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Öğe A case study on the modeling and simulation of UAVs(Yildiz Technical Univ, 2024) Koc, Osman Kerem; Sertkaya, Ali; Gonul, Alisan; Taner, Tolga; Dalkilic, Ahmet SelimThe flow and structure of an application design for un-manned aerial vehicles (UAVs) are examined in this research. We also show an example of modeling and simulation study with the ANSYS Fluent and Mechanical programs. This research reveals the unmanned aerial vehicle's structural and mechanical design, structure configurations, energy-flow and struc-tural analysis, propulsion and firing systems, prototype production and testing, and design flow models. This study aims to complete the unmanned aerial vehicle design by determining its aerodynamic configurations. Due to the complexity of the design, a preliminary preparation for flow analysis is performed with simplified geometry as well as flow analysis. The unmanned aerial vehicle is tested at different velocities by numerical analysis. In addition, different density flow analyses provide predictions about the aerodynamic forces of the UAVs at different heights and temperatures. The thrust results are 4240 g, power became 1711.62 W with 2.48 g/W efficiency, and 12179 [rpm] revolution for 22.2 V voltage and 77.1 A current, respectively. The 5 different analyses are performed in the range of 2.9-12 million elements, and the solution meshes with the lowest number of elements by performing parametric studies with the ANSYS program that gives the most accurate result.Öğe A parametric study on weld zone shape of resistance spot welded 22MnB5 steel(Taylor & Francis Ltd, 2023) Tuncel, Oguz; Aydin, Hakan; Gonul, AlisanThe resistance spot welding of 22MnB5 with different weld currents, weld times, and quenching conditions is investigated in the current study. A Kriging Response Surface Methodology-based local sensitivity analysis is performed to investigate the effect of weld current, weld time, and quench condition on weld zone morphology and tensile shear load (TSL). When welding current, welding time, and quenching conditions are varied between the minimum and maximum values, the geometry of the weld zone was influenced by 40-60%, 20-40%, and 0-20%, respectively, according to sensitivity studies. It is also found that increasing values of welding current are the most effective welding parameter, increasing TSL by about 45%. In order to better understand the TSL variation at different welding parameters, various hardness measurements are applied for each specimen in the fusion zone and the heat-affected zone (HAZ) regions of the weld zone. Based on the location, the HAZ was divided into three regions: the inner, middle, and outer. The middle HAZ had hardness values 12% higher than the base material, while the outer HAZ had hardness values up to 36% lower than the base material. Also, macro-and microstructure images of the sample produced by combining the quenched and non-quenched materials are obtained to demonstrate how the hardness zones are identified.Öğe A sensitivity analysis of the effect of curvature ratio on the thermal-hydraulic performance in helically coiled tubes with corrugated walls(Elsevier France-Editions Scientifiques Medicales Elsevier, 2023) Kirkar, Safak Metin; Gonul, Alisan; Dalkilic, Ahmet SelimTo enhance thermal-hydraulic performance by rising the heat transfer rate with reasonable pressure loss, heat transfer augmentation methods should be considered in the heat exchanger designs. The use of two distinct passive heat transfer augmentation methods, helically coiled tube structure and helically corrugated tube wall, is considered in this study to investigate numerically the effect of coil diameter on the heat transfer and flow characteristics of single-phase liquid water flowing in the corrugated coiled tubes. Curvature ratio, the ratio of tube-to-coil diameter, and the use of corrugation are one of the most influential factors on heat transfer in coiled tubes due to their contributions to the formation of secondary and swirl flows. The curvature ratios between 0.0958 and 0.2875 are considered for smooth and equivalent corrugated coiled tubes with the same tube diameter of 5.75 mm and length of 390 mm. In all simulations, the water flows through the investigated tubes at Dean numbers between 150 and 3270 under boundary conditions of uniform surface heat flux. The influence of coil diameter on Nusselt number, friction factor, and thermal-hydraulic performance is examined by a com-mercial software. As a result, the enhancement in the thermal-hydraulic performance of corrugated coiled tubes compared to smooth straight ones is much higher, up to 270%, at Reynolds numbers below 2300 than those at higher Reynolds numbers. Additionally, the Genetic Aggregation Response Surface Methodology for the esti-mation of output parameters and their sensitivity analysis is employed by evaluating the Reynolds number and curvature ratio as inputs, and Nusselt number, friction factor, and performance evaluation criteria as outputs. Finally, the output parameters are estimated with an error range of +/- 5%, and the Reynolds number on Nusselt number and performance evaluation criteria, and curvature ratio on friction factor are realized to be more effective.Öğe Assessment of heat transfer characteristics of a corrugated heat exchanger based on various corrugation parameters using artificial neural network approach(Elsevier Science Inc, 2024) Colak, Andac Batur; Kirkar, Safak Metin; Gonul, Alisan; Dalkilic, Ahmet SelimThe complexity of the fluid flow process involved makes it difficult to estimate the characteristics of corrugated tubes. Heat exchangers are often designed to be more efficient by using numerical techniques. Recently, machine learning algorithms have become a viable method for assessing the behaviors of flow and heat transfer in corrugated tubes. Based on a set of data, machine learning algorithms can better estimate how efficient a heat exchanger is. In the present study, an artificial neural network is conducted to figure out the Nusselt number, friction factor, and performance evaluation criteria for heat transfer in straight corrugated tubes based on flow rate and corrugation parameters. The Reynolds number varies between 480 and 6100, spanning various flow regimes in the corrugated tubes, while the corrugation pitch and corrugation depth change between 6 mm and 18 mm and 0.6 and 1.0 mm, respectively. After totaling 220 data points, the network structure with a multilayer perceptron structure is trained. The Levenberg-Marquardt algorithm is performed for training with 17 neurons in the hidden layer. The established neural network structure forecasts Nusselt number, friction factor, and performance evaluation criteria parameters with deviation rates of 0.11 %, - 0.63 %, and 0.17 %, respectively. The neural network exhibits higher performance when compared to related correlations from the literature. This study is a novel one in open sources due to using artificial neural networks to estimate the flow and thermal behaviors in corrugated tubes operating at low flow rates. The current recommended approach may be regarded as a beneficial tool particularly for thermal systems as it aids designers in enhancing the system efficiency with accurate estimations.Öğe Enhanced performance of a microchannel with rectangular vortex generators(Yildiz Technical Univ, 2023) Gonul, Alisan; Okbaz, AbdulkerimMicrochannel heat sinks and heat exchangers are widely used in the cooling of electronic systems. However, it is still important to enhance the heat transfer in the microchannel so that the intense heat generated can be removed. Vortex generators (VGs) create secondary flow s tructures i n t he fl ow, in creasing th e flu id mix ing, thi nning the the rmal bou ndary layer, and ultimately boosting heat transfer. Here, we have controlled the flow structure and improved the heat transfer with the lowest possible pressure loss by placing VGs of different sizes, numbers, and angles of attack in a microchannel. The improvement in heat transfer is accelerated as vortex intensity increases. The angle of attack has a significant impact on vortex formation lengths, which reach high dimensions around 90 & DEG;. Furthermore, increasing the VG length significantly increases the vortex formation lengths. The number of VG pairs has a significant impact on heat transfer and pressure losses. As the number of VG pairs increases, so does the area occupied by the secondary flow regions in the microchannel, increasing the fluid mixture and boosting heat transfer. The highest enhancement in heat transfer using VGs is obtained at around 230%, while the corresponding increase in pressure loss is 950%. According to the JF factor which we consider a performance evaluation criteria, the best result is around 1.38. The G enetic A ggregation R esponse S urface Methodology has been applied to numerical results. The related method i s realized t o produce results that are consistent with the numerical results within a & PLUSMN;5% error interval. All the input parameters considered in the sensitivity analysis have an impact of at least 10% on the output parameters.Öğe Enhancement of heat transfer characteristics in wavy microchannel heat sinks with streamlined micropins within convergent-divergent flow passages(Pergamon-Elsevier Science Ltd, 2025) Gonul, AlisanIn the current study, the heat transfer characteristics of a novel design microchannel with a wavy sinusoidal convergent-divergent wall structure featuring streamlined pins have been numerically investigated under laminar flow conditions. Various amplitudes, wavelengths, pin heights, and Reynolds numbers are considered as parameters. The thermal and hydraulic characteristics are analyzed in terms of Nusselt number, Fanning friction factor, and Performance Evaluation Criteria number (PEG), PEG ), which evaluates the heat transfer enhancement against the associated pressure drop. It is revealed that increasing the amplitude and decreasing wavelength, along with moderate pin heights, significantly augment heat transfer. The streamlined pins effectively direct the flow, and the resulting secondary flow and chaotic advection considerably enhance heat transfer in the designed configuration. The study demonstrates that the heat transfer can be improved by a factor of 4.79 compared to a straight microchannel. Under these geometric and flow conditions, the pressure drop increases by a factor of 9.87, and the PEG is found to be around 2.23. A multi-objective optimization study using the Non-dominated Sorting Genetic Algorithm (NSGA-II) is conducted with Genetic Aggregation Response Surface Methodology to evaluate the impact of various parameters on thermal-flow performance and to identify the optimal design with material quantity variation. According to the optimal results, a 5 % increase in material can augment thermal- flow performance by approximately 206.6 % compared to traditional microchannels. Finally, practical correlations for the Nusselt number and friction factor, accounting for various parameters, have been developed to facilitate in designing of microchannel cooling systems.Öğe Enhancement of thermal and flow characteristics in helically coiled tubes with corrugated surfaces by Genetic Algorithm based optimization(Elsevier Science Inc, 2024) Kirkar, Safak Metin; Gonul, Alisan; Dalkilic, Ahmet SelimThis study investigates the combined use of helically coiled tubes and corrugated surface structures as two different heat transfer enhancement techniques. Both the curvature ratio and corrugation form swirl and secondary flows, resulting in higher heat transfer rates. The effects of pitch and depth of corrugation on the performance evaluation criteria, Nusselt number, and friction factor are studied parametrically at different Reynolds numbers. A multi -objective optimization is performed to obtain the best thermal-hydraulic performance, and a sensitivity analysis is conducted to investigate how wall corrugation specifications affect performance. The numerical results indicate that corrugated helically coiled tubes have significantly higher thermal and hydraulic performance at Reynolds numbers lower than 2300 compared to smooth plain tubes. The corrugated coiled tubes can improve Nusselt numbers by up to 7.39, 2.02, and 1.84 compared to the smooth plain, corrugated plain, and smooth coiled tubes of the same size, respectively. They can also improve friction factors by up to 33.26, 1.82, and 10.42, and performance evaluation criteria by up to 2.83, 1.66, and 1.09. The proposed novel correlations are the first and fourth in the literature, respectively, for predicting the Nusselt number and friction factor of corrugated helically coiled tubes. Based on 240 data points that were acquired via parametric and optimization studies, these correlations have been established within 10% error margins.Öğe Evaluation of exergy destructions of different refrigerants in a vaccine cooling system with artificial intelligence(Inderscience Enterprises Ltd, 2024) Kahriman, Elif Altintas; Gonul, Alisan; Kose, Ali; Parmaksizoglu, Ismail CemNowadays, low-temperature storage and distribution of many vaccines are as important as their production. In this study, the performance of a storage device operating in a vapour compression refrigeration cycle designed to provide low-temperature cooling between 201 K and 275 K using R134a, R1234yf, R502, and R717 fluids is evaluated by both thermodynamic and artificial neural network (ANN) methods. Levenberg-Marquardt, Bayesian regularisation, and scaled conjugate gradient algorithms are compared with thermodynamical calculations to predict the energy efficiency and exergy destruction of the cooling system. All the considered artificial intelligence algorithms are found to accurately predict the expected outputs with R2 values greater than 0.9.Öğe Flow optimization in a microchannel with vortex generators using genetic algorithm(Pergamon-Elsevier Science Ltd, 2022) Gonul, Alisan; Okbaz, Abdulkerim; Kayaci, Nurullah; Dalkilic, Ahmet SelimIn this study, delta winglet-type vortex generators, widely used in conventional macro channels and proven to be effective, are used in microchannels to increase their heat transfer capacities. The effects of vortex generators on heat transfer and pressure loss characteristics are studied numerically for different angles of attack, vortex generator arrangement type, the transverse and longitudinal distance between vortex generators, vortex generator length and height, and different Reynolds numbers. The thermal and hydraulic characteristics are presented as the Nusselt number, the friction factor, and the performance evaluation criteria number (PEC) that takes into account the heat transfer enhancement and the corresponding increase in pressure loss. The variation of Nu/Nu0, f/f0, and PEC are found to be in the range of 1.03-1.87, 1.04-1.8, and 0.92-1.62, respectively. A multi-objective optimization study are performed with the response surface methodology analysis to see how different parameters affect heat transfer and pressure loss and to determine the most optimum design. Besides, local sensitivity analysis study is carried out through the RSM, and water inlet velocity for heat transfer enhancement is found to be the most effective parameter. Among the geometric parameters, vortex generator height is determined as the most effective factor. Finally, practical Nusselt number and friction factor correlations taking many parameters into account are proposed to be able to compare the results of other researchers, and for engineers designing microchannel cooling systems.Öğe Multi-objective optimization of single-phase flow heat transfer characteristics in corrugated tubes(Elsevier France-Editions Scientifiques Medicales Elsevier, 2023) Kirkar, Safak Metin; Gonul, Alisan; Celen, Ali; Dalkilic, Ahmet SelimIn this study, the use of corrugated surfaces as one of the passive heat transfer improvement methods on straight tubes is numerically investigated related to the determination of Nusselt number, friction factor, and perfor-mance evaluation criteria. With the same diameter of 5.75 mm and length of 390 mm, 9 corrugated tubes having corrugation pitches of 6, 12 and 18 mm, and depths of 0.6, 0.8 and 1.0 mm are considered for the parametric studies. Water is employed as a operating fluid with Reynolds number values from 480 to 6100 covering different flow regimes. Sensitivity analyses by Genetic Aggregation Response Surface Methodology and multi-objective optimization analyses by NSGA-II are performed in order to maximize heat transfer and minimize pressure drops. It is determined that the thermal-flow augmentation created by the use of corrugated surfaces in laminar flow conditions is quite higher than those in the turbulent region of the smooth tube. According to the obtained optimum parameters and flow conditions, the maximum value of the performance evaluation criteria is 2.48 in comparison to the use of equivalent smooth and corrugated tubes. In addition, Nusselt number and friction factor equations are suggested by using 220 data points within deviation bands of +/- 10% and +/- 15%, respectively.Öğe Novel air duct designs to estimate the windshield demisting issue for a commercial vehicle(Sage Publications Ltd, 2024) Akgunlu, Safak; Ozcan, Onur; Bacak, Aykut; Gonul, Alisan; Taner, Tolga; Dalkilic, Ahmet SelimThis study is about the fog on the windshields of passenger buses because it makes it hard for drivers to see, which is dangerous. The goal of the research is to come up with an effective way to spread the produced mist. According to the study, the air duct design, which is connected to the car's defroster and defrosting system by Kraft hoses, has to be upgraded. The analysis identifies areas in which the current air duct design might be enhanced and then makes design modifications to create a superior design. By conducting climatic chamber experiments on a vehicle equipped with the first air duct design and tracking the actual air velocity values at the nozzle tips, the success of the new technique is assessed. The boundary conditions for the analysis are the observed values. The study involves the utilization of a commercially available software package to conduct investigations on both the original and modified air duct designs. The software package employs a k-epsilon turbulence model that is known to produce reliable results. The data demonstrate that the adjustments made in light of the comparison produced beneficial effects. The maximum air velocities were increased by 23%, while the pressure loss values of the left and right fans were reduced by 2.5% and 2.9%, respectively, due to the modification of the air duct. Significant energy was saved because of the decrease in fan pressure loss, which led to decreases in the power consumption of the left and right fans of 4.2% and 4.7%, respectively. This comparison shows that the newly built air ducts actually increased the flow rate at the system's fan outlets by 40%.Öğe Prediction of heat transfer characteristics in a microchannel with vortex generators by machine learning(Walter De Gruyter Gmbh, 2023) Gonul, Alisan; Colak, Andac Batur; Kayaci, Nurullah; Okbaz, Abdulkerim; Dalkilic, Ahmet SelimBecause of the prompt improvements in Micro-Electro-Mechanical Systems, thermal management necessities have altered paying attention to the compactness and high energy consumption of actual electronic devices in industry. In this study, 625 data sets obtained numerically according to the change of five different geometric parameters and Reynolds numbers for delta winglet type vortex generator pairs placed in a microchannel were utilized. Four dissimilar artificial neural network models were established to predict the heat transfer characteristics in a microchannel with innovatively oriented vortex generators in the literature. Friction factor, Nusselt number, and performance evaluation criteria were considered to explore the heat transfer characteristics. Different neuron numbers were determined in the hidden layer of each of the models in which the Levethenberg-Marquardt training algorithm was benefited as the training algorithm. The predicted values were checked against the target data and empirical correlations. The coefficient of determination values calculated for each machine learning model were found to be above 0.99. According to obtained results, the designed artificial neural networks can provide high prediction performance for each data set and have higher prediction accuracy compared to empirical correlations. All data predicted by machine learning models were collected within the range of +/- 3% deviation bands, whereas the majority of the estimated data by empirical correlations dispersed within & PLUSMN;20% ones. For that reason, a full evaluation of the estimation performance of artificial neural networks versus empirical correlations data is enabled to fill a gap in the literature as one of the uncommon works.
