Sürdürülebilir Kalkınma Amaçları
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- ArticleAçık Erişim2024Investigation on the heat transfer and pressure loss of flow boiling in smooth and microfin tubes using machine learning methods
Sezer, Şükrü; Sezer, Cihan; Celen, Ali; Bacak, Aykut; Dalkılıç, Ahmet Selim
The estimation of heat transfer coefficients (HTC) and pressure drop (ΔP) in flow boiling processes is essential for the effective design and operation of refrigeration systems. In this study, the artificial neural network (ANN), locally weighted regression (LWR), and gradient boosted machine (GBM) methods are employed to predict the boiling heat transfer coefficient (HTC) and pressure drop (ΔP) in flow boiling of R134a. The study focuses on horizontally positioned both straight and microfin tubes. The ANN, LWR, and GBM methodologies are utilized to ascertain the parameters of boiling HTC and ΔP as outputs. These parameters are determined by considering the mass flux, saturation pressure, heat flux, vapor quality, Reynolds number, Lockhart–Martinelli parameter, Froud number, Weber number, and Bond number as inputs. The training dataset is partitioned into 5 sections for the purpose of hyperparameter tweaking for each model. Out of these sections, 4 parts, consisting of approximately 111 samples, are utilized for training, while 1 part, including around 27 samples, is allocated for validation. The optimal hyperparameters are determined by calculating the average R2 score over the 5 validation sets. Using raw measurements, HTC and ΔP are successfully modeled using a relatively much smaller dataset of 174 measurements, with 82.4% R2 score and 0.7% weighted average relative deviation for HTC, and 88.9% R2 score and 4.1% weighted average relative deviation for ΔP across multiple tube types, achieved by LWR algorithm. Model performances are validated with an extrapolation test and found to be consistent with traditional train–validation–test sampling scheme with 75.9% R2 score and −6.2% weighted average relative deviation for HTC, and 89.3% R2 score and −3.9% weighted average relative deviation for ΔP, showing the consistency of the hypotheses created by a hybrid of parametric and nonparametric model families even outside the observed measurement range for multiple tube types. Local weighted regression models are the most performant, especially for limited data availability. However, calculated measurements increase error rates, suggesting that HTC and ΔP models work best with raw measurements.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2023NUMERICAL INVESTIGATION OF A SERPENTINE-TUBE COLD PLATE COOLED LITHIUM-ION BATTERY UNDER WIDE PARAMETRIC CONDITIONS
Kalkan, Orhan; Celen, Ali; Bakirci, Kadir
This paper examines the thermal management of a commercial 20 A h lithium ferro phosphate battery with the cold plates containing the serpentine tube structure, which is frequently preferred in heat exchanger applications. A numerical analysis is performed to explore the battery surface temperature distribution under varying operating conditions. In the study, an experimentally verified electrochemical thermal compound model was created and temperature distributions at the end of discharge at 1C, 3C, and 5C rates are obtained. The effects of different inlet temperatures (15°C, 25°C, and 35°C) and volumetric flow rates (0.1 L/min, 0.6 L/min, and 1.1 L/min) of the coolant on the two vital parameters of battery thermal management –- maximum battery temperature and maximum battery temperature difference –- are investigated for each discharge rate. As a key finding in this study, there is an acceleration of temperature variation from the middle part of the battery with the minimum temperature to the terminals with the maximum temperature, at the end of the discharge, in the use of a serpentine cold plate. Under the conditions where the coolant flow rate is maximum and the inlet temperature is minimum, the highest maximum temperature difference is 14.4°C, while the lowest maximum temperature difference is 10.8°C under the conditions where the coolant flow rate is minimum and the inlet temperature is maximum. Besides, the correlation equations in which the adjusted R2 values for maximum battery temperature difference and maximum battery temperature are 98.0% and 99.6%, respectively, are developed.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2023Experimental Investigation on Single-Phase Immersion Cooling of a Lithium-Ion Pouch-Type Battery under Various Operating Conditions
Celen, Ali
The selection of a battery thermal management technique is important to overcoming safety and performance problems by maintaining the temperature of batteries within a desired range. In this study, a LiFePO4 (LFP) pouch-type battery having a capacity of 20 Ah was experimentally cooled with both air and liquid (immersion cooling) techniques. Distilled water was selected as the immersion fluid in the experiments, and the impact of discharge rate (1–4C), immersion ratio (50–100%), and coolant fluid inlet temperature (15–25 °C) on the battery temperature were investigated during the discharge period. The experiments revealed that maximum temperatures were reached at approximately 45 °C and 33 °C for air and distilled water cooling techniques, respectively, at the discharge rate of 4C. The average and maximum battery surface temperatures can be reduced by 28% and 25%, respectively, with the implementation of the liquid immersion technique at the discharge rate of 4C compared to the air technique. Moreover, the experiments demonstrated that the maximum temperature difference could be lowered to 4 °C by means of 100% liquid immersion cooling at the highest discharge rate, where they are approximately 11 °C and 12 °C for air and 50% for immersion cooling, respectively. In addition, it was observed that the coolant fluid inlet temperature has a significant impact on battery temperature for %100 liquid immersion.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2023Multi-objective optimization of single-phase flow heat transfer characteristics in corrugated tubes
Kirkar, Safak Metin; Gönül, Alişan; Celen, Ali; Dalkilic, Ahmet Selim
In 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 performance 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.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2022Energy and Exergy Analysis of a Shell and Tube Heat Exchangers Having Smooth and Corrugated Inner Tubes
Celen, Ali
Shell and tube heat exchangers are one of the most used heat exchanger types in applications and it is important to predict heat transfer capacity and pressure loss in both design stage. Heat transfer capacity of a heat exchanger can be enhanced by using tubes having enhanced surfaces instead of smooth ones. In this study, the usage of corrugated tubes in a shell and tube heat exchanger is investigated by using ε-NTU method, energy/exergy analysis. The impact of the usage of corrugated tubes on hot and cold fluid outlet temperatures, energy/exergy efficiencies, entropy generation and total exergy destruction are researched for various operation conditions. The results revealed that the difference between fluid outlet temperatures can be decreased by using tubes having corrugated surfaces instead of smooth ones because of fluid mixing and secondary flows obtained by means of the corrugations. Overall heat transfer coefficient of heat exchanger is enhanced up to 8% with the usage of corrugated tube in considered operation conditions. It is exhibited that the energy and exergy efficiencies of heat exchanger can be improved up to 18% and 16% with the usage of corrugated tubes instead of one having smooth tubes. Moreover, the entropy generation because of heat transfer and pressure loss and total exergy destruction of considered heat exchangers are determined to reveal the impact of corrugated tubes.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2022Energy and Exergy Analysis of Solar Collectors Having Different Tilt Angles: Case Study of Erzincan City
Kaba, Muhammet Yasin; Kurnuc Seyhan, Aslihan; Celen, Pinar; Celen, Ali
Solar collectors are frequently used in domestic water heating applications. In the design stage, the positioning of solar collector with suitable title angle is important in order to utilize from sun energy efficiently. In this study, the effect of tilt angle of a solar collector located to Erzincan city on monthly/daily average radiation values, water outlet temperature, energy and exergy efficiencies are theoretically investigated. It is seen that the maximum and minimum values of optimum tilt angles are 63 degrees ve 0 degrees for December and June, respectively. Tilt angles which are suggested for Erzincan (27.14 degrees) and calculated are compared for daily average hourly radiation values and it is seen that the maximum variation is 26% for January. In addition, energy and exergy efficiencies of solar collector are estimated and the maximum efficiencies are determined as 74.2% ve 9.7% for optimum tilt angles.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2022Prediction of experimental thermal performance of new designed cold plate for electric vehicles’ Li-ion pouch-type battery with artificial neural network
Kalkan, Orhan; Colak, Andac Batur; Celen, Ali; Bakirci, Kadir; Dalkilic, Ahmet Selim
Since liquid-based thermal management systems are usually preferred methods for battery electric vehicles and cold plates are generally preferred to circulate the coolant, studies on their design are becoming increasingly essential. Besides, it seems useful to work artificial intelligence approaches to evaluate different battery thermal management systems, as it is known that the use of artificial intelligence is increasing in many applications today. The aim of this paper is to build up an artificial neural network model due to predict average battery temperature and maximum temperature difference on the battery surface which are also the artificial neural network outputs. The model inputs are depth of discharge, coolant flow rate (0.1, 0.6 and 1.1 l/min), discharge rate (1C- 5C), coolant inlet temperature (15, 25 and 35 °C). It is developed for a serpentine tubed cold plate, and mini channeled one which has novel design. To shorten the training time, after the optimization of the data set, a total of 270 data sets were utilized for training, validation, and test phases. In addition, the developed model predicts successfully average battery temperature and maximum temperature difference on the battery surface in the 10% error band range. Finally, the maximum margin of deviation and R values are 7.3% and 0.997%, respectively.
RDL Kalıcı Kaydıİncele - Book ChapterYalnız künye2022Thermophysical and rheological properties of unitary and hybrid nanofluids
Mercan, Hatice; Celen, Ali; Taner, Tolga
Understanding the thermophysical properties of the working fluids in a heat transfer system is essential for improving the thermal performance of heat transfer equipment. Clarification of the complicated and entangled mechanisms of the thermophysical properties and the operating conditions need detailed experimental and modeling efforts. Nanofluids, although showing the desired improvements in the thermophysical properties, are more sensitive to operating conditions compared to traditional working fluid. The working fluid can be a single fluid, its mixtures, as well as a nanosuspension. Ethylene glycol, ethanol, water, motor oil, ammonia, and halogenated hydrocarbons are some instances of working fluids in thermal systems. This book chapter reveals the thermophysical and rheological properties of unitary and hybrid nanofluids. The behavior of nanofluids used as working fluid in a thermal system affects the thermophysical and rheological properties of the flow within the system, as well as the thermal performance of the overall system. Nanofluids are complex dispersed suspensions, and the stability, chemical and thermal compatibility of nanoparticles must be ensured during the preparation procedures and during the operation conditions. This chapter includes thermal conductivity, heat capacity, density, and viscosity alteration of nanofluids under different operating conditions such as nanoparticle type, size, temperature, and concentration. The application of nanofluids is very promising and can be a good candidate for new-generation working fluids in industrial applications. Recently the application of hybrid nanofluids has become more popular since they enhance thermophysical properties according to the selection of compatible two nanoparticle types compared to unitary nanofluids. The thermal conductivity, the viscosity and the density of the nanofluids rise with increasing concentration and alter with base fluid and nanoparticle type. Temperature increase augments the thermal conductivity but it reduces the viscosity and density of the nanoblend. Specific heat capacity of the nanofluid decreases with increasing concentration and it is directly proportional to the temperature. This study contains a thorough digest of recent novel works of researchers in the nanofluid field and aims to model and encourage the research in the academic community, as well as to lead to the more efficient use of thermal applications, industrial processes, and new technologies.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2022New flow boiling frictional pressure drop multipliers for smooth and microfin tubes
Celen, Ali; Dalklllç, Ahmet Selim
The accurate calculation of pressure drop of evaporators/condensers are crucial and related with the pumping power, performance coefficient and energy consumption in a refrigeration equipment. This work aligns frictional pressure drop models/correlations with the experimental outcomes of boiling pressure drop of R134a in horizontal smooth and microfin copper tubes with equivalent outer diameter of 9.52 mm. The pressure drop through the test tube is obtained with a differential pressure transducer directly. Effective parameters are specified for smooth and microfin tubes and the most compatible models/correlations, 12 for smooth tubes and 9 for microfin ones, are determined accurately in relation to the consequences of investigation during intermittent and annular flow regime. Moreover, new two-phase multipliers have been developed by using regression analyses of 182 data points based on Lockhart-Martinelli parameter for each test tubes separately, and their predictability are found to be better than others in the literature as novel ones. Average errors of the developed empirical correlations are 11% for smooth and for 7% for microfin tubes. Finally, the measured data is given for the validation issues of researchers who can benefit from most of the investigated pressure drop models with tolerable accuracy regarding with their HEX design analyses.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2022Experimental investigation on the effect of anode functional layer on the performance of anode supported micro-tubular SOFCs
Timurkutluk, Cigdem; Bilgil, Keremhan; Celen, Ali; Onbilgin, Sezer; Altan, Tolga; Aydin, Ugur
In this study, anode supported micro-tubular solid oxide fuel cells (SOFCs) are fabricated by extrusion method and the effects of powder size, thickness and sintering temperature of the anode functional layer (AFL) on the electrochemical performance is experimentally investigated. For this purpose, four different commercial NiO powders are tested as initial powder for the fabrication of the anode functional layer. The thickness of AFL is also considered by varying the number of coatings. After deciding the optimum initial NiO powder size used in AFL and AFL thickness, the effect of pre-sintering temperature is examined. The performance tests are performed at an operating temperature of 800 °C under hydrogen and air. The microstructures of the samples are also investigated by a scanning electron microscope. The best peak power density is obtained as ∼0.5 W/cm2 from the cell having a single layer anode functional layer pre-sintered at 1250 °C prepared by NiO powders with 4 m2/g surface area.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2022Heat transfer and pressure drop characteristics of two phase flow in helical coils
Onal, Busra Selenay; Kirkar, Safak Metin; Akgul, Dogan; Celen, Ali; Acikgoz, Ozgen; Dalkilic, Ahmet Selim; Kazi, Salim Newaz; Wongwises, Somchai
This paper presents a review on heat transfer coefficient and pressure drop during condensation and boiling in helically coiled tubes. The geometric parameters such as coil diameter, coil pitch and operating parameters containing saturation temperature, system pressure, mass flux, heat flux and vapor quality have significant effects on the heat transfer characteristics. The frictional pressure drop during flow boiling increases with increasing vapor quality and mass flux, and decreases with increasing system pressure. Also, the effect of the curvature on the two-phase frictional multiplier is negligible. The frictional pressure drop in condensation increased with increasing average vapor quality and mass flux, and decreased with increasing saturation temperature. According to the results reported, heat flux had little effect on the pressure drop during condensation. Flow boiling heat transfer coefficient in helical coils of large diameter showed the similar characteristics and trend with the straight tube as the system pressure decreased. Lockhart-Martinelli parameter was generally preferred to be used by the authors as a function in the correlations to predict flow boiling heat transfer coefficient. There was a decrease in the average Nusselt number with increasing heat flux for the constant Dean number during condensation. This reduction in the average Nusselt number indicated that the turbulence effect created by the secondary flow in the helically coiled tubes eliminated the effects caused by the difference in density. The correlations used for determination of Nusselt number and pressure drop in helical coils with their major findings are presented in details.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2022Multi-objective optimization of a mini channeled cold plate for using thermal management of a Li-Ion battery
Kalkan, Orhan; Celen, Ali; Bakirci, Kadir
Mini channeled cold plates (MCCP) are an impressive choice for electric vehicles with a liquid-based thermal management system to keep the battery temperature within the desired range and to achieve a homogeneous temperature distribution. This paper came up with an optimum solution for maximum battery temperature (MBT), maximum temperature difference on the battery surface (MTD) and pressure drops in the channels (ΔP), which are vital parameters. Multi-objective optimization of geometric parameters and coolant flow rate of a designed MCCP which is experimentally investigated is carried out using the Desirability Function Approach. Firstly, the design of experiments (DoE) is generated using response surface method after determining the input variables and their levels. Then, each sample of DoE are modeled and analyzed numerically. Furthermore, the regression equations of the objective functions (MBT, MTD and ΔP) depending on the design parameters are developed and their variance analyzes are performed. Prediction accuracies of model equations developed for MBT, MTD and ΔP are 97.75%, 95.49% and 97.15%, respectively. As a result, optimum values of design variables, namely channel width (mm), distance between branches (mm), channel depth (mm), number of crossovers in branches and coolant flow rate (l/min) are 5, 5, 10, 13 and 0.7061, respectively.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2022Single-phase flow heat transfer characteristics in helically coiled tube heat exchangers
Akgul, Dogan; Kirkar, Safak Metin; Onal, Busra Selenay; Celen, Ali; Dalkilic, Ahmet Selim; Wongwises, Somchai
The aim of this review is to present a summary of the published papers of the heat transfer and pressure drop characteristics for single-phase flow in helically coiled tubes. The effect of geometrical parameters such as curvature ratio, coil pitch and working conditions such as Reynolds number, Dean number, flow rate and flow arrangement on heat transfer and pressure drop in helically coiled tubes are determined in the light of the experimental, numerical and analytical studies in the literature. Also, the effect of using nanofluids in comparison with conventional fluids, using enhanced surfaces such as corrugated, micro-finned, dimpled with regards to smooth surfaces and wire coil insert usage in helically coiled tubes are discussed. The correlations proposed for determination of Nusselt number and friction factor in helically coiled tubes are presented in detail separately under laminar and turbulent flow regimes. The studies show that usage of helically coiled tube merely gives higher heat transfer rate and pressure drop in comparison to straight one, additionally, the heat transfer performance increases with the inclusion of the combination of other passive heat transfer enhancement methods to helically coiled tube. Moreover, the subject of single-phase flow in helically coiled tubes is ascertained to be worth researching due to the fact that there are limited number of studies and is still no empirical or analytical model/correlation in the case of using enhanced surfaces and wire coil insert. Forthcoming researches on this issue in the near future will be considered as pioneer ones in literature.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2022Numerical determination of condensation pressure drop of various refrigerants in smooth and micro-fin tubes via ANN method
Çolak, Andaç Batur; Celen, Ali; Dalkılıç, Ahmet Selim
In the current work, the pressure drop of the refrigerant flow in smooth and micro-fin pipes has been modeled with artificial neural networks as one of the powerful machine learning algorithms. Experimental analyses have been evaluated in two groups for the numerical model such as operation parameters/physical properties and dimensionless numbers used in two-phase flows. Feed forward back propagation multi-layer perceptron networks have been developed evaluating the practically obtained dataset having 673 data points covering the flow of R22, R134a, R410a, R502, R507a, R32 and R125 in four different pipes. The outputs acquired from the artificial neural network have been evaluated with the target ones, and the performance factors have been estimated and the prediction accuracy of the network models has been resourced comprehensively. The results revealed that the neural networks could predict the pressure drop of the refrigerant flow in smooth and micro-fin pipes between 10% deviation bands.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2021Elektrikli Araçlarda Kullanılan Silindirik Lityum İyon Bataryaların Soğutulmasının Parametrik İncelenmesi
Celen, Ali; Kaba, Muhammet Yasin
Çten yanmalı motorlara sahip araçlarla kıyaslandıklarında çevreci olmaları sebebiyle elektrikli araçlar ön plana çıkmaya başlamıştır. Elektrikli araçların bataryalarının performansına ve ömrüne etki eden parametrelerden birisi de batarya çalışma sıcaklığıdır. Bataryaların istenilen sıcaklık seviyesinde tutulması için havayla soğutma, sıvıyla soğutma, ısı borusuyla soğutma, faz değiştiren malzemeyle soğutma ve termoelektrik ile soğutma gibi farklı soğutma yöntemleri kullanılmaktadır. Bu çalışmada, elektrikli araçlarda kullanılan silindirik lityum iyon bataryalardan oluşan 10x10 şeklinde dizilmiş bir batarya grubu göz önüne alınmış ve bataryaların havayla ve elektriksel olarak yalıtkan olan sıvıyla (Novec 7200) soğutulması parametrik olarak incelenmiştir. Akışkan giriş sıcaklığının (15oC-35oC), farklı deşarj hızlarında bataryada meydana gelen ısı üretiminin (2-6 W) ve Reynolds sayısının (22559-67678) ortalama batarya sıcaklığına ve basınç kaybına etkisi araştırılmıştır. Yapılan hesaplamalar sonunda hava sıcaklığının 15oC üzerine çıktığı hava şartlarında doğrudan soğutmanın yeterli olmadığı bu sebeple sıvı soğutmanın kullanılmasının gerekli olduğu belirlenmiştir. Buna ek olarak, sabit Reynolds sayılarında hava ve sıvı soğutma kullanımı ile ortaya çıkacak basınç kayıpları hesaplanmıştır. Sabit Reynolds sayıları için sıvı hızının hava hızından daha düşük olması sebebiyle, hava ve sıvı soğutma şartlarında basınç kaybında ciddi bir değişim gözlemlenmemiştir.
RDL Kalıcı Kaydıİncele - Review ArticleAçık Erişim2021The Investigation of Batteries and Thermal Management Systems Used in Electric Vehicles
Celen, Ali; Kaba, Muhammet Yasin; Kalkan, Orhan
Nowadays, electric vehicles come to the fore more than vehicles with internal combustion engines since electric vehicles are environmentally friendly and highly more efficient. Selection and thermal management of the battery, which is one of the most important equipment that constitutes electric vehicles, is important. In this study, the general view (history, classification, sales numbers, market shares) of electric vehicles, battery types that can be used in electric vehicles and battery thermal management systems were investigated. Different types of batteries commonly used in applications are compared according to their characteristics, and among these batteries, it has been observed that the type of battery that can be used in electric vehicles is lithium-ion batteries which have high specific energy (118-250 Wh/kg), high energy density (200-400 Wh/L), high specific power (200-430 W/kg), high cycle life (2000) and ideal operating temperature (-20oC-60oC). The thermal management systems, which can be used to obtain maximum performance from these batteries, are investigated and advantages and disadvantages of these methods are investigated. While it has been seen that air cooling is sufficient in vehicles with low thermal load (hybrid electric vehicles, etc.), it is observed that the use of liquid and hybrid cooling methods is appropriate in vehicles with high thermal load (full electric vehicles).
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2021Numerical investigation on the usage of finned surface in lithium nickel manganese cobalt oxides batteries by using air cooling method
Celen, Ali; Kalkan, Orhan
In this study, a numerical thermal analysis of a lithium nickel manganese cobalt oxide prismatic battery having nominal voltage of 3.7 V and capacity of 26Ah was performed during air cooling conditions. The effects of discharge rate (in the range of 3C-5C) and air velocity (in the range of 1-3 m s(-1)) on average battery temperature, maximum battery temperature, and total heat transfer rate are investigated for both flat and finned cooling surfaces. The results showed that air cooling by means of flat cooling surface is only sufficient for low discharge rate and it is necessary to use finned surfaces in order to keep battery temperature in desired operation temperature range for high discharge rate conditions. Analysis results showed that average battery temperature is reduced up to 29%, 32%, and 30% by increasing air velocity for discharge rates of 3C, 4C, and 5C with the usage of flat surface, respectively. In addition, it was seen that the average and maximum battery temperatures are reduced up to 7.9 and 8.6 K with the usage of finned cooling surface instead of flat one. The heat removed from the battery is increased 8.7 W by using finned surface at the maximum air velocity of 3 ms(-1).
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2021Experimental investigation of thermal performance of novel cold plate design used in a Li-ion pouch-type battery
Kalkan, Orhan; Celen, Ali; Bakirci, Kadir; Dalkilic, Ahmet Selim
The world's tendency towards electric vehicles has accelerated and the thermal management of them are critical part of the actual studies. Liquid-based cooling is known as the most common one among other cooling techniques. However, there is still need on the use of various heat transfer enhancement techniques to reduce the maximum temperature and maintain homogenous temperatures. This study experimentally investigated thermal performance of water-cooled cold plates used in thermal management of batteries by using conventional serpentine tube and a novel mini channel designs including a lithium-ion phosphate battery under certain discharge rates from 1C to 5C. Experiments are conducted for different water flow rates from 0.1 to 1.1 L/min as the coolant with inlet temperatures from 15 to 35 °C. Experimental results show that lower coolant inlet temperature causes the largest maximum temperature difference on battery surface. The use of mini channel cold plate resulted in 5.7 °C reduction in the maximum average battery surface temperature compared to serpentine one. Battery surface temperature homogeneity is improved up to 40% for operating conditions for mini channel cold plate usage. Thus, enhancement on thermal performance of proposed new mini channel cold plate is accomplished by temperature measurements.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2021Experimental and numerical investigation of the LiFePO4 battery cooling by natural convection
Kalkan, Orhan; Celen, Ali; Bakirci, Kadir
In this study, the thermal performance of a LiFePO4 (LFP) pouch type battery in the range of 1C-5C discharge rate at 23 °C ambient temperature and natural convection conditions is experimentally and numerically investigated. Time-dependent temperature changes of the battery are imaged with a thermal camera for each discharge, and the maximum, minimum and average changes on the battery surface are examined. In addition, the heat transfer rate through the battery is calculated for each discharge rate under natural convection conditions of the battery, and the temperature and velocity distributions on the battery surface are investigated. For the experiment with the highest discharge rate (5C), the measured maximum and average battery temperatures are determined as 52.2 °C and 50.1 °C, respectively. The calculated maximum temperature difference on the battery surface is also 6.7 °C. Moreover, the homogeneity index defined for battery surface temperature is 0.147 at 5C discharge rate. It has been observed that natural convection cooling is not sufficient for the battery at high discharge rates Furthermore, a new correlation equation has been proposed for the estimation of the heat transfer rate from a 20 Ah LFP pouch type battery under natural convection conditions at 23 °C ambient temperature.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2020Experimental study on the specific heat capacity measurement of water-based al2o3-cu hybrid nanofluid by using differential thermal analysis method
Çolak, Andaç Batur; Yıldız, Oğuzhan; Bayrak, Mustafa; Celen, Ali; Dalkılıç, Ahmet Selim; Wongwises, Somchai
Background: Researchers working in the field of nanofluid have done many studies on the thermophysical properties of nanofluids. Among these studies, the number of studies on specific heat is rather limited. In the study of the heat transfer performance of nanofluids, it is essential to raise the number of specific heat studies, whose subject is one of the important thermophysical properties. Objective: The authors aimed to measure the specific heat values of Al2O3/water, Cu/water nanofluids and Al2O3-Cu/water hybrid nanofluids using the DTA procedure, and compare the results with those frequently used in the literature. In addition, this study focuses on the effect of temperature and volume concentration on specific heat. Methods: The two-step method was tried to have nanofluids. The pure water selected as the base fluid was mixed with the Al2O3 and Cu nanoparticles and Arabic Gum as the surfactant, firstly mixed in the magnetic stirrer for half an hour. It was then homogenized for 6 hours in the ultrasonic homogenizer. Results: After the experiments, the specific heat of nanofluids and hybrid nanofluid were compared and the temperature and volume concentration of specific heat were investigated. Then, the experimental results obtained for all three fluids were compared with the two frequently used correlations in the literature. Conclusion: Specific heat capacity increased with increasing temperature, and decreased with increasing volume concentration for three tested nanofluids. Cu/water has the lowest specific heat capacity among all tested fluids. Experimental specific heat capacity measurement results are compared by using the models developed by Pak and Cho and Xuan and Roetzel. According to experimental results, these correlations can predict experimental results within the range of ±1%.
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