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Öğe An optimization study on thermo-hydraulic performance arrays of circular and diamond shaped cross-sections in periodic flow(Pergamon-Elsevier Science Ltd, 2021) Erdinc, Mehmet Tahir; Aktas, Arif Emre; Kuru, Muhammet Nasif; Bilgili, Mehmet; Aydin, OrhanIn this study, thermo-hydraulic characteristics of arrays of circular and diamond shaped cross-sections in periodic flow are investigated numerically. The main purpose of this study is to configure diamond shaped cross-sections in order to obtain better thermal performance compared to circular shaped cross-section. The optimization frameworks are constructed by using multi-objective genetic algorithm (MOGA) for both circular and diamond shaped cross-sections to obtain maximum heat transfer and minimum pressure drop while keeping the mass flow rate constant. The study can be divided into two parts: Firstly, an optimization study is carried out to achieve an optimum design for the circular type. Later, a new optimization scheme is constructed where the optimum design of circular type's heat transfer and pressure drop values are given as constraints. Thus, the optimization algorithm seeks better thermal performances with respect to the circular one. Moreover, optimum designs are illustrated graphically and given in the tabular form. Compared to circular geometries, it is found that the average Nusselt number of diamond shaped geometry can be increased by 10.11%, while pressure drop and volume of diamond shaped geometries are reduced by 11.90% and 52.76%, respectively.Öğe Effects of alternative refrigerants on the ejector dimensions for single and dual ejectors enhanced bus air conditioning system(Pergamon-Elsevier Science Ltd, 2023) Unal, Saban; Erdinc, M. Tahir; Akgun, Hakan; Bilgili, MehmetOne of the most critical criteria influencing the performance of an ejector enhanced vapor compression refrigeration system is the ejector size. R134a was chosen as the refrigerant in the majority of the research studies since it is widely used in practical applications. The use of R134a refrigerant, on the other hand, is restricted under the Kyoto Protocol due to its high global warming potential (GWP). In this study, an investigation was conducted to evaluate the differences in ejector dimensions that may occur when alternate refrigerants such as R1234yf, R1234ze(E), or R600a were used in the ejector enhanced bus air conditioning system. The cycle is analyzed thermodynamically to determine the state points. The diameters and lengths of the ejectors were determined using continuity, energy, and momentum equations. It can be observed that the kind of refrigerant has a significant impact on the size of the ejector. It is also determined that the R1234yf has the closest size to the R134a, and it can be deduced that utilizing a dual ejector decrease the overall size of the ejector, hence eliminating technical concerns in the ejector production process.Öğe Influence of mixing section inlet and diffuser outlet velocities on the performance of ejector-expansion refrigeration system using zeotropic mixture(Elsevier, 2022) Unal, Saban; Cihan, Ertugrul; Erdinc, M. Tahir; Bilgili, MehmetIt is known that the performance of vapor compression cooling systems can be increased thanks to the ejector. In the literature, there are many studies on the subject, in which mathematical models of ejector-expansion cooling systems are developed. However, the refrigerant velocities at the mixing section inlet for the secondary flow (suction stream) and diffuser outlet were neglected in these studies. In the mathematical model used in this study, the velocities in both sections are considered and the system performance is calculated. The performance assessment of an ejector-expansion refrigeration system was realized in the case of using the R600a/R290 refrigerant mixture as a working fluid. Thus, the effect of zeotropic refrigerant mixtures on the system performance is also investigated, considering the refrigerant velocities at the mixing section inlet and diffuser outlet. According to the obtained results, it has been found that the cooling performance of the system that uses R600a/R290 mixture as a refrigerant is 5.8%-7% higher when the velocities at the mixing section inlet and diffuser outlet are considered compared to the neglected one. The exergy efficiency is also calculated to be around 4.6% lower when the ejector mixing section inlet and diffuser outlet velocities are neglected.Öğe Optimizing the tube geometry to enhance thermohydraulic performance of tube bank heat exchanger(Elsevier France-Editions Scientifiques Medicales Elsevier, 2023) Aktas, Arif Emre; Kuru, Muhammet Nasif; Erdinc, Mehmet Tahir; Aydin, Orhan; Bilgili, MehmetIn this study, optimum design parameters of circular, diamond and enhanced shaped geometries for staggered tube banks are explored utilizing a multi-objective genetic algorithm (MOGA-II). For given three geometries, two step optimization studies are compared: (1) circular and diamond shaped geometries, (2) diamond and enhanced shaped geometries. Steady, incompressible, and turbulent flow around three-dimensional numerical models is solved using finite volume method. Initially, using literature experimental data numerical results are validated for circular and diamond geometries. In the optimization studies, maximization of heat transfer and minimization of required pumping power are preferred as objective functions. The results of optimization studies are demonstrated graphically. Furthermore, velocity and temperature distribution for the optimum cases are illustrated. The results of first step optimization studies exhibited that diamond shaped tube bank shows higher heat transfer rate than circular one for the same given volume (156%). Besides, as a result of second step optimization studies, optimal enhanced shaped geometry showed 0.59% higher heat transfer rate, 21.73% lower pumping power requirement and 9.65% lower total tube bank volume than optimal diamond shaped one.
