• Energy Research
• engineering and technology close
• MX close
• CO close

This paper is presents the design and implementation of an energy conversion system based on a single-phase inverter for an application in the context of microgrids. In this context, it was conducted a study, an analysis, an design and the implementation by means of simulations of two novel controllers techniques based on control of two degrees of freedom plus repetitive controller configurations (R2DOF) and PI-P controller plus resonant controller configuration (PI-P + ResC) in droop control scheme that island mode operation of the inverter allowed maintain the characteristics of the voltage signal to be supplied to the load effectively. With these control configurations was maintained the amplitude, waveform and frequency of the voltage signal and attend increases linear and nonlinear load in island mode operation of a single phase inverter. Finally is implemented the above controllers within a droop control schemes were implemented through simulations for the active and reactive power control required by the loads. With these control schemes is achieved that several inverters connected to the microgrid, working to the voltage sources can operate in parallel, without interfering with each other and provide to loads the active and reactive power, dividing the power supplies by each inverter.

In honor of Prof. Dr. Fritz Scholz in his recent retirement. This work proposes a theoretical framework to obtain the frequency response of molar electrochemical Peltier heat and entropy changes induced by a modulated electrical signal. This is based on an internal energy balance developed for a working electrode thermistor in ac regime. Then, from an analysis that correlates the electrochemical impedance and the interfacial temperature variation, two new transfer functions that depend on the frequency ω , named as entropy changes Δ S ω , and molar electrochemical Peltier heat, Π ω are obtained. This strategy is tested in two electrochemical systems: the ferrocyanide/ferricyanide couple and the copper ions in an acid sulphate-chloride medium. Both systems are analyzed by dc thermometric measurements, electrochemical impedance spectroscopy and ac-thermometric experiments namely variation of interfacial temperature. As a result, Δ S ω and Π ω , are obtained and their values are correlated to the relaxation processes involved in the electrochemical reaction. Additionally, a brief discussion is included concerning the differences between the classical dc thermoelectrochemical methodology and the proposed approach here.

Abstract A theoretical study of the heat transfer process that takes place in a special calorimeter of conical cavity named CAVICAL is presented. This instrument is used to measure the thermal power of a point focus solar concentrator system named DEFRAC, developed at the Center for Energy Research of the National University of Mexico. The DEFRAC concentrator has a power of 1.3 kWth and a very fine optical system. The calorimeter has a cavity opening of 8.24 cm 2 . A detailed heat transfer study was done using FLUENT code. The heat transfer processes taken into account for the analysis were the radiative energy absorbed by the inner cavity wall, the energy transfer from the outer cavity wall to the air by natural convection, the energy transferred by conduction through the inner metallic wall of the calorimeter, and by forced convection to the fluid in the cooling system. The calorimetric information gathered allowed determining the thermal power that the concentrator is able to capture. Temperature and velocity fields have been calculated for each of the thermal fluids considered inside of the calorimeter. The analysis gave thermal losses and measured the thermal efficiency of the device. The information generated is useful to further optimize the design of the calorimeter.

In this work a thermal performance analysis of the solar drying process is presented. It describes semi-empirical models for the thermal characterization of an experimental indirect solar dryer device. A procedure for designing drying equipment, which takes into account the varying operating conditions given by the variations of the environmental conditions is also presented. On the other hand, a simplified method to design solar collectors based on the determination of minimum entropy generation during the thermal conversion of solar energy, is described. Finally, the results of the preliminary design of the solar dryer are presented using the thermal analysis procedure and the method derived from the Second law of thermodynamics.

Abstract Cobalt oxide and cobalt oxide–silver selective surfaces were prepared in a galvanostatic mode by means an electrodeposition bath, using different deposition times, on stainless steel substrates. Later, the roughness factor of the selective surfaces, were determined in order to establish one relation with the electrodeposition time and the solar absorptance of the black cobalt and black cobalt–silver coatings.

Hydrogels are suitable materials to promote cell proliferation and tissue support because of their hydrophilic nature, porous structure and sticky properties. However, hydrogel synthesis involves the addition of additives that can increase the risk of inducing cytotoxicity. Sterilization is a critical process for hydrogel clinical use as a proper scaffold for tissue engineering. In this study, poly(ethylene glycol) (PEG), poly(ethylene glycol)-chitosan (PEG-CH) and multi-arm PEG hydrogels were synthesized by free radical polymerization and sterilized by gamma irradiation or disinfected using 70 % ethanol. The biocompatibility assessment in human fibroblasts and hemocompatibility studies (hemolysis, platelet aggregation, morphology of mononuclear cells and viability) in peripheral blood from healthy volunteers (ex vivo), were performed. The sterilization or disinfection effect on hydrogel structures was evaluated by FT-IR spectroscopy. Results indicated that hydrogels do not induce any damage to fibroblasts, erythrocytes, platelets or mononuclear cells. Moreover, there was no significant difference in the biocompatibility after the sterilization or disinfection treatment. However, after gamma irradiation, several IR spectroscopic bands were shifted to higher or lower energies with different intensity in all hydrogels. In particular, several bands associated to carboxyl or hydroxyl groups were slightly shifted, possibly associated to scission reactions. The disinfection treatment (70 % ethanol) and γ-irradiation at 13.83 ± 0.7 kGy did not induce morphological damages and yielded sterile and biocompatible PEG hydrogels potentially useful for clinical applications.

Abstract Ultimate and proximate analyses, HHV and BET surface area have been assessed in the unburned materials obtained by combustion in a conical spouted bed of four types of vegetable biomasses representative of forestry residues, grass and food industry. The results show that the materials are mainly of carbonaceous structure, which stems from the incomplete decomposition of cellulose and lignin, and their content decreases with combustion temperature. The unburned materials have a high surface area, which is of the same order as certain commercial active carbons, rendering them suitable properties for use as low-cost adsorbent. In order to verify this fact, removal efficiencies have been determined in amoxicillin removal tests, and the characteristic parameters, as well as mass transfer coefficients, have been calculated for two adsorption models following Langmuir and Freundlich isotherms. The results confirm that this byproduct obtained in the recovery of energy from waste biomass performs well in the removal of emerging pollutants from wastewater, and is a viable alternative of commercial adsorbents.

This work studied the effects on the anaerobic digestion of sewage sludge by zero valent iron nanoparticles (NZVI) dosage. Biochemical methane potential tests were carried out with 5-9 mg/gVS (99.7%, 40-60 nm). The biogas yield increased from 132 (control) to 310 mL/gVS with 9 mg/gVS. The methane content increased from 63.2% (control) to 77.6% with NZVI, which corresponded to a maximum yield of 238 mLCH4/gVS with 9 mg/gVS. The maximum VS reduction was 19.6%. The highest INT-ETS activity (20.1-37.1 µgINTred/gVS·h) corresponding to the maximum values of sCOD was reached within the first days. NZVI decreased the ORP to -300 mV and increased the VFA's concentration (+2000 mg/L). The ORP-VFA-pH analysis showed that NZVI promoted the acidogenesis-acetogenesis without acidification. That is, NZVI was effective in intensifying the performance and stability of the process.

Abstract This work addresses a multi-objective strategy for defining the relationships between design and utility policy prices in water-energy off-grid systems. Levelized cost of utility is introduced for valuating the price of power, heat and water supply in an isolated community from Mexico. Besides, levels of subsidies and impacts of social, energy and economic policies are considered for defining the utility price for the end user. Levelized cost of electricity has been used as a common metric for determining the economic impact of implementing energy systems in off-grid systems. Normally, it is defined as a fixed cost associated to energy utilities. However, it is possible to define levelized cost of utilities associated to the design of multi-product systems. The proposed methodology allows determining the levelized cost of utilities using a flat-tariff scheme, as it is used in most of literature, and according to the demand-generation dynamics. For testing these ideas, it is presented the design of a water-energy off-grid system consisting of combined heat and power units fed by natural gas and biogas. The water-energy surplus management is performed using pumping and battery systems. The optimal design considers the size and selection of units according with objective functions as minimizing total annual cost and land usage as well as maximizing the social opportunity of community. The utility cost influence over operational policy is defined by partial load and storage levels of the units. For reaching a trade-off between objective functions, it is used a utopia-tracking approach. Results show the suitable level of subsidies as well as the advantages of implementing dynamic levelized cost of utilities according with the behavior of the water-energy supply system.