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51.
52.
Nowadays, doped graphenes are attracting much interest in the field of Li‐ion batteries since it shows higher specific capacity than widely used graphite. However, synthesis methods of doped graphenes have secondary processes that requires much energy. In this study, in situ synthesis of N‐doped graphene powders by using of cyclic voltammetric method from starting a graphite rod in nitric acid solution has been discussed for the first time in the literature. The N‐including functional groups such as nitro groups, pyrrolic N, and pyridinic N have been selectively prepared as changing scanned potential ranges in cyclic voltammetry. The electrochemical performance as anode material in Li‐ion batteries has also been covered within this study. N‐doped graphene powders have been characterized by electrochemical, spectroscopic, and microscopic methods. According to the X‐ray photoelectron spectroscopy and Raman results, N‐doped graphene powders have approximately 16 to 18 graphene rings in their main structure. The electrochemical analysis of graphene powders synthesized at different potential ranges showed that the highest capacity was obtained 438 mAh/g after 10 cycles by using current density of 50 mA/g at N‐GP4. Furthermore, the sample having higher defect size shows better specific capacity. However, the more stable structure due to oxygen content and less defect size improves the rate capabilities, and thus, the results obtained at high current density indicated that the remaining capacity of N‐GP1 was higher than the others.  相似文献   
53.
Burak Markal  Mete Avci 《传热工程》2017,38(16):1415-1428
This study focuses mainly on the prediction of saturated flow boiling heat transfer in microchannels. A wide range of experiments has been carried out with de-ionized water to obtain a comprehensive data set. Experiments of mass fluxes of 51–728.7 kg/m2s, wall heat fluxes of 36–221.7 kW/m2, vapor qualities of 0.01–0.69, liquid Reynolds number of 7.72–190, aspect ratios of 0.37–5.00 (with a constant hydraulic diameter of 100 µm) and hydraulic diameters of 100–250 µm (for constant aspect ratio = 1). A new correlation including the aspect ratio effect is proposed to predict the heat transfer coefficient for saturated flow boiling in microchannels. The proposed correlation shows very good predictions with an overall mean absolute error of 16.9% and 86.4%, 96.2% and 99.5% of the predicted data falling within ±30, ±40 and ±50% error bands, respectively.  相似文献   
54.
In this study, the impacts of non‐integer order controller on the stable parameter space of the microgrid (MG) frequency control system with fixed communication time delay are investigated and discussed with the help of the stability boundary locus (SBL) method. This study proposes a non‐integer order controller for the load frequency control (LFC) of the MG systems. To that end, the load frequency model of the MG is formulated and then the characteristic equations of this model are obtained. Then, with the help of this characteristic equation, the stable parameter space of the non‐integer controller is determined with regard to different time delay (τ ) and fractional integral order values (α ) using the SBL method. In order to show the accuracy of the obtained stable parameter space, time domain and generalized modified Mikhailov (GMM) criterion studies are carried out for different values of (τ ) and (α ). According to the results obtained, the areas of stable parameter space according to different α values and τ = 1.6 are calculated as 444.8860 for α = 0.4 , 342.9728 for α = 0.7 , 259.3578 for α = 1 , 216.2541 for α = 1.3 and 159.6826 for α = 1.6 . In addition, the areas of stable parameter space according to different τ values and α = 1.4 are calculated as 784.5222 for τ = 1 , 106.3219 for τ = 2 , 29.6959 for τ = 3 and 11.5946 for τ = 4 . Despite the extreme variability arising from nature of resources that make up the MG, the designed non integer order controller with the values selected within the stable parameter space stably carries out LFC control of the MG.  相似文献   
55.
The techniques used in the cooling of electronic equipments vary widely depending on the particular application. Cooling with liquids and impinging air jets become important where classical cooling techniques may be insufficient, while a single or array jet is employed where highly localised cooling is desired. This paper provides a comparative survey of advanced methods of cooling for electronic systems and an economical analysis of cooling electronic equipments using slot and circular jets.  相似文献   
56.
Nowadays, with the increase in the amount of power generation related to renewable energy resources, the need for energy storage and management is raised. In this regard, the hydrogen energy plays a critical role in the development of renewable technologies. In view of the above, advanced controller design is presented in this paper to effectively perform load frequency control of islanded fuel cell microgrid based on the wind turbine, photovoltaic, fuel cell, electrolyzer, battery energy storage systems, and residential and commercial loads. The controller design is based on the determination of the controller parameters that the fuel cell microgrid system will provide the desired dynamic properties. In the proposed controller design, virtual gain and phase margin testers are added to provide the desired dynamic properties. The controller's stable parameter plane is determined with the help of the stability boundary locus method, taking into account time delay, gain, and phase margin. First, the accuracy of the stable parameter plane determined for the proposed controller design is demonstrated by means of time domain and eigenvalue analyzes. Finally, in order to show the performance of the advanced controller design and the success of the fuel cell as a backup generator, analysis studies have been carried out using actual data of solar and wind, and appropriate changes of load in studied microgrid.  相似文献   
57.
In order to improve filtering efficacy, nanoparticles are often deposited as photocatalytic degrading agents onto porous ceramics. This study aimed to deposit ZnO nanoparticles on ceramic substrates produced from fly ash and red mud with adjustable porosity and investigate their photocatalytic properties. To achieve this goal, at first porous ceramics were produced and sintered at various temperature/time intervals. It was observed that sintering at 800°C for 120 min provided a proper structure and porosity. In addition, MgO replacement with MgCO3 lowered the water absorption of the samples from 25.63% to 11.45%. The samples were then coated with ZnO nanoparticles using the sol–gel method and the ZnO structures obtained were micron-sized plates. It was observed that increasing porosity increased the ZnO amount and accordingly the photocatalytic properties of the products. During the adsorption tests conducted in the dark, the coated ceramic samples were stained with MB with a maximum MB adsorption ratio of ∼14%. On the other hand, no visible MB stain was observed on the samples that were exposed to UV irradiation, and the MB removal after the UV irradiation was 93.6%; therefore, it was concluded that the dominant MB removal mechanism was photocatalytic.  相似文献   
58.
In this study, N-pyrrole (Py), N-phenylpyrrole (PhPy), and 1[4-methoxyphenyl]-1H-pyrrole (MPhPy) homopolymers were synthesized electrochemically onto carbon fiber microelectrodes (CFMEs). The influences of the substituent effect on electrochemical impedance spectroscopy (EIS) were studied comparatively. All the monomers were electrodeposited in 0.05 M tetraethyl ammonium perchlorate (TEAP)/dichloromethane (CH2Cl2) solution and characterized by cyclic voltammetry (CV), Fourier transform infrared reflectance spectrophotometry (FTIR-ATR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The morphological study reveals that the polymers were deposited as a continuous and well adhered film to surface of the CFME. An equivalent electrical circuit for three different monomers on CFMEs was proposed and experimental data were simulated to obtain the numerical values of circuit components. All results support the high quality film deposition that resulted in desired electronic properties due to the electron donating behaviors of substituent group of phenyl and methoxy.  相似文献   
59.
This paper presents a new dynamic error compensation approach with novel data-based closed-loop tuning scheme to enhance tracking accuracy of machine tool feed-drives. Both servo dynamics and friction disturbance induced positioning errors are pre-compensated by modifying the reference trajectory. Velocity and acceleration profiles of reference trajectory are modulated to achieve perfect tracking. Reference position profile is modified based on the pre-sliding friction regime to eliminate quadrant glitches. Optimal error compensation is achieved by a digital trajectory pre-filter whose parameters are tuned automatically by making on-the-fly iterative adjustments. Effectiveness of proposed compensation approach is validated experimentally in multi-axis feed-drive systems.  相似文献   
60.
In the present study, the ultrasonication method was used to investigate the effect of ultrasonic energy on the hydrolysis of corn, rice, and wheat starch by using the alpha-amylase enzymes produced by Bacillus species and Bacillus licheniformis. The effects of sonifier operation variables such as duty cycle and acoustic power rate on the stability of alpha-amylase enzymes and hydrolysis degrees of three types of starches were investigated at a temperature of 40°C and pH 6.5. To determine the effect of temperature with sonication on the hydrolysis process, wheat starch hydrolysis experiments were also carried out at a temperature of 50°C. Then, the relation between duty cycle and enzyme stability during hydrolysis for each enzyme at 50°C was expressed by a zero-order inactivation model.  相似文献   
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