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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 comparison of heating and cooling systems having radiant and ventilation systems regarding thermal comfort(Springer, 2024) Rahmanparast, Amir; Bacak, Aykut; Camci, Muhammet; Karakoyun, Yakup; Acikgoz, Ozgen; Dalkilic, Ahmet SelimThermal comfort is crucial for indoor environmental quality, impacting occupant well-being and intellectual productivity. Despite the widespread use of HVAC technologies in residential and commercial buildings, there is growing awareness of thermal comfort, leading to more studies on this issue. According to international publication indexes nearly 60% of publications belongs to the categories of construction building technology, energy fuels, and civil engineering. It should also be noted that 40% of world energy consumption pertains to construction sector. In this context, radiant cooling and heating systems come forward with their low exergy destruction rates pointing out the potential to be energy-efficient due to their higher and lower operation temperatures. Displacement ventilation, with its low heating and cooling capacity, has not gained widespread preference. However, the increasing consciousness of global warming and energy efficiency, along with the fear of airborne virus contamination, views stand-alone or hybrid applications of radiant heating/cooling and displacement ventilation as potential future solutions. This review study investigates the impact of radiant heating/cooling and ventilation types, mixing, and displacement on thermal comfort performance, focusing on factors affecting thermal comfort in trending radiant cooling and heating applications like radiant walls, ceilings, and floors. The study emphasizes the importance of considering occupant preferences, building characteristics, and energy efficiency when choosing the most suitable heating and cooling systems for different indoor environments. Stand-alone and hybrid applications of radiant heating/cooling and displacement systems can enhance thermal comfort performance, with the exception of specific cases requiring a high thermal load or ventilation rate.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 Case studies on local mixed convection heat transfer coefficients along a radiant heated wall subjected to displacement ventilation(Springer, 2023) Camci, Muhammet; Karakoyun, Yakup; Acikgoz, Ozgen; Dalkilic, Ahmet SelimAs the demand for energy-efficient air conditioning systems enabling thermal comfort criteria increases, the research into innovative systems that combine displacement ventilation and radiant heating is being more up-to-date. This work discusses local mixed convection heat transfer coefficients over a radiant heated wall in an experimental room coupled with displacement ventilation provided by a floor level nozzle. In the experimental chamber, the air enters the room either from the floor level of the analyzed heated wall as in scenario 1 or the opposite wall in scenario 2 in the upward direction. The intervals of air inlet temperature and velocity are set between 13-27 & DEG;C and 0-2.5 ms(-1), respectively. The obtained data have been analyzed from a physical point of view, and four correlations having R-sq. numbers of 0.93, 0.94, 0.94, and 0.98 have been developed for the local mixed convective heat transfer coefficients along a heated wall. The alterations of local convection heat transfer coefficients along an examined radiant heated wall affected by a slot diffuser delivering a lowest air inlet velocity of 0.5 ms(-1) and highest air inlet velocity of 2.5 ms(-1) are gained in the intervals of 2-5.8 Wm(-2) K-1 and 2.5-10 W m(-2) K-1, in turn.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 Experimental investigation of mixed and forced convection generated by displacement ventilation with radiant wall heating(Pergamon-Elsevier Science Ltd, 2022) Camci, Muhammet; Karakoyun, Yakup; Acikgoz, Ozgen; Dalkilic, Ahmet SelimThere is a rising necessity concerning low energy consumption and thermal comfort, thus, new systems combining displacement ventilation and radiant heating are becoming common as a research topic. The current paper covers free, mixed, and forced convection in an experimental chamber consisting of a radiant wall heating system and a baseboard level diffuser. Air temperature in the test room is adjusted using an air blower via a novel designed baseboard level slot diffuser along with a hydronic wall heating circuit. Simultaneously; an upward direction air jet is blown through the heated or the opposite wall under two scenarios. The ranges of air inlet velocity and temperature are selected to be between 0.25 and 12.5 m/s and 14-26 degrees C, correspondingly. The heat transfer characteristics pertaining to the heated wall are studied with respect to the influences of wall and air temperatures, air inlet velocities, and the location of the diffuser. To derive convective heat transfer coefficient correlations valid for mixed and forced types for a radiant heated wall, acquired data have been processed. The convective, radiative, and total heat transfer coefficient intervals of 3-14.1, 5.2-5.5, and 9.3-21.7 W/m2K have been obtained for the radiant heated wall coupled with airflows, correspondingly.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.
