Defect and Diffusion Forum Vol. 362

Abstract: In this paper some important parameters affecting the temperature increase of the fluid inside an absorption tube of parabolic trough collector have been experimentally investigated using the Design of Experiments (DOE) method. These parameters are: absorption tube length, fluids type and fluid flow rate. The design of an absorption tube as well as a solar parabolic trough collector has been changed into different ways in order to increase the fluid temperature inside the absorption tube. The design of experiments plays a major role in identifying which factors are significant in increasing the temperature absorption inside the tube. The DOE method was validated using an experimental setup that is designed and fabricated by the Department of Mechanical Technology at Riyadh College of Technology. The experiments have been done on all the factors considered randomly using factorial design by merging all the factors together to know which factors and their interactions can affect more on increasing the fluid temperature inside absorption tube. Eight experiments with three replicates have been chosen randomly. From the results it is seen that the most significant effective factor to maximize fluid temperature is the flow rate and the interaction between absorption tube length and fluid type. It also was found that fluid temperature inside the collector was maximized when hydraulic oil was used as the heat transfer fluid and when the tube length was 436 mm.

Abstract: In this paper we analyze a special type of Inter Digital Transducer (IDT), named Slanted Finger Transducer (SFIT) that can be used in microfluidic applications. Using SFIT in microfluidic technology are progressing during recent years. We will analyze the structure of basic SFIT and then a simulation is performed using a finite element software.

Abstract: Rotating effects and magnetohydrodynamic (MHD) free convection flow of second grade fluids in a porous medium is considered in this paper. It is assumed that the bounding infinite inclined plate has ramped wall temperature with the presence of heat and mass diffusion. Based on Boussinesq approximation, the analytical expressions for dimensionless velocity, temperature and concentration are obtained by using the Laplace transform method. All the derived solutions satisfying the involved differential equations with imposed boundary and initial conditions. The influence of various parameters on the velocity has been analyzed in graphs and discussed.

Abstract: Process quality control utilizes inspection of a product while it is being produced through testing periodic samples of products. After this, if product quality characteristics have been changed, the process is stopped, and a search is made for an assignable cause. The objective of a process-capability study is to assess the ability of a process to meet product specifications. During a quality improvement initiative, capability-estimates are obtained at start and at end of study to reflect the occurred improvement. Several capability-estimates show how a process is capable of meeting its specification limits. Essentially, capability-estimates reflect the non conformance rate of a process in a single number form. This involves calculating some ratio of process specification limits. In this study, the production of a fluorescent lamp consisting of a glass tube is considered. Tube quality is affected by the production line conditions. So, the maintenance of the production line is an important stage to increase tube quality. In this paper glass tube quality is studied. Minitab is a statistical software was used to analyze obtained data. The results showed an obvious improvement of part quality after maintenance stage. All measurements were done in Toshiba factory for fluorescent lamp manufacturing.

Abstract: In this work it is numerically studied the wave flow inside a tank and the main operational physical principle of three different wave energy converters (WEC): oscillating water column (OWC), overtopping and submerged plate. The wave energy converters are evaluated in laboratory and real scales. For all studied cases the conservation equations of mass, momentum and one equation for the transport of volumetric fraction are solved with the finite volume method (FVM). To tackle with water-air mixture, the multiphase model Volume of Fluid (VOF) is used. Several results showed the accuracy of the numerical approach for estimation of the physical phenomenon of wave flow inside tanks, as well as, its interaction with the studied devices. For the cases with geometrical optimization, Constructal Design is employed for geometrical evaluation of the devices. Results presented several theoretical recommendations about the influence of geometrical parameters (such as ratios between heights and lengths of OWC chamber and ramp of overtopping device and the distance from the plate to the seabed of wave tank) over the available power take off (PTO) in the OWC and submerged plate devices and over the amount of water stored in the reservoir of the overtopping device. Results showed the importance of geometric shapes over the devices performance. Moreover, it is evaluated the influence of several wave parameters (such as wave period and relative depths) over the fluid dynamic performance of the devices and geometrical parameters of the devices. It is noticed the non-occurrence of universal optimal shapes.

Abstract: Mesoscale analyses of cracked porous volumes are performed. The fluid flows through a multiphase volume comprising one macro-crack, macro-pores and random micro-porous solid inclusions. Mesostructures are defined by thresholding of spatially correlated Gaussian random fields.Transport through macropores and crack, as well as the diffusion in micro-porous solid inclusions, are taken into account. Homogeneous (without cracks) porous volumes illustrated the asymptotical behaviors. The corresponding macroscopic permeability tensors are obtained and correlated with the geometrical/statistical properties of the analyzed porous systems. A new equivalent electrical scheme, including shunt resistance, is proposed to evaluate the apparent diffusion coefficient. Macro-cracked porous volumes are then investigated.The increases in mass flux due to the crack, as well as the mass/energy exchanges with the surrounding porous medium, are quantified by direct numerical simulation. A drying region due to the macrocrack was illustrated and the corresponding apparent permeability was identified. For different geometrical configurations (macro-porosity, micro-porosity, macro-crack orientation and aperture) we quantify the macropore –crack interlink by comparing such structure with structure without possible flow between the macro-crack and the porous structure.The equivalence scheme between mass flow in cracked porous media and heat flow in porous media was underlined.

Abstract: The structural integrity of a BWR nuclear power plant can be compromised due to severe dynamic loads. Acoustic loads coming from a Safety Relief Valve branch can be adversely amplified if the steam flow is increased at the Main Steam Piping. This phenomenon has been reported previously in one BWR nuclear power plant. Its steam dryer was fractured and loose parts were generated due to high-cycle fatigue. This event has driven the United States Nuclear Regulatory Commission to issue specific regulations to evaluate acoustic loads which would be detrimental to the BWR steam dryer. In this paper, the acoustic loads were simulated when the steam flow is incremented from normal operation conditions to an Extended Power Uprate condition. It was analyzed, when the output power was incremented 14% and 28%. The initial conditions were determined with Computational Fluid Dynamics under steady state condition. This data was used in subsequent transient analysis. The model of Large Eddy Simulation was used and the acoustic simulation was performed with the Fowcs Williams and Hawkings Method. The Power Spectral Density was obtained with Fast Fourier Transform. The frequency peaks were found between 148 Hz and 155 Hz. These results are consistent with those obtained with the Helmholtz model and other results reported in the open literature. The results show that the peak pressure can be increased up to six times in resonance conditions, corresponding to a power uprate of 28%.

Abstract: The bubble growth modelling in a supersaturated solution is difficult to be accomplished as it requires coupling of many interrelated hydrodynamics and mass transfer parameters which include pressure drop, supersaturation ratio, bubble size, etc. In the current work, all these factors have been taken into consideration to predict bubble growth in a supersaturated solution using Computational Fluid Dynamics (CFD) – Population Balance Model (PBM) approach. A classical bubble growth model has been used in the simulation. The bubble growth rate was successfully validated with experimental data in terms of bubble size. The attempt to simulate the bubble growth phenomenon of more than a single bubble condition has also been presented. The outcome of this approach is expected to be applied in many engineering areas.

Abstract: In the paper the selected problems related to the modeling of microscale heat transfer are presented. In particular, thermal processes occurring in thin metal films exposed to short-pulse laser are described by two-temperature hyperbolic model supplemented by appropriate boundary and initial conditions. Sensitivity analysis of electrons and phonons temperatures with respect to the microscopic parameters is discussed and also the inverse problems connected with the identification of relaxation times and coupling factor are presented. In the final part of the paper the examples of computations are shown.

Abstract: This paper deals with a universal simulation strategy for the calculation of process-induceddistortions and residual stresses of a composite part. The mechanical material behavior is describedby a viscoelastic material model depending on temperature and degree of cure . The required materialparameters are derived by dynamic mechanical analyses. For the description of the reaction kinetic aphenomenological based model considering chemical and diffusion-controlled reactions is introduced.The reaction model parameters are fitted to isothermal and dynamic DSC measurements via globaland local optimization. The thermal expansion and chemical shrinkage are characterized by thermalmechanical analysis and using the contact angle measurement method. The simulation strategy isdemonstrated for a GFRP suspension blade for the automobile industry. Based on a sequential coupledtemperature-displacement analysis thermal hot spots, temperature and degree of cure distributions aswell as the final corresponding process-induced distortions and residual stresses are calculated andanalyzed. The development of the stiffness and the correlated stress during the curing process arediscussed in more detail. Furthermore, the effect of a degree of cure dependent stiffness on the stressesis investigated.