Sharif Digital Repository

The present study examines both Direct Current (DC) and Alternating Current (AC) electroosmotic flows in a parallel plate microchannel. The method consists of a central finite difference scheme for spatial terms and a forward difference scheme for the temporal term. Asymmetric boundary conditions are assumed for Poison-Boltzmann equation used to determine the electric double layer (EDL) potential distribution. The potential distribution is then used to evaluate the velocity distribution for both DC and AC electroosmotic flows. The velocity distributions are obtained by applying slip boundary conditions on the walls to account for probable hydrophobicity of the surfaces. After determining the... 

Lab-on-a-chip devices have gained a lot of attention in chemical and biomedical analyses during the past two decades. These devices employ microfluidics basics and fundamentals to combine multifold laboratory processes in one single portable chip. The electric field has been often used in most microfluidics applications for the ease of sample control as well as become easily integrated to other chip components. Instabilities in microflows would occur when two fluids of different electric properties are exposed to an adequately strong electric field. Studying these electrokinetic instabilities is not only important for the fundamental studies but also for practical applications in micromixers... 

Recent developments in MEMS related areas have increased the demand for practical and novel pumping methods. Utilizing Electroosmotic force for flow generation in microchannels has become really popular recently, because of its reliable operation and control. One of potential applications of MEMS devices is biological and medical analysis which most samples are considered to be non-Newtonian; consequently, thermal transport characteristics of non-Newtonian electroosmotic flow of power-law fluids is investigated in this paper. In this study, thermal and hydrodynamic behavior of non-Newtonian electroosmotic flow of power-law model in a slit microchannel is analyzed. It is assumed that the flow... 

Electroosmosis is the predominant mechanism for flow generation in lab-on-a-chip devices. These microfluidic devices are microscale laboratories on a microchip that can perform clinical diagnoses. Since most biofluids encountered in these devices are considered to be non-Newtonian and the cross section of microchannels in these devices is close to a rectangular shape, In this study, the hydrodynamically and thermally fully developed combined electroosmotically and pressure driven flow of power-law fluids in rectangular microchannels is analyzed. The governing equations are first made dimensionless and then transformed into new ones based on the computational parameters which provide mesh... 

The lab-on-a-chip (LOC) devices utilizing electroosmosis for flow actuation are usually encountered with non-Newtonian behavior of working fluids. Hence, studying the flow of non-Newtonian fluids under an electroosmotic body force is of high importance for accurate design and active control of these devices. In this thesis, mixed electroosmotically and pressure driven flow of salivathrough a rectangular microchannel is examined utilizing two viscoelastic constitutive equations, namely PTT and FENE-P models. Since the hydrodynamic entry length is usually negligible for microflows, a hydrodynamically developed flow is considered in the analysis. The governing equations in dimensionless form... 

The fabrication of micron-sized instruments MEMS have been in fast progress in different fields of science and technology such as those of chemical processes in chemical engineering, propulsion in aerospace industries, microchip cooling and inkjet printers in electrical industries, and medical appliances in medical and biomedical science. They have forced the manufacturers and researchers to work and think in fabricating such small-scale sizes. However, the complexity of fabricating MEMS with moving parts has also promoted the manufacturers to think of alternative ways. For example the use of moving parts to pump fluid in such devises causes such difficulties and the researchers could adopt... 

Dissemination of an analyte under the laminar flows plays a major role in measuring and assessment of biological fluids such as sample preparation in the context of microfluidic systems. Due to the development of manufacturing technology in the Lab-on-a-chip devices, the production of rectangular microchannels with finite aspect ratios and micron and submicron sizes has been provided by which the effect of electrokinetic phenomena on concentration distribution will be magnified in these systems. On the other hand, these biofluids are viscoelastic and show extraordinary flow behaviors, not existing in Newtonian fluids and adopting appropriate constitutive equations these exotic flow behaviors... 

The “Lab-on-a-Chip” is a micro-scale device which uses fluids as working medium and can handle number of functions such as sample preparation and transfer, separation, bio-sensing and detection. One of the important parts of these devices is micro-mixer, that should blend two fluid species in a short time with desirable mixing quality. Micro-mixers are classified as passive and active. By considering the micro-scale of mixers, turbulence phenomena cannot occur due to dominance of viscous forces, therefore the mixing only depends on molecular diffusion. This thesis consists of two main parts, in the first part algebraic multigrid has been studied and implemented in Rayan (in-house CFD code).... 

This is a theoretical study on heat and mass transfer in electrokinetically driven microfluidic devices with particular consideration to the lab-on-a-chip (LOC) applications. Special attention is given to disclose the effects of the fluid rheology and the aspect ratio of the rectangular geometry on the surface reaction kinetics and the temperature rise due to the Joule heating. Along this line, two different viscoelastic constitutive equations namely PTT and FENE-P models along with the power-law viscosity model are being considered. The secondary aims also include exploring the influences of the fluid properties variations throughout the channel cross section on the hydrodynamic and thermal... 

In recent two decades, with developments in micro and nano scale fabricating techniques, use of microfluidic systems is increasing in different fields. How to drive fluid is a hard question because of high pressure drop in micro scale. Different methods has been suggested to solve this problem, among which, electroosmotic pump is preferred because of its advantages. One of the main applications of microsystems is in biomechanical devices like microreactors which are usually working with non-Newtonian fluids. The cross section of these devices are most often close to rectangular shape.Therefor, in this study,Hydrodynamic charactristics and mass transport of non-Newtonian fluids under... 

Nowadays, technology has facilitate the miniaturization of laboratory systems, medical and drug delivery tools. As a result, researchers are interested to miniaturize these tools. The extensive research in this field led to invention of lab-on-a-chips, which with the size of a few µm to a few mm, can do multiple tasks in human body. One of most important components of these devices, is microreactor. A wide range of measurements and reactions in microreactors, need to bind with the receptors at the surface of the cylindrical microchannels. For this purpose, this study, investigates the effects of surface heterogeneity on microreactors performance. In this Thesis, the governing equations were... 

The integrated development of small-scale electronic and mechanical systems has drawn attention, since they lead to increase in speed and decrease in volume of industry dimensions in the manufacturing sector. That is why microelectromechanical systems are highly considered. MEMS are widely used in Microfluidic systems that can be used in medicine, biology and drug injection. Due to the fact that consistent fluid velocity is necessary in biological applications, electroosmotic flow is more important than ever. To investigate the behavior of biofluids, Newtonian models cannot be used and it is required to use models that predict the behavior of these fluids accurately. In this research...