Browsing by Author "Altay, Lutfiye"

Now showing 1 - 13 of 13

Citation - WoS: 38
Citation - Scopus: 52
A parametric study of a renewable energy based multigeneration system using PEM for hydrogen production with and without once-through MSF desalination
(PERGAMON-ELSEVIER SCIENCE LTD, 2022) Ahmet Bozgeyik; Lutfiye Altay; Arif Hepbasli; Hepbasli, Arif; Bozgeyik, Ahmet; Altay, Lutfiye
The importance of renewable energy compared to fossil fuels is increasing due to growing energy demand and environmental challenges. Multi-generation systems use one or more energy sources and produce several useful outputs. The present study aims at investigating and comparing solar energy based multi-generation systems with and without once -through MSF desalination unit from the thermodynamic point of view. Firstly hydrogen electricity and hot water for space heating and domestic usage are produced using the system which consists of a parabolic trough collector an organic Rankine cycle (ORC) and a PEM electrolyzer and heat exchanger as sub-systems. The performance of the entire system is evaluated from the energetic and exergetic points of view. Various parameters affecting hydrogen production rate and efficiency values are also investigated with the thermodynamic model implemented in the Engineering Equation Solver (EES) package. The system can produce hydrogen at a mass flow rate of 20.39 kg/day. The results of the study show that the energy and exergy efficiency values of the ORC are calculated to be 16.80% and 40% while those for the overall system are determined to be 78% and 25.50% respectively. Secondly once-through MSF desalination unit is integrated to the system between ORC evaporator and heat exchanger producing domestic hot water in the solar cycle in order not to affect hydrogen production rate while thermodynamic values are compared. Fresh water production capacity of the system is calculated to be at a volumetric flow rate of 5.74 m(3)/day with 10 stages. (C) 2022 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.
Citation - WoS: 12
Citation - Scopus: 12
A parametric study on energy exergy and exergoeconomic assessments of a modified auto-cascade refrigeration cycle supported by a dual evaporator refrigerator
(Elsevier Ltd, 2024) Ibrahim Karacayli; Lutfiye Altay; A. Hepbasli; Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
This paper presents an evaluation of the energetic exergetic and exergoeconomic performances of a modified auto-cascade refrigeration (MACR) cycle integrated with a dual evaporator refrigerator (DER) to determine optimum operating conditions. DER facilitates a reduction in the compression ratio allowing the low-boiling-point component to release more heat before entering the evaporator. In this study the R170/R290 refrigerant mixture which has a low global warming potential but an explosion risk was used. The main purpose of this study is to eliminate the risk of explosion by reducing the compressor discharge temperature and at the same time to enhance the overall cycle performance. To achieve this DER is used instead of air-cooled coils which have limited cooling performance. Despite an ambient temperature of 35°C the MACR cycle achieved a remarkable 51.29 % reduction in compressor discharge temperature when the separator inlet temperature was reduced to 10°C by the DER. It also results in a 72.73% reduction in compression work rate and a significant 137.02% increase in cooling effect compared to the conventional auto-cascade refrigeration cycle. Furthermore the MACR cycle exhibits notable improvements in total exergy destruction rate and exergy destruction cost rate with a 75.23% and a 76.07% reduction respectively. Simultaneously the exergy efficiency and the exergoeconomic factor increased by 266.67% and 179.15% respectively. The MACR cycle achieves optimum energy and exergy performance with a 60% R170 mass fraction and 0.50 vapor quality resulting in 1.429kW compression work rate a COP of 0.70 and an exergy efficiency of 26.66 %. The optimum exergoeconomic performance is achieved with a 40% R170 mass fraction and 0.50 vapor quality. © 2024 Elsevier B.V. All rights reserved.
An exergetic performance improvement potential of a modified ejector-enhanced auto-cascade refrigeration cycle
(INDERSCIENCE ENTERPRISES LTD, 2025) Ibrahim Karacayli; Lutfiye Altay; Arif Hepbasli; Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
This study examines both conventional and advanced exergy analyses of a modified ejector-enhanced auto-cascade refrigeration (MEACR) cycle. Conventional exergy analysis shows that the proposed model significantly improves exergy efficiency compared to similar ejector-enhanced auto-cascade refrigeration cycles in the literature. Advanced exergy analysis reveals that 63.47% of the total exergy destruction is avoidable. When the components of the MEACR cycle are investigated 56.31% of the exergy destruction is attributed to the endogenous part. The low-temperature cycle (LTC) compressor has the highest avoidable endogenous exergy destruction rate of 12.64 kW with 38.5%.
Citation - WoS: 7
Citation - Scopus: 8
Auto-cascade refrigeration systems: A key review with energetic and exergetic perspectives
(Elsevier Ltd, 2025) Ibrahim Karacayli; Lutfiye Altay; A. Hepbasli; Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
Auto-cascade refrigeration (ACR) systems are known for their innovative solutions especially suitable for low and ultra-low temperature applications. However ACR cycles are not solely confined to refrigeration applications, they are also utilized in heating and electricity generation cycles. While the fact that this subject has been addressed in only two studies in the literature reveals the gap in this regard this study offers an important contribution by comprehensively reviewing ACR systems in terms of energy exergy exergoeconomics and exergoenvironmental aspects for the first time to the best of the authors’ knowledge. This review also differs from others in that it categorizes ACR cycles in their most general form and outlines basic operating principles not covered in previous reviews such as not only refrigeration but also heating and electricity generation. Modifications aimed at improving ACR cycle performance are then summarized covering both experimental and theoretical studies available in the literature. This review paper also addresses the selection of refrigerants. Another unique aspect of this study is its examination of the refrigerant mixtures used in ACR cycles based on the type of application and the improvements they involve. Finally to illustrate the obtained results from review the study concludes with an illustrative example where an ACR cycle is modelled for performance evaluation in terms of energetic and exergetic aspects. This work is expected to be highly beneficial for individuals interested in the design simulation analysis and performance assessment of ACR cycles. © 2024 Elsevier B.V. All rights reserved.
Citation - WoS: 3
Citation - Scopus: 3
Comparative analysis of a modified cascade refrigeration cycle including an auto-cascade refrigeration cycle using different zeotropic refrigerant mixtures for reducing the environmental impact
(ELSEVIER, 2025) Ibrahim Karacayli; Lutfiye Altay; Arif Hepbasli; Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
The two primary challenges in auto-cascade refrigeration (ACR) cycles are high compressor discharge temperatures and low efficiency at ultra-low temperatures. This study proposes a modified cascade refrigeration cycle (MCR) combined with an ACR cycle for cooling to -60 degrees C. The innovative aspect of this work is to improve the ACR performance with simpler designs without increasing the system complexity contrary to the common trend. For the high-temperature cycle (HTC) a dual evaporator refrigeration cycle with R1234yf is used while an ACR cycle is used for the low-temperature cycle (LTC). Environmentally friendly refrigerant mixtures such as R170/ R290 R170/R600a and R170/R600 were analyzed using energy exergy and exergoeconomic methods. The results show that compared to R23/R134a the R170/R600 significantly improves the performance of the MCR by increasing the COP and exergy efficiency by 24.0 % and reducing the exergy destruction by 26 % unit cooling cost by 11.2 % and total investment cost by 9.7 %. Moreover when compared with theoretical studies COP improvements range from 38.7 % to 94.1 % demonstrating the importance and superiority of the system proposed in this study.
Değişen Su Debisi ve Yoğuşma Basıncı İçin Bir Su Soğutmalı Yoğuşturucunun Isı Transferi Katsayısının Deneysel ve Analitik İncelenmesi
(2018) Lutfiye Altay; Arif HEPBAŞLI; IBRAHIM KARACAYLI; ERDOGAN SIMSEK; Sımsek, Erdogan; Altay, Lutfiye; Hepbaşlı, Arif; Karacaylı, Ibrahım
Faz değişiminde gizli ısı transfer edilir ve transfer edilen ısı miktarı duyulur ısı transferi miktarına kıyasla aşırı yüksek olur. Bu nedenle transfer edilen ısı miktarını artırmak için yoğunlaşma ve buharlaşma işlemleri soğutma çevrimindeki ana basamaklardır. Bu çalışmanın temel amacı toplam ısı transferi katsayısını deneysel ve analitik olarak incelemek ve su debisi ile soğutucu akışkan basıncının yoğuşma hal değişimi üzerindeki etkisini ortaya koymaktır. Bu amaçla ısı transferi yüzey alanı 0.075 m2 olan su soğutmalı yoğuşturuculu bir soğutma sistemi kurulmuştur. Soğutucu akışkan olarak R134a kullanılmış ve soğutucu akışkan suyun içinde dolaştığı borunun dış yüzeyinde yoğuşmaktadır. Bu çalışmada sabit 7 0 bar yoğuşma basıncında 15 20 25 30 ve 35 g/s su debileri için deneyler tekrarlanmıştır. Daha sonra 25 g/s su debisinde yoğuşma basınçları 6 5 6 75 7 0 7 25 ve 7 5 bar olacak şekilde değiştirilmiştir. Yoğuşma ısı transfer katsayısı bağıntısı yoğuşturucu ünitesinin soğutucu tarafına uygulanmıştır. Öte yandan ısı transfer katsayısını hesaplamak için logaritmik ortalama sıcaklık farkı (LMTD) ve geçiş birimi sayısı (ε-NTU) metotları deneysel sonuçlara uygulanmıştır. Sabit yoğuşma basıncında farklı su debileri ve sabit su debisinde farlı yoğuşma basınçları için soğutma makinası ünitesinden elde edilen deneysel sonuçlar yoğuşma ısı transferi katsayısı bağıntısından elde edilen sonuçlarla kıyaslanmıştır.
Energetic and Exergetic Performance Evaluation of Modified Two-Phase Ejector-Enhanced Cascade Refrigeration Cycles
(Springer Science and Business Media Deutschland GmbH, 2026) Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
Citation - WoS: 64
Citation - Scopus: 68
Energetic- exergetic- exergoeconomic- environmental and sustainability analyses of a solar- geothermal and biomass based novel multi-generation system for production of power- hydrogen- heating- cooling and fresh water
(ELSEVIER, 2023) Ahmet Bozgeyik; Lutfiye Altay; Arif Hepbasli; Hepbasli, Arif; Bozgeyik, Ahmet; Altay, Lutfiye
The present study proposes and investigates a novel solar geothermal and biomass based multi-generation system producing multiple outputs to generate power hydrogen heating cooling and fresh water. Parabolic trough solar collectors a two stages Rankine cycle two organic Rankine cycles two absorption cooling systems a gas turbine system a once-through (OT) multi stage flash (MSF) desalination unit a geothermal unit a heat pump an electrolyser and a thermal energy storage are used as sub-systems. The novelty of the system is to focus on novel sub-system design pattern for the proposed multi-generation system by using multiple energy inputs as there is a gap about those studies in the literature. The overall system performance is evaluated from energetic exergetic exergo-economic environmental (4E) and sustainability points of view by using the EES software package. The total installed power and hydrogen mass flow rates are 7.76 MW and 3.52 kg/h respectively. The energy and exergy efficiency values of the overall system are found to be 65.55% and 27.09%. Fresh water flow rate is calculated to be 6.16 kg/s with 10 stages. The overall unit product cost is determined to be 2179 $/GJ and the overall social ecologic factor is calculated to be 1.37.
Citation - WoS: 2
First and second law analyses of wastewater cooled condenser for a refrigeration system
(INDERSCIENCE ENTERPRISES LTD, 2019) Ibrahim Karacayli; Lutfiye Altay; Arif Hepbasli; Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
In this study a vapour compression refrigeration (VCR) system with a wastewater (WW) cooled condenser at a temperature range of 27-29 degrees C was designed. The cooling capacity of the system using R134a as the refrigerant was 1.09 kW. The condenser consisted of a coaxial heat exchanger with a capacity of 1 kW. This paper dealt with energy and exergy analyses of the VCR system using WW as a heat sink. Experiments were performed in order to evaluate the energetic and exergetic performances of the wastewater-cooled condenser (WWC) and the overall system. The convective heat transfer coefficient of WW and refrigerant in the condenser overall heat transfer coefficient of the WWC total amount of heat removed by WW amount of cooling effect coefficient of performance (COP) exergy destruction rate and second law efficiencies of the WWC and VCR system were calculated under different WW temperatures and flowrates. Increasing volumetric flowrate of WW from 200 L/h to 400 L/h caused 4.4% improvement in COP 12.0% reduction in exergy destruction and 10.3% increase in exergy efficiency.
Citation - Scopus: 2
First and second law analyses of wastewater cooled condenser for a refrigeration system
(Inderscience Publishers, 2019) Ibrahim Karacayli; Lutfiye Altay; A. Hepbasli; Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
In this study a vapour compression refrigeration (VCR) system with a wastewater (WW) cooled condenser at a temperature range of 27-29°C was designed. The cooling capacity of the system using R134a as the refrigerant was 1.09 kW. The condenser consisted of a coaxial heat exchanger with a capacity of 1 kW. This paper dealt with energy and exergy analyses of the VCR system using WW as a heat sink. Experiments were performed in order to evaluate the energetic and exergetic performances of the wastewater-cooled condenser (WWC) and the overall system. The convective heat transfer coefficient of WW and refrigerant in the condenser overall heat transfer coefficient of the WWC total amount of heat removed by WW amount of cooling effect coefficient of performance (COP) exergy destruction rate and second law efficiencies of the WWC and VCR system were calculated under different WW temperatures and flowrates. Increasing volumetric flowrate of WW from 200 L/h to 400 L/h caused 4.4% improvement in COP 12.0% reduction in exergy destruction and 10.3% increase in exergy efficiency. © 2020 Elsevier B.V. All rights reserved.
Investigating the Novel Ejector-Enhanced Auto-Cascade Refrigeration Cycle with R170/R600 Under Variable Evaporation and Condensation Temperatures
(Springer Science and Business Media Deutschland GmbH, 2026) Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
Citation - WoS: 2
Citation - Scopus: 2
Mathematical modelling and performance analysis of a novel auto-cascade refrigeration cycle for ultra-low temperature applications
(INDERSCIENCE ENTERPRISES LTD, 2023) Ibrahim Karacayli; Lutfiye Altay; Arif Hepbasli; Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
The main objective of this study is to assess both energetically and exergetically the performance of a novel auto-cascade refrigeration (NACR) cycle enhanced by an internal heat exchanger using R290/R170. In contrast to the ACR cycle with a -60 degrees C evaporation temperature the NACR cycle displays a COP increase of 140.78% and a 148.67% improvement in exergy efficiency. Additionally there is a notable decrease of 13.77% in compressor discharge temperature. For an evaporation temperature of -55 degrees C the NACR cycle achieves a COP of 0.403 and an exergy efficiency of 14.61% with the compressor discharge temperature registering at 126.60 degrees C.
Performance Evaluation of an Ejector-Enhanced Modified Cascade–Auto-Cascade Refrigeration System for Ultra-Low-Temperature Cooling
(SAGE Publications Ltd, 2026) Karacayli, Ibrahim; Hepbasli, Arif; Altay, Lutfiye
Auto-cascade refrigeration (ACR) systems can reach ultra-low temperatures but often suffer from two major drawbacks: high compressor exit (discharge) temperatures and low system performance. Many previous studies have focused on performance enhancement while neglecting the critical issue of compressor discharge temperature. Although techniques such as vapor injection, two-stage compression, and additional heat exchangers can enhance system efficiency, they also introduce structural complexity and higher costs. To address these challenges, this study proposes a novel hybrid refrigeration cycle that integrates a cascade cycle with an ACR system. The objective is to lower the compressor discharge temperature and improve the overall performance while maintaining simplicity through the use of environmentally friendly refrigerant mixtures. Four different configurations were studied: three modified cascade refrigeration cycles and one ejector-enhanced cascade refrigeration (MECR) cycle. The MECR system achieved the best results, with a coefficient of performance of 0.894 and an exergy efficiency of 30.1% at evaporator exit and condensation temperatures of -60 degrees C and 30 degrees C, respectively. The compressor discharge temperature was reduced by 36.9%, improving safety when using low-global warming potential refrigerants. Relative to comparable systems reported in the literature, the proposed design improved exergy efficiency by up to 58.2% without compromising structural simplicity. These findings demonstrate that the MECR configuration provides a practical balance between performance improvement, safety, and system simplicity, offering meaningful advantages for ultra-low-temperature applications without increasing the system complexity.