http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15589 Thu, 23 Apr 2026 03:02:26 GMT 2026-04-23T03:02:26Z http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15651 THE EFFECTS OF TWISTED STRIPS WITH DIFFERENT LENGTH ON HEAT TRANSFER AND PRESSURE DROP IN CONCENTRIC HEAT EXCHANGER ARGUNHAN, Zeki; YILDIZ, Cengiz; EL, Emin This study investigated the use of twisted strips as passive turbulators to improve heat transfer efficiency in concentric heat exchangers. In the experiments, four different lengths of twisted strips were designed (l = 0.25 m, 0.5 m, 0.75 m, and 1 m) and their performance was evaluated in a system with air and water fluids. The effects of twisted strips on heat transfer and pressure drops are investigated in both parallel and countercurrent flow patterns, and the results are analyzed in terms of Nusselt and Reynolds numbers. The results indicated that tubes using twisted strips achieved significant increases in the heat transfer coefficient compared to straight tubes. The highest increase in heat transfer performance reached 78% when the length of the twisted strip was l/L=1. The Nusselt number increased by a factor of 1.2 to 1.8, depending on the length of the twisted strips. The shortest strip length (l/L=0.25) resulted in the lowest heat transfer performance. However, these improvements were accompanied by significant increases in pressure drop; for full-length strips, the pressure drop increased by nearly 100%. The pressure drop increased slightly as the Reynolds number increased. The swirling flow generated by the twisted ribbons plays an important role in increasing the heat transfer. Despite the increases in pressure drops, the energy loss is negligible compared to the heat transfer gain achieved. In conclusion, the length ratio of the twisted strips significantly affects the thermal performance of the heat exchanger while increasing the pressure losses. These findings demonstrate the effectiveness of twisted strips as passive turbulators. Wed, 01 Jan 2025 00:00:00 GMT http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15651 2025-01-01T00:00:00Z http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15650 A TWO-STEP WITH FIRST AND SECOND DERIVATIVE SCHEME FOR NUMERICAL SOLUTION OF FIRST-ORDER PROBLEMS IN DYNAMICAL SYSTEMS Garba, Jamiu; Mohammed, Umaru; Oyelami, Oyewole One of the numerical techniques used to solve differential equations is the linear multistep method (LMM). A two-step secondderivative intra-point block numerical method of uniform order ten is proposed for solving dynamical systems in ordinary differential equations. The derived two-step method with multi-derivatives effectively addresses the challenges in solving nonlinear dynamical systems – exhibiting phenomena such as multiple steady states, oscillations, and chaos. The inclusion of second derivative in the block method makes sure more information about the ODE is used in generating the solution thereby improving the accuracy of the method. The method is A-stable, making it suitable for solving nonlinear dynamic systems in ordinary differential equations (ODEs). In addition, the method possesses a higher order of accuracy, and the associated error constants are very small. This block method generates numerical solutions that provide solution profiles and phase portraits for the problems considered under various situations of dynamical systems. The results generated from this method underscore its potential as a robust and versatile tool for solving a wide range of practical problems arising in real-life. Wed, 01 Jan 2025 00:00:00 GMT http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15650 2025-01-01T00:00:00Z http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15649 IMPROVEMENT OF HEAP LEACHING PRACTICES IN UŞAK KIŞLADAĞ GOLD MINE USING LIMESTONE Rashidi, Aminullah; Yılmaz, Serdar This study focuses on improving gold recovery from ore samples from the Uşak Kışladağ Gold Mine, specifically those sized -18+0 mm. The ore was crushed below 2.36 mm and mixed with locally abundant alkaline limestone to enhance permeability and gold dissolution efficiency. Permeability tests were conducted on the -18+0 mm and -2.36+0 mm sized ores, with results of 1.28 x 10⁻³ cm/s and 0.62 x 10⁻³ cm/s, respectively. Additionally, the 2.36 mm ore was mixed with various limestone sizes (-18+10 mm, -10+5 mm, and -5+0 mm) at ratios of 15%, 50%, 100%, 150%, and 200%. The best permeability results were observed with the 2.36+0 mm ore and -10+5 mm limestone mixture. Consequently, leaching experiments were conducted with 1:1 and 1.5:1 ratio of the -2.36+0 mm sample mixed with limestone, resulting in gold dissolution efficiencies of 63% and 53%, respectively. Furthermore, bottle-roll tests were performed on -2.36+0 mm and -75+0 μm samples for 48 hours, with gold recoveries of 64% and 83%, respectively. Wed, 01 Jan 2025 00:00:00 GMT http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15649 2025-01-01T00:00:00Z http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15648 OPTIMIZATION STUDY OF FUEL BLENDS IN AN SI ENGINE RUNNING WITH GASOLINE/ISOPROPANOL/ISOAMYL ALCOHOL BLENDS Şimşek, Doğan; Karabacak, Yusuf; Çolak, Niyazi Yılmaz; Aksu, Bahri In this study, was focused on determining the optimum alcohol mixtures of gasoline iso-propanol and isoamyl alcohol mixtures according to minimum exhaust emission and BSFC (Brake Specific Fuel Consumption) and maximum CGP (Cylinder Gas Pressure) parameters. In the optimization study, 3 different isopropanol (vol. 10, 20 and 30) and 3 different iso-amyl (vol. 5, 10 and 20) rate were used as input parameters at maximum power and torque speed. The experimental study, it was performed in a singlecylinder air-cooled, spark-ignition engine (SI), at full throttle position, maximum power speed (3600 min-1) and maximum torque speed (2400 min-1). In the optimization study, ANOVA supported RSM (Response Surface Methodology) and CCD (Central Composite Design) were used as the experimental design. In the results obtained, it was determined as an effective parameter for BSFC of engine speed, and for CGP were effective also alcohol types along with engine speed. As a result of the optimization, as the optimum operating parameters were determined as 3600 min-1 engine speed, 27.7778% iso-propanol and 13.9394% iso-amyl alcohol. In the confirmation tests, the error rates were obtained as 3.36%, 3.45%, 9.81%, 4.76% and 4.67% for BSFC, CGP, HC, CO and NOX, respectively. Wed, 01 Jan 2025 00:00:00 GMT http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/15648 2025-01-01T00:00:00Z