Analysis of heat transfer and entropy generation for a low-Peclet-number microtube flow using a second-order slip model: an extended-Graetz problem

Cataloged from PDF version of article.The classical Graetz problem, which is the problem of the hydrodynamically developed, thermally developing laminar flow of an incompressible fluid inside a tube neglecting axial conduction and viscous dissipation, is one of the fundamental problems of internal-flow studies. This study is an extension of the Graetz problem to include the rarefaction effect, viscous dissipation term and axial conduction with a constant wall temperature thermal boundary condition. The energy equation is solved to determine the temperature field analytically using general eigenfunction expansion with a fully developed velocity profile. To analyze the low-Peclet-number nature of the flow, the flow domain is extended from −∞ to +∞. To model the rarefaction effect, a second-order slip model is implemented. The temperature distribution, local Nusselt number, and local entropy generation are determined in terms of confluent hypergeometric functions. This kind of theoretical study is important for a fundamental understanding of the convective heat transfer characteristics of flows at the microscale and for the optimum design of thermal systems, which includes convective heat transfer at the microscale, especially operating at low Reynolds number

Microchannel heat transfer with slip flow and wall effects

Cataloged from PDF version of article.Analysis is presented for conjugate heat transfer in a parallel-plate microchannel. Axial conduction in the fluid and in the adjacent wall is included. The fluid is a constant property gas with a slip-flow velocity distribution. The microchannel is heated by a small region on the channel wall. The analytic solution is given in the form of integrals by the method of Green's functions. Quadrature is used to obtain numerical results for the temperature and heat transfer coefficient on the heated region for various Peclet number, Knudsen number, and wall materials. A region downstream of the heater is also explored. These results have application in the optimal design of small-scale heat transfer devices for biomedical applications, electronic cooling, and advanced fuel cells

Determination of appropriate areas in terms of bio comfort by using summer temperature index with the help of GIS throughout Ordu province

Threshold values for climate elements have been determined and some indices have been developed, especially with studies on human comfort. It is a fact that the feeling of comfort is subjective and there are different psychological and physical factors affecting this feeling. However, the presentation of threshold values and indices is very interesting in determining the current state of the climate conditions of the environment in terms of average and optimal values and the extent of deviation from the most appropriate values. The values of the climate elements that need to be looked at in order to provide bioclimatic comfort; it as a combination of 21-27.5 °C temperature, 30-65% relative humidity and wind speed up to 5 m/s in open area. These values have been used in many bioclimatic assessments. In addition to being an effective factor in almost every aspect of people's lives, bio comfort is also important in the periods when tourism activities are carried out. Thus, it is extremely important to determine the regions that are not suitable for bio comfort in the season of tourism in the regions that tourism activities are carried out. The aim of this research is to determine the suitable and unsuitable areas in terms of bio comfort in summer by using New Summer Index throughout Ordu province via GIS. As a conclusion, it has been determined that the area covering approximately 57.62% of the southern part of the province is cold, and the most comfortable part of the province is the part covering approximately 11.12% of the province and located by the sea in the north of the province

Design and fabrication of a microfluidic device for synthesis of chitosan nanoparticles

Cataloged from PDF version of article.Chitosan nanoparticles have a biodegradable, biocompatible, nontoxic structure, and are commonly used for drug delivery systems. In this study, design, modeling, and fabrication methodology of a microfluidic device for the synthesis of chitosan nanoparticles is presented. In the modeling, 2D flow and concentration field is computed using COMSOL Multiphysics® simulation environment to predict the performance of the device. The microfluidic chip is fabricated out of PDMS. The fabrication of the mold for the microfluidic device is performed using high-precision micromachining. Some preliminary proof-of-concept experiments were performed. It was observed that compared to conventional batch-type methods, the proposed microfluidic device can perform the synthesis much faster and in a much automated and convenient manner. Copyright © 2013 by ASME

Warpage characterization of microchannels fabricated by injection molding

Cataloged from PDF version of article.Mass-production of microfluidic devices is important for biomedical applications in which disposable devices are widely used. Injection molding is a well-known process for the production of devices on a mass scale at low-cost. In this study, the injection molding process is adapted for the fabrication of a microfluidic device with a single microchannel. To increase the product quality, high-precision mechanical machining is utilized for the manufacturing of the mold of the microfluidic device. A conventional injection molding machine is implemented in the process. Injection molding was performed at different mold temperatures. The warpage of the injected pieces was characterized by measuring the part deformation. The effect of the mold temperature on the quality of the final device was assessed in terms of the part deformation and bonding quality. From the experimental results, oneto-one correspondence between the warpage and the bonding quality of the molded pieces was observed. It was found that as the warpage of the pieces decreases, the bonding quality increases. A maximum point for the breaking pressure of the bonding and the minimum point for the warpage were found at the same mold temperature. This mold temperature was named as the optimum temperature for the designed microfluidic device. It was observed that the produced microfluidic devices at the mold temperature of 45 !C were able to withstand pressures up to 74 ba

A Material Perspective on Consequence of Deformation Heating During Stamping of DP Steels

Recent studies showed that, during stamping of high strength steels at industrially relevant production rates, local temperature in the blank may rise up to 200°C – 300°C due to deformation heating. Moreover, die temperature may also rise up to 100°C – 150°C for progressive stamping dies. Based on the common assumption that the blank softens as the temperature increases, thermal softening creates a margin in Forming Limit Diagram (FLD) and therefore the FLD determined at room temperature can safely be used for those cases. In this article, the validity of this assumption on DP590 steel is questioned by high temperature tensile tests (RT - 300°C) at various strain rates (10-3 s-1 – 1 s-1). The results indicated a decrease both in uniform and total elongation in 200°C – 300°C range together with several other symptoms of Dynamic Strain Aging (DSA) at all strain rates. Concurrent with the DSA, the simulated FLD confirms the lower formability at high temperature and strain rates. Thus, it is concluded FLD determined at RT may not be valid for the investigated steels

Moving Object Detection in Wavelet Compressed Video

Cataloged from PDF version of article.In many surveillance systems the video is stored in wavelet compressed form.In this paper, an algorithm for moving object and region detection in video which is compressed using a wavelet transform (WT) is developed.The algorithm estimates the WT of the background scene from the WTs of the past image frames of the video.The WT of the current image is compared with the WT of the background and the moving objects are determined from the difference.The algorithm does not perform inverse WT to obtain the actual pixels of the current image nor the estimated background. This leads to a computationally efficient method and a system compared to the existing motion estimation methods. (C) 2005 Published by Elsevier B.V

Expansion and Rehabilitation of the State Fish Pier in Gloucester, Massachusetts

The State Fish Pier in Gloucester, Massachusetts, has been expanded and rehabilitated to provide an upgraded facility to support the local fishing industry. Expansion consisted of a new Finger Pier and solid fill extension of the existing pier. Rehabilitation consisted of replacing a deteriorated wharf with a new higher load carrying wharf. Subsurface conditions ranged from rock outcrops exposed at low tide at some locations to thick marine deposits overlying rock at other locations. Foundation support for the new Finger Pier and rehabilitated wharf consisted of concrete filled steel pipe piles, a portion of which had to he socketed into bedrock due to lack of soil overburden. Compression and tension load tests were performed to verify the pile design capacities