Browsing by Author "Yoladi, Mehmet"

Now showing 1 - 2 of 2

Experimental Investigation of Cross-Flow Heat Exchangers with Helical Fins: Performance Analysis Via RSM and ANN
(Elsevier France-Éditions Scientifiques Médicales Elsevier, 2025) Yoladi, Mehmet; Akyurek, Eda Feyza; Kotcioglu, Isak
In this study, the thermal and flow characteristics of cross-flow heat exchangers with helical fins were analyzed experimentally and numerically. The Box-Behnken Design (BBD) was used to examine the effects of air velocity, air inlet temperature, and water flow rate on key performance parameters including Nusselt number (Nu), Reynolds number (Re), friction factor (f), Colburn j factor, and Stanton number (St). Experimental results showed that increasing the Reynolds number improved heat transfer, with Nu increasing by up to 35 % and f decreasing by approximately 70 %. Among the variables, air velocity (x(3)) was the most dominant, while water flow rate had a minor effect. Experimental results were also compared with ANSYS Discovery simulations, which revealed a temperature deviation of 15 % and a pressure drop error of 7.9 %, highlighting the limitations of simplified turbulence models. RSM regression models showed high accuracy, especially for Reynolds number (R-2 = 1.00, p < 10(-12)), while models for Nu (R-2 = 0.899), f (R-2 = 0.971), and j (R-2 = 0.940) showed minor deviations due to turbulence-induced nonlinearities. Artificial Neural Networks (ANN) yielded even higher predictive accuracy, particularly for f (R-2 = 0.9996), Nu (error: 6.6 %), and j (error: 7.3 %), confirming their potential in thermal modeling. Overall, air velocity was the most influential parameter, and the hybrid use of RSM and ANN provided a strong framework for heat exchanger optimization. Future work should focus on AI-based optimization techniques and advanced CFD analysis.
Experimental Study on the Influence of Inclination Angle on Phase Change Materials and Natural Convection During Melting
(Elsevier, 2024) Yoladi, Mehmet; Akyurek, Eda Feyza; Afshari, Faraz
Phase change materials are greatly affected by the inclination angle, which is one of the important parameters affecting natural convection during the melting process. The thermal performance of the phase-changing material was experimentally examined in this study by centrally passing a 1.21 mm diameter minichannel through it within the cylindrical casing. Water was employed as the working fluid, and RT-50 paraffin was utilized as the phase-changing material. The thermal impact of the phase-changing material during the heat transfer fluid charging process was experimentally analyzed, considering various inlet temperatures, depths, durations, and inclination angles. Additionally, Response Surface Methodology was applied to analyze the effects of the mentioned parameters on thermal performance and to establish a correlation for temperature values. The results indicated that the inclination angle greatly affects the formation and development of natural convection during the melting of pure phase change material, as well as the propagation of the solid-liquid interface and the rate of heat transfer. From the findings, at an inlet temperature of 55 degrees C, between 3 and 6 mm depth, max temperature change at 0 degrees angle was 28.4 %, between 6 and 9 mm depth, max change at 0 degrees angle was 7.51 %, and between 9 and 12 mm depth, max change at 90 degrees angle was 30.5 %.