Performance analysis and neural modelling of a greenhouse integrated photovoltaic system

In the modern agriculture, greenhouses are well established as technological solutions aimed to increase plants productivity and crops quality. Greenhouses can include added capabilities for the energy generation by the integration of photovoltaic solar modules in their cladding areas provided that the blocking effect of photosynthetically active radiation is not significant for plants growing. After a comprehensive literature survey on the integration of photovoltaic systems in greenhouses, this work describes the results of an experience carried out at Almería (South Eastern Spain), where it has been built and monitored a 1.024 m² pilot photovoltaic greenhouse. The experimental set up has consisted of a greenhouse roof 9.79% coverage ratio by means of 24 flexible thin film modules, installed in two different checkerboard configurations. The obtained results indicate that, for the conditions of the undertaken experiment, the yearly electricity production normalised to the greenhouse ground surface is 8.25 kW h m^?2, concordant to previous findings for the used type of modules. In addition to this, an artificial neural network model has been elaborated to predict the electricity instantaneous production of the system, showing the suitability of this modelling technique for complex and non linear systems, as it is the case of the constructively integrated PV plants, either in greenhouses and buildings, where both impinging radiation and system configuration are highly constrained by the pre-existing structures.     

Convective drying characteristics of sludge from treatment plants in tomato processing industries

The present work is mainly focused on the study of the thin layer drying behaviour of sludge from water treatment plants in tomato processing industries, using a convective dryer. The drying experiments were conducted at inlet temperatures of drying air of 30 °C, 40 °C and 50 °C and at an airflow rate of 0.9 m/s and 1.3 m/s. The drying rate was found to increase with temperature and velocity, hence reducing the total drying time. In particular, as drying temperature was raised from 30 °C up to 50 °C, the time period needed to reduce the moisture content of the sample from 173 wt% down to 7 wt% (dry basis) was observed to decrease from more than 760 min to 470 min (0.9 m/s) and from 715 min to 295 min (1.3 m/s).Using a non-linear regression (Marquart's method) together with a multiple regression analysis, a mathematical model for the thin-layer convective drying process of sludge from treatment plants in tomato processing industries was proposed. The values of the diffusivity coefficients at each temperature were obtained using Fick's second law of diffusion, and varied from 6.11 × 10^?10 m²/s to 2.54 × 10^?9 m²/s over the temperature and velocity range. The temperature dependence of the effective diffusivity coefficient was described following an Arrhenius-type relationship. The activation energy for the moisture diffusion was determined as 30.15 kJ/mol and 36.70 kJ/mol, for airflow rates of 0.9 m/s and 1.3 m/s respectively. Air temperature 40 °C and drying airflow rate 1.3 m/s were found adequate to reduce drying energy consumption as well as to optimise the dryer loading/unloading periods.     

Optimizing location and size of rural schools in Chile

The Chilean Ministry of Education oversees preschool, primary, and secondary education in both urban and rural areas. Many parts of Chile are sparsely populated and there are currently over 4,000 rural schools (almost 38% of all schools in Chile) educating 9.5% of the students in the country. Many of the rural schools are small with only one teacher responsible for instruction of all local students (multigrade schools). The geographical distribution of the rural schools has not been coordinated and this has resulted in unequal utilization of existing schools and some unreasonably long travel distances by students. Good management of the rural schools is fundamental to meeting Chile's goal of providing quality education to its citizens. Seeking to improve the situation, the Ministry of Education ordered a study of the optimal location and size of rural schools with the general goals of reducing the number of lesser quality multigrade schools and reducing student travel distances while maintaining reasonable costs. This paper presents results of this study obtained using an integer linear program that has been embedded in a geographical information system. We present computational results for the entire country. Recommendations include where to open new rural schools as well as where to expand, reduce, close, or leave unchanged existing schools. We show how recommendations are sensitive to key parameters such as the cost of transportation.     

Study of Complete Thermoelectric Generator Behavior Including Water-to-Ambient Heat Dissipation on the Cold Side

Reduction of the thermal resistances of the heat exchangers of a thermoelectric generation (TEG) system leads to a significant increase in TEG efficiency. For the cold side of a thermoelectric module (TEM), a wide range of heat exchangers have been studied, from simple finned dissipators to more complex water (water–glycol) heat exchangers. As the Nusselt number is much higher in water heat exchangers than in conventional air finned dissipators, the convective thermal resistances are better. However, to conclude which heat exchanger leads to higher efficiencies, it is necessary to include the whole system involved in the heat dissipation, i.e., the TEM-to-water heat exchanger, the water-to-ambient heat exchanger, as well as the required pumps and fans. This paper presents a dynamic computational model able to simulate the complete behavior of a TEG, including both heat exchangers. The model uses the heat transfer and hydraulic equations to compute the TEM-to-water and water-to-ambient thermal resistances, along with the resistance of the hot-side heat exchanger at different operating conditions. Likewise, the model includes all the thermoelectric effects with temperature-dependent properties. The model calculates the net power generation for different configurations, providing a methodology to design and optimize the heat exchange in order to maximize the net power generation for a wide variety of TEGs.     

A Box–Behnken Design-Based Model for Predicting Power Performance in Microbial Fuel Cells Using Wastewater

Although modeling is regarded as a useful tool to understand the performance of microbial fuel cells (MFCs), the number of MFC models remains very low compared with the number of experimental works available in the literature. Moreover, there are very few MFC modeling attempts dealing with the use of wastewater as fuel in these devices, which is essential for the practical implementation of MFCs since the potential of this technology lies in the two-fold benefit of wastewater treatment and bioenergy generation. In this work, a four-factor three-level Box–Behnken design was developed to model the electrochemical power generation in two-chamber MFCs using wastewater as fuel. The optimum values of temperature, external resistance, feed concentration and anodic pH that maximized power output were investigated. Optimum conditions were found at T = 35°C and R = 1 kΩ, corresponding to a maximum power density of 0.88 W·m^?3, while feed concentration and pH did not show statistical significance in the ranges studied. Thus, a Box–Behnken design-based model as empirical approach could provide an effective tool for the optimization study of MFC systems.     

Combined effect of antimicrobial edible coatings with reduction of initial microbial load on the shelf-life of fresh hake (Merluccius merluccius) medallions

Two distinct strategies were combined to preserve fresh fish (Merluccius merluccius) under refrigeration at 4 °C for 12 days: (i) the application of an antimicrobial edible coating enriched with oregano essential oil (OEO) or carvacrol (CV) and (ii) the reduction of initial microbial load by good handling practise and the use of sodium hypochlorite (NaOCl). The action of antimicrobial coatings alone retarded the growth of Enterobacteriaceae, lactic acid bacteria (LAB) and H₂S producing bacteria on fish samples. The reduction of initial microbial load by itself only affected the evolution of LAB, but not the rest of the bacterial groups. When using both techniques combined, edible antimicrobial coatings were significantly more effective with additional and significant delays in the growth of mesophilic, psychrotrophic and Pseudomonas bacteria. Thus, the use of both strategies combined resulted in a reduction of the counts of all bacterial groups after 12 days of storage which ranged from 1.5 log and 8 log, in Pseudomonas and H₂S producing bacteria, respectively. Moreover, no significant differences were observed when comparing the microbiological evolution of samples treated with OEO compared to those only treated with CV.