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    Air-Water Two-Phase Flow Dynamics Analysis in Complex U-Bend Systems through Numerical Modeling
    (Mdpi, 2024) Kukrer, Ergin; Eskin, Nurdil
    This study aims to provide insights into the intricate interactions between gas and liquid phases within flow components, which are pivotal in various industrial sectors such as nuclear reactors, oil and gas pipelines, and thermal management systems. Employing the Eulerian-Eulerian approach, our computational model incorporates interphase relations, including drag and non-drag forces, to analyze phase distribution and velocities within a complex U-bend system. Comprising two horizontal-to-vertical bends and one vertical 180-degree elbow, the U-bend system's behavior concerning bend geometry and airflow rates is scrutinized, highlighting their significant impact on multiphase flow dynamics. The study not only presents a detailed exposition of the numerical modeling techniques tailored for this complex geometry but also discusses the results obtained. Detailed analyses of local void fraction and phase velocities for each phase are provided. Furthermore, experimental validation enhances the reliability of our computational findings, with close agreement observed between computational and experimental results. Overall, the study underscores the efficacy of the Eulerian approach with interphase relations in capturing the complex behavior of the multiphase flow in U-bend systems, offering valuable insights for hydraulic system design and optimization in industrial applications.
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    Data-driven building energy benchmark modeling for bank branches under different climate conditions
    (Elsevier, 2023) Kukrer, Ergin; Aker, Tugce; Eskin, Nurdil
    Energy benchmarking in buildings is a significant analytical method to determine and classify the energy performance of buildings. The objective of the present paper is to establish a compre-hensive data-driven energy benchmark model for banking buildings. In this context, 587 bank branches are selected to cover every climatic region in Turkey, with more than 210,000 data obtained from the installed energy analyzers and building energy audits. A mathematical model is developed and verified to define the EUI of the existing bank branches. Calculated energy scores and benchmark study implied an energy efficiency potential across the sector. Investigating the results of underperforming buildings, the building shell and construction date are found to be significant. As results indicated an efficiency potential, a scenario-based energy benchmark model is proposed based on the new insulation regulations in Turkey to see the possible energy con-sumption and carbon gas emission reductions. The developed model is adapted to the scenario -based model by revising U-values concerning the regulation and climate zones. The scenario -based strategy has led to a 2136.7 MWh/year reduction in energy consumption. The total EUI was found to decrease from 159.44 to 124.35 kWh/m2year, also resulting in a 20.5% improve-ment equal to 2057.3 equivalent tons of CO2/year in annual GHG emissions with the application of new regulations.
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    Experimental and computational design improvement assessment of a household toast grill
    (Elsevier, 2020) Gunes, Dogan; Kukrer, Ergin; Yildirim, Canberk
    Small kitchen appliances have become very popular with increasing needs. One of the most common household appliances is the toast grills. The grills are available in every home or restaurant. It is necessary to reach a high temperature for the operation of these grills. However, some contact surfaces should also be kept within a certain temperature range for safety. In this paper, development and assessment of some design changes to reduce the high temperature on the upper (contact) surface of the grill and the overall performance effect are studied. Compliance with EU small domestic appliances standard (SDA), which states conditions that could threaten user health, overheating and electrical accidents constitute the A13 standard. Compliance of the new design proposals are also reported in this paper. Laboratory tests at several locations of the grill and infrared examination are carried out to analyze the results of the proposed changes. Temperature drops of up to 20. are observed on the top cover surfaces with the application of insulation as part of the new design proposal. Savings obtained in accordance with Electrotechnical Commission (ICE) standards and heat and energy efficiency gain are reported. Computational model of the toast grill developed in this paper is found in line with experimental and infrared results. The model may be used to improve new designs for further studies.
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    Experimental assessment of local void fraction and flow development in a U-bend piping system for air-water two-phase flow
    (Pergamon-Elsevier Science Ltd, 2023) Kukrer, Ergin; Eskin, Nurdil
    This paper presents an experimental investigation of air-water flow in a complete piping system, covering the two-phase flow development in injector, upstream, U-bend and downstream sections separately. Local void fractions and bubble numbers were measured with a dual optical probe. Two-phase flow conditions were established through a 40 mm diameter pipe with 180 l/min water and 30, 35 and 40 l/min air flow rates by the designed circular injector. In the horizontal upstream section, where a transition from bubbly to plug flow with elongated Taylor bubbles was observed, the fully-developed flow is reached at 37.5D. The average void fraction in the upstream region was acquired as 9.2%, 11.5% and 13.4%. The effect of two vertical 90-degree and one vertical 180-degree elbows is assessed in the U-bend section. While bubble break-up and locally annular flow were observed in the vertical upward section; bubble coalescence and accumulation resulting in higher average void fractions (30.8%, 33.8%, and 35.6%) were present in the downward section due to body forces and interphase interactions. After the bend section, disturbances were detected in the gas phase due to the increased water velocity and centripetal forces. Accordingly, a local transition to temporary churn flow is observed in the earlier downstream sections. The experimental assessment in our study shows that the system should be considered and analyzed as a whole to determine local transitions and differences in the flow regimes due to singularities in geometry.
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    Flat Terrain Performance Rating Analysis of a Novel Airborne Rotor-Type Vertical Axis Wind Turbine (VAWT) by Applying Three-Dimensional Rotating Mesh Unsteady RANS Simulation Method
    (Springer International Publishing Ag, 2024) Kukrer, Ergin; Gunes, Dogan
    This paper presents the extended study on the performance analysis of a proposed airborne rotor type wind turbine design in flat terrain wind conditions. The innovative design proposal by the inventor was presented in our earlier work. The proposal is based on the airborne structure rotation with blades attached to the airborne zeppelin, thus called an airborne rotor generator. In our previous work, we developed a solid model of the airborne rotor and obtained the power generation potential for 12 m/s standard wind velocity. In this study, we present the extended work and results obtained by applying a Rotating Mesh Method developed in ANSYS/FLUENT at average wind speed conditions of 6, 9 and 12 m/s with rotation velocities of 0.8,1.0, 1.2 and 1.4 rad/s. 12m/s results indicate that the expected power generation potential for the rotor is around 80 kW on average at a rotation speed of 1.4 rad/s. Preliminary results indicate that the airborne zeppelin with sail-type blades may produce powers of around 40 kW at around 300 m altitude.
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    Performance Rating and Flow Analysis of an Experimental Airborne Drag-Type VAWT Employing Rotating Mesh
    (Mdpi, 2024) Gunes, Dogan; Kukrer, Ergin
    This paper presents the results of a performance analysis conducted on an experimental airborne vertical axis wind turbine (VAWT), specifically focusing on the MAGENN Air Rotor System (MARS) project. During its development phase, the company claimed that MARS could generate a power output of 100 kW under wind velocities of 12 m/s. However, no further information or numerical models supporting this claim were found in the literature. Extending our prior conference work, the main objective of our study is to assess the accuracy of the stated rated power output and to develop a comprehensive numerical model to analyze the airflow dynamics around this unique airborne rotor configuration. The innovative design of the solid model, resembling yacht sails, was developed using images in the related web pages and literature, announcing the power coefficient (Cp) as 0.21. In this study, results cover 12 m/s wind and flat terrain wind velocities (3, 5, 6, and 9 m/s) with varying rotational velocities. Through meticulous calculations for the atypical blade design, optimal rotational velocities and an expected Tip Speed Ratio (TSR) of around 1.0 were determined. Introducing the Centroid Speed Ratio (CSR), which is the ratio of the sail blade centroid and the superficial wind velocities for varied wind speeds, the findings indicate an average power generation potential of 90 kW at 1.4 rad/s for 12 m/s and approximately 16 kW at a 300 m altitude for a 6 m/s wind velocity.
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    Transient Computational Fluid Dynamics Modeling of Air-Water Two-Phase Flow for Elbows
    (Springer International Publishing Ag, 2024) Kukrer, Ergin; Eskin, Nurdil
    This study presents a computational fluid dynamics model investigation of the air-water multiphase flow in elbows, which can be commonly found in many practical applications. The computational model was developed in ANSYS Fluent. The Eulerian-Eulerian approach was used in modelling, which employs individual equations for each phase. Air is injected at a 30 l/min airflow rate to water through nozzles at 16 points placed at equal angles in the circumferential direction. The water flow rate is determined as 180 l/min at the inlet. The test section consists of a complete U-bend system, which is a combination of two horizontal to vertical (upward and downward) and one vertical 180-degree elbow. Our study not only provides a detailed presentation of the numerical modelling methods developed for this complex geometry elbow but also discusses the results obtained from the model. The results are presented for each phase regarding local void fraction and phase velocities. In addition to numerical studies, experimental works were carried out for validation. Computational results were compared with the experimental acquisitions, and the results were in good agreement. It is observed that the Eulerian approach gives reasonable results to predict the flow characteristics of air-water flow in elbows.