Heat dissipation is an important issue in compactness and weight of equipment. Heat dissipaters are not only chosen for their thermal performance but also for other design parameters such as weight, cost and reliability depending on applications. The present paper reports an experimental study to investigate the heat transfer enhancement over vertical rectangular fin arrays equipped with lateral circular perforations. The cross‐sectional area of the rectangular duct was 200 mm × 80 mm. The data used in performance analysis were obtained experimentally for aluminum at 200 Watts heat input, by varying the fin thickness, size of perforations and varying Reynolds number range 2.1 × 104 to 8.7 × 104. Using the Taguchi experimental design method, optimum design parameters and their levels were investigated. Average Nusselt number was considered as a performance characteristics. An L9 (33) orthogonal array was selected as an experimental plan. Optimum results were found by experimenting with porosity, Reynolds number and thickness of the fin. It is observed that the Reynolds number and maximum porosity have a larger impact on Nusselt number. 相似文献
In recent years, a number of direct coal liquefaction processes have been developed. All processes use a slurry type reactor. Although for lab-scale reactors of large length-to-diameter ratio the use of highly sophisticated slurry reactor model may be justified, simple considerations can meaningfully elucidate the behavior of industrial reactors. A simple analysis shows that the coal liquefaction is controlled by intrinsic kinetics. Both gas and slurry phases can be assumed to be completely backmixed in large diameter reactors. A simple analysis of the thermal behavior revealed multiplicity for a fairly wide range of operating conditions. In most cases, the intermediate unstable steady state is close to the temperature observed in adiabatic coal liquefaction reactors (with and without quench). Due to the unstable character of the operation, point pathological phenomena like runaway may be possible and a close feedback control of the commercial reactor may be required. 相似文献
A jaw-like bis-porphyrin (bis-TPP) molecule was synthesized anchoring of two porphyrin molecules to a benzene ring at the meta positions through the ester linkage. The bis-TPP molecule and its zinc-derivative (Zn-bis-TPP) were spin-coated on glass surfaces to construct two chemiresistive room temperature NH3 gas sensors. Both the films showed high selectivity, reproducibility and reversibility in sensing NH3 gas (5–40 ppm) in air. The sensing characteristics of the Zn-bis-TPP films (response (2 s) and recovery (2.5 min) times; linear response (952%)) were better than that of the bis-TPP films (response (8 s) and recovery (7.5 min) times; linear response (131%)). This is attributed to the amorphous nature of the former. 相似文献
A new, simple and highly selective method for spectrophotometric determination of selenium in waste water samples is described. Selenium(IV) oxidizes I(-) ions into I(2) which subsequently reacts with excess of I(-) ion in the acidic media to give tri-iodide ions (I(3)(-)), and it further reacts with cetylpyridinium cation (CP(+)) to give a violet colored species. The value of molar absorptivity of the ion-associate species in terms of selenium is 1.80 x 10(4) L mol(-1)cm(-1) at lambda(max) 510 nm. The detection limit of the method is 10 ng mL(-1) Se. The calibration curve is linear over 50-1000 ng mL(-1) Se with slope, intercept and co-relation coefficient of 0.23, -4.0 x 10(-4) and +0.99, respectively. None of the tested diverse ions interfered in the present method. The method has been tested for the determination of selenium in waste water samples. 相似文献
A novel and sensitive spectrophotometric method for the determination of molybdenum at trace levels in environmental and biological samples is proposed. The method is based on the reaction of Mo (V) with thiocyanate (SCN(-)) and methyltrioctyl ammonium chloride (MTOAC) in acidic medium. The red colored complex of molybdenum is extracted with N-phenylbenzimidoyl thiourea (PBITU) in 1-pentanol for its determination by spectrophotometry. The sensitivity of the present method is higher than other conventional thiocyanate method, due to the use of MTOAC in liquid-liquid extraction. The value of molar absorptivity of the complex with respect to molybdenum is 7.6x10(4)Lmol(-1)cm(-1) at 470nm. The limit of detection of the metal is 5ngmL(-1). The system obeys Beer's law between 20 and 1000ngmL(-1) with slope, intercept and correlation coefficient values of 0.81, 2.5x10(-3) and +0.999, respectively. Most of the metal ions tested did not interfere in the determination of molybdenum. The proposed method has been successfully applied for the determination of the molybdenum in environmental and biological samples. 相似文献
This paper focuses on developing an area efficient hyperbolic Coordinate Rotation Digital Computer (CORDIC) algorithm with performance improvement. The algorithm eliminates the need of scale factor calculation in the Range of Convergence (ROC). At the same time the range of convergence offered is higher than the conventional CORDIC ROC in the hyperbolic rotation mode. Being the only kind of algorithm in hyperbolic rotation with sign sequence μ?=?1 always, one complete operation requires just 5 iterations. Thus the pipelined implementation has 5 stages which provides a 50% increase in throughput in comparison to conventional CORDIC. As far as the area improvement is considered, 16-bit processor can be realized using 56% less number of full adders required by Flat-CORDIC. The x and y datapath are based on series expansion of hyperbolic functions. The complete algorithm design along with pipelined architecture implementation is detailed. 相似文献
The growth of Wireless Sensor Networks (WSN) becomes the backbone of all smart IoT applications. Deploying reliable WSNs is particularly significant for critical Internet of Things (IoT) applications, such as health monitoring, industrial and military applications. In such applications, the WSN’s inability to perform its necessary tasks and degrading QoS can have profound consequences and can not be tolerated. Thus, deploying reliable WSNs to achieve better Quality of Service (QoS) support is a relatively new topic gaining more interest. Consequently, deploying a large number of nodes while simultaneously optimizing various measures is regarded as an NP-hard problem. In this paper, a Grey wolf-based optimization technique is used for node deployment that guarantees a given set of QoS metrics, namely maximizing coverage, connectivity and minimizing the overall cost of the network. The aim is to find the optimum number of appropriate positions for sensor nodes deployment under various p-coverage and q-connectivity configurations. The proposed approach offers an efficient wolf representation scheme and formulates a novel multi-objective fitness function. A rigorous simulation and statistical analysis are performed to prove the proposed scheme’s efficiency. Also, a comparative analysis is being carried with existing state-of-the-art algorithms, namely PSO, GA, and Greedy approach, and the efficiency of the proposed method improved by more than 11%, 14%, and 20%, respectively, in selecting appropriate positions with desired coverage and connectivity.
In recent years, the Internet has enabled access to widespread remote services in the distributed computing environment; however, integrity of data transmission in the distributed computing platform is hindered by a number of security issues. For instance, the botnet phenomenon is a prominent threat to Internet security, including the threat of malicious codes. The botnet phenomenon supports a wide range of criminal activities, including distributed denial of service(DDoS) attacks, click fraud, phishing, malware distribution, spam emails, and building machines for illegitimate exchange of information/materials. Therefore, it is imperative to design and develop a robust mechanism for improving the botnet detection, analysis, and removal process. Currently, botnet detection techniques have been reviewed in different ways; however, such studies are limited in scope and lack discussions on the latest botnet detection techniques. This paper presents a comprehensive review of the latest state-of-the-art techniques for botnet detection and figures out the trends of previous and current research. It provides a thematic taxonomy for the classification of botnet detection techniques and highlights the implications and critical aspects by qualitatively analyzing such techniques. Related to our comprehensive review, we highlight future directions for improving the schemes that broadly span the entire botnet detection research field and identify the persistent and prominent research challenges that remain open. 相似文献