Laser cutting of Kevlar laminates: First and second law analysis

Bekir S. Yilbas,Ahmet Z. Sahin,C. Chatwin,Tahir Ayar 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.4

Kevlar laminates are difficult to machine using conventional machining methods because of their thermal and mechanical properties. Laser cutting offers advantages over conventional machining methods, such as precision of operation, non-frictional processing, and operational cost. This provides the motivation for the present study, which reports on laser cutting of Kevlar laminates of different thicknesses. The first and second law efficiencies of the cutting process are formulated and predicted in line with the experimental parameters. The laser cut surfaces are examined using optical and electron scanning microscopes. It is demonstrated that the first and second law efficiencies improve at high laser cutting speeds and low laser output power levels. For these conditions parallel sided kerfs with no sideways burning are produced.

Designing an Efficient and Secure Credit Card-based Payment System with Web Services Based on the ANSI X9.59-2006

Cheong, Chi Po,Fong, Simon,Lei, Pouwan,Chatwin, Chris,Young, Rupert Korea Information Processing Society 2012 Journal of information processing systems Vol.8 No.3

A secure Electronic Payment System (EPS) is essential for the booming online shopping market. A successful EPS supports the transfer of electronic money and sensitive information with security, accuracy, and integrity between the seller and buyer over the Internet. SET, CyberCash, Paypal, and iKP are the most popular Credit Card-Based EPSs (CCBEPSs). Some CCBEPSs only use SSL to provide a secure communication channel. Hence, they only prevent "Man in the Middle" fraud but do not protect the sensitive cardholder information such as the credit card number from being passed onto the merchant, who may be unscrupulous. Other CCBEPSs use complex mechanisms such as cryptography, certificate authorities, etc. to fulfill the security schemes. However, factors such as ease of use for the cardholder and the implementation costs for each party are frequently overlooked. In this paper, we propose a Web service based new payment system, based on ANSI X9.59-2006 with extra features added on top of this standard. X9.59 is an Account Based Digital Signature (ABDS) and consumer-oriented payment system. It utilizes the existing financial network and financial messages to complete the payment process. However, there are a number of limitations in this standard. This research provides a solution to solve the limitations of X9.59 by adding a merchant authentication feature during the payment cycle without any addenda records to be added in the existing financial messages. We have conducted performance testing on the proposed system via a comparison with SET and X9.59 using simulation to analyze their levels of performance and security.

Real-Time Occlusion Tolerant Detection of Illegally Parked Vehicles

Waqas Hassan,Philip Birch,Rupert Young,Chris Chatwin 제어·로봇·시스템학회 2012 International Journal of Control, Automation, and Vol.10 No.5

Illegally parked vehicle detection systems are considered crucial elements in the development of any video-surveillance based traffic-management system. The major challenges in this task lie in making the end solution real time, illumination invariant and occlusion tolerant. A two-stage application framework is presented which efficiently identifies vehicles parked illegally in restricted parking-zones. A real-time approach has been followed and an improved foreground segmentation method based on Segmentation History Images (SHI) is developed to identify stationary objects. A three step pixel based classification method is applied on the background segmentation output to segment adjacent moving pixels that become stationary for certain periods of time. The process then locks on to all identified stationary pixel patches, parts of which overlap with the regions of interest marked interac-tively a priori. The second stage of the process is applied subsequently to track all the stationary pixel patches detected during the first stage using an adaptive edge orientation based tracking method. Experimental results show that the tracking technique gives more than a 90% detection success rate, even if objects are partially occluded. The technique has been tested on the UK Home Office i-LIDS Parked Vehicle video sequences along with the University of Sussex Traffic Dataset and results are compared with other available state of the art methods.

Experimental study of effects of wicks and boundary conditions on thermal performance of heat pipes

Foster Kwame Kholi,Hariharan Kallath,Alberto Mucci,Man Yeong Ha,Jason Chetwynd-Chatwin,민준기 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.1

The inherent two-phase heat transport of heat pipes (HPs) is progressively being examined for potential uses. These thermal devices are affected by many operating factors, prompting this study to investigate the effects of different types of wicks and working conditions on the time-dependent thermal behavior. Primarily, the effects of different wick performances were investigated under various operating conditions. The resulting surface temperatures depicted in the time to steady performance and the dry-out behavior revealed the conditions to improve the HPs design. The thermal resistance decreased from 0.6 K/W (at 25 W) to 0.05 K/W (at 200 W) by increasing the HP diameter from 6 to 10 mm; these values are relative to those of copper rods, which decrease from 2.70 K/W (at 25 W) to 0.40 K/W (at 200 W). Nonlinear and linear temperature responses were recorded when the HPs diameter and length were varied. Compared to conventional mesh and groove wicks, the composite groovesintered, mesh-sintered, and groove-mesh wicks recorded lower thermal resistance with distinctively faster startup times, lower startup temperatures, better temperature uniformity and less dynamic instability. Tilting the HPs relative to the horizontal position lessens failure tendencies. Usually, dynamic responses are typically first-order under the conditions studied. Hence, proper sizing of HPs and correct wick selection can improve their performance.

An improved correlation to predict the heat transfer in pulsating heat pipes over increased range of fluid-filling ratios and operating inclinations

Foster Kwame Kholi,Alberto Mucci,Hariharan Kallath,하만영,Jason Chetwynd-Chatwin,민준기 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6

Previous correlations that have been used to predict the heat transfer performance of pulsating heat pipes (PHPs) offer limited thermal predictions within a narrow range of fluid-filling ratios and PHP inclinations. In this paper, a novel semi-empirical correlation with improved scope is proposed, with an increased range of fluid-filling ratios and PHP inclinations. The proposed correlation employs the dimensionless numbers governing the thermohydrodynamic operation of PHPs, and achieved ±30 % accuracy when predicting selected experimental data, showing reasonably good agreement. Unlike previous correlations, the new correlation can be used for different working fluids, geometrical aspect ratios, and heat loads. A comprehensive assessment of the relative significance of the correlation parameters on the total heat transfer performance is discussed. The new correlation with its flexible application range is expected to assist in faster and more enhanced thermal predictions as interest in PHPs grows.

An improved numerical analysis of the transient oil de-congealing process in a heat exchanger under low temperature conditions

박재현,Foster Kwame Kholi,Michael Klingsporn,Jason Chetwynd-Chatwin,하만영,민준기 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.1

In the present study, an improved heat exchanger model is proposed to efficiently analyze the cold oil removal process inside a fuel-cooled oil cooler. When exposed to low temperature condition, oil within a heat exchanger begins to congeal, preventing oil flow and causing loss of cooling. The conventional heat exchanger models, however, shows limits in reflecting the highly varying viscosity effects due to large temperature difference. To overcome this, the conventional porous media model was rewritten with the friction and Colburn j-factors that include the temperature dependent property variation. The property correction method by Shah and Sekulic [31] was added to enhance the prediction accuracy. Also, a relief valve model based on the porous media approximation is developed. The developed models were validated against the experimental data. Transient three-dimensional numerical simulations are carried out to analyze the effects of operating conditions on de-congealing phenomenon inside the FCOC.

A SIMPLIFIED PREDICTION OF THE COOLING PERFORMANCE OF A FUEL-COOLED OIL COOLER UNDER LOW-TEMPERATURE CONDITIONS: EXPERIMENTAL AND NUMERICAL STUDY

Foster Kwame Kholi,Jaehyun Park(박재현),Hyo Je Son(손효제),Hariharan Kallath,Michael Klingsporn,Jason Chetwynd-Chatwin,June Kee Min(민준기) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.4

This study examined the cooling performance of a fuel-cooled oil cooler (FCOC) under typical operating conditions. The oil cooler can fail due to the congealing of oil in the FCOC core at low-temperature conditions, which could be recovered by de-congealing the oil flow. The de-congealing time can be affected by changes in oil pressure and temperature conditions, flow re-routing, and malfunctioning of the oil bypass valve (OBV). In this study, we proposed a prediction model for the transient oil de-congealing phenomenon in the FCOC. The numerical procedure was based on the one-dimensional (1D) flow and thermal network analysis and the effectiveness (ε)-NTU method. The commercial code was customized to implement the de-congealing phenomena. Pre-defined empirical correlations and property corrections aided the modeling of the detailed de-congealing process. Moreover, the 3D CFD temperature contours provided a visual insight into the internal flow inside the FCOC core during the de-congealing process. An experimental study was conducted in parallel to validate the prediction result. Both experimental and numerical methods showed a loss of cooling when the OBV fails. The oil temperature and pressure, and flow directions affect the de-congealing process. The present model proved useful for various oil cooler configurations that are difficult to investigate experimentally and could quickly provide oil de-congealing results.