Applied Mechanics and Materials Vols. 110-116

Abstract: Nanofluids have attracted great interest from researchers worldwide because of their reported superior thermal performance and many potential applications. However, there are many controversies and inconsistencies in reported experimental results of thermal conductivity, convective heat transfer coefficient and critical heat flux of nanofluids. In this paper, two major features of nanofluids, which are boiling and convective heat transfer characteristics are presented besides critically reviewing recent research and development on these areas of nanofluids.

Abstract: A heat transfer model was developed to predict a transient thermal behavior of asphalt concrete during service life at different weather conditions. The developed model has the capability to predict the distribution of temperature field with respect to time within the Hot-Mix asphalt body based on surrounding environmental conditions. This will greatly help pavement engineers to select the suitable asphalt grade to achieve the best pavement performance and avoid pavement distresses might be caused due to extreme pavement temperatures. These distresses include fatigue cracks, rutting, and thermal cracking. The resulted model required data on asphalt mixture, incident radiation, surface, and ambient temperatures in addition to thermal properties of Hot-Mix asphalt including absorptivity, heat transfer coefficient, and the emissivity. A sensitivity analyses was performed to study the impact of a number of thermal environmental and pavement geometric parameters on predicted temperature responses. The results of analysis indicated that the incident radiation, absorptivity, and the heat transfer coefficient have the most significant effect on Hot-Mix asphalt temperature. Also, the emissivity has insignificant effect on surface temperature Hot-Mix asphalt.

Abstract: The hydrodynamics and thermal behaviors of fluid in micro - Couette flows is investigated numerically. The model that combines both the continuum approach and the possibility of slip at the boundary is adopted in the study. The Effects of Knudsen number Kn, Brinkman number and the pressure gradient on the Couette microchannel hydrodynamics and thermal behaviors are investigated. It is found that as Kn increases the slip in the hydrodynamic and thermal boundary condition increases. Also, it is found that the slip velocity and the temperature jump at the boundaries increases as the Brinkman number and the pressure gradient increases.

Abstract: The determination of a spacecraft’s mass properties is critical during its conceptual design phase. Obtaining reliable mass property information, early in the design of a spacecraft, could prevent design mistakes that can be extremely costly in the development process. The process of the determination of the mass properties consist in a systematic work, that include the taking part of all the sub systems or design teams that conforms the preliminary tasks for the design of the communications satellite. The VX-SAT project is a system engineering exercise, realized in the China Academy of Space Technology (CAST) like training for the future designs in communication satellites for the Bolivarian Agency of Space Activities (ABAE) in Venezuela. This paper aim to show an analysis of the procedures in the calculation of the mass properties in communication satellite using suitable software’s and the importance of the process to collect the mass budget information to get the more reliable results. Also includes an overview of the VX-SAT system, the preliminary design of the structure requirements and finally the methods used to the analysis of the general determination of the mass properties with its results.

Abstract: In the present study, two preconditioners proposed by Eriksson, and Choi and Merkel are implemented on a 3D upwind Euler flow solver on unstructured meshes. The mathematical formulations of these preconditioning schemes for the set of primitive variables are drawn and their eigenvalues and eigenvectors are compared with each others. A cell-centered finite volume Roe's method is used for discretization of the 3D preconditioned Euler equations. The accuracy and performance of these preconditioning schemes are examined by computing low Mach number flows over the ONERA M6 wing for different conditions.

Abstract: Diesel engines are widely used as power sources for medium and heavy-duty applications because of their lower fuel consumption and lower emissions of carbon monoxide (CO) and unburned hydrocarbons (HC) compared with gasoline engines. Efficient use of natural resources is one of the fundamental requirements for any country to become self-sustainable. Both in organized and unorganized sectors internal combustion engine has become an indispensable prime mover. With the increasing demand on the use of fossil fuels, a stronger threat to clean environment is being posed as the burning of fossil fuels is associated with emissions like CO2, CO, SOx, NOx and particulate matter, which are currently the dominant global source of emissions. In diesel engines, NOx formation is a highly temperature-dependent phenomenon. Therefore, in order to reduce NOx emissions in the exhaust, it is necessary to keep peak combustion temperatures under control. Exhaust gas recirculation is the most important technique for reducing NOx emissions. Re-circulating part of the exhaust gas helps in reducing NOx, but appreciable particulate emissions are observed at high loads, hence there is a trade-off between NOx and smoke emission. To get maximum benefit from this trade-off, a particulate trap may be used to reduce the amount of unburnt particulates in EGR, which in turn reduce the particulate emission also. An experimental investigation was conducted to observe the effect of exhaust gas re-circulation on the exhaust gas temperatures and exhaust opacity. The experimental setup for the proposed experiments was developed on a single-cylinder, direct injection, air-cooled, compression ignition engine. A matrix of experiments was conducted for observing the effect of different quantities of EGR on exhaust gas temperatures and opacity.

Abstract: To improve the calculation of the flow properties of an aerospike nozzle, different turbulent models are studied in this research. The primary shape of the nozzle and the plug is determined through utilizing an approximate method. The flow field is then simulated using Navier-Stokes equations for compressible flow. The computational methodology utilizes steady state density-based formulation and a finite volume cell centered scheme to discretize the flow field equations. To accelerate the solution convergence, the flow field is divided into several zones. Each zone is facilitated with proper unstructured grid and appropriate initial conditions are implemented to each zone. The accuracy and the robustness of wall function based turbulence models i.e. standard and RNG k-ε models are compared with those of Spalart-Allmaras (S-A) and k-ω turbulence models.

Abstract: An extensive experimental investigation of inplane crushing of composite hexagonal ring system between platens has been carried out. Woven roving glass/epoxy hexagonal ring system with different angles and arrangement were employed. The rings angles are varying between 45 and 70°. The wet winding process was used to fabricate the woven E-glass fabric /epoxy specimens. Four layers of woven E-glass fabric/epoxy wrapped over wooden mandrel to get thickness of about 3 mm. The composite hexagonal tubes were then cured at room temperature (32oC) for 24 hours to provide optimum hardness and shrinkage. Repeatability of the results was ensuring by performing the experiments on three identical specimens. Typical histories of their crushing mechanism are presented. Behavior of ring as regards the initial crushing load, post crushing load, energy absorbed and mode of crushing has been presented and discussed. Results showed that the crush failure loads and energy absorption capability are greatly affected by the hexagonal ring geometry, arrangement and loading conditions. As the ring angle increases the energy absorption capacity increases. Composite hexagonal ring with 70 degree exhibited the highest energy absorption capability among tested specimens. It is also found that energy absorption capability for systems crushed in-plane X2 higher than X1.

Abstract: Spinning is used in some of solid rocket motors to increase the flight trajectory precision or for stability requirements. The angular acceleration due to the spin effect increases the burning rate of solid propellant and changes the motor performance by increasing the operating pressure and decreasing the burning time. So it is important to know the grain regression taken place in the solid propellant rocket motor in the acceleration field. In this study, we represent the grain regression analysis of two-dimensional axis-symmetric star grain configuration of the solid propellant rocket motor under spin induced acceleration effect to study how the spin affects on the internal ballistics of the solid rocket motor. Grain regression is done by two methods - geometrical approach and numerical approach. The burning rates on the propellant surface are different with its radial distance, acceleration vector angle and surface slope when the rocket is spinning. With the different burn rates on the propellant surface, the propellant surface perimeter and port area are computed by using the numerical method, and the results are compared with that of constant burn rate.

Abstract: Acid treatment using H₂SO₄, HCl and H₃PO₄ has been carried out in an attempt to improve catalytic performance of silica-titania aerogel. X-ray diffraction results showed the amorphous structure of the aerogels remained after the acid impregnation and calcinations steps. Hammert analysis revealed these acid modified silica-titania aerogels were superacids with pKa < -14.52. Different Ti species was observed in the samples upon the acid treatment. As compared to silica-titania aerogel, Lewis acidity increased remarkably in HCl treated sample without formation of any Brønsted acid site. Meanwhile, H₂SO₄ and H₃PO₄ treated samples possessed both Lewis and Brønsted acid sites. The catalytic performance of these samples was evaluated through a consecutive transformation of 1-octene to 1,2-octanediol through the formation of 1,2-epoxyoctane using aqueous hydrogen peroxide as oxidant.