Browsing by Author "Hepbasli, A."

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Citation - WoS: 12
Citation - Scopus: 13
A comparative study on estimating the landfill gas potential: Modeling and analysis
(Taylor and Francis Inc. 325 Chestnut St Suite 800 Philadelphia PA 19106, 2016) Ali Kemal Çakir; Huseyin Gunerhan; A. Hepbasli; Hepbasli, A.; Gunerhan, H.; Cakir, A. K.
The main objective of this study is to investigate the use of the landfill gas as potential energy and electricity obtained from the municipal solid waste (domestic industrial medical waste and sewage sludge) stored regularly in the Harmandali solid waste landfill area within the boundaries of the contiguous area of Izmir. The most important factor in making a decision about energy potential in the landfill is the amount of methane in the landfill gas. There are several approaches that have been used to determine the amount of the landfill gas. In this study three different methods and one approach in the literature were used for this purpose. The methods used are the Multi-Phase the LandGEM and the IPCC 2006. The results of the landfill gas obtained using the three methods namely the Multi-Phase the LandGEM (k = 0.35 k = 0.1 and k = 0.05) and the IPCC 2006 were as follows respectively: 291897215 792073359 769734749 681685027 and 491752247 m3. It may be concluded that the Harmandali Landfill has high landfill gas potential based on the measurements and mathematical methods used in the Harmandali landfill. © 2017 Elsevier B.V. All rights reserved.
Citation - WoS: 28
Citation - Scopus: 29
A sub-system design comparison of renewable energy based multi-generation systems: A key review along with illustrative energetic and exergetic analyses of a geothermal energy based system
(ELSEVIER, 2022) A. Bozgeyik; L. Altay; A. Hepbasli; Hepbasli, A.; Bozgeyik, A.; Altay, L.
In recent years it has gained a significance importance to decrease ecological footprint so to have a positive contribution to environmental quality. Renewable energy plays a significant role in future trends for efficiency and environmental issues. Efficiency of systems is to be increased to meet future demands in terms of sustainability with increased consumption. There is a need for new and innovative research studies on promising technologies processes and strategies to have sustainable water and energy management in cities. This review paper investigates the use of energy sources in single or multiple forms with different system designs from simple to complex structures. The examined studies were presented in a tabulated form including energy and exergy efficiency values as well as the methods and tools used. The results indicated that the systems with the highest energy and exergy efficiency values had several useful outputs such as hydrogen fresh water drying heating and cooling etc. The maximum exergetic efficiency was determined to be 94% for a multiple energy sourced multi-generation system while the maximum energetic efficiency was calculated to be 111.3% for a solar assisted and heat pump integrated multi-generation system amongst the reviewed studies. To illustrate the obtained results from review a geothermal energy based multi-generation system was considered. Some parametric studies were also undertaken to see the effects of geothermal water temperature and flow rates on efficiency values. For a single production case they were determined to be 13.7% and 50% respectively while they were obtained to be 98.6% and 67.7% for a multi-generation system in which electricity low grade hot water production high temperature hot water production and hydrogen were useful outputs. However it should be noted that there was a threshold about the number of products to have an optimum increase in the efficiency values.
Citation - WoS: 173
Citation - Scopus: 206
An experimental investigation of heat transfer enhancement of a minichannel heat sink using Al2O3-H2O nanofluid
(Elsevier Ltd, 2014) M. R. Sohel; S. S. Khaleduzzaman; Rahman Saidur; A. Hepbasli; Mohd Faizul Mohd Sabri; Islam Mohammed Mahbubul; Sabri, M.F.M.; Sohel, M.R.; Khaleduzzaman, S.S.; Mahbubul, I.M.; Hepbasli, A.; Saidur, R.
The thermal performances of a minichannel heat sink are experimentally investigated for cooling of electronics using nanofluid coolant instead of pure water. The Al2O3-H2O nanofluid including the volume fraction ranging from 0.10 to 0.25 vol.% was used as a coolant. The effects of different flow rates of the coolant on the overall thermal performances are also investigated. The flow rate was ranged from 0.50 to 1.25 L/min as well as the Reynolds number from 395 to 989. The coolant was passed through a custom made copper minichannel heat sink consisting of the channel height of 0.8 mm and the channel width of 0.5 mm. The experimental results showed the higher improvement of the thermal performances using nanofluid instead of pure distilled water. The heat transfer coefficient was found to be enhanced up to 18% successfully. The nanofluid significantly lowered the heat sink base temperature (about 2.7 °C) while it also showed 15.72% less thermal resistance at 0.25 vol.% and higher Reynolds number compared to the distilled water. © 2014 Elsevier Ltd. All rights reserved. © 2014 Elsevier B.V. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 4
An experimental study of solar thermal system with storage for domestic applications
(Universiti Malaysia Pahang editor.ijame@gmail.com, 2018) Muhammad Abid; Bashria A.A. Yousef; Mamdouh El Haj Assad; A. Hepbasli; Khalid Saeed; Abid, M.; Yousef, B.A.A.; Saeed, K.; Hepbasli, A.; Assad, M.E.
Building sector consumes a greater portion of energy for heating and cooling applications. The utilization of fossil fuels for space and water heating in buildings cause a negative effect on the environment by producing larger CO2. In this study solar thermal water heating system for building application have been analyzed from the first and second law perspectives of thermodynamics considering various scenarios and water consumption pattern. The solar flat collector is very commonly used to extract energy from sunlight. Therefor energy and exergy efficiency curves for the solar flat collector were presented. The energetic and exergetic values for the system were calculated based on the experimental values for the overall system the heat exchanger and the pumps using the approach of exergetic product/fuel basis. The greatest and lowest relative irreversibility’s occurred at the solar collector and the heat exchanger with values of 85.73% and 2.45% respectively and the system overall exergy efficiency was determined to be 20.28%. The energy and exergy efficiencies of the solar collector were analyzed at three different cases depending on the mass flow rates in the solar collector and the secondary circuit of the system. Three different mass flow rates were applied to the inlet of the secondary circuit to observe the efficiency effect on the solar collector circuit. This study can assist in selecting a proper solar collector and storage size for buildings of various capacity and possible improvement in the design of the system components. © 2019 Elsevier B.V. All rights reserved.
Citation - WoS: 18
Citation - Scopus: 22
An Experimental Study on the Performance and Emission Assessment of a Hydrogen/Diesel Fueled Engine
(TAYLOR & FRANCIS INC, 2015) M. H. Morsy; A. M. El-Leathy; A. Hepbasli; Hepbasli, A.; El-Leathy, A.M.; Morsy, M.H.
This study investigates the engine performance and exhaust emission of the dual-fuel operation on a single cylinder compression ignition engine from the energetic exergetic and sustainability points of view using experimental values. Hydrogen with different concentrations is used as fuel with diesel as the main fuel. Comparative results of the dual-fuel operation with conventional diesel fuel through experimental results demonstrated its benefits for the engine performance. The engine specific fuel consumption shows improvement and dual-fuel operation is able to achieve a better performance under most operating conditions. The emission levels of oxides of nitrogen (NOx) show a slight increase using dual fuel due to the increase in the temperature. For the speeds of 1000 and 1400 rpm with a power range from 0.74 to 3.1 kW under variable composition hydrogen/diesel mixtures the minimum and maximum values for energy (thermal) are found to be 8.0 and 20.1% while those for the corresponding exergy are calculated to be 7.6 and 18.8% respectively.
Citation - WoS: 135
Citation - Scopus: 155
Analyses of entropy generation and pressure drop for a conventional flat plate solar collector using different types of metal oxide nanofluids
(ELSEVIER SCIENCE SA, 2013) M. A. Alim; Z. Abdin; R. Saidur; A. Hepbasli; M. A. Khairul; N. A. Rahim; Abdin, Z.; Alim, M. A.; Khairul, M. A.; Hepbasli, A.; Saidur, R.; Rahim, N. A.
This paper theoretically analyzes entropy generation heat transfer enhancement capabilities and pressure drop of an absorbing medium with suspended nanoparticles (Al2O3 CuO SiO2 TiO2 dispersed in water) inside a flat plate solar collector. Steady laminar axial flow of a nanofluid is considered. These nanofluids considered have different nanoparticles volume fractions and volume flow rates in the range of 1-4% and 1-4 L/min respectively. Based on the analytical results the CuO nanofluid could reduce the entropy generation by 4.34% and enhance the heat transfer coefficient by 22.15% theoretically compared to water as an absorbing fluid. It also has a small penalty in the pumping power by 1.58%. (C) 2013 Elsevier B.V. All rights reserved.
Citation - WoS: 22
Citation - Scopus: 22
Dynamic Exergetic Analysis and Evaluation of Photovoltaic Modules
(TAYLOR & FRANCIS INC, 2015) M. Abid; A. Hepbasli; Abid, M.; Hepbasli, A.
Due to the growing demand for renewable energy sources photovoltaic solar has been one of the most promising renewable energy sources in the world. In this article the performance of photovoltaic modules through energy and exergy efficiencies sustainability index improvement potential factors and in terms of their exergy costs is investigated. The thermodynamic variables such as environmental temperature module temperature wind velocity density and humidity of air were considered in the analysis. The investigation helped identify the irreversibilities due to various exergy losses and exergy destructions present in the system for its possible improvements. A case study is presented to show the importance of the efficiency modeling and compare them using the actual operational data of Riyadh Saudi Arabia. It is determined that the energy efficiency varied between 34.09 and 52.14% while the exergy efficiency ranged from 0.16 to 15.23% respectively. The exergy efficiency for the PV/T analysis changed between 1.36 and 19.86% with an average value of 9.65%. The sustainability index was between 1 and 1.17 for the system. The improvement potential factor had minimum and maximum values of 3376 and 24559.42 W respectively while the exergy rate of solar radiation was in the range of 3850.9 and 25115.95 W on the test date. There was obviously a large scope for improvement in the existing system as a very small amount of exergy from solar radiation was utilized.
Dynamic modeling of a refrigeration system with an internal heat exchanger and dual evaporators through exergoeconomic analysis
(Engg Journals Publications, 2016) Muhammad Abid; A. Hepbasli; Khalid Saeed; Abid, M.; Hepbasli, A.; Saeed, Khalid
In this study exergy and exergoeconomic analyses of a refrigeration system with two evaporators and an internal heat exchanger were performed. The analysis of the whole system included various thermodynamics parameters such as sustainability index exergetic improvement potential ratio of the thermodynamic losses(energetic and exergetic losses) to the capital cost relative irreversibility for each component of the system. Furthermore the efficiencies for each component were analyzed using two different approaches one was the net rational efficiency basis and another one was the product/fuel basis. The whole system efficiency on the net rational basis was determined to be 7.24% and on the product/fuel basis it was obtained to be 43.92%. The system has a huge capacity for improvement. The greatest Irreversibility occurs in the compressor with a value of 0.29 kW and the efficiency values for the compressor using both the approaches were found to be 16.9% and 21.57% respectively. © 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 104
Citation - Scopus: 110
Energetic and exergetic comparison of basic and ejector expander refrigeration systems operating under the same external conditions and cooling capacities
(PERGAMON-ELSEVIER SCIENCE LTD, 2015) N. Bilir Sag; H. K. Ersoy; A. Hepbasli; H. S. Halkaci; Halkaci, H. S.; Bilir Sag, N.; Hepbasli, A.; Sag, N. Bilir; Ersoy, H. K.
An experimental study was conducted on vapor compression refrigerators using R134a refrigerant for the purpose of achieving energy recovery and decreasing the effects of irreversibility. An ejector was used as an expander instead of an expansion valve. The coefficient of performance of the ejector refrigeration system and the amount of irreversibility and efficiency of each of its components were determined and compared with those of a basic vapor compression refrigeration system of the same cooling capacity under the same external conditions. It was found that the ejector expander system exhibited a lower total irreversibility in comparison with the basic system. When the ejector was used as the expander in the refrigeration system the coefficient of performance was higher than in the basic system by 7.34-12.87% while the exergy efficiency values were 6.6-11.24% higher than in the basic system. (C) 2014 Elsevier Ltd. All rights reserved.
Citation - WoS: 127
Citation - Scopus: 145
Energy and exergy efficiency of a flat plate solar collector using pH treated Al2O3 nanofluid
(ELSEVIER SCI LTD, 2016) Z. Said; R. Saidur; M. A. Sabiha; A. Hepbasli; N. A. Rahim; Said, Z.; Sabiha, M. A.; Saidur, R.; Hepbasli, A.; Rahim, N. A.
Application of nanofluid to increase the thermal efficiency of a traditional solar collector is getting tremendous attention among the scientific community. Al2O3-water nanofluid as a working fluid and its effect on the energy and exergy efficiencies of a flat plate solar collector was examined experimentally. Volume fraction used for this study was 0.1% and 0.3% while the size of the nanoparticles was similar to 13 nm. Experiments were carried out using a stable nanofluid which was obtained by controlling the pH of the solution over a period of 30 days. The mass flow rates of the nanofluid varied from 0.5 to 1.5 kg/min. Energy and exergy efficiencies of a flat plate solar collector using water and nanofluids as working fluids were matched. The results revealed that nanofluids increased the energy efficiency by 83.5% for 0.3% v/v and 1.5 kg/min whereas the exergy efficiency was enhanced by up to 20.3% for 0.1% v/v and 1 kg/min. Thermal efficiency of the system was found to be more than 50% compared to the existing system available in the literature. New findings on the stability and exergy analysis of the solar collector system operated with a pH controlled nanofluid are reported. (C) 2015 Elsevier Ltd. All rights reserved.
Citation - WoS: 106
Citation - Scopus: 122
Energy- economic- and environmental analysis of a flat-plate solar collector operated with SiO2 nanofluid
(SPRINGER, 2015) M. Faizal; R. Saidur; S. Mekhilef; Arif Hepbasli; I. M. Mahbubul; Mekhilef, S.; Mahbubul, I. M.; Saidur, R.; Hepbasli, A.; Faizal, M.
To overcome the environmental impact and declining source of fossil fuels renewable energy sources need to meet the increasing demand of energy. Solar thermal energy is clean and infinite suitable to be a good replacement for fossil fuel. However the current solar technology is still expensive and low in efficiency. One of the effective ways of increasing the efficiency of solar collector is to utilize high thermal conductivity fluid known as nanofluid. This research analyzes the impact on the performance fluid flow heat transfer economic and environment of a flat-plate solar thermal collector by using silicon dioxide nanofluid as absorbing medium. The analysis is based on different volume flow rates and varying nanoparticles volume fractions. The study has indicated that nanofluids containing small amount of nanoparticles have higher heat transfer coefficient and also higher energy and exergy efficiency than base fluids. The measured viscosity of nanofluids is higher than water but it gives negligible effect on pressure drop and pumping power. Using SiO2 nanofluid in solar collector could also save 280 MJ more embodied energy offsetting 170 kg less CO2 emissions and having a faster payback period of 0.12 years compared to conventional water-based solar collectors.
Citation - WoS: 18
Citation - Scopus: 20
Estimating and comparing the exergetic solar radiation values of various climate regions for solar energy utilization
(Taylor & Francis Inc, 2014) A. Hepbasli; Zeyad A. Al-Suhaibani; Hepbasli, A.; Alsuhaibani, Z.
Energy resources and their utilization intimately relate to sustainable development. In attaining sustainable development increasing the energy efficiencies of processes utilizing sustainable energy resources plays an important role. The utilization of renewable energy offers a wide range of exceptional benefits. There is also a link between exergy and sustainable development. Exergy analysis has been widely used in the design simulation and performance evaluation of various energy systems as well as renewable energy sources. In this regard determination of exergy of solar radiation is very crucial for various solar energy-related applications and is based on the relative potential of the maximum energy available from radiation. The efficiency factor limiting the gain of the maximum useful energy from the solar radiation is significantly similar to that of the Carnot efficiency for the heat engines. The main objectives of this study are two-fold namely (i) to comprehensively review various solar exergy models used in solar energy-related applications and (ii) to determine the solar exergetic values for some regions of Saudi Arabia and Turkey which are taken as two illustrative examples to which various models have been applied and compared. In this regard the ratios of solar radiation exergy to solar radiation energy (exergy-to-energy ratio) for northeastern Saudi Arabia are calculated to be on average 0.933 for both approaches of Petela and Spanner and 0.950 for Jefer's approach at outside air temperatures between 16.18 and 33.01°C. These ratios for Izmir Turkey are obtained to be on average 0.935 and 0.951 for the same approaches at a temperature range of 15-22°C respectively. The values found using Jefer's approach appear to be 2% larger than the approaches of Petela and Spanner while those are very close to the value of 0.95 proposed by Nobusawa. © Taylor & Francis. © 2014 Elsevier B.V. All rights reserved.
Citation - Scopus: 1
Exergetic performance analysis and comparison of various building heating options
(IEEE Computer Society help@computer.org, 2014) H. Tuzcu; Huseyin Gunerhan; A. Hepbasli; Hepbasli, A.; Gunerhan, H.; Tuzcu, H.
Heating cooling and lighting appliances in buildings account for more than one third of the world's primary energy demand. Therefore they are considered one of the main parts of the energy consumption in buildings. This study deals with energy/exergy and sustainability performance comparison of a building heating energy system from the primary energy production to the building envelope. A four story building located in Eskisehir Turkey is considered for the analysis. The indoor and outdoor air temperatures of the building are 22°C and -12°C respectively. For heating applications three options are studied namely (i) standard boiler (ii) condensing boiler and (iii) ground heat pump water-water as driven by renewable and nonrenewable energy sources. Energy and exergy analysis methods which are based on the lowex approach are performed to evaluate their performances and compare them through energy and exergy efficiencies and sustainability index. Energy and exergy flows are also studied and illustrated accordingly to have an insight into for possible improvements in the system components. Also the energetic and exergetic renewability ratios are employed here along with sustainability index. For a building with a net area of 2430.4 m2 the total exergy efficiencies of the considered heating systems are 25.3% 6.1% and 6.9% respectively for three cases. The sustainability index for three cases found as 1.196 1.236 and 1.274 respectively. © 2014 Asian Institute of Technology. © 2014 Elsevier B.V. All rights reserved.
Citation - WoS: 28
Citation - Scopus: 33
Experimental investigation of the relation between yield stress and ultrasonication period of nanofluid
(Elsevier Ltd, 2016) Islam Mohammed Mahbubul; Rahman Saidur; A. Hepbasli; Muhammad Afifi Amalina; Amalina, M. A.; Mahbubul, I. M.; Saidur, R.; Hepbasli, A.
Nanofluids are the mixtures of solid nanoparticles in liquid. Like most other fluids nanofluids could behave as yield stress fluids which require a certain amount of stress to flow. This flow characteristic may depend on the preparation of nanofluids. This paper investigates the effect of the ultrasonication periods (used during the nanofluid preparation) on the yield stress. The Al2O3 nanoparticle with 0.5 vol.% of solid concentration was added to the distilled water using an ultrasonic horn and applied for different durations from 0 to 5 h. The microstructures of the nanoparticles were observed by transmission electron microscopy. The flow characteristics as the shear stresses at different shear rates (12.23-305.75 s-1) were observed for various temperatures from 10 to 50 °C. The yield stress the flow behavior index and the consistency index were studied using the Herschel-Bulkley rheological model. From this study non-Newtonian flow characteristic was observed. The yield stress decreased with increasing the fluid temperature. At the start of the ultrasonication the yield stress decreased rapidly, however for further ultrasonication it decreased slowly. © 2015 Elsevier B.V. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 8
Future Aspects of Geothermal Energy in Saudi Arabia
(TAYLOR & FRANCIS INC, 2013) Z. Alsuhaibani; A. Hepbasli; Hepbasli, A.; Alsuhaibani, Z.
Geothermal energy seems to be a clean proven and reliable resource for supplying the needs of a sustainable society and helping to improve the global environment. Although the studies on geothermal resources exploration in Saudi Arabia were started in 1980 since then any serious geothermal projects have not been undertaken excepting to the availability of some potentially resources-rich geothermal locations. The first in situ determination of the thermal properties of the underground soil required for the design of borehole heat exchangers was reported in 2009 for the first time. In this study future aspects of geothermal energy were treated first. The exergetic aspects of some geothermal resources available were then explained using a specific exergy index. Finally the results obtained were given and discussed. It is expected that some barriers hindering the utilization of geothermal resources in Saudi Arabia will be overcome and geothermal energy utilization will become a viable option in the near future.
Citation - WoS: 20
Citation - Scopus: 24
Heat transfer and pressure drop characteristics of a plate heat exchanger using water based Al2O3 nanofluid for 30° and 60° chevron angles
(Springer Verlag service@springer.de, 2018) M. M. Elias; Rahman Saidur; Rached Ben Mansour; A. Hepbasli; Nasrudin Abd Rahim; Jesbains Kaur; Ben-Mansour, R.; Hepbasli, A.; Saidur, R.; Jesbains, K.; Elias, M. M.; Rahim, N. A.
Nanofluid is a new class of engineering fluid that has good heat transfer characteristics which is essential to increase the heat transfer performance in various engineering applications such as heat exchangers and cooling of electronics. In this study experiments were conducted to compare the heat transfer performance and pressure drop characteristics in a plate heat exchanger (PHE) for 30° and 60° chevron angles using water based Al2O3 nanofluid at the concentrations from 0 to 0.5 vol.% for different Reynolds numbers. The thermo-physical properties has been determined and presented in this paper. At 0.5 vol% concentration the maximum heat transfer coefficient the overall heat transfer coefficient and the heat transfer rate for 60° chevron angle have attained a higher percentage of 15.14% 7.8% and 15.4% respectively in comparison with the base fluid. Consequently when the volume concentration or Reynolds number increases the heat transfer coefficient and the overall heat transfer coefficient as well as the heat transfer rate of the PHE (Plate Heat Exchangers) increases respectively. Similarly the pressure drop increases with the volume concentration. 60° chevron angle showed better performance in comparison with 30° chevron angle. © 2018 Elsevier B.V. All rights reserved.
Citation - WoS: 149
Citation - Scopus: 168
Heat transfer performance and exergy analyses of a corrugated plate heat exchanger using metal oxide nanofluids
(Elsevier Ltd, 2014) M. A. Khairul; Mohammad A. Alim; Islam Mohammed Mahbubul; Rahman Saidur; A. Hepbasli; Altab Hossain; Khairul, M.A.; Alim, M.A.; Mahbubul, I.M.; Hossain, A.; Hepbasli, A.; Saidur, R.
Heat exchangers have been widely used for efficient heat transfer from one medium to another. Nanofluids are potential coolants which can afford excellent thermal performance in heat exchangers. This study examined the effects of water and CuO/water nanofluids (as coolants) on heat transfer coefficient heat transfer rate frictional loss pressure drop pumping power and exergy destruction in the corrugated plate heat exchanger. The heat transfer coefficient of CuO/water nanofluids increased about 18.50 to 27.20%with the enhancement of nanoparticles volume concentration from 0.50 to 1.50% compared to water. Moreover improvement in heat transfer rate was observed for nanofluids. On the other hand exergy loss was reduced by 24% employing nanofluids as a heat transfermediumwith comparing to conventional fluid. Besides 34% higher exergetic heat transfer effectiveness was found for 1.5 vol.% of nanoparticles. It has a small penalty in the pumping power. Hence the plate heat exchanger performance can be improved by adapting the working fluid with CuO/water nanofluids. © 2013 Elsevier Ltd. © 2017 Elsevier B.V. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 1
Integrated energy advanced exergy environmental and enviroeconomic assessment of azeotropic and zeotropic refrigerants in vapor compression refrigeration systems
(Springer Science and Business Media B.V., 2025) Alaattin Metin Kaya; Abid Ustaoglu; Hakan Caliskan; A. Hepbasli; Hepbasli, A.; Kaya, A. M.; Ustaoglu, A.; Caliskan, H.
This study presents a comprehensive and original evaluation of CFC HCFC HFC and HFO-type refrigerants using energy exergy advanced exergy environmental enviroeconomic and total equivalent warming impact (TEWI) analyses within a single integrated framework. While previous studies have typically focused on limited refrigerant categories or used only one type of evaluation method this research combines advanced exergy analysis with TEWI and enviroeconomic assessments to examine performance environmental impact and economic cost together. This combination allows the study to identify where system improvements are possible to measure total environmental impact over the system’s lifetime and to estimate the related environmental costs in one consistent approach. The refrigerants were selected based on their historical significance current applications and future potential ensuring a broad and relevant analysis. R-12 is included as a benchmark to highlight the efficiency and environmental trade-offs associated with older refrigerants. R-410A and R-32 widely used in modern air-conditioning systems are analyzed to assess their performance and sustainability. Additionally R-513A an HFO-based alternative with lower global warming impact is evaluated for its potential to replace high-GWP refrigerants while maintaining efficiency. The results reveal that R-12 achieves the highest coefficient of performance (COP) at 3.525 and the lowest exergy destruction rate (1.505 kW) with only a slight margin from other refrigerants. R-410A exhibits the highest exergy destruction rate (1.781 kW) more than half of which is avoidable (55.05%). Enviroeconomic analysis identifies R-513A (66.47 € kg−1) as the most cost-effective option closely followed by R-32 (78.53 € kg−1). TEWI analysis highlights R-32 (70152 kgCO2-eq) as the refrigerant with the lowest environmental impact slightly outperforming R-513A (72280 kgCO2-eq). However the system operating with R-513A requires 50% more refrigerant charge than R-32. This integrated approach provides a clearer and more complete basis for selecting sustainable refrigerants by linking performance results with environmental and economic considerations. © 2025 Elsevier B.V. All rights reserved.
Citation - WoS: 10
Citation - Scopus: 12
Investigation of environmental and exergetic performance for coal-preparation units in cement production processes
(Elsevier Ltd, 2012) M. Ziya Sogut; Zuhal Oktay; Hikmet Tahir Karakoc; A. Hepbasli; Sogut, Z.; Oktay, Z.; Hepbasli, A.; Karakoc, H.
The main objectives of the present study are to perform energy and exergy analyses of a coal-preparation unit in a cement plant and investigate the effect of varying dead state (ambient) temperatures on exergy efficiency. This is the first study conducted on a coal-preparation unit located in a cement plant with respect to the perspective of exergy. The consumption of exergy the potential improvement of the unit and the effects of CO2 emission by the unit are also examined in terms of the chosen type of fuel. Based on the results of the analyses the mean values of energy and exergy efficiencies of the unit are found to be 74.03% and 21.36% respectively while the average potential improvement of the unit is calculated as 78.24%. The analyses demonstrate that the exergy destruction ratio affects the CO2 emission rate of the unit. Consequently the present technique is proposed as a useful tool for purposes of developing energy policies and providing energy conservation measures especially concerning similar types of industrial processes. © 2012 Elsevier Ltd. © 2017 Elsevier B.V. All rights reserved.
Citation - WoS: 69
Citation - Scopus: 86
New thermophysical properties of water based TiO2 nanofluid-The hysteresis phenomenon revisited
(PERGAMON-ELSEVIER SCIENCE LTD, 2014) Z. Said; R. Saidur; A. Hepbasli; N. A. Rahim; Said, Z.; Saidur, R.; Hepbasli, A.; Rahim, N.A.
Homogeneous stable suspensions acquired by dispersing dry Al2O3 and TiO2 nanoparticles in controlled pH solution and distilled water respectively were prepared and investigated in this study. First of all the mean nanoparticle diameters were studied by dynamic light scattering (DLS) technique and the nanofluid stability was analyzed by zeta potential measurements. The nano-crystalline structures were characterized by scanning electron microscope and transmission electron microscope. The rheological behavior was determined for both nanofluids at nanoparticle volume concentrations up to 0.3%. The effect of temperature for the heating and cooling phases was analyzed from 25 degrees C to 80 degrees C. Furthermore the influence of temperature pressure drop pumping power zeta potential size and densities were analyzed for fresh prepared samples as well as for samples used in a flat plate solar collector over a period of 30 days. The thermal conductivity enhancement of the two nanofluids demonstrated a nonlinear relationship with respect to temperature and volume fraction with increases in the volume fraction and temperature. All resulted in an increase in the measured enhancement. Existence of a critical temperature was observed beyond which the particle suspension properties altered drastically which in turn triggered a hysteresis phenomenon. The hysteresis phenomenon on viscosity measurement which is believed to be the first observed for Al2O3/water and TiO2/water-based nanofluids has raised serious concerns about the use of nanofluids for heat transfer enhancement. The pressure drop and pumping power of the nanofluid flows are found to be very close to those of the base liquid for low volume concentration. It may be concluded that nanofluids can be utilized as a working medium with a negligible effect of enhanced viscosity and/or density. Our findings provide a view on the thermo physical properties of nanofluids that is compared with that in the literature and new findings (such as viscosity hysteresis phenomenon and pumping power) have been presented which are not available in literature as yet. (C) 2014 Elsevier Ltd. All rights reserved.