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    Computational thermal analysis of cylindrical fin design parameters and a new methodology for defining fin structure in LED automobile headlamp cooling applications
    (Pergamon-Elsevier Science Ltd, 2016) Sökmen, Kemal Fürkan; Yuruklu, Emrah; Yamankaradeniz, Nurettin
    In this study, the effects of fin design, fin material, and free and forced convection on junction temperature in automotive headlamp cooling applications of LED lights are researched by using ANSYS CFX 14 software. Furthermore a new methodology is presented for defining the optimum cylindrical fin structure within the given limits. For measuring the performance of methodology, analyses are carried out for various ambient temperatures (25 degrees C, 50 degrees C and 80 degrees C) and different LED power dissipations (0.5 W, 0.75 W, 1 W and 1.25 W). Then, analyses are repeated at different heat transfer coefficients and different fin materials in order to calculate LED junction temperature in order to see if the fin structure proposed by the methodology is appropriate for staying below the given safety temperature limit. As a result, the suggested method has always proposed proper fin structures with optimum characteristics for given LED designs. As another result, for safe junction temperature ranges, it is seen that for all LED power dissipations, adding aluminum or copper plate behind the printed circuit board at low ambient temperatures is sufficient. Also, as the ambient temperature increases, especially in high powered LED lights, addition of aluminum is not sufficient and fin usage becomes essential. High heat transfer coefficient and using copper fin affect the junction temperature positively. (C) 2015 Elsevier Ltd. All rights reserved.
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    THE EFFECT OF WATER VAPOR DIFFUSION RESISTANCE FACTOR OF INSULATION MATERIALS FOR OUTER WALLS ON CONDENSATION
    (2018) Bademlioğlu, Ali Hüsnü; Kaynaklı, Ömer; Yamankaradeniz, Nurettin
    Condensation, which is the result of water vapor diffusion, affects the heat transfer in the building material negatively. The condensation which is seen mostly in winter seasons at building materials, occurs when the surface temperature of the building material in contact with air falls below the raw temperature of the air. In this case, condensed water may cause mildew, fungal growth, odors, and deterioration of dye and building materials or adversely affected thermal insulation on the walls. Materials used for thermal insulation in buildings constitute resistance against water vapor diffusion. Water vapor diffusion resistance factor (VDRF) of materials can vary over a wide range. In this study, considering VDRF range that is commonly encountered in insulation applications, the effect of VDRF of insulation materials on condensation within constructions, and on the minimum thickness of insulation required to prevent this condensation accordingly were examined. Externally insulated wall was taken as sample wall model, heat and mass transfer calculations from wall unit area and insulation thickness minimization were performed for different indooroutdoor temperatures and relative humidity values. As a result of the analysis conducted, in constant indoor-outdoor conditions in general, as VDRF increases, the risk of condensation inside the wall first decreases and then increases. Minimum insulation thickness that is required to be applied to prevent condensation also shows a similar trend depending on the VDRF. For constant VDRF, it was come to the conclusion that as the difference between indooroutdoor temperatures and relative humidity increases, the risk of condensation and consequently required insulation thickness increases.
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    A PARAMETRIC ANALYSIS OF THE PERFORMANCE OF ORGANIC RANKINE CYCLE WITH HEAT RECOVERY EXCHANGER AND ITS STATISTICAL EVALUATION
    (2019) Bademlioğlu, Ali Hüsnü; Canbolat, Ahmet Serhan; Yamankaradeniz, Nurettin; Kaynaklı, Ömer
    In this study, the performance of a case study of Organic Rankine Cycle with heat recovery exchanger using different fluids is analyzed. As the fluids worked in the cycle, the commonly used R134a, R236fa, R245fa, R600a, R717 and R718 are preferred. Cycle performances of the selected fluids are compared based on both the heat source’s temperature that changes between 80°C and 109°C and the effectiveness of the heat exchanger. Furthermore, the contribution ratios and the order of importance of the parameters affecting the performance of the cycle are evaluated using the Taguchi statistical method. As a result, the effect of the waste-heat source temperature on the performance of the system is greater than the other parameters examined, and the contribution ratio of this parameter is determined as 59.80%. However, effectiveness of heat exchanger is found to be the least effective parameter and the effect ratio is calculated as 2.18%. In addition, the best and worst operating conditions are determined from the statistical analysis, and in these conditions, the thermal efficiencies of the Organic Rankine Cycle are obtained as 15.26% and 8.61%, respectively
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    Performance Assessments of Organic Rankine Cycle With Internal Heat Exchanger Based on Exergetic Approach
    (Asme, 2018) Yamankaradeniz, Nurettin; Bademlioğlu, Ali Hüsnü; Kaynakli, Omer
    This study makes energy and exergy analysis of a sample organic Rankine cycle (ORC) with a heat exchanger which produces energy via a geothermal source with a temperature of 140 degrees C. R600a is preferred as refrigerant to be used in the cycle. The changes in exergy destructions (of irreversibility) and exergy efficiencies in each cycle element are calculated in the analyses made based on the effectiveness of heat exchanger used in cycle and evaporator temperature changing between 60 and 120 degrees C for fixed pinch point temperature differences in evaporator and condenser. Parameters showing system performance are assessed via second law approach. Effectiveness of heat exchanger and temperature of evaporator are taken into consideration within the scope of this study, and energy and exergy efficiencies of cycle are enhanced maximum 6.87% and 6.21% respectively. Similarly, exergy efficiencies of evaporator, heat exchanger, and condenser are increased 4%, 82%, and 1.57%, respectively, depending on the effectiveness of heat exchanger and temperature of evaporator.