Yaşar Mutlu

This study presents a predictive modeling framework for estimating transient flow rates in PWM-driven solenoid valves. Building on a previously validated dynamic model, the proposed framework enables flow prediction under varying process conditions and valve configurations. Flow rates at fully open conditions are obtained using computational fluid dynamics (CFD) and validated experimentally. CFD analyses are further performed at partial valve openings, and the resulting data are incorporated into a numerical algorithm based on piecewise linear interpolation for prediction throughout the opening–closing cycle of the valve. The model is validated under PWM operation, and parametric analyses are conducted to examine the effects of duty ratio, period, and coil voltage. The maximum difference between the experimental and numerical results was 1.3% under fully open conditions and 2.8% under PWM operation, demonstrating good agreement across the investigated conditions. By incorporating flow characteristics at intermediate spool positions that cannot be directly measured experimentally, the proposed approach allows accurate prediction of both transient and time-averaged flow rates. This provides a computationally efficient alternative to fully coupled transient CFD simulations.

This study investigates the possible causes of radioactive leakage occurring during the Tc-99m generation process. For this purpose, hanging film examination and annular film thickness calculations are conducted within the needle of the generation unit using micro flow approximations. Additionally, local and line losses are calculated for each component in the Tc-99m generation setup, and the capillarity effect of the needle is also considered. Further modifications are made to the experimental setup to examine the effects of needle diameter, orifice influence, and an increase in the local loss coefficient. Finally, a two-phase, unsteady computational fluid dynamics study is conducted to gain detailed insights into fluid behavior during the elution process. As a result, it is recommended that a mechanical seal system positioned between the middle needle and the vacuum vial could provide an effective solution to the leakage problem.

This extensive study is carried out to minimize the pressure drop of a relief valve featuring quick-releasing coupling used in radar systems. The 3D two-phase computational fluid dynamic (CFD) study is verified with the experiments, and Taguchi’s orthogonal method is implemented for pressure drop optimization. Realizable k–ε turbulence model with enhanced wall treatment and the Schnerr and Sauer cavitation model are enforced within the numerical study. Four angles—the collet angle, the inlet angle, the plug angle, and the outlet angle—are considered at five levels of variation for the orthogonal optimization process. According to the statistical analysis, two more designs are suggested, and one of them resulted in further improved pressure drop performance. Moreover, the cavitation behavior of the proposed design is compared with the base design through water vapor volume fractions. While the water vapor volume fraction of the base design is 0.0045, no vapor formation is observed in the optimized designs at 20 l/min. The results of the proposed design are also validated by the experiments. The outcomes of the study showed that the inlet angle has a significant effect on the pressure drop phenomenon.

In the study, water jet pump transfers the slurry in the well through pipe system to centrifugal pump. Sand-water mixture causes amount of material loss in the water jet pump structure computed by a software program. The purpose of the study is to determine the most critical part in the water jet pump. The wear amount is affected by many parameters such as sand particle diameter, mass flow rate of abrasive and inlet velocity. So, it is investigated that the wear amount on the jet pump is changed according to sand percentage in the well water, inlet velocity and erodent diameter. Mass flow rates of sand have a value of 0.097 kg/s for w.p. % 5, 0.194 kg/s for w.p. % 10, 0.291 kg/s for w.p. % 15 at an inlet velocity of 3.98 m/s. The maximum erosion wear rate is raised from 2.26x10-4 kg/(s m2) to 6.84x10-8 kg/s2m2 for inlet velocities of 1.99 m/s, 3.98 and 7.96 m/s, respectively for the case of weight percentages of %15 in Finnie erosion wear model. Finnie, Mclaury, Generic and Oka erosion models have been compared. It is found that Mclaury’s erosion model demonstrates the highest erosion value of 1.38x10-3 kg/(s m2) for w.p. % 15 at 3.98 m/s inlet velocity for the erodent diameter of 0.0005m in all. It is claimed that erosive wear has been concentrated on the nozzle of the water jet pump. The wear rate can be predicted as straightforwardly for different conditions.