Onur Taylan

Dissociation of carbon dioxide using a microhollow cathode discharge plasma reactor: effects of applied voltage, flow rate and concentration

This paper reports an experimental study on dissociating carbon dioxide (CO2) using a microhollow cathode discharge (MHCD) plasma reactor operated at 1 atm. The MHCD plasma reactors can be a promising technology for dissociating gases, including CO2, as they do not require catalysts, they operate at around room temperature, and can be inexpensively built and operated. In this study, CO2 balanced with the carrier gas argon (Ar) was fed through the MHCD reactor, and parametric experiments were conducted to investigate the effects of applied voltage, flow rate, and CO2 mole fraction in the influent on the composition of the products, energy conversion efficiency, and yield. Within the investigated parameter ranges, the maximum energy conversion efficiency of 14% was achieved when the specific energy input was 1.1 eV mol−1, whereas the maximum CO yield of 10.5% was achieved when the specific energy input was 4 eV mol−1. The results also showed that diluting CO2 with Ar increased the yield at an expense of a decrease in energy conversion efficiency. The results of this study provide insights for operating MHCD reactors for efficient gas dissociation at atmospheric pressure.

Fuel Production Using Concentrated Solar Energy

Limited reserves of fossil fuels and their negative environmental effects impose significant problems in our energy security and sustainability. Consequently, researchers are looking for renewable energy sources, for instance solar energy, to meet the energy demands of a growing world population. However, terrestrial solar energy is a dilute resource per foot‐ print area and is intermittent showing substantial variability depending on the season, time of the day, and location.

Rheological properties of "dry water"

This study reports the rheological properties of the novel material “dry water” which contains about 98% by weight water but resembles a dry powder. Dry water is a water-in-air inverse foam which consists of microscopic water droplets encapsulated with hydrophobic fumed-silica nanoparticles. This novel material offers a large surface to volume ratio on the order of 2 × 105 m2 /m3 for the gas and water phases. Thus, it provides a convenient medium for surface area limited processes and finds applications from cosmetics to gaseous fuel storage. In this study both steady and dynamic rheological properties of dry water were measured. In particular, the elastic (G′ ) and viscous (G″ ) moduli, and the complex dynamic shear viscosity (η* ) were recovered from experimental data. Results showed that both the elastic and viscous moduli decreased with increasing strain at strains larger than 4%, and both moduli are weak functions of rotational frequency. Complex dynamic shear viscosity decreased with strain and rotational frequency. When compared with the studies in literature, rheological experiments and obtained results indicated that dry water behaves as a gel rheologically under the investigated conditions.Copyright

Feasibility study of a grid connected hybrid PV-wind power plant in Gwanda, Zimbabwe

The depletion of fossil fuel resources on worldwide basis has necessitated an urgent search for alternative energy sources to meet up the present day demands. Energy demand is growing in developing nations which makes a hybrid power system, consisting of a hybrid Solar Photovoltaic together with wind energy to be considered one of the best alternatives in renewable energy. These sources of energy can partially or fully meet Gwandas demand with little or no disturbance on the countrys stability. The objective of this study is to convert the wind and solar resources in Gwanda into electrical energy to meet the growing demand. This system ensures a suitable utilization of resources and hence improves the efficiency as compared with their individual modes of generation. The annual energy generated by the hybrid system is calculated and energy accounting is performed according to the demand. The main goal is to have a hybrid system with a suitable Levelized Cost of Electricity (LCOE). Comparative analysis was made with the existing grid tariff of Zimbabwe to investigate the feasibility of such a system.

Technical and Economic Analyses for Sizing PV Power Plant With Storage System for METU NCC

The use of renewable energy with storage systems is particularly important in small and unreliable grids, such as islands. This paper reports sizing of a photovoltaic (PV) power plant with storage system for Middle East Technical University Northern Cyprus Campus through technical and economic analyses. PV system was modeled considering fixed tilted, one-axis and two-axis tracking systems using hourly data. Energy storage system was included in the model to overcome the temporal mismatch between the electricity demand of the campus and the electricity supplied by the PV system. The reduction in CO2 emissions by deploying these systems was studied. The results showed that although it would not be economically feasible to meet the entire demand of the campus, a PV system of 4.5 MW with 15 MWh of storage size would generate enough electricity to meet the demand for 83% of the time in a year, yielding the cost of 0.25 USD/kWh.Copyright

Discharge of Carbon Dioxide Using a Non-Thermal Plasma Reactor

This paper reports a numerical study on the discharge of carbon dioxide using a non-thermal dielectric barrier discharge (DBD) plasma reactor at ambient conditions. DBD plasma reactors have been used for various applications due to their ease of production, process control, operation at different conditions. The applications of DBD plasma reactors include discharge of gases. Carbon dioxide is a greenhouse gas formed as a byproduct of fossil fuel combustion. Use of DBD non-thermal plasma reactor can be a promising technology for carbon dioxide mitigation due to its operation at low temperatures, lack of need for catalysts, and flexibility in controlling the products generated. In this study, a tubular DBD non-thermal plasma reactor was modeled with different electrode materials separated by different dielectric materials. The aim was to provide guidelines for the design and material selection for optimizing DBD plasma reactors for CO2 discharge. A parametric set of simulations was performed using a finite element solver to investigate how electrode and dielectric materials affect the discharge volume of CO2 and power requirement of the non-thermal plasma discharge of CO2. The results showed that electrode material did not affect the discharge or the power requirement. However, dielectric material with higher permittivity or lower conductivity increased the gas discharge and power requirement. Among the analyzed materials, aluminum electrode and mica tube were suggested based on the simulation results for the maximum gas discharge and low power requirement.Copyright

Dissociation of carbon dioxide using a microdischarge plasma reactor

This paper reports an experimental study on dissociation of carbon dioxide using a microdischarge plasma reactor at ambient conditions. Carbon dioxide contributes to more than 80% of the greenhouse gas emissions in United States. The microdischarge plasmas can be a very promising method in dissociating gases, including carbon dioxide, due to their lack of need for catalysts, operating at temperatures lower than conventional thermochemical dissociation processes and ease of operation. A microhollow cathode discharge plasma reactor was designed and prototyped for CO2 dissociation. The reactor included metal electrodes that were attached to both sides of a dielectric material with a micro-size through hole. The electrodes and the dielectric material were placed perpendicular to flow direction for dissociation to occur as carbon dioxide passed through the hole. A set of experiments were conducted to investigate the effect of flow rate and applied voltage on the composition of the products, energy conversion efficiency and CO2-to-CO conversion yield of the microdischarge plasma reactor. Temperature of reactants and products were continuously measured; applied voltage was set using a high-voltage power supply; and molar composition of products for each case was analyzed using gas chromatography. Results showed that CO2 dissociation rate, energy conversion efficiency and CO2-to-CO conversion yield increased with applied voltage. Moreover, CO2 dissociation rate and conversion yield decreased while energy conversion efficiency increased with increasing flow rate.Copyright

Modeling of a Microhollow Cathode Discharge Reactor for Carbon Dioxide Dissociation

This paper reports a numerical study on carbon dioxide dissociation using a microhollow cathode discharge (MHCD) plasma reactor. These reactors can produce non-equilibrium plasmas and can be a promising technology for converting carbon dioxide into valuable chemicals and renewable fuels. However, these applications are currently in their early stages. In order to understand the effects of major design and operational parameters on the reactor performance a MHCD system was modeled and simulated. In this study, different types of dielectrics including mica, alumina, acrylic and quartz were used, and applied DC voltage was varied from 250 to 10,000 V. First the operating voltage regions of this reactor were determined based on the breakdown thresholds of the dielectric and gas phase. Then, the effects of applied voltage on the discharge volume and power requirement of operation were determined. Results showed that the reactor with mica as the dielectric material showed the largest operating voltage range, as well as the highest power requirement. In addition, the discharge volume increased with applied voltage and it was possible to discharge about 96% of the gas in the MHCD reactor with mica at 10 kV.Copyright

Thermal Radiation Transport in a Cloud of Dry Water Particles

This paper reports a numerical study on the thermal radiative transport in a cloud of dry water particles. Dry water is a water-in-air inverse foam which consists of micrometer-sized water droplets encapsulated by hydrophobic fumed-silica nanoparticles. The radiative properties of this novel material were estimated using the Mie theory for coated spheres. The radiative transport equation (RTE) was solved for a one-dimensional geometry using the discrete ordinates method. The effects of silica particle and water droplet size as well as the volume fraction of dry water particles on reducing radiative heat transfer were studied numerically. The results were compared with respect to two limiting cases: (i) system with no particles and (ii) silica particles with no water. The results showed that dry water reduced the local radiative heat flux as much as 20% more than that by silica particles alone. Additionally, reduction of the diameter of dry water particles from 75 to 25 μm reduced the radiative heat flux by 17%. Finally, parametric analysis showed that increasing the volume fraction of dry water by 10 times decreased the radiative heat flux by about 30% at the receiver end.Copyright