M. Zeki Yilmazoglu

Experimental and Numerical Study on Thermoelectric Generator Performance Applied to a Condensing Combi Boiler

In this study, thermoelectric generator (TEG) adaptation in a condensing combi boiler was investigated. The first part of the study comprises experimental analysis, performance tests of a commercially available TEG, and efficiency tests of a condensing combi boiler without TEG adaptation. In the second part of the study, a numerical analysis was carried out to determine the locations of TEGs inside the heat cell. According to the results of the performance tests, approximately 16 V open circuit voltage was generated under 201°C temperature difference. The electrical efficiency of the tested TEG is calculated to be 4.5%. Natural gas was used as fuel in the efficiency tests of the condensing combi boiler and the thermal efficiency was calculated to be 92.3% for 40–60°C water supply and return temperatures. Numerical study showed that the highest temperature difference could be obtained at the upper side of the heat cell with a value of 270°C. The hot side of the TEG module was heated from the inner surface of the heat cell via conduction through the wall, and the water channel was used as the heat sink. Therefore, TEGs were located inside the water channel of the heat cell, with a modification process on the heat cell itself. The performance tests and numerical results show that it is possible to integrate TEGs into the heat cell and decrease the electricity consumption or use combi boilers without an electricity network connection with a properly designed TEG integrated heat cell.

Numerical Analysis of Active Control of Flow on a DBD Plasma Actuator Integrated Airfoil

In recent years, flow control methods on an airfoil have gained interest. Flow control methods can be classified as passive and active control systems. Dielectric barrier discharge (DBD) plasma actuator is an active control method. A DBD plasma actuator can be defined as; a flow control device, without moving parts and same airfoil shape after installation. In this study, numerical analysis of DBD plasma actuator integrated airfoil was performed. Instead of modeling plasma generation, thermal effects, ionization, and momentum forces, a momentum source term was applied to the airfoil in order to observe the effects of plasma actuator integration on airfoil such as drag, lift, etc. ANSYS Fluent was used in the simulations. The cord length was assumed to be 150 mm. The effects of the attack angles were also investigated with 0°, 5°, 10°, and 15° attack angles. Hexahedral mesh structure was selected in order to model boundary layer with lower y+ values and k-ω SST turbulence model was used. The air velocity was assumed to be 1.9 m/s at the inlet and 200 N/m3 body force was applied to 10 mm after the leading edge for plasma effect analogy.

Waste Heat Utilization in Natural Gas Pipeline Compression Stations by an Organic Rankine Cycle

Utilizing compressors, natural gas compression stations (NGCS) supply the required pressure to transport the natural gas in pipelines. This study proposes to utilize the waste heat of gas turbines (GT), employed in these stations, to produce shaft power for compressors. A NGCS coupled to an Organic Rankine Cycle (ORC) is simulated by THERMOFLEX in this study. Ten different working fluids are compared against each other in the ORC to select a working fluid with the highest possible efficiency and obtainable power, and lowest possible environmental impacts. According to the results, n-Pentane is selected to be the working fluid, as compared to others, it better meets these criteria. The effects of the variation of the ambient temperature and the condenser pressure on the net power of the cycle working with n-Pentane are investigated in details. It was found that the utilization of waste heat in NGCS by an ORC can improve the energy efficiency and generates electricity for near rural areas.

Disposal of olive mill wastewater with DC arc plasma method

Olive mill wastewater is an industrial waste, generated as a byproduct of olive oil production process and generally contains components such as organic matter, suspended solids, oil, and grease. Although various methods have been developed to achieve the disposal of this industrial wastewater, due to the low cost, the most common disposal application is the passive storage in the lagoons. The main objective of this study is to reduce pollution parameters in olive mill wastewater and draw water to discharge limits by using plasma technology. Plasma-assisted disposal of olive mill wastewater method could be an alternative disposal technique when considering potential utilization of treated water in agricultural areas and economic value of flammable plasma gas which is the byproduct of disposal process. According to the experimental results, the rates of COD (chemical oxygen demand) and BOD (biological oxygen demand) of olive mill wastewater are decreased by 94.42% and 95.37%, respectively. The dissolved oxygen amount is increased from 0.36 to 6.97 mg/l. In addition, plasma gas with high H2 content and treated water that can be used in agricultural areas for irrigation are obtained from non-dischargeable wastewater.

CFD analyses of the serpentine and parallel flow fields for PEM fuel cells

Proton exchange membrane (PEM) fuel cells can be manufactured with different flow field designs, which can affect the performance substantially. The most common types of flow fields are serpentine and parallel flow field configurations. In this study, 3D Computational Fluid Dynamics (CFD) models of the parallel and the serpentine flow fields are simulated. Governing equations and electrochemical phenomena are modelled by ANSYS FLUENT-PEMFC module and temperature, pressure and water vapour distributions inside the flow fields are obtained. According to the oxygen consumption rate, the electrical current values are obtained and, as a result, the serpentine flow field is found to be more efficient than that of parallel flow field.

Decreasing energy consumption and carbon footprint in a school building: a comparative study on energy audits

Energy audit of a school building was carried out to evaluate the effects of the building retrofitting on energy efficiency and carbon footprint. Lighting intensities of the selected areas in the building were measured and thermal images of the building envelope were compared before and after retrofitting. Combustion performance of the boilers was measured and the effects of the insulation on the natural gas consumption were investigated. According to the results, the lighting system renovation decreased the share of lighting in total electricity consumption of the buildings by 53.2% for the recommended lighting intensities in the selected zones. As a result of the lighting system renovation, carbon footprint of the campus decreased 308,715 kgCO2 per year. Natural gas consumption decreased by 25.3% after building envelope insulation which equals to 137,078 kgCO2 per year.

Comparison of Thermal Repowering Alternatives for Thermal Power Plants

In this study, thermal repowering alternatives were compared in terms of net installed power, net electrical efficiency, emissions, and unit electricity generation costs. Soma A thermal power plant with 2 × 22 MWe capacity, was simulated in Thermoflex with design parameters. Three different repowering alternatives were simulated to compare the results; feedwater heating, hot windbox, and parallel repowering. According to the results, net power and net electrical efficiency were increased. Total CO2 mass flow rate was also increased; however, CO2 mass flow rate per installed capacity was sharply decreased. Therefore, repowering of old thermal power plants can be a short term solution in decreasing the CO2 emissions while the electricity demand increasing continuously.