Defect and Diffusion Forum Vol. 392

Abstract: The present study investigates the effects of slip and heat transfer on peristaltic mechanism of Bingham fluid in an inclined tube. The sinusoidal, multi-sinusoidal, triangular, square and trapezoidal wave forms are considered. The analysis has been carried out under the assumptions of long wavelength and small Reynold's number approximations. The closed-form solutions are obtained for velocity, plug flow velocity, pressure gradient, streamlines, and temperature. The numerical integration is employed to investigate the effects of pressure rise and frictional force. The influence of relevant parameters on physiological quantities of interest is analyzed and discussed through graphs. The study reveals that velocity and thermal slip have a decreasing effect on velocity and temperature. Further, it is noticed that the volume of trapped bolus increases for increasing values of velocity slip parameter.

Abstract: This article investigates the transfer of heat with reactant (oxygen) consumption in a stockpile of reactive material. A reactive material is any carbon or hydrocarbon containing component in a stockpile that readily reacts with the oxygen due to exothermic chemical reaction, where self-ignition may take place if heat generation rate during the combustion process within the stockpile, may exceed the rate of heat release to the surrounding environment. The study is modeled in a long cylindrical pipe whose material thermal conductivity varies with the temperature at a given time. The heat and mass transfer partial differential equations governing the problem were solved numerically using the finite difference method (FDM). Kinetic parameters embedded within the reaction system were analyzed to understand their effects on the temperature and the reactant consumption process. The results shew that the parameters that influence the increase in temperature, increase also the consumption rate of the reactant.

Abstract: The objective of this study is to give the designer an appreciation of the heat transfer enhancement in turbulent flows through corrugated channels in a heat plate exchanger. Precisely, the influence of a new technic named the artificial roughness is probed on corrugated walls, with their variable wall amplitudes for assessing the effectiveness of the heat exchange. For that purpose, a numerical simulation approach is adopted. The rectangular, triangular, trapezoidal and sinusoidal corrugated wall and artificial roughness wall shapes are investigated, in order to determine the optimal wall profile resulting in significance increase in the heat exchange process with a minimum friction loss. The numerical results are presented in the form of isotherms, streamlines, contour, Nusselt number (Nu) and friction coefficient (Cf ) using commercial software ANSYS- Fluent where the Reynolds number is in the range from 3 000 to 12 000. Our simulations reveal that the sinusoidal-corrugated channel has the highest heat transfer enhancement followed by rectangular, triangular and trapezoidal-corrugated channel. In addition, introduction of artificial roughness in the wavy channel induces stronger secondary flow which makes the flow three-dimensional and improve the heat transfer by a maximum 40% at a Reynolds number equal to 12 000. This may indicate benefits for designing heat plate compact exchangers capable of higher performances in the turbulent flow regimes.

Abstract: In the building, roof is a major element contributing to the space thermal load. Due to its importance, this component has been widely studies in the literature and under various climatic conditions. In this paper, a numerical study was carried out for the coupling of natural convection and surface radiation heat transfer in a triangular shaped roof with eave (Gabel roof) for cold climates. The numerical solution is obtained using a finite volume method based on the SIMPLER algorithm for the treatment of velocity-pressure coupling. Concerning the radiation exchange, the working fluid (air) is assumed to be transparent, so only the solid surfaces (assumed diffuse-grey) give a contribute to such exchange. Governing parameters on heat transfer and flow fields are Rayleigh number (Ra), aspect ratio (A) and eave lengths (e^*). Numerical results are obtained to display the isotherms, streamlines and the heat transfer rate in terms of local and average Nusselt numbers. We found that the production of several circular cells is proportional to the decrease of aspect ratio and the increase of Rayleigh number. In addition, the heat transfer is much more pronounced in the presence of thermal radiation.

Abstract: The study on heat flow in welding is essential as the quality of the weld depends on mainly heat flow through the welded plate. The heat input from welding source flows in a limited zone, and it subsequently flows into the workpiece by conduction. In this study, an attempt is taken to predict the transient temperature distribution and solidification pattern through a numerical model and the associated mathematical technique considering the solidification and heat transfer, of molten weld pool when it is covered with flux and without flux in arc welding process. The numerical model developed in this study solves fluid flow and heat transfer considering solidification and melting phase change the along with natural convection in the meltpool. It was found that the flux is functioning as insulation on the welded pool, hence it restricts rapid solidification and increases the mushy zone width.

Abstract: Transportation of fluids in pipelines is common in many industrial processes. The energy requirements for this transport is high because of the need to overcome the occurring frictional pressure drop or drag. However, the addition of high molecular weight polymers to fluid flows has been known to cause a reduction in the frictional pressure drop. It has also been reported to cause other changes in the flow including changes in the turbulence characteristics, holdup as well as asymmetry of the velocity profiles. In this work some experimental results are presented in order to gain better insight into the deviations from axisymmetry of velocity profiles of water flow in pipes when drag reducing agents are added. Drag reduction studies were carried out in a horizontal 14mmID acrylic pipe with hydrolyzed polyacrylamide and different molecular weights polyethylene oxide used as additives in fully developed flows. Asymmetry was observed at both transitional and turbulent flow regimes for all tested polymer types and it increased with molecular weights. While the molecular weight and degree of formation of entanglements and aggregates of the polymer fibers are indicated as the causes of the observed profile asymmetry, the contribution of system/setup imperfections can be ruled out.

Abstract: The existing methods of design and calculating the gas-dynamic characteristics of turbo-machines do not allow an accurate computation of parameters of a turbo compressor unit as part of a compound internal-combustion engine. The evaluation of a new design and estimation method for the blading section of the turbine of the turbocharged engine was carried out in this paper. The developed technology was used to design impellers for radial-axial turbines of a turbocharged engine operating in various modes. The features of these turbines are presented in the steady and unsteady stream. As a result of the application of the new design and calculating technology, the following data was obtained: the parameters of the turbine design mode as part of a turbocharged engine; the blading section of the turbine TKR-14 of the turbocharger. As a part of a turbocharged engine, this blading section will allow the unsteady action from the piston part to operate more efficiently than the standard turbine of the 6 CHN 18/22 (Russian Marine Diesel) engine. The computation of turbine performance characteristics in a steady stream showed that a decrease in the geometric dimensions at the inlet and outlet of the impeller leads to a decrease in the efficiency of the turbine and an increase in its effective power. The computation of performance characteristics of a turbine as part of the turbocharged engine showed that reducing the height of the impeller blades causes scavenging duration reduction, an increase in a pressure drop on scavenging, an increase in pressure in the exhaust pipeline, an increase in the efficiency of the turbine and its effective power. Comparison of these characteristics with experimental data proves the adequacy of the applied technology.