Entropy generation analysis of convective airflow in a solar updraft tower power plant

The main objective of this numerical investigation is to interpret the entropy generation for free convection airflow in a solar tower updraft system. The ground surface is subjected to uniform hot temperature and the collector cover is maintained at lower constant temperature while the chimney wall is adiabatic. Two dimensionless equations of steady laminar free convective airflow are discretized using the finite volume approach. Numerical solutions were accomplished for different values of the Rayleigh number. Results are given in terms of isotherms, velocity magnitude, local entropy generation associated with thermal and fluid friction, local total entropy generation and local Bejan number contours for Rayleigh number ranging between 10³ and 10⁸. The reported results show that thermal and frictional irreversibilities are proportional to the Rayleigh number. Also, it was found that, at lower Rayleigh, total irreversibility is attributable to the thermal irreversibilities and occurs essentially in the collector section. At higher Rayleigh, frictional irreversibilities are increased significantly and become the dominant source of irreversibility in the solar tower, and the chimney section is the main contributor in the total irreversibility in the system.     

Study of 55Al-43.6Zn-1.6Si Alloy Coating Parameters over St37 Steel Sheet via Hot-Dipping Process and its Corrosion Behavior

In this work the 55Al-43.4Zn-1.6Si alloy coating produced by hot-dipping technique was studied. The St37 steel sheets were coated through dipping in the molten at different bath temperature and various dipping time. Microstructure of the coatings was evaluated using Optical Microscope (OM) and Scanning Electron Microscope (SEM). Elemental analysis of the specimens was investigated by the Energy Dispersive X-ray Spectroscopy (EDX) analysis. The results showed that, by increasing the bath temperature, the thickness of the both coating (55Al-43.4Zn-1.6Si) and the intermetallic layer (Fe₄Al₁₃) increased. The results revealed that, the growth rate of the intermetallic layer was much lower than that of the coating. Adhesiveness and hardness of the coating evaluated by the bending and Vickers microhardness tests. The hardness results showed that by increasing the temperature and duration time, the hardness of the coating was decreased. Additionally, flexibility of the coatings in the all three different temperatures of the molten bath was slightly decreased. Salt spray test was used to study the corrosion behavior of the coatings. Results showed that the specimens coated at 650 ^°C for 60 s revealed the best performance in the salt spray test.     

Synthesis of mesoporous cobalt ferrite/hydroxyapatite core-shell nanocomposite for magnetic hyperthermia and drug release applications

In this study, cobalt ferrite/hydroxyapatite nanocomposite was developed by a new approach to design a uniform core-shell combination. The prepared powders were characterized by different techniques such as Brunauer–Emmett–Teller (BET) analyses, transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), Vibrating-sample magnetometer (VSM), and field emission scanning electron microscopy (FESEM). TEM micrographs showed the formation of a uniform core/shell structure with a particle size of about 85$\pm 65$ nm. The controlled drug release experiments showed that the samples have a good drug loading capability and controlled delivery ability up to 50 h. Moreover, with different magnetic fields or different cobalt ferrite ratios to hydroxyapatite, it is possible to manipulate the amount of produced heat, making this composite promising for various kinds of magnetic hyperthermia-based treatment. Cytotoxicity of the nanocomposite was evaluated by MTT assay using MG63 cells. MTT and VSM results revealed that incorporating hydroxyapatite on cobalt ferrite nanoparticles' surface significantly increases cell compatibility, whereas it reduces magnetization saturation. The results suggest that cobalt ferrite/hydroxyapatite nanocomposite with multifunctionality and uniform structure has a great capability to be applied for medical uses.     

MEASUREMENT TECHNIQUES AND DATA INTERPRETATIONS FOR VALIDATING CFD MULTI PHASE REACTOR MODELS

One problem associated with the use of Computational Fluid Dynamics(CFD) in reactor modeling is the proper validation of the models. Proper validation in this context means that the physical fluid dynamic model, the mathematical implementation and the data used for validation must be consistent. The present paper addresses this issue and to provide appropriate relations between experimental method and modeling approach

A critical review of currently used measurement techniques for characterizing multiphase now systems is presented. The interpretation of the data obtained from the various techniques is discussed as well as how these data can be used for validation of various CFD model formulations

Steady state models can be validated using time averaged data, making sure that the averaging time for the experimental data is long enough so that low frequency periodic oscillations also are evened out. If homogeneous systems are considered, then a volume average approach may be used for modeling, If the system cannot be considered homogeneous and steady, as is the most common case, then a dynamic ensemble averaging technique should be preferred. The validation of such models must be done with methods fast enough to resolve periodic fluctuating structures of interest. These methods are cumbersome and tedious to operate and the ergodic hypothesis may be invoked enabling the use of volume or time averaged data for the validation of ensemble averaged models.     

Robust iterative learning control design is straightforward for uncertain LTI systems satisfying the robust performance condition

This note demonstrates that the design of a robust iterative learning control is straightforward for uncertain linear time-invariant systems satisfying the robust performance condition. It is shown that once a controller is designed to satisfy the well-known robust performance condition, a convergent updating rule involving the performance weighting function can be directly obtained. It is also shown that for a particular choice of this weighting function, one can achieve a perfect tracking. In the case where this choice is not allowable, a sufficient condition ensuring that the least upper bound of the /spl Lscr//sub 2/-norm of the final tracking error is less than the least upper bound of the /spl Lscr//sub 2/-norm of the initial tracking error is provided. This sufficient condition also guarantees that the infinity-norm of the final tracking error is less than the infinity-norm of the initial tracking error.     

Genotypic heterogeneity and phenotypic variation among patients with type 2 Gaucher''s disease

Electrophysiological examination of the function of perceptive organs, like eye or cochlea, works up more and more interest in scientists to look for an objective method of vestibular end organ investigation. In many papers authors attempt to estimate the efficiency of vestibular organs after using angular or linear acceleration as stimulus, which required special and expensive apparatus. Papers that described vestibular evoked myogenic potentials (VEMPs) seem to be very promising. In this study an attempt was taken to obtain VEMPs with own modification of stimulus and response register. Preliminary examinations in 14 healthy volunteers were performed. Two subjects with sensorineural deafness on one side and symmetric, normal excitability of vestibular organs and 4 with bilateral hearing loss and unilateral weakness of vestibular excitability were examined. There were also 6 patients with only weakness of vestibular excitability. On the basis of practical observations, there is a possibility that evoked potentials were a result of stimulation of vestibular part of the inner ear--sacculus. The method of the study is objective, simple, secure and comfortable for patients.     

Investigation of factors affecting on viscosity reduction of sludge from Iranian crude oil storage tanks

Crude oil is a kind of water/oil emulsion, which the oil phase consists of organic molecules with different molecular weights such as alkanes, paraffin, asphaltene, and resins. Due to the change in physicochemical conditions during the production, transportation, storage, and refining, heavier molecules can precipitate from crude oil. Thus, viscous sludge formed at the bottom of storage tanks can cause many problems including reduction of storage capacity of tank, oil contamination, corrosion, repair costs, environmental pollution, etc. The reduction of sludge viscosity can be achieved by reduction of its interfacial tension. In this study, different chemical and physical factors, influencing prepared emulsions (made of sludge, water and surfactant), such as surfactants, solvents, temperature, pressure, and mixing conditions were investigated. Results showed that non-ionic surfactants (like bitumen emulsifier), and solvents (such as mixed xylene, AW-400, and AW-402), injection of additives, applying pressure, and mixing operations had a positive effect on reduction of emulsion viscosity. All experiments were carried out with sludge obtained from crude oil storage tanks at Kharg Island, Iran.