Evan Lemley
University of Central Oklahoma, Engineering & Physics, Faculty Member
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Blood flow into the kidneys through the renal artery determines the systemic blood pressure which is regulated by the baroreceptors in the kidneys. When the baroreceptors sense decreases in local fluid pressure they stimulate the... more
Blood flow into the kidneys through the renal artery determines the systemic blood pressure which is regulated by the baroreceptors in the kidneys. When the baroreceptors sense decreases in local fluid pressure they stimulate the renin-angiotensin aldosterone (RAA) system, which increases systemic blood pressure by constricting blood vessels throughout the body. An aneurysm in the renal artery leads to high systemic blood pressure in most patients with this condition, but the mechanisms by which the pressure increase occurs are not well understood. One explanation of the pressure increase could be a drop in local fluid pressure near the aneurysm itself causing the RAA system to “correct” this low pressure by systemically increasing the blood pressure. The ongoing work reported here has focused on a model renal artery network with and without an aneurysm by simulating the flow with computational fluid dynamics (CFD) software. The fluid for the simulations was meant to mimic blood in terms of density and viscosity for shear stresses where Non-Newtonian flow effects should not be a concern. Flow into the renal artery was at a Reynolds number of almost 700, to mimic the flow rate in the renal artery. The simulations were performed to determine the difference in pressure between an inlet to the renal network and the exits from the network. These results indicate that the pressure difference through the network differed by less than 10 Pa comparing networks with and without saccular aneurysm. The pressure change that would trigger the RAA system is nearly 1000 Pa. So we conclude that the effect of changing the geometry with only a saccular aneurysm is not responsible for triggering the RAA system alone. Other effects that could lead to triggering of the RAA system are discussed as well as our initial construction of a system to perform validation experiments of our CFD results.
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ABSTRACT Laminar flow is increasingly important area of study as it dominates microscale and milliscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows.... more
ABSTRACT Laminar flow is increasingly important area of study as it dominates microscale and milliscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows. Studies of pressure losses in junctions have mostly been focused on turbulent flow conditions that exist in larger scale piping systems. There is a need for laminar flow studies of energy losses in junctions so that engineers can better predict, design, and analyze flow in microscale and other small scale systems. Unlike in the turbulent regime, Reynolds number plays a dominant role in energy losses for laminar flow, so new studies should document the effects of Reynolds number. This paper documents laminar flow experiments in a milliscale junction. This work builds on previous experience of the authors in computational fluids dynamics simulations of junctions. The planar junction under study consists of a circular tubes with two outlets and one inlet. A general technique has been developed to produce computer and physical models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. The junction test sections for experiments are milled from cast acrylic in two pieces to match three-dimensional computer models. The test sections are placed in a system that provides steady-state flow of water to test sections and has been designed to measure pressure losses and flow rates through the test section.
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Students are often looking for internet resources to supplement college courses. Solutions manuals for course textbooks are readily (if illicitly) available and reduce the amount of time students spend outside of class actually learning... more
Students are often looking for internet resources to supplement college courses. Solutions manuals for course textbooks are readily (if illicitly) available and reduce the amount of time students spend outside of class actually learning to problem-solve. At the same time, the content for many courses is readily available online in many forms some reliable, some not. There are currently valid concerns about both of these trends; related to the ability of students to solve problems independently and the quality of the information they may find online (due to poor information literacy). Pencasts® provide a way to have students become familiar with course content outside of class, leaving more time in class for problem-solving exercises and discussion and explanation of lecture materials. A Pencast® consists of a video that displays the written work of the instructor with overlayed audio explanations; this is accomplished with a smartpen and a notebook with small, closely-spaced dots (d...
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The potential applications of micromixers continues to expand in the bio-sciences area. In particular, passive micromixers that may be used as part of point-of-care (POC) diagnostic testing devices are becoming commonplace and have... more
The potential applications of micromixers continues to expand in the bio-sciences area. In particular, passive micromixers that may be used as part of point-of-care (POC) diagnostic testing devices are becoming commonplace and have application in developed, developing, and relatively undeveloped locales. Characterizing and improving mixing efficiency in these devices is an ongoing research effort. Micromixers are used in some lab-on-chip (LOC) devices where it is often necessary to combine two or more fluids into a mixed solution for testing or delivery. The simplest micromixer incorporates a tee junction to combine two fluid species in anti-parallel branches, with the mixed fluid leaving in a branch perpendicular to the incoming branches. Micromixers rely on two modes of mixing: chaotic advection and molecular diffusion. In micro-mixers flow is typically laminar, making chaotic advection occur only via induced secondary flows. Hence, micromixers, unless carefully designed, rely alm...
Research Interests: Physics and Micromixer
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Biography Evan Lemley received his BA in Physics from Hendrix College and MS and Ph.D in Engineering (Mechanical) from the University of Arkansas. His thesis work was focused on modeling and simulation of various neutron detectors. Post... more
Biography Evan Lemley received his BA in Physics from Hendrix College and MS and Ph.D in Engineering (Mechanical) from the University of Arkansas. His thesis work was focused on modeling and simulation of various neutron detectors. Post graduation Evan worked for the engineering consulting firm Black & Veatch in a group responsible for modeling coal power plants with custom written software. In August 1998, Evan became an Assistant Professor in the Department of Engineering and Physics (formerly Physics) at the University of Central Oklahoma, and has been there since, teaching mechanical engineering, physics, and engineering computation courses. Early research at UCO was focused on neutron transport in materials. More recently, Evan has been involved in simulation of flow in microtubes and microjunctions and simulation of flow in porous networks.
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Micro-mixing in different channel geometries may increase entropy generation and lead to improved efficiency of fluid mixing. The entropy generation rate corresponds to irreversibility due to the heat transfer and viscous effects in fluid... more
Micro-mixing in different channel geometries may increase entropy generation and lead to improved efficiency of fluid mixing. The entropy generation rate corresponds to irreversibility due to the heat transfer and viscous effects in fluid flow through a channel. The objectives of this study are to validate the entropy generation rate of three expansion/contraction geometries [1] by using an analysis based on the Second Law of Thermodynamics (SLT) numerically and to study how entropy generation rate changes by placing flow obstacles in the channel. The geometries presented are not unique. In this paper the focus is on using CFD combined with the SLT as a tool to explore the effectiveness of micro-mixers. The entropy generation field in the expansion/contraction region between a 100 micrometer wide and a 200 micrometer wide rectangular micro-channel was analyzed using computational fluid dynamics (CFD) ANSYS-Fluent, and compared with the experimental results from Saffaripour et al. [1...
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Particle image velocimetry (PIV) has transformed fluid mechanics research in recent years. PIV also holds the possibility to transform fluids engineering undergraduate education with the ability of students to get hands-on experience in... more
Particle image velocimetry (PIV) has transformed fluid mechanics research in recent years. PIV also holds the possibility to transform fluids engineering undergraduate education with the ability of students to get hands-on experience in visualization of real flow fields. One barrier to use of PIV is the cost of a system. Research grade systems are often over $100,000 and inaccessible to many undergraduate students. Recent availability of low-cost high-frame-rate digital cameras, lasers, and public domain software offer potential accessibility for PIV for many labs at academic institutions. In this paper we describe the development of a PIV system for under $1000 including specific components and their costs. In our lab this system is currently being used for several liquid flow experiments including obtaining the flow field in and near small bifurcations. Although we are using the system for liquid flows, it may be used for gas flows as well. One issue that is addressed is the cost ...
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Neutron spectra have been calculated using the ANISN one-dimensional discrete ordinates code for the case of a ¹âµÂ²Cf source in a transport cask of a particular design. All computations were done on personal computers (PCs) (mostly 486... more
Neutron spectra have been calculated using the ANISN one-dimensional discrete ordinates code for the case of a ¹âµÂ²Cf source in a transport cask of a particular design. All computations were done on personal computers (PCs) (mostly 486 models) with the ANISN-ORNL (486 version) computer code. With a source of ²âµÂ²Cf fission neutrons, the neutron flux spectrum in the cask cannot be characterized as {open_quotes}moderated.{close_quotes} Concern about an appropriate choice for the cross-section data set has led to a comparison, for this application, of three different cross-section libraries: DABL, HILO, and BUGLE-80. Although the cross-section sets were not originally designed for PC use, the libraries have been successfully employed for PC computations. Work with yet another data library, BUGLE-93, is incomplete at this stage. From neutron flux spectra on the surface of the cask, personnel dosimetric quantities (such as dose equivalent) have been determined for the DABL, HILO, a...
This paper presents a capacitive liquid crystal-based technique to measure wall shear stress. In this work, the authors have developed an alternative method which utilizes LC film embedded in an interdigital capacitive microstructure.... more
This paper presents a capacitive liquid crystal-based technique to measure wall shear stress. In this work, the authors have developed an alternative method which utilizes LC film embedded in an interdigital capacitive microstructure. This innovation will transduce the shear force, which deforms the LC profile, into a measurable capacitive quantity via tracking the LC deformation. This promising sensor has strong potential applications in bioengineering systems where monitoring the blood shear stress is critical such as carotid artery experiments. Some of the issues addressed in this work are the impact of the shear stress on the liquid crystal molecular ordering (order parameter) and the influence of electrode geometries and material properties on the measured capacitances.
The precise and selective destruction of tumor tissue through hyperthermia, when combined with immunoadjuvant applications, has shown promise in the treatment of cancer. The combination of an 805-nm laser and indocyanine green (ICG) has... more
The precise and selective destruction of tumor tissue through hyperthermia, when combined with immunoadjuvant applications, has shown promise in the treatment of cancer. The combination of an 805-nm laser and indocyanine green (ICG) has been shown to be highly effective in laboratory experiments in satisfying both the precision and selectivity requirements of such a procedure. A systematic study was conducted
Research Interests: Engineering, Materials Science, Biomedical Engineering, Laser, Monte Carlo Simulation, and 10 moreCancer, Cancer treatment, Laboratory experiment, Temperature Distribution, Temperature measurement, Photothermal Therapy, Boolean Satisfiability, Thermal Effects, Monte Carlo Method, and Indocyanine green
ABSTRACT Laminar flow dominates microscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows. Studies of pressure losses in junctions have mostly been... more
ABSTRACT Laminar flow dominates microscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows. Studies of pressure losses in junctions have mostly been focused on turbulent flow conditions that exist in larger scale piping systems. There is a need for laminar flow studies of energy losses in junctions and networks of junctions so that engineers can better predict, design, and analyze flow in microscale systems. Unlike in the turbulent regime, Reynolds number plays a dominant role in energy losses for laminar flow. Studies focused on Reynolds number dependence are needed.This paper documents laminar flow experiments in networks constructed from microscale junctions (microjunctions). This work builds on previous experience of the authors in computational fluids dynamics simulations of junctions and networks of junctions. The planar junctions studied consist of circular tubes with two outlets and one inlet. A general technique has been developed to produce computer and physical models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. There have been several techniques used to create the experimental microjunction networks: a “lost wax” method that creates the network in Polydimethylsiloxane (PDMS), stereolithography-based junctions connected by tubing, and photopolymer cured by ultraviolet radiation. Results are presented for pressure losses in various microjunction networks as a function of Reynolds number.
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ABSTRACT Laminar flow is increasingly important area of study as it dominates microscale and milliscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows.... more
ABSTRACT Laminar flow is increasingly important area of study as it dominates microscale and milliscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows. Studies of pressure losses in junctions have mostly been focused on turbulent flow conditions that exist in larger scale piping systems. There is a need for laminar flow studies of energy losses in junctions so that engineers can better predict, design, and analyze flow in microscale and other small scale systems. Unlike in the turbulent regime, Reynolds number plays a dominant role in energy losses for laminar flow, so new studies should document the effects of Reynolds number. This paper documents laminar flow experiments in a milliscale junction. This work builds on previous experience of the authors in computational fluids dynamics simulations of junctions. The planar junction under study consists of a circular tubes with two outlets and one inlet. A general technique has been developed to produce computer and physical models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. The junction test sections for experiments are milled from cast acrylic in two pieces to match three-dimensional computer models. The test sections are placed in a system that provides steady-state flow of water to test sections and has been designed to measure pressure losses and flow rates through the test section.
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Blood flow into the kidneys through the renal artery determines the systemic blood pressure which is regulated by the baroreceptors in the kidneys. When the baroreceptors sense decreases in local fluid pressure they stimulate the... more
Blood flow into the kidneys through the renal artery determines the systemic blood pressure which is regulated by the baroreceptors in the kidneys. When the baroreceptors sense decreases in local fluid pressure they stimulate the renin-angiotensin aldosterone (RAA) system, which increases systemic blood pressure by constricting blood vessels throughout the body. An aneurysm in the renal artery leads to high systemic blood pressure in most patients with this condition, but the mechanisms by which the pressure increase occurs are not well understood. One explanation of the pressure increase could be a drop in local fluid pressure near the aneurysm itself causing the RAA system to “correct” this low pressure by systemically increasing the blood pressure. The ongoing work reported here has focused on a model renal artery network with and without an aneurysm by simulating the flow with computational fluid dynamics (CFD) software. The fluid for the simulations was meant to mimic blood in ...
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Energy losses in junctions are often found by using an assumed loss coefficient for the particular geometry. While this coefficient remains nearly constant under turbulent conditions, this is not true for laminar flow. The loss... more
Energy losses in junctions are often found by using an assumed loss coefficient for the particular geometry. While this coefficient remains nearly constant under turbulent conditions, this is not true for laminar flow. The loss coefficient through a dividing junction tends to decrease as a function of Reynolds number converging to some value once fully turbulent flow occurs. Research has been done to catalog losses for various geometries under turbulent flow; yet, there has not been the same detailed research for the laminar conditions. This is mostly due to many applications at the macro scale where turbulent flow is prevalent. Flow in microchannels and nanochannels is mostly laminar. Applications at this small scale have created a demand for the study of these loss coefficients under the laminar flow conditions.This paper focuses on simulations done of flow through a square-cornered tee-junction with a rectangular cross sectional area of 6 by 7 millimeters. The fluid consisted of a glycerin and water mixture that was 30 percent water and 70 percent glycerin by volume. Measurements were made of an actual mixture’s density and viscosity and these parameters were used in the simulations. The mixture was chosen to give sufficient pressure drop to measure in validation experiments. Using these simulations, a detailed account of the energy losses in the junction was observed as a function of Reynolds number. The Reynolds number range in this study was 1–100. Higher Reynolds numbers were simulated where signs of a transition to turbulence were observed.The stagnation loss coefficient, which includes kinetic energy and pressure changes through the junction, was found to be inversely proportional to Reynolds number. Initial experimental verification has been performed, in which the experimental stagnation loss coefficient followed the same trend as the simulations. Additional experimental validation is underway.Copyright © 2014 by ASME
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The goal of this study was to determine laminar pressure loss coefficients for flow in microelbows with circular and trapezoidal cross-sections. Flow conditions and pressure losses in these elbows are of interest in microfluidic devices,... more
The goal of this study was to determine laminar pressure loss coefficients for flow in microelbows with circular and trapezoidal cross-sections. Flow conditions and pressure losses in these elbows are of interest in microfluidic devices, in porous media, and in other types of microfluidic networks. The literature focuses almost exclusively on loss coefficients due to turbulent flow in macroelbows with very little data on laminar flow in macroelbows. The pressure loss coefficients determined in this study are intended to aid in realistic simulation of existing laminar flow networks or the design of these networks. This study focused on an elbow of constant cross-section with inlet and outlet tubes of sufficient length so as to allow fully developed laminar flow at the entrance to the elbow and at the outlet tube exit. For the circular elbow, both the ratio of elbow radius to inner diameter and inlet Reynolds number were allowed to vary over the ranges of 0.5—10.5 and 1—2500, respecti...
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ABSTRACT In fluid flow piping systems, tee and wye junctions are commonly encountered and the study of flow through them has been well documented. Most of these studies have focused on flow characterized as turbulent for which there are... more
ABSTRACT In fluid flow piping systems, tee and wye junctions are commonly encountered and the study of flow through them has been well documented. Most of these studies have focused on flow characterized as turbulent for which there are nearly constant losses in pressure and kinetic energy in the junctions. Laminar flow has received much less attention since it is not frequently observed in macro scale piping systems where pipe diameters are measured in centimeters. The recent increase in use of micro scale flow devices calls for more research into laminar flow behavior that dictates the design and operation of these devices. This paper documents results from computational fluid dynamics (CFD) simulations of flow in planar tee and wye junctions. The junctions studied consisted of circular pipes with two outlets and one inlet. The angles between the tee and wye junctions were fixed to 180 and 60 degrees, respectively. The inlet pipe diameter was fixed at 50 microns and the outlet pipe diameters were chosen to satisfy the continuity equation constrained to have equal velocities in all pipes. The lengths of the inlet and outlet pipes were varied to achieve fully developed flow within the junction. Following a grid resolution study performed on a sample tee junction, a generalized algorithm was designed and implemented to create three-dimensional models of these junctions subject to the former conditions. In the CFD simulations, Reynolds number was varied in the laminar characterized region between 1 and 2000. The simulations calculated static pressure and velocity magnitude values for a number of planes intersecting the junctions along the inlet and outlet pipes. From these values, pressure and kinetic energy gradients were calculated to estimate the static pressure and kinetic energy at the inlet and outlet pipes of each junction. Finally, these inlet and outlet values were used to calculate the stagnation pressure loss coefficient, which reflects dimensionless losses of pressure and kinetic energy for the junction. These coefficients ranged from 1 to 300 for the tee junction and 1 to 400 for the wye junction over the specified range of Reynolds number. The values were inversely proportional to Reynolds number and curve fits were provided for valid ranges.
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This validation study is part of a larger ongoing study to improve flow simulation in three dimensions in porous materials. Obtaining porous flow parameters such as permeability and Forchheimer’s coefficient is time consuming and... more
This validation study is part of a larger ongoing study to improve flow simulation in three dimensions in porous materials. Obtaining porous flow parameters such as permeability and Forchheimer’s coefficient is time consuming and expensive, and may be very sample dependent. This study is aimed at verifying a simulation technique that predicts flow parameters, including permeability and Forchheimer’s coefficient, by comparing simulation results to empirical results. The simulation technique used performs Monte Carlo trials by using statistical information about pore size distributions to generate random pore networks consisting of pipes and junctions, then simulating flow through the network. The validations have been performed for a packed bed of glass beads and for sandstone. For glass beads the relationship between permeability and Forchheimer’s coefficient follows an empirical relationship known as Ergun’s equation, while sandstone has been compared to measured data for the perme...
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The goal of this study was to determine laminar stagnation pressure loss coefficients for circular ducts in which flow encounters a planar bifurcation. Flow conditions and pressure losses in these laminar bifurcations are of interest in... more
The goal of this study was to determine laminar stagnation pressure loss coefficients for circular ducts in which flow encounters a planar bifurcation. Flow conditions and pressure losses in these laminar bifurcations are of interest in microfluidic devices, in porous media, and in other networks of small ducts or pores. Until recently, bifurcation geometries had been studied almost exclusively for turbulent flow, which is often found in fluid supply and drain systems. Recently, pressure loss coefficients from simulations of a few arbitrary bifurcation geometries in two-dimensions have been published — the present study describes the extension of these two-dimensional simulations to three-dimensional circular ducts. The pressure loss coefficients determined in this study are intended to allow realistic simulation of existing laminar flow networks or the design of these networks. This study focused on a single inlet duct with two outlet ducts, which were allowed to vary in diameter, ...
Research Interests: Bifurcation and Ducts
The goal of this study was to determine the entrance length — the distance from a microtube entrance to the point where flow is fully developed — for laminar liquid flow in smooth, straight, circular-microtubes and trapezoidal... more
The goal of this study was to determine the entrance length — the distance from a microtube entrance to the point where flow is fully developed — for laminar liquid flow in smooth, straight, circular-microtubes and trapezoidal microchannels. Knowledge of the entrance length and pressure losses in this region for microtubes are of interest in microfluidic devices, in porous media, and in other networks of small ducts or pores. Although laminar entrance length has been studied extensively in macroscale tubes, only recently has attention been paid problem of entrance length in microtubes. Some differences do exist in macro versus micro flow, sometimes attributed to the relatively small volume to surface area ratio at the microscale. The entrance length determined in this study is intended to provide a means to analyze and design microtubes or networks of microtubes. The inlet velocity was varied to provide a Reynolds number of 10 to 2000 and the length was varied based on Reynolds numb...