Academic Thesis for receiving a master's degree in the field of advanced chemical engineering
Abstract
The limitation of heat transfer fluids in various industries due to their poor thermal conductivity has caused the improvement of heat transfer of working fluids to be considered as a new method of advanced heat transfer. So that the idea of ??dispersing solid particles in fluids, which started with millimeter and micrometer particles, has been completed by using solid nanoparticles, and today nanofluids are considered as fluids with high heat transfer capability, a suitable alternative to ordinary fluids such as water, ethylene glycol, and oil. In this study, molecular dynamics simulation method was used to predict the thermal conductivity coefficient of nanofluids. For this work, water was used as the base fluid, as well as the SPC/E model for simulating water and the Ewald summation method for simulating electrostatic interactions and the Lennard-Jones potential for van der Waals interactions between water molecules and the KTS potential relationship for and the Heisinger relationship for the interactions between water molecules and platinum nanoparticles. The values ??obtained from the simulation have been compared with the experimental data. To investigate the effect of temperature on the thermal conductivity coefficient of nanofluid, this coefficient was calculated at three temperatures of 20, 30 and 50 degrees Celsius and it was found that the ratio of the thermal conductivity coefficient of nanofluid to the thermal conductivity coefficient of water decreased with increasing temperature. The effect of changes in nanoparticle concentration on the thermal conductivity coefficient of nanofluid was investigated in three concentrations of 0.45, 1.85 and 4% and compared with experimental data and it was found that the thermal conductivity coefficient of nanofluid increases with the increase in concentration. The effect of particle size on the thermal conductivity coefficient of nanofluid was calculated for two particles of 0.3 and 0.6 nm and it was found that the increase in particle size decreased the thermal conductivity coefficient. The effect of the type of particles was investigated by replacing the nanoparticle with platinum nanoparticle, and the results showed that the type of particle does not have a great effect on increasing the thermal conductivity coefficient of the nanofluid. Keywords: nanofluid, molecular dynamics simulation, thermal conductivity coefficient, heat transfer. Introduction 1-1- History of computer simulations.
Almost 60 years have passed since the first computer simulation of a fluid. This simulation was done in the Los Alamos National Laboratories [1] in the United States. The computer used in Los Alamos was called MANIAC. Today, powerful microcomputers are available to the public at reasonable prices and can be used to perform numerous simulations. What Metropolis and his colleagues did in 1953 formed the basis of the modern Monte Carlo simulation. Their simple technique is still widely used in simulations and is called MD for short. In the initial model, ideal approximations such as the hard sphere[2] were considered for molecules, but within a few years, simulations based on the Lennard-Jones interaction were carried out. Later, molecular dynamics or MD for short was successfully applied for the first time to a set of hard atoms. In this study, it was assumed that the particles are moving at a constant speed among perfectly elastic collisions. A few years later, the first successful attempt was made to solve Newton's equations of motion assuming Lennard-Jones interactions. This simulation was done with a step-by-step approximation and assuming that the forces change continuously with the movement of the particles. The characteristics of the Lennard-Jones model were later fully investigated. After the initial fundamental studies on the system of atoms were completed, simulations developed rapidly. Attempts have been made to simulate diatomic liquids using molecular dynamics and Monte Carlo in previous years. Water simulation has always been a topic of interest. Small rigid molecules, flexible hydrocarbons and even long molecules such as proteins have all been among the targets of interest in recent years. We remind you that computer simulation techniques have made significant progress by providing non-equilibrium methods for measuring transfer coefficients. Depending on the size of the atom, between 3 and 6 atoms can be placed in one nanometer.By establishing a relationship between the size of atoms and the nanoscale, a nanometer can be imagined more easily. According to the definitions, the length scale between 1 and 100 nm is called nanoscale.
Nanotechnology is: the art of manipulating materials on an atomic or molecular scale and especially making microscopic parts and accessories (such as microscopic robots). This technology is based on the manipulation of individual atoms and molecules, in order to produce a complex structure with atomic properties. This knowledge has the ability to work at the atomic level and create structures that have a new molecular order. The modified substance on a new scale has new and useful properties that were not seen before. Nanotechnology can include the development and use of tools and parts that are only a few nanometers in size. In general, nanotechnology is a term that refers to all advanced technologies in the field of nanoscale work.
While there are many definitions for nanotechnology, the International Nanotechnology Center[3] provides a definition for nanotechnology that includes the following three definitions:
Technology development and research at the atomic, molecular and or macromolecules on the scale of 1 to 100 nanometers.
Creation and use of structures and tools and systems that have new properties and functions due to their small or medium size.
The ability to control or manipulate at atomic levels [1].
1-2-1 Applications
The potential fields of nanotechnology are: electronics, communication, electricity (power), computer, chemical and pharmaceutical industries, health and environment, information technology, biotechnology, national security, medicine and energy. Gaining or achieving the power and ability to control at the molecular level throughout the structure of matter will bring a wide variety of positive applications. The fields in which nanotechnology has already been used include: medicine and pharmaceuticals, production and energy, textiles, communication and communication, chemical materials, materials science and engineering, environment, information technology, micro-electromechanical systems[4], wear-resistant materials, invisible improvement and correction of damaged materials (with structural defects), nanomachines and nanoelasticity, nanoelectrical and magnetic devices, new computing devices and tools. They will be optoelectronic [2].
1-3-Nanoparticles
Nanometric particles are used as precursor nanomaterials to produce complex structures and devices, and their use improves and changes physical, chemical or biological processes and causes new properties. These properties create a driving force and cause further follow-up and motivation to continue research[1].
Nano materials are sometimes called nano powder[5] when they are not dense and compressed, and their grain size is at least in one dimension and usually three dimensions in the range of 1 to 100 nm. It includes metal nanoparticles, metal oxides, conductors and semiconductors, composite nanoparticles such as core-layer structures and even carbon nanotubes. Nanoparticles, as materials with a high cross-sectional area, show better chemical, mechanical, and magnetic properties that distinguish them from mass materials with normal and large dimensions [3]. And Moghna Tais, environment and energy pointed out [3]. Insulating materials, machine tools, phosphors or radiant materials, batteries, high-power magnets, motor vehicles and airplanes, medical implants, medical applications, and nanofluids that result from mixing nanoparticles in a base fluid are also among other applications of nanoparticles [1].