Sharif Digital Repository

This study presents a comprehensive investigation on hydrodynamic and thermal transport properties of mixed electroosmotically and pressure driven flow in microtubes. Particular emphasis is given to investigating the combined consequences of viscous dissipation, non-uniform Joule heating, and variable thermophysical properties. Analytical solutions are obtained using the Debye-Hückel linearization and constant fluid properties assumption, while a numerical solution is presented for variable fluid properties and non-uniform distribution of Joule heating. The results indicate that, viscous heating effect is pronounced significantly when a favorable pressure gradient exists and cannot be... 

The objective of the present work is to compare the performance of the regenerator of pulse tube refrigerators at low and high frequencies. The hydrodynamic and thermal behavior of the regenerator is investigated in this respect. To consider the system performance, a system of conservation equations including two energy equations for the regenerator as a porous media is employed. The present model considers one-dimensional, periodic, unsteady, compressible flow in the regenerator. The conservation equations are transformed by implementing the volumetric average scheme. The method of harmonic approximation is employed to derive an analytical solution. To explore the system performance, net... 

Aiming at improving efficiency in combustion systems, the study on droplet behavior and its trajectory is of crucial importance. Vortex engine is a kind of internal combustion engine which uses swirl flow to achieve higher combustion efficiency. One of the important advantages of designing vortex engine is to reduce the temperature of walls by confining the combustion products in the inner vortex. The scopes of this investigation are to study vortex engine flow field as well as effective parameters on fuel droplet behavior such as droplet diameter, droplet initial velocity and inlet velocity of the flow field. The flow field is simulated using Reynolds Stress Transport Model (RSM). The... 

The limitations of the microfabrication technology do not allow producing perfectly smooth microchannels. Hence, exploring the influences of roughness on transport phenomena in microtubes is of great importance to the scientific community. In the present work, consideration is given toward the corrugated roughness effects on fully developed electroosmotic flow and heat transfer in circular microtubes. Analytical solutions based on perturbation technique are presented for the problem assuming a low zeta potential under the constant heat flux boundary condition of the first kind. It is revealed that higher values of the corrugation number and relative roughness give rise to smaller Nusselt... 

In this research a phase change micropump as a novel type of non-mechanical micropumps has been investigated. A one dimensional model has been developed to describe the pumping mechanism and assess the working characteristics of the micropump. Conservation of mass, momentum and energy have been employed to obtain an algebraic equation for the flow rate which depends on seven non-dimensional numbers. The governing equation has been solved to study the effect of various operating parameters on the micropump performance. To verify the analytical approach, an experimental set up has been constructed. The results show that the theoretical model is in reasonable agreement with the experimental... 

This paper presents the modeling of a desiccant wheel used for dehumidifying the ventilation air of an air-conditioning system. The simulation of the combined heat and mass transfer processes that occur in a solid desiccant wheel is carried out with MATLAB Simulink. Using the numerical method, the performance of an adiabatic rotary dehumidifier is parametrically studied, and the optimal rotational speed is determined by examining the outlet adsorption-side humidity profiles. The solutions of the simulation at different conditions used in air dehumidifier have been investigated according to the previous published studies. The model is validated through comparison the simulated results with... 

One of the key solutions to improve engine performance and reduce exhaust emissions of internal combustion engines is direct injection of bio-fuels. A new modified bio-ethanol is produced to be substituted by fossil fuels in gasoline direct injection engines. The key advantages of modified bio-ethanol fuel as an alternative fuel are higher octane number and oxygen content, a long-chain hydro-carbon fuel, and lower emissions compared to fossil fuels. In the present study spray properties of a modified bio-ethanol and its atomization behaviors have been studied experimentally and theoretically. Based on atomization physics of droplets dimensional analysis has been performed to develop a new... 

Heteropoly acid was found to be an effective and efficient catalyst for the ring opening reaction of epoxides with various aromatic amines to produce the corresponding β-amino alcohols in moderate to excellent yields in water. This method provides a new and efficient protocol in terms of mild reaction conditions, clean reaction profiles, small quantity of catalyst, and simple work-up procedure  

A simple, rapid, atom economy and highly efficient procedure has been developed for thiolysis of epoxides by aromatic and aliphatic thiols under solvent-free conditions. A high regioselectivity in favor of nucleophilic attack at the benzylic carbon atom of aromatic epoxides, such as styrene oxide, is observed. However, aliphatic unsymmetrical alkenyl oxides undergo selective nucleophilic attack at the sterically less hindered carbon atom. A variety of β-hydroxy sulfides were obtained in short reaction time and excellent yields with nearly complete regioselectivity  

The present research proposes an effective method to enhance the heat transport capability of conventional electronic coolers and improve their thermal management. Pulsating heat pipes (PHPs) are outstanding heat transfer devices in the field of electronic cooling. In the present study, two sets of open-loop pulsating heat pipes (OLPHPs) for two different magnetic nanofluids (with and without surfactant) were fabricated and their thermal performance was experimentally investigated. Effects of working fluid (water and two types of magnetic nanofluids), heating power, charging ratio, nanofluid concentration, inclination angle, application of a magnetic field, and magnet location are described.... 

An operationally simple, practical, and economical protocol for iron(III) chloride catalyzed Paal-Knorr pyrrole synthesis in water in good to excellent yields has been developed. Several N-substituted pyrroles are readily prepared from the reaction of 2,5-dimethoxytetrahydrofuran and aryl/alkyl, sulfonyl and acyl amines under very mild reaction conditions. © Georg Thieme Verlag Stuttgart  

A new mathematical method is proposed to model the transport of polydisperse submicron aerosol particles in a heterogeneous porous media, and as an example, it is applied to study the transport of mainstream smoke aerosol particles in the cigarette tobacco column. The tobacco column is composed of randomly distributed pores and the aerosol particle transport is modeled utilizing a pore sub-model and taking into account aerosol particle coagulation and deposition. Copyright © 2009 Begell House, Inc  

In order to safe design and optimize performance of some industrial systems, it's often needed to categorize two-phase flow into different regimes. In each flow regime, flow conditions have similar geometric and hydrodynamic characteristics. Traditionally, flow regime identification was carried out by flow visualization or instrumental indicators. In this research3 kind of neural networks have been used to predict system characteristic and flow regime, and results of them were compared: radial basis function neural networks, self organized and Multilayer perceptrons (supervised) neural networks. The data bank contains experimental pressure signalfor a wide range of operational conditions in... 

Recent developments of superconductive industry require cryocoolers with cooling power higher than one Watt in the 70-80 K temperature range. High capacity pulse tube cryocoolers assure the cooling power required for operation of superconducting devices. The purpose of this paper is to investigate the influence of the pressure wave generator on high capacity pulse tube cryocooler performance. In this respect the hydrodynamic and thermal behavior of the cryocooler is explained by applying the mass and energy balance equations to different components of the cryocooler cycle. A linear temperature profile is assumed in the regenerator and nodal analysis technique is employed to simulate the tube... 

Biomechanical forces and hemodynamic factors influence the blood flow and the endothelial cells (ECs) morphology. These factors behave differently beyond the coronary artery stenosis. In the present study, unsteady blood flow in the left coronary artery (LCA) and its atherosclerotic bifurcating vessels, left anterior descending (LAD) and left circumflex (LCX) arteries, were numerically simulated to investigate the risk of plaque length development and secondary plaque formation in the post-stenotic areas. Using fluid–structure interaction (FSI) model, compliance of arterial wall and vessel curvature variations due to cardiac motion were considered. The arteries included plaques at the... 

Biomechanical forces and hemodynamic factors influence the blood flow and the endothelial cells (ECs) morphology. These factors behave differently beyond the coronary artery stenosis. In the present study, unsteady blood flow in the left coronary artery (LCA) and its atherosclerotic bifurcating vessels, left anterior descending (LAD) and left circumflex (LCX) arteries, were numerically simulated to investigate the risk of plaque length development and secondary plaque formation in the post-stenotic areas. Using fluid–structure interaction (FSI) model, compliance of arterial wall and vessel curvature variations due to cardiac motion were considered. The arteries included plaques at the... 

Lithium-ion batteries should continuously be operated at the optimum temperature range (15∼40∘C) for the best performance. Surface temperature monitoring is critical for the safe and efficient operation of the battery. In this study, initially, the electrical parameters of the battery are determined by applying a second-order equivalent circuit model. This model then is integrated with a thermal model based on the temperature dependent behavior of the electrical parameters and the heat generated. The input parameters to the electro-thermal model include the current, the ambient fluid temperature and the output parameters include the terminal voltage, state of charge, cell core temperature... 

The battery management system (BMS) in electric vehicles monitors the state of charge (SOC) and state of health (SOH) of lithium-ion battery by controlling transient parameters such as voltage, current, and temperature prevents the battery from operating outside the optimal operating range. The main feature of the battery management system is the correct estimation of the SOC in the broad range of vehicle navigation. In this paper, to estimate real-time of SOC in lithium-ion batteries and overcome faults of Extended Kalman Filter (EKF), the Square-Root Sigma Point Kalman Filter is applied on the basis of numerical approximations rather than analytical methods of EKF. For this purpose, the... 

The solid LiClO4-mediated one-pot reaction of aldehydes with secondary amines and C nucleophiles afforded the corresponding aminoalkylation products in high yields. Unlike the previous reported procedure, the aminoalkylation of aldehyde was achieved in the presence of only 0.5 equivalents of solid lithium perchlorate in dichloromethane as the solvent with good to high yields at room temperature. © Springer-Verlag 2003  

Heat transfer is one of the prevalent concepts with many usages in different fields of science, industry and so on. In different applications we need more or less to know about this phenomenon. Control of this phenomenon is too important in some cases and we should be aware how to control it. The importance of heat transfer rate and effect of various parameters on it, is a reason of performing this research. Because of changes of air pressure in different applications, we need to know how heat transfer affected by air pressure. In different places air pressure is higher or lower than atmospheric pressure and we can't use more of experimental equations (e.g. Morgan or Churchill-Chu for a...