COMPARATIVE ANALYSIS OF THE ENERGY CONSUMPTION OF FIXED AND VARIABLE SPEED PRESSURE SYSTEMS

The objective of this study was analyzing two pressure systems relative to energy consumption. One of the systems operates at a fixed speed and the other with variable speed by using a frequency inverter. It was selected two product models based on the water demand, which was calculated with the average flow rate spent per each type of sanitary appliance. Thus, it was possible to estimate the power consumed in each hour and then, calculate the electric energy consumption. The cost of energy per hour was also found, considering the current energy tariff. The results showed an economical use of the inverter compares to non-use. The average potential energy savings was 44.7%, and it was found R$ 369.11 of reduction in the monthly energy cost. Therefore, it is concluded the use frequency inverter is economically viable in relation to energy consumption and reduce the costs of electric energy.

Toughness Differentiation of Welded Low Carbon Steel By Using Baked Low Hydrogen Electrode (E7018) and Low Hydrogen Electrode Without Baking Process

Low hydrogen electrode known as lime type, due lime ferritic or lime flourspar countain. This electrode produce low hydrogen weld metal, which can dissolve weld metal from embrittlement and or cracking, the coating developed to contain low amount of moisture so storage handling should be carefully, unused electrode must rebaked at temperatures between 260-425ºC for 2-6 hours. This research purpose to know imfluence of toughness welding result by using baked low hydrogen electrode on low carbon steel. This research using experimental method, 12 speciment divided into 4 groups specimen, specimen A welded by using electrode without baking process, specimen B welded by using baked electrode at 260ºC, specimen C welded by using baked electrode at 343ºC and spesimen D welded by using baked electrode at 435ºC. After the test obtained the average potential energy amount 65,8107 Nm and average impact amont 0,81539x106 N/m from spesimen A, spesimen B obtain average potential energy amount 81,9396 Nm and average impact amount 1,00251x106 N/m, spesimen C obtain average potential energy amount 126,3913 Nm and average impact amount 1,56703x106 N/m, and spesimen D obtain average potential energy amount 92,5795 Nm and average impact amount 1,13445x106 N/m. The most tough specimen in C group, with average potential energy amount 126,3913 Nm and average impact amount 1,56703x106 N/m.

Torsional Properties of Boron Nitride Nanocones with Different Cone Heights, Disclination Angles and Simulation Temperatures

The torsional properties of single-walled boron nitride (BN) nanocones at different cone heights, disclination angles and simulation temperatures have been investigated using molecular dynamics (MD) simulation. The simulation results indicate that the torque and average potential energy decrease with the increasing cone height and disclination angle, and the failure torsion angle increases with the increasing cone height and disclination angle. For different simulation temperatures, the torsional behavior of BN nanocones at higher simulation temperature is more serious and earlier to reach a failure point, the maximum torque and average potential energy of the system decrease with the increasing simulation temperature. For different loading rates, the failure torsion angle decreases with the increasing loading rate, so the fracture of BN nanocone occurred earlier with higher loading rate. Therefore, the cone height, disclination angle, simulation temperature and loading rate are considered to be four main influencing factors for the torsional properties of the BN nanocones.

Size dependent melting of Silicon nanoparticles

Melting of crystalline silicon nanoparticles is studied by molecular dynamics (MD) simulations using Stillinger-Weber potential. Models are heated up from a crystalline to a normal liquid state. Temperature dependence of total energy and the Lindemann ratio exhibit a first-order-like behavior of the transition at the melting point. Heat capacity of the system presents a single peak at around the melting point. The size dependent melting is presented. As the size of the nanoparticles increases, the variation of the melting point becomes more monotonic and the temperature range of bistability shifts to higher temperatures. In large nanoparticles, the proportion of interior atoms increases and the average potential energy per atom converges to the bulk or thin films.

Multiscale Analysis on Two Dimensional Nanoscale Sliding Contacts of Textured Surfaces

Nanoscale sliding contacts are the major factors that influence the friction and result in wear in micro/nanoelectromechanical systems. Many experimental studies indicated that some surface textures could help improve the contact characteristics and reduce friction forces. However, the experimental results may be biased, due to the contamination of the sample surface or substantial defects in the materials. Numerical methods, such as continuum mechanics, meet great challenges when they are applied at length of nanoscale, and the time cost of molecular dynamics (MD) simulation can be extremely high. Therefore, multiscale method, which can capture atomistic behaviors in the region underlying micro/nano physical processes by MD simulations and models other regions by continuum mechanics, offers a great promise. Coupling MD simulation and finite element method, the multiscale method is used to investigate two dimensional nanoscale sliding contacts between a rigid cylindrical tip and an elastic substrate with textured surface, in which adhesive effects are considered. Two series of nanoscale surface textures with different asperity shapes, different asperity heights, and different spacings between asperities are designed. For different heights of asperities or different spacings between asperities, average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces are compared to observe how these parameters influence friction characteristics; then, the optimal asperity height or spacing is discovered. Through the average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces comparisons between smooth surface and textured surfaces, a better shape is advised to indicate that asperity shape plays an important role in friction force reduction. The influences of the indentation depth and radius of the rigid cylindrical tip are analyzed to find out the sensitivity of surface textures to these two parameters. Effects of sliding speed on the characteristics of nanoscale sliding contacts are also discussed. The results show that, with proper asperity height and proper spacing between asperities, surface textures can reduce friction forces effectively. Coefficients of friction (COFs) of all the cases are calculated and compared. Some negative COFs caused by significant adhesive effects are discovered, which are different from traditional macroscopic phenomena.

Molecular Dynamics Simulation Studies of p-Xylene in OH-free Si-MCM-41

We report on modeling efforts and molecular dynamics computer simulations of the structure and self-diffusion of p-xylene in OH-free Si-MCM-41 as a function of loading. Both the guest molecules and Si-MCM-41 are modeled as flexible entities. With this newly developped intermolecular force field the average potential energy of p-xylene in the pore increases with increasing loading. The adsorption of p-xylene in MCM-41 is primarily associated with the van der Waals interactions of the model, whereas the contribution from electrostatic interactions is relatively small (about 2 kcal/mol), in accordance with other aromatic hydrocarbons adsorbed in zeolite catalysts. The calculated selfdiffusion coefficients of p-xylene in Si-MCM-41 are well comparable with diffusion coefficients of pyridine in MCM-41 and of the same order of magnitude as in liquid p-xylene. Increasing the loading results in non-negligible mutual p-xylene interaction, thus leading to a decrease of the self-diffusion coefficient.

DETERMINATION OF THE VAPOR-LIQUID CRITICAL POINT FROM THE SHORT-TIME DYNAMICS

Considering the average potential energy per particle as the parameter, we investigate the early-time dynamics of vapor-liquid transition in the critical region for 2D Lennard-Jones fluids by using NVT molecular dynamics simulations. The results verify the existence of short-time dynamic scaling in the fluid systems and show that the critical point Tc can be determined by the universal short-time behavior. The obtained value of Tc = 0.540 from the short-time dynamics is very close to the value of 0.533 from the Monte Carlo simulations in the equilibrium state of the systems.

MELTING AND FRAGMENTATION OF NICKEL NANOPARTICLES: MOLECULAR–DYNAMICS SIMULATIONS

Melting and fragmentation behaviors of Ni 429 cluster have been studied with molecular-dynamics simulations using a size-dependent empirical model potential energy function. To monitor thermal behaviors of the cluster, we calculated some physical quantities such as average potential energy per atom, specific heat, radial atomic distribution, bond length distribution, average interatomic distance, nearest neighbor distance and average coordination number as a function of temperature. The roles of the surface and core atoms in the melting and fragmentation process of the cluster are also investigated by considering the surface and the bulk coordination numbers of the cluster.

A theoretical simulation of bulk water: the effect of the dispersion-energy contribution

Inclusion of the dispersion-energy contribution, within the framework of a formulation developed at this laboratory for the study of molecular interactions, leads to an average potential energy of 39.3 kJ/mol for bulk water, in excellent agreement with the experimental value.