Sharif Digital Repository

Today microbubbles are broadly used as ultrasound contrast agents. These bubbles enhance the image resolution of B-mode pictures. Flow focusing in microchannels could provide us the goal of one-size bubbles generation. Microbubbles could use as tracers in Echo_PIV method to determine the velocity profile in main body vessels such as carotid. In this paper we introduce a new production method to fabricate a low-cost microchannel for preparing Microbubble contrast agents (less than 50 microns) by using some surface active agents and a viscosity enhancing material to obtain appropriate Microbubbles with desired life time and stability for any in vitro infusion for velocity measurement. By... 

Pulsating heat pipes (PHP) are complex heat transfer devices which unlike conventional heat pipes do not contain any wick in their structure. The effective parameters consist of; working fluid, volumetric filling ratio, operational orientation and input heat power have been investigated here. The experimental set-up we have contemplated, fabricated and tested included five turns, made of copper tube coupled with two glass tube of internal diameter 1.8 mm. The height of evaporator, condenser and adiabatic section was 60, 60 and 150 mm, respectively. The evaporator was heated with electrical element connected to an AC variant power supply and the condenser was connected to a constant... 

Reducing fossil fuels and increasing urban air pollution, has made the automotive industry to reduce the fuel consumption of their engines by various approaches. Removing the compressor of air conditioning system by replacing the absorption chiller instead of inverse rankin cycle is a shortcut to reduce the fuel consumption which at the same time reduces costs of using air conditioning system for occupants. Design of a 3 kW lithium bromide-water absorbent chiller has verified based on environmental conditions and car space limitations and using the combustion products as the heat source of system. K4M engine of L90 sedan Car as an internal combustion engine sample’s exhaust manifold has been... 

Nowadays energy consumption increases in our daily life and incredibly enhancement of growth rate can be seen recent years. Hence, the use of renewable energy is prioritized. Solar energy is one of the choices because it is free and available. In this research, it has been tried to get electrical and thermal power at a reasonable cost both during the day and night. The system is equipped with a linear parabolic concentrator with a collector installed in the center of the concentrator which has been installed on its faces photovoltaic cells and thermoelectric modules, and five different systems have been tested with different components. Also, the paraffin has been used as a phase change... 

The main purpose of this study was to increase the flow circulation within the flat plate oscillating heat pipes as a result Increase the heat transfer rate by placing diagonal grooves in the evaporator. The project in two stages a simple page and diagonal companion page are provided to investigate the effect of diagonal grooves. First a simple plate and then a second one with diagonal grooves in the evaporator it was made. Thermal performance of the heat pipes at each of the stages at different filling ratios of 40%, 50%, 60% and 70% for variable input capacities have been studied and compared. The results of the second stage showed that the performance of the new heat pipe at the optimum... 

Ever-increasing energy consumption and consequent extensive greenhouse gas (GHG) emissions are two major urgent problems faced by all human beings in the 21st century. As a major contributor, the energy production section appears to be the most suitable field where further improvements could be explored to tackle these problems. Multi carrier energy system is a typical type of next generation energy production technology with higher energy efficiency and lower/zero GHG emissions. The conversion of energy between different carriers establishes a coupling of the corresponding power flows resulting in system interactions. The investigation of such phenomena requires the development of tools for... 

Nowadays Lab-on-a-chip systems are being widely used in medical applications, especially in analyzing minute volumes of blood for diagnosis and treatment of some crucial diaseses like diabetic. A Lab-on-a-chip is comprised of a variety of components such as micromixer, microdispenser, detection and separation units and so on. In this thesis, however, we have analyzed and numerically simulated a microdispenser which is electrokinetically driven. In other words, electrical potentials are applied to electrodes in order to conduct two fluids within a cross microchannel, and distribution of a sample fluid takes place due to appropriately applied potentials. In order to analyze and simulate the... 

Various application of polyethylene material in different industries caused to modern techniques for controlling and measuring specifications of micro-particle suspension. Many industries try to increase stability of suspensions in front of their phase separation.
Because of the consequences of suspension homogeneity, at first, we measured this property. Then, the stability was tested by three different methods. In the first method, the transmitted laser light was measured to assay the suspensions stability. In the second, number of sediments of particles was counted. Sedimentation velocity of particles was measured directly by using a horizontal microscope as the third method. The... 

The use of nano-fluid, which is a stable solid liquid mixture, has been proposed as a new strategy for heat transfer operations. Much research has been done on heat transfer of nano-fluids until now, whereas the study of phenomena associated with phase change, such as boiling where there is heat transfer in larger scales is very necessary. The boiling process based on its potential for transferring high amounts of heat at low temperatures is a very effective and common mechanism, and it occurs in many engineering systems, including boilers at plants, evaporators in refrigeration systems and nuclear reactors. Also, a considerable amount of research was done recently in the field of... 

Considerable increase in speed and decrease in size of electronic devices results in increase of heat flux, so there is a need to enhance efficiency of cooling electronic devices. In the present research two sets of OLPHPs with five turns for two different magnetic nano-fluids were fabricated and the effects of working fluid (water, and two types of magnetic nano-fluids), working pressure, concentration, magnetic field, magnets location, and inclination angle on the thermal performance of OLPHPs have been considered in both startup and steady thermal conditions.
Experimental results show that magnetic nano-fluids can improve thermal performance of the OLPHPs. Application of magnetic... 

Dissipative particle dynamics (DPD) is an emerging mesoscopic computational method in which the interparticle forces arise because of coarse-graining at the molecular level. In the asymptotic limit of large length scales, the governing equations of continuum are reproduced, as demonstrated in this work. This method of simulation has the capability of simulating larger order of time and space in compare with dynamic molecular method. One of the important applications of DPD is simulating the dilute polymer solution. In this project, we developed a general code to simulate dilute polymer behavior which consists of polymeric forces and different types of usual DPD boundary conditions. This code... 

The main purpose of this thesis is to analyze the total productive maintenance based on computerized maintenance management system. At first, a detailed study on total productive maintenance is performed and then the requirements of this maintenance strategy are specified. Also, a computerized maintenance management system is defined which can help total productive maintenance to reach to its requirements. Finally, a conceptual model and entity-relationship model for computerized maintenance management system data base has been created  

Experiments were performed to explore the free convective hat transfer characteristics of water based nanofluids. Experiments of natural convection over a vertical flat plate with constant heat flux in water-based nanofluids with Ag and TiO2 nanoparticles were performed. Velocity boundary layer measured using PIV method. Also convective heat transfer coefficient obtained using three thermometers behind the wall. Various test cases with different heat fluxes on the wall are considered. Two volumetric concentrations of Ag nanofluid, 1% and 2%, and TiO2 nanofluid, 1% and 2%, were tested in the present study. It was shown that, with increasing nanofluid concentration, velocity boundary layer...