Browsing by Author "Hepbasli, A"

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    Assessment of exergy-based performance and sustainability indicators of a sewage water source heat pump system
    Celik, AG; Hepbasli, A
    Exergy analysis helps identify the amount and the positions of exergy losses in any system along with its main components. To achieve sustainability, these irreversibilities should be diminished. This study aims at presenting the exergetic-based performance of a sewage water source heat pump system based on experimental data. Initially, the exergetic performance assessments are carried out and then the exergetic performance results are evaluated using exergy-based sustainability indicators. The SWSHP system had the values for exergetic efficiency 57.77%-63.81% and overall sustainability index 2.31-2.72, respectively. Eight other exergy-based indicators are applied to determine and compare the most impacted component among the others.
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    Avoidable thermodynamic inefficiencies evaluation of a sewage water source heat pump system
    Celik, AG; Hepbasli, A
    The performance of a sewage water source heat pump system is assessed through conventional/enhanced exergy-based methods in this present study. The experimental data used in the analyses are based the cooling mode. According to the conventional-based results, the condenser has the lowest exergy efficiency. Beside this, the enhanced exergy-based analysis results show the sewage water heat exchanger should be considered as the most significant component as it has the highest avoidable exergy destruction rate in the whole system and takes the improvement priority. Based on the enhanced exergy analysis, 56% of the total exergy destruction belongs to the avoidable part.
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    Exergoeconomic analysis of geothermal district heating systems: A case study
    Ozgener, L; Hepbasli, A; Dincer, I; Rosen, MA
    An exergoeconomic study of geothermal district heating systems through mass, energy, exergy and cost accounting analyses is reported and a case study is presented for the Salihli geothermal district heating system (SGDHS) in Turkey to illustrate the present method. The relations between capital costs and thermodynamic losses for the system components are also investigated. Thermodynamic loss rate-to-capital cost ratios are used to show that, for the devices and the overall system, a systematic correlation appears to exist between capital cost and exergy loss (total or internal), but not between capital cost and energy loss or external exergy loss. Furthermore, a parametric study is conducted to determine how the ratio of thermodynamic loss rate to capital cost changes with reference temperature and to develop a correlation that can be used for practical analyses. The correlations may imply that devices in successful district heating systems such as the SGDHS are configured so as to achieve an overall optimal design, by appropriately balancing the thermodynamic (exergy-based) and economic (cost) characteristics of the overall systems and their devices. (c) 2006 Elsevier Ltd. All rights reserved.
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    A REVIEW ON COMPUTATIONAL FLUID DYNAMICS SIMULATION METHODS FOR DIFFERENT CONVECTIVE DRYING APPLICATIONS
    Coban, SO; Selimefendigil, F; Oztop, HF; Hepbasli, A
    This paper focuses on the CFD studies on one of the commonly used drying pro-cesses for different applications. First, a brief information about drying is given with determining important properties that effect drying characteristics. Next, ba-sic principles of CFD modelling are explained while capabilities of computational processing are presented. A detailed literature survey about CFD studies in con-vective drying process is then conducted. Finally, some sound concluding remarks are listed. It may be concluded that the CFD is a powerful and flexible tool that can be adopted to many different physical situations including complex scenarios, results of CFD simulations represent good predictions for fluid-flow, heat and mass transfer of various drying methods and those numerical studies can be used for validation and controlling of applicability of new drying systems.
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    Environmental and exergetic aspects of geothermal energy
    Baba, A; Ozgener, L; Hepbasli, A
    Geothermal energy is already in the form of heat, and from the thermodynamic point of view, work is more useful than heat because not all heat can be converted to work. Therefore, geothermal resources should be classified according to their exergy, which is a measure of their ability to do work. In recent years there has been a remarkable growth of interest in environmental issues-sustainability and improved management of development in harmony with the environment. Environmental impact assessment is one of the most widely used tools in environmental management. In this study, the environmental and exergetic aspects of geothermal energy, namely the rapid impact assessment matrix method, and, specific exergy index, were studied first. They were then applied to the Tuzla geothermal field in Canakkale and Balcova geothermal field in Izmir, Turkey, respectively. Finally, the results obtained are given and discussed.
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    A parametric study on the exergoeconomic assessment of a vertical ground-coupled (geothermal) heat pump system
    Ozgener, O; Hepbasli, A; Ozgener, L
    An exergoeconomic model of a vertical ground-source heat pump residential heating system presented in this study uses exergy and cost energy mass (EXCEM) methods. The data obtained from a ground-source heat pump (GSHP) residential heating system installed at the Solar Energy Institute, Ege University, Turkey, are utilized for calculations at different reference temperature values in the range 0-25 degrees C. The performance of the geothermal heat pump residential heating system is evaluated to indicate how exergoecomic parameter values change with system. We also undertake a parametric study to investigate how varying reference temperatures will affect the exergoeconomic analysis of the GSHP system. A correlation between the ratio of thermodynamic loss rate to capital cost and reference state temperature is developed. (c) 2006 Elsevier Ltd. All rights reserved.
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    Parametric study of the effect of reference state on energy and exergy efficiencies of Geothermal District Heating Systems (GDHSs): An application of the Salihli GDHS in Turkey
    Ozgener, L; Hepbasli, A; Dincer, I
    A parametric study of the effect of reference state on the energy and exergy efficiencies of geothermal district heating systems is presented. In this regard, the work consists of two parts: a modeling study covering energy and exergy analysis and a case study covering the actual system data taken from the Salihli Geothermal District Heating System (SGDHS) in Manisa, Turkey. General energy and exergy analysis of the geothermal district heating systems is introduced along with some thermodynamic performance evaluation parameters. This analysis is then applied to the SGDHS using actual thermodynamic data for its performance evaluation in terms of energy and exergy efficiencies. In addition, a parametric study on the effect of varying dead state properties on the energy and exergy efficiencies of the system that has been conducted to find optimum performance and operating conditions is explained. Two parametric expressions of energy and exergy efficiencies were developed as a function of the reference temperature. Both energy and exergy flow diagrams illustrate and compare results under different conditions. It has been observed that the exergy destructions in the system particularly take place as the exergy of the fluid lost in the heat exchanger, the natural direct discharge of the system ( pipeline losses), and the pumps, which account for 31.17%, 8.98%, and 4.27% of the total exergy input to the SGDHS, respectively. For the actual system that is presented, the system energy and exergy efficiencies vary between 0.53 and 0.73 and 0.58 and 0.59, respectively.
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    Exergy analysis of two geothermal district heating systems for building applications
    Ozgener, L; Hepbasli, A; Dincer, I
    This study evaluates the exergetic performance of two local Turkish geothermal district heating systems through exergy analysis. The exergy destructions in these geothermal district heating systems are quantified and illustrated using exergy flow diagrams for a reference temperature of 1 degrees C using the 2003 and 2004 actual seasonal heating data. The results indicate that the exergy destructions in these systems particularly occur due to losses in pump, heat exchangers, pipelines, and the reinjection of thermal water. Exergy efficiencies of the two systems are investigated for the system performance analysis and improvement and are determined to be 42.89% and 59.58%, respectively. (c) 2006 Elsevier Ltd. All rights reserved.
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    Investigation of the energetic and exergetic performance of the Gonen geothermal district heating system
    Ozgener, L; Hepbasli, A; Dincer, I
    This article describes a performance evaluation of the Gonen geothermal district heating system (GGDHS) in Balikesir, Turkey on the basis of energy and exergy analyses. The case study covers the actual system data taken from the GGDHS in Balikesir, Turkey. General energy and exergy analyses of the geothermal district heating systems are introduced. Then, these analyses applied to the GGDHS using actual thermodynamic data for its performance evaluation in terms of energy and exergy efficiencies are presented. In addition, a parametric study on the effect of varying reference state properties on the energy and exergy efficiencies of the system that has been conducted to find the optimum performance and operating conditions is explained. In this article, the authors undertake a parametric study to investigate how varying reference temperature from 0 degrees C to 20 degrees C will affect the energy and exergy efficiencies of the GGDHS and develop two significant correlations (with a correlation coefficient of 0.99), which can be used for predicting the efficiencies. Two parametric expressions for energy and exergy efficiencies were developed as a function of the reference temperature. Both energy and exergy flow diagrams illustrate and compare the results under different conditions. For the actual system that is presented, the system energy and exergy efficiencies vary between 0.41 and 0.60 and 0.60 and 0.70, respectively.
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    A key review on performance improvement aspects of geothermal district heating systems and applications
    Ozgener, L; Hepbasli, A; Dincer, I
    This paper deals with a comprehensive analysis and discussion of geothermal district heating systems and applications. In this regard, case studies are presented to study the thermodynamic aspects in terms of energy and exergy and performance improvement opportunities of three geothermal district heating systems, namely (i) Balcova geothermal district heating system (BGDHS), (ii) Salihli geothermal district heating system (SGDHS), and (iii) Gonen geothermal district heating system (GGDHS) installed in Turkey. Energy and exergy modeling of geothermal district heating systems for system analysis and performance evaluation are given, while their performances are evaluated using energy and exergy analysis method. Energy and exergy specifications are presented in tables. In the analysis, the actual system operational data are utilized. In comparison of the local three district heating systems with each other, it is found that the SGDHS has highest energy efficiency, while the GGDHS has highest exergy efficiency. (c) 2006 Elsevier Ltd. All rights reserved.