Flow Phenomena: Fluids, Heat and Mass

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Authors: Bohdan Mochnacki, Alicja Piasecka-Belkhayat
Abstract: Thermal processes in the domain of a thin metal film which are subjected to a laser pulse are considered. The mathematical model based on the dual phase lag equation (DPLE) results from the generalized form of the Fourier law. The governing equation is supplemented by appropriate boundary and initial conditions. The numerical model of metal heating is constructed using the explicit scheme of the finite difference method for hyperbolic equations. The thermophysical parameters of the material (gold) are treated as interval numbers and at the stage of the FDM algorithm construction the rules of interval arithmetic are applied. In this way the numerical solution is obtained in the fuzzy form. Such an approach gives interesting practical information about the course of the process because the values of thermophysical parameters collected in the literature often differ significantly. In the final part of the paper an example for a numerical solution is presented.
Authors: Erfan Maleki, Hani Sadrhosseini
Abstract: In this article a comprehensive numerical study is performed to compare the effect of fluid flow across a duct with various cross sectional shapes and with different velocities of the flow. Circular, elliptical and rectangular cross sections have been chosen for the ducts and air flows across them with four values of low Reynolds numbers in the range of Re = 1 to Re = 1000. Continuity and momentum equations with proper boundary conditions are solved in two dimensions. Streamlines, pressure distribution and Velocity profiles are obtained and creation of vortices, boundary layers, separation region, wake region, reattachment point and stagnation points are studied in detail and the results are compared for various cases. The value of the Reynolds number which the flow transits from steady to unsteady has been compared for the different cross sectional shapes.
Authors: Jyh Jian Chen, Tsung Sheng Sheu, Yuan Jyun Wang
Abstract: Since polymerase chain reaction (PCR) was invented, it has become one of the most significant approaches for generic identification during the last few decades. PCR is a useful procedure to magnify the number of copies of a specific DNA template exponentially. Integrated microfluidic DNA amplification devices that employ a serpentine polydimethylsiloxane microchannel, a glass cover with micro heaters and sensors, and a cooling polymethylmethacrylate channel are demonstrated in the present study. With the aid of commercial computational fluid dynamics software, we design the continuous-flow DNA amplification device. The influences of various chip materials, water cooling conditions and geometric parameters on the temperatures of the chip are expressed. Using the MEMS process, two micro aluminum heaters and sensors are fabricated. This device represents the first demonstration of Al heaters and sensors integrated in continuous-flow PCR microfluidics. The LabVIEW control module is used to manage the temperatures of the micro-domain heating. One important feature of this system is the temperature of the annealing zone is controlled by the flow rate of the fluid inside a water channel under the glass chip. The cooling channel cannot only provide great thermal insulation between two temperature zones at the opposite sides of the chip, but also improve the temperature uniformity at the chip center temperature zone. By utilizing an IR thermometer, the images of the surface temperature distributions are captured to show the effects of the employed microheaters and the cooling channel on the thermal field of the PCR device. Finally, we find the temperature regions generated in the present device are suitable for completing the PCR process.
Authors: M. Al-Marouf, R. Samtaney
Abstract: We present an embedded ghost-fluid method for numerical solutions of the compressible Navier Stokes (CNS) equations in arbitrary complex domains. The PDE multidimensional extrapolation approach of Aslam [1] is used to reconstruct the solution in the ghost-fluid regions and impose boundary conditions at the fluid-solid interface. The CNS equations are numerically solved by the second order multidimensional upwind method of Colella [2] and Saltzman [3]. Block-structured adaptive mesh refinement implemented under the Chombo framework is utilized to reduce the computational cost while keeping high-resolution mesh around the embedded boundary and regions of high gradient solutions. Numerical examples with different Reynolds numbers for low and high Mach number flow will be presented. We compare our simulation results with other reported experimental and computational results. The significance and advantages of our implementation, which revolve around balancing between the solution accuracy and implementation difficulties, are briefly discussed as well.
Authors: Rui Li Wang, Xiao Liang, Wen Zhou Lin, Xue Zhe Liu, Yun Long Yu
Abstract: Verification and validation (V&V) are the primary means to assess the accuracy and reliability in computational fluid dynamics (CFD) simulation. V&V of the multi-medium detonation CFD model is conducted by using our independently-developed software --- Lagrangian adaptive hydrodynamics code in the 2D space (LAD2D) as well as a large number of benchmark testing models. Specifically, the verification of computational model is based on the basic theory of the computational scheme and mathematical physics equations, and validation of the physical model is accomplished by comparing the numerical solution with the experimental data. Finally, some suggestions are given about V&V of the detonation CFD model.
Authors: Pey Shey Wu, Min Jho Young, Jun Yun Wu, Chia Chian Wang, Hao Yu Hu, Chih Fei Chang
Abstract: Aerodynamic characteristics of three supermileage car chassis with new design concepts for improving the driver’s view field and driving comfort is investigated and compared with that of one with traditional low-height design. New car shapes with shorter axle distance and higher center of gravity are created. Feasibility of the new design is verified from the aspects of rollover safety, due to the maximum crosswind speed of 40 km/h, and the drag coefficient at straight driving up to 40 km/h. The analytical verification is conducted with a commercial CFD software. Comparing to the traditional design, the analysis shows that it is possible to obtain a lower drag coefficient and lower total drag, while rollover safety is still guaranteed, for a supermileage car with wider view field and taller appearance. Reduction of the form drag is intimately related to the decrease of velocity curl in the flow direction and the size of the vortices in the wake. Results of this study can provide new concepts that are different from those used in the past for the development of supermileage cars.
Authors: Milena Kušnerová, Lukáš Gola, Jan Valíček, Vojtěch Václavík, Marta Harničárová, Iveta Pandová, Pavol Koštial
Abstract: The aim of the publication is the comparative measurements of changes in temperature of the significant material coefficient - thermal conductivity for newly developed construction materials (lightweight concrete). The aim is met by using a newly proposed method and a newly developed device by the approximation modelling of the temperature dependence of the thermal conductivity coefficient of the new composites and also the interpretation of measurement results in the context of optimally desired characteristics of thermal insulation concrete. Construction materials for residential buildings should have good thermal insulation properties, i.e. relatively low coefficients of thermal conductivity. With regard to the relatively most important property of concrete – strength, however, the reduction in thermal conductivity of concrete is limited. Thermal conductivity of concrete can be reduced very effectively by increasing its porosity; on the other hand, by increasing the porosity, the strength of concrete is significantly reduced. The publication, therefore, compares the results of temperature dependences of thermal conductivity for three newly designed concretes, namely in the context of their compressive strength.
Authors: Reza Saifi, Afshin Shaygani, Mahdi Sani, Mohammad Said Saidi
Abstract: Aerosol measurement is used in a variety of fields such as nanotechnology, materials science, pollution monitoring, air quality measurements, combustion and engine exhaust analysis, inhalation toxicology, and medical studies. One of the most prevalent methods for aerosol measurement is to use electrical mobility. An electrical mobility spectrometer (EMS) is used to measure aerosol particles size distribution ranging from 10 – 1000 nanometers, under the influence of an electric field. The accuracy of this distribution is influenced by flow conditions, the geometry of the EMS, the electric field, and the number of electrode rings. In this work, a multi-channel EMS is studied using computational fluid dynamics to numerically simulate the flow pattern, electric field and particle trajectories in the device. We found that neglecting the effect of the electric field on particles outside the sizing region generates an oversimplified model leading to high particle loss to the flow guide. In order to reduce the number of particle losses and obtaining a more realistic particle distribution we proposed a modification to the electrode electric potential which effectively reduces the particle loss. The applied modification has quintupled the number of particles which are classified by the EMS.
Authors: Raquel da Cunha Ribeiro da Silva, Carlos Salinas Sedano, Kamal A.R. Ismail, Paúl Adrian Delgado Maldonado
Abstract: An experimental study was reported earlier on the development of frost formation by humid flow passing over the cylinder. In this study, dimensionless correlations used in previous experimental data, and reported empirical correlations of the Nusselt number, were used. This paper reports results of an experimental and numerical investigation where the emphasis was placed on obtaining empirical correlation for the Nusselt number. In this work some experimental results of the frost thickness around every cylinder in a triangular arrangement are presented, an estimated experimental correlation to find Nusselt number. This correlation is based on the experimental measurements in a wind tunnel situated in the Laboratory of Thermal storage and Fluids in the Mechanical Engineering Faculty at Unicamp. A numerical study is performed to study the frost formation in the cylindrical system.
Authors: M.C. Haupt, D. Kowollik, K. Lindhorst, F. Hötte
Abstract: This paper describes the simulation approach for the analysis of fluid structure interactions(FSI) of rocket thrust chambers. It is based on a partitioned approach and includes several buildingblocks: codes for computational fluid dynamics (CFD) and computational structural mechanics(CSM) as well as techniques to handle non conforming surface grid and to solve the nonlinear coupledequations in time. One target application is the life time prediction and to simulate the structuralfatigue behaviour. Thus, cyclic loading conditions are important and are the motivation for a surrogatemodel, which is the focus of this contribution. It uses nonlinear mapping algorithms between surfacetemperature and heat flux in combination with a reduction of dimensionality via proper orthognal decomposition(POD). It can be used as a replacement of the time consuming CFD code and acceleratesthe FSI analysis several orders in time. Some applications regarding the validation of the FSI softwareenvironment finalize the description of the simulation approach showing that the simulation ofcomplex and multidisciplinary problems is laborious and needs a widespread understanding.

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