil to overcome the drawbacks of the WAG process.

In this study, a comparison of enhanced heavy-oil recovery by three methods (CGI, WAG, and GAGD) is conducted by a commercial numerical simulator in a sector model of an Iranian offshore field. For this purpose, different production scenarios are designed. Moreover, the effect of several parameters such as injection fluid (CO₂, hydrocarbon gas), in situ oil viscosity (heavy or extremely heavy oil), rate and volume of injection, and also three different WAG ratios are studied.

The results show that the GAGD method is not suitable for this field as the thickness of pay zone is low for vertical sweep efficiency and causes early breakthrough of injected gas. Also, CGI leads to lower recoveries compared to the WAG process, due to its unfavorable mobility ratio. Injection of CO₂ instead of hydrocarbon gas results in higher sweep efficiency because of its viscosity reduction and swelling effects. In case of extremely heavy-oil recovery, with decreasing well spacing, the oil recovery factor increases as the drainage radius of wells reduces substantially due to high-viscosity oil.     

Residual Least-Squares Error Estimate for Unstructured h-Adaptive Meshes

An a posteriori error estimate suitable for finite-volume adaptive computations is presented. The error estimate combines the least-squares method regressions with the residual computation, which provides information from the grid quality and the governing equations for a better local adaptation of the unstructured grid.

The decision algorithm uses the information provided by the error estimate and does not require problem-dependent constants; it also uses a grid interface correction step to provide a smoother and a high-quality adaptive grid.

The proposed error estimate and the adaptive refinement algorithm are verified against analytic solution for different two-dimensional problems. In addition, calculations of three-dimensional laminar flows with different types of unstructured grids have demonstrated the applicability of the adaptive method.     

The Adrano Project

The aim of the Adrano Photovoltaic Project is to permit direct on site testing and comparison of different P.V. generators.

The Project includes the design, fabrication, installation and testing of four 2.5-3 kW blocks, representing two different types of fixed flat-plate modules and one type of sun-tracking modules.

Each block consists of the array (P.V. modules, sun-tracker devices, support structures, wiring connectors, protection devices), the power conditioning system (MPPT-inverter) and the suitable instrumentation. Therefore each block is a fully independent P.V. system able to supply electric energy to a 380 V, 50 Hz three-phase line.

Furthermore, two experimental 200 W_p systems with GaAs cells and amorphous silicon cells are installed in the same area for the testing of these particular technologies.     

Hydrophilic and hydrophobic materials and their applications

Wettability of a material’s surface plays a significant role in how fluids interact with such surfaces. Wetting behavior is universal but can vary depending on the chemical nature of the solid and liquid phases. Plants and animals adapt to their environment by having evolved special properties. These properties are such as hydrophilic and hydrophobic. Hydrophilic surface has a strong affinity to water and spreading of water on such surface is preferred. The degree of hydrophilicity of the substance can be measured by measuring the contact angle between the liquid and solid phases. Hydrophobic materials are known as non-polar materials with a low affinity to water, which makes them water repelling. A contact angle of less than 90° indicates hydrophilic interaction where as an angle greater than 90° indicates a hydrophobic interaction. More recently, superwetting such as superhydrophilicity has been receiving an increased focus in the literature due to its potential significance. Superhydrophilic surface has a contact angle of less than 5°.

The fabrication of hydrophilic materials can be carried out in two main ways: depositing molecules on surfaces or modification of surface chemistry. Both methods have been successful historically in achieving their intended purposes. Hydrophobic and superhydrophobic materials can be produced with many fabrication methods such as layer-by-layer assembly, laser process, the solution-immersion method, sol-gen techniques, chemical etching, and Hummer’s method.

The applications of such an important property are significant. For example, hydrophilic surfaces can be used in anti-fogging applications, biomedical, filtration, heat pipes, and many others. Hydrophobic and superhydrophobic materials have been successfully applied in many sectors, such as: (I) the removal of petroleum from aqueous solutions, (II) applied to plastic, ceramics, and mesh to contribute to the oil removal from aqueous solutions, (III) hydrophobic layers have a strong self-cleaning effect on plastics, heat pipes, metals, textiles, glass, paints, and electronics, (IV) hydrophobic layers improve the anti-freezing behavior of heat pipes which prevents unwanted build-up and (V) they function as a water and dust protecting coat on electronics.

The presence of this property is historic but there is still a huge potential for development for its applications in many sectors such as water treatment, heat transfer applications, biomedical devices, and many more.     

Oxidation stability of biodiesel derived from high free fatty acid feedstock

At present, with fluctuating feedstock prices, the biodiesel manufacturing industries are facing some downfall. High free fatty acid (FFA) non-edible oil, which is a byproduct of vegetable oil refineries, is available at low price and in considerable quantities at vegetable oil refinery sites. This high FFA oil can be utilized as a potential low cost feedstock for biodiesel production. In the present work, high FFA (51.6%) oil was synthesized into biodiesel by a two-step process. Except oxidation stability, other fuel properties of the produced biodiesel were found to be comparable with that of biodiesel specifications. Oxidation stability was found to be only 2.1 h at 110°C as determined by the Rancimat apparatus.

In order to study and further improve the oxidation stability, the biodiesel (B100) was dosed with a suitable antioxidant (pyrogallol) and stored for 6 months. The acid value, peroxide value, and kinematic viscosity which are closely associated with oxidation behavior were studied. It was found that biodiesel dosed with an antioxidant showed the least increase in the acid value, peroxide value, and kinematic viscosity. Also, induction period was improved and found to be within the American Society for Testing and Materials limit . Thus, the high FFA oil-based biodiesel with a suitable antioxidant can be used as a potential feedstock to resolve the issue of the high cost of biodiesel production.