Microfluidic Mixing Using Microchannels in High School ...



FLUID DYNAMICS & Micro-fluidic Mixing Using Micro-channels in High School Science and Mathematics.

Jason Bledsoe

Pullman High School

Pullman, WA

&

Jonathan Heflick

Lewis-Clark State College

Lewiston, ID

Washington State University Mentors

Dr. Prashanta Dutta

Mechanical Engineering

&

Nazmul Huda

Graduate Research Assistant

July 2006

Summary

This module attempts to enhance student understanding of fluid dynamics using the context of the emerging discipline of micro-fluidic mixing and “Lab-on-a-Chip” fluid analysis technology. Students will explore the basics of fluid dynamics before attempting to tackle the more sophisticated concepts of micro-fluidics and nanotechnology.

Intended Audience

This module is intended for use in a 9th grade physical science course or equivalent level general science class. The labs are intended to be adapted for teaching mathematical applications in basic algebra, and are scalable up to the high school physics level in science and algebra II level in mathematics.

Estimated Duration

The duration for this module is just under three weeks, incorporating seven 100 minute class periods or 12-14 standard 55 minute sessions.

A brief summary of the project follows:

Session 1 Introduction to fluid dynamics presentation/discussion

-Fluid Flow Worksheet

Session 2 Introduction to fluid dynamics II – Mathematical applications.

-Unit of Measure and Capillary Action worksheets

Session 3 Fluid Dynamics Lab #1 – Viscosity and rate of flow.

-Stokes’ Law Worksheet

Session 4 Fluid Dynamics Lab #2 – Stoke’s Law.

Session 5 Micro fluidic Mixing Presentation.

-Macro to Micro Worksheet.

-Start Fluid Dynamics Lab #3 –microchannels.

Session 6 Complete microchannel lab. Unit review

Session 7 Assessment

Introduction

Surveys indicate that students in middle and high school typically do not have enough information to thoroughly consider engineering as a career. As teachers, we are less likely to stimulate interest if we have not had opportunities to learn about engineering. Beyond career considerations, understanding engineering is important so that citizens can make informed decisions about the impact of technology on society. So as to improve the learning curve across the board, Washington State University, with funding from the National Science Foundation, conducts a 6-week, hands-on engineering program that serves to familiarize middle and high school teachers with engineering processes, which they can then carry into their classrooms in the form of comprehensive, in-depth learning modules (SWEET, 2006). The goal of the program is to develop teachers who are prepared and committed to nurture student-interest in the sustained study and application of various forms of engineering. This module represents one product of that effort.

A Brief History of Fluid Mechanics

Fluid mechanics owes its development to numerous minds but in particular is indebted to the work of Isaac Newton, Leonard Euler, and Ludwig Prandtl. Newton’s contributions include the development of calculus and the fundamental laws of physics. His name is also attached to the linear stress-rate of strain, which in conjunction with Newton's 2nd Law facilitated the Navier-Stokes equations that provide the modern basis of fluid mechanics. Euler introduced the idea of a material particle to the study of fluid mechanics, as well as the classical differential element of material on which forces act. With these discoveries the motion of fluids was no longer limited to endless exercises in geometry or physical reasoning but for the first time could be analyzed quantitatively. Ludwig Prandtl's contributions include his development of aerodynamic lifting line theory and his work in turbulence. His discovery of the boundary layer is regarded as one of the most important breakthroughs in fluid mechanics of all time, earning him the title of Father of Modern Fluid Mechanics (Cramer, 2004).

Current Application of Fluid Mechanics

Fluid mechanics has a wide range of modern applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, and predicting weather patterns. Some of its principles are even used in traffic engineering, where traffic is treated as a continuous fluid. Fluid dynamics problems typically consider various properties of a fluid, such as surface tension and viscosity, and calculate for flow variables such as volume, velocity, pressure, temperature, and density as functions of space and time (Fluid Dynamics, 2006). About twenty years ago the field of micro-fluidics emerged with the manufacture of inkjet printers, in which the inkjet tubes combine and isolate from each other to change the hue of colors that are imparted on the printed page.

The Future of Fluid Mechanics

Modern micro-fluidics involves the handling and manipulation of minute amounts of fluids; volumes thousands of times smaller than a common droplet, which requires measuring in micro liters, nano-liters or even pico-liters. Micro-fluidics lies at the interfaces between biotechnology, the medical industry, chemistry and micro-electro-mechanical systems (MEMS). MEMS involves the integration of mechanical elements, sensors, actuators, and electronics on a silicon substrate through microfabrication technology. While the electronics are fabricated using integrated circuit process sequences, the micromechanical components are fabricated using compatible “micromachining” processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices. On these microchips complete laboratories can be created, comprised of channels, mixers, reservoirs, diffusion chambers, integrated electrodes, pumps, and valves. With the lab-on-a-chip technology, complete laboratories on a square centimeter can be created. The goal of the technology is to automate standard laboratory processes, improving speed and cost efficiency; lab results can be obtained within a few seconds instead of hours or days. Lab-on-a-chip devices are commonly used for capillary electrophoresis, drug development, high throughput screening and biotechnological assays. Microelectronic integrated circuits can be thought of as the “brains” of a system while MEMS augments this decision-making capability with “eyes” and “arms,” allowing micro-systems to sense and control the environment. Sensors gather information from the environment through measuring mechanical, thermal, biological, chemical, optical, and magnetic phenomena. The electronics then process the information derived from the sensors and through some decision making capability direct the actuators to respond by moving, positioning, regulating, pumping, and filtering, thereby controlling the environment for some desired outcome or purpose. MEMS and nanotechnology are still the subject of broad and diverse research efforts, and the field is constantly changing.

Rationale for Module

This module is intended to introduce students to fluid dynamics and micro fluidic mixing. The intent was to create a module that could be plugged into several different areas of a physical science classroom to provide enrichment and application. The basic module can be used as an introduction to physical science unit or as part of the properties of matter section in the chemistry unit. The module may also be used as the capstone to a basic mechanics module, with the addition of more instruction on advanced concepts like; buoyant forces, types of pressure, capillary action, sedimentation, etc. The engineering and fabrication aspect of the module also makes it appropriate as part of a materials science or applied technology program.

Science

The unit will cover several basic concepts in fluid dynamics, including:

Fluid Pressure (Pascal’s Principle: Pout = Pin). Pascal's principle states that when pressure is applied to a confined liquid, this pressure is transmitted, without loss, throughout the entire liquid and to the walls of the container.

See discussion at: . See web applet at:

Bouyancy (Archimedes’ Principle). The buoyant force on a submerged object is equal to the weight of the fluid it displaces.

See discussion at: .

See applet at: .

Flow Rate. (Continuity Equation: A1V1 = A2V2).

See discussion and diagram at: .

See web applet at: .

Laminar Flow. A flow in which thin layers of fluid flow over one another at different speeds with virtually no mixing between layers. The flow velocity profile for laminar flow in circular pipes is parabolic in shape, with a maximum flow in the center of the pipe and a minimum flow at the pipe walls. The average flow velocity is approximately one half of the maximum velocity.

Turbulent Flow. A flow which is characterized by the irregular movement of particles of the fluid. The flow velocity profile for turbulent flow is fairly flat across the center section of a pipe and drops rapidly extremely close to the walls. The average flow velocity is approximately equal to the velocity at the center of the pipe.

Transitional Flows: For fluids flowing in pipes, the transition from laminar to turbulent motion depends on the diameter of the pipe and the velocity, density, and viscosity of the fluid. The larger the diameter of the pipe, the higher the velocity and density of the fluid, and the lower its viscosity, the more likely the flow is to be turbulent.

Viscosity (Stokes’ Law). Viscosity is the fluid property that measures the resistance of the fluid to deforming due to a shear force. For most fluids, temperature and viscosity are inversely proportional. See Appendix for detailed discussion of Stokes’ Law for falling spheres.

Surface tension. The tendency of liquids to reduce their exposed surface to the smallest possible area. The phenomenon is attributed to cohesion, the attractive forces acting between the molecules of the liquid. The molecules within the liquid are attracted equally from all sides, but those near the surface experience unequal attractions and thus are drawn toward the center of the liquid mass by this net force. The surface then appears to act like an extremely thin membrane.

Capillary Action. Capillary action is the result of adhesion and surface tension. Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact, so instead of just the edges moving upward, the whole liquid surface is pulled upward.

Kinetic Theory. The Kinetic Molecular Theory is a single set of descriptive characteristics of a substance known as the Ideal Gas. All real gases require their own unique sets of descriptive characteristics. Considering the large number of known gases in the world, the task of trying to describe each one of them individually would be an awesome task. In order to simplify this task, the scientific community has decided to create an imaginary gas that approximates the behavior of all real gases. In other words, the Ideal Gas is a substance that does not exist. The Kinetic Molecular Theory describes that gas. While the use of the Ideal Gas in describing all real gases means that the descriptions of all real gases will be wrong, the reality is that the descriptions of real gases will be close enough to ideal that any errors can be overlooked.

Engineering

The engineering aspects of the module cover a broad range of areas from fabrication to technologies to overcome key issues. Micro-channel fabrication, for example, requires the use of clean rooms and computer automated design and fabrication machines (CAD/CNC).

Mixing is the primary challenge for most micro fluidic systems, resulting in innovations in how materials are pumped and channel design. The small diameter of the channels (.

Cramer, M.S. (2004) Fluid Mechanics. NY: Cambridge Univ. Press. Retrieved July 12, 2006, from .

Drakos, N. (1997). Computer Based Learning Unit. Physics 1501 - Modern Technology. UK: University of Leeds.

Fluid Dynamics. (2006, July 18). In Wikipedia, The Free Encyclopedia. Retrieved July 18, 2006, from .

Johnson, John & George Petrina. (Jul 2005). Microfluidic Mixing Using Microchannels in High School Science and Math. Pullman, WA: WSU.

NSTA. (2004). Inquiring Safely: A Guide for Middle School Teachers.

NSTA. (2004). Investigating Safely: A Guide for High School Teachers.

OSPI. (2000). OSPI: Health and Safety Guide, section K.

OSPI (2004). Science K–10 Grade Level Expectations: A New Level of Specificity. OSPI Document Number 04-0051.

RSC. (Sept. 2003). AMC Technical Brief. Analytical Methods Committee, Royal Society of Chemistry. London.

Stokes’ Law: .

SWEET. (2006). Summer at WSU- Engineering Experiences for Teachers. Brochure. Retrieved July 17, 2006 from .

-----------------------

The project herein was supported by the National Science Foundation Grant # EEC-0338868: Dr. Richard L. Zollars, Principal Investigator and Dr. Donald C. Orlich, co-PI. The module was developed by the authors and does not necessarily represent an official endorsement by the National Science Foundation.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download