LAMINAR FLOW FUEL CELLS & FLUID DYNAMICS IN THE HIGH SCHOOL CLASSROOM

Transcription

1 LAMINAR FLOW FUEL CELLS & FLUID DYNAMICS IN THE HIGH SCHOOL CLASSROOM Chayne Ibrahim Sunnyside High School Sunnyside, WA Joseph Forsman Lewis-Clark State College Lewiston, ID Washington State University Mentors Dr. Prashanta Dutta Mechanical Engineering Zaki Jubery Graduate Research Assistant July 2009 The project herein was supported by the National Science Foundation Grant Award No. EEC : Dr. Richard L. Zollars, Principal Investigator. The module was developed by the authors and does not necessarily represent an official endorsement by the National Science Foundation.

2 Table of Content Summery.. 3 Introduction 4 Science 5 Engineering. 6 Prerequisite Knowledge. 7 Equipment 7 Project Fabrication. 8 Syringe Pump Design. 9 Lab Activity Lab Activity Student Lab Reports.. 17 Lab Activity References. 21 Acknowledgements. 22 2

3 Summary Overview of the Project: The purpose of this project is to explore the dynamics of laminar flow within a micro fuel cell to generate electricity. Laminar flow is a dynamic characteristic of fluids that will eliminate the use of membranes within the fuel cell. This allows for free flowing of electrons and creates a more durable portable fuel cell. This fuel cell would be ideal for powering small portable devices such as radios, cell phones, and notebook computers. The following module will introduce the idea of laminar flow and show how the concept is used in various applications with special focus on micro fluidic mixing in order to generate power. Intended audience: The intended audience for this module is High School students in a science classroom. It is important to ensure that all students participating in this exercise have the appropriate pre-requisite knowledge to successfully complete the tasks. The labs are intended for use during physical science and physics classes. This module will also find application in earth science classes to discuss alternative fuels. Estimated Duration: 3

4 The duration of this module is 5-7 class periods and includes lesson labs in the following areas: 1. Laminar Flow/Turbulent Flow demonstration 2. Reynolds number properties 3. A. Laminar flow in a fuel cell B. Fuel cell power generation 4. Web quest fuel cell Introduction: Over the past several decades, consumers and scientists alike have become aware of the necessity to bridge the gap between fossil fuel consumption and renewable energy production. Several options are available to create a viable renewable energy infrastructure, one of which is the vast utility of fuel cells. This lab is designed to show the concept of laminar flow through a micro-fuel cell and the consequential power generated. Fluid dynamic concepts are described and students should grasp the ideas of turbulent and laminar flow, as well as how these properties on a micro level enable fuel cells to function without the use of a membrane. The fuel cell was developed in the 19 th century and through discovery the fuels ethanol and methanol have shown energy generation on a small level. Based on fuel and fueling strategy there are several kinds of fuel cells to include; direct methanol fuel cells, alkaline fuel cells, microbial fuel cells and laminar flow fuel cells. All are similar to batteries and offer a possible renewable portable energy. Fuel cells use an oxidant electrode (cathode), a fuel electrode (anode), an electrolyte which carries the charged particles, a catalyst, and a fuel source. Waste production and utility are all important when deciding which design and which fuel to use for a fuel cell. Due to portable and 4

5 microscopic size, a laminar flow fuel cell offers an option to power small electronics. Laminar flow fuel cells are the only fuel cells that do not require a membrane in the design, which makes them far less fragile. The oxidant and the fuel are pumped into the fuel cell at the same rates, in turn minimizing the diffusion of the two fluids, eliminating a membrane while allowing electrons to pass through. By controlling the flow rate of the fuel and the oxidant, both enter into the channel and flow parallel between the anode and the cathode reacting with the catalysts in the channel, and releasing electrons. There is no mixing when the fluids enter the channel; however a slight diffusion is noted toward the end of the channel. The power generated may be measured using a multi-meter. Rational For Module This module is intended to serve as an introduction to several engineering concepts. By generating interest in real world application of practical engineering ideas, students will become better acquainted with what engineers do, and hopefully start to build a budding interest in pursuing further engineering experiences. Science The following scientific concepts are discussed in this learning module. 1. Electron flow within a simple closed circuit. 2. Properties of fluids 3. Behavior of certain materials i.e. catalysts, gold, chemical fuels. 5

6 vocabulary. As the students work through the lesson objectives, they will be introduced to the following Electricity: The energy created by electron movement Power: The amount of energy transferred or work done within a unit of time. Current: The flow of electrical charge Voltage: Electrical potentials unit of measurement Conductivity: A materials measured ability to conduct an electrical current. Oxidant: A chemical compound that easily transfers oxygen atoms. Diffusion: A transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion. Anode: An electrode through which an electrical current flows into a polarized electrical device. Cathode: An electrode through which electric current flows out of a polarized electrical device. Electrode: An electrical conductor used to make contact with non-metallic parts of the circuit. Catalyst: The process by which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Engineering Micro channel fabrication requires computer automated design and fabrication machines which incorporate several branches of engineering to ensure optimum design criteria. The small diameter of the channels provide for only laminar flow under most conditions, however another problem arises in pumping strategies for such sensitive micro fluidic systems. Very expensive micro scale voltage pumps are used to move fluids through the cell channel, however in this module a less expensive substitute is 6

7 recommended. The several steps of fuel cell fabrication and energy generation touch upon a wide variety of engineering disciplines to include; Mechanical, Electrical, and Chemical. Prerequisite Student Skills/ Knowledge Successful completion of this module will depend on the students desire to learn, a teachers ability to facilitate motivation for lesson objectives and a grasp of the following terms or concepts: Basic chemistry to include: atoms, molecules, electrons, protons. Math skills to include: Algebra, multiple variable, graphical analysis and unit conversions. Basic physical science to include: Energy transformation, mass, volume, density, and pressure. (Symbols) Equipment 10 fabricated fuel cells 700 ml of fuel (0.5 M Methanol M Sulfuric Acid) 700 ml of oxidant ( 0.5 M Sulfuric Acid, bubbled with 0 2 gas) ml syringes 10 syringe pumps ( mechanical or as module design shows) Paper towels 1500 ml deionized water 1 or more multi-meters that measure in milli-volts and milli-ohms. 7

8 Fabrication of Classroom Supplies Laminar-Flow Channels: The channel is constructed with a rectangle piece of plexi-glass (7.5cm X 3.8cm). Within the rectangle the channel is created. The two inlet sites are 5 mm in diameter and 2mm deep. The length of the two individual channels before joining is 5 mm. The main channel is 2 mm wide, 4 cm in length and 1 mm in depth. Four screw holes are drilled in the corners and two dowel holes are drilled centered on the long side of the bottom piece. Electrodes and Catalyst: Gold-Leaf is applied using Mona Lisa Gold Leaf Adhesive inside of the side wall of the channel and on top of the channel leading from the channel to the side of the plexi-glass. Gold-Leaf was applied generously so that the inside of the channel walls are completely covered. Inside the channel on the side walls, catalyst is applied on top of the gold leaf. Note; be careful when applying the catalyst as not to disturb the gold leaf underneath. Platinum black is applied on the cathode side and Platinum-Ruthenium black is applied on the anode side. Two or three applications of the catalyst are necessary. After each application, allow 15 minutes for the catalyst to set prior to applying the next layer. Ideally wait 24 hours prior to using the fuel cell. Electric wires are applied to the anode and cathode sides of the channel using silver conducting epoxy. Follow the directions on the package. Channel Lid: The channel lid is constructed using a rectangle piece of plexi-glass the same dimensions as the channel. Screws are used to hold the channel and lid together with a gasket made of polydimethyl siloxane (PDMS). Shape the PDMS to a width of 2.5cm wide by 7.5cm long. This 8

9 will cover the channel and the is as long as the fuel cell. Cut out small holes in the PDMS to allow fluids to pass into the inlet sites and waste out of the outlet site. Clear plastic tubing is used at both the inlet and outlet sites. The inlet sites contain tubing 1/8 ld (1/16 wall) 1/4 Od. The outlet site contained a tube that was 5/16 ld x 1/16 wall (7/16 Od). The length of the tubing will depend on where the fuel cell is and how far the fuel, or waste needs to travel. Syringe Pump: The syringe pump is designed by Joseph Forsman of Lewis Clark State College as a member in SWEET Pump Equipment 600 ml beaker Firm plexi-glass or material of similar density, with 2 holes the diameter of the ring stands. Recommended 11 cm x 14 cm. One hole is placed on each end of the glass, at 5.5 cm, or in the middle. 2 Science ring stands with 2 rings and 2 test tube holders 450 ml water Syringe Pump Set-Up: 1. Fill syringes with 12 ml water. 2. Place syringes side by side with the ring stands facing each other. 3. Place the plexi-glass press over the ring stands directly on top of the two syringes. 9

10 4. Center the beaker over the syringes, on top of the plexi-glass press. 5. Fill the beaker with water until the syringes begin to pump chemical into the fuel cell. 10

11 Lab Activity #1 Laminar Flow/ Turbulent Flow Purpose: To show students natural behavior of fluids, and the difference between Laminar and Turbulent flows. Note: A nearby stream or river is a great place to show students real world movement of water and several examples of both laminar and turbulent behavior. Materials: 5 section rain gutter Cooler or tea bottle with reliable spout 5 gallon bucket 1-5 small rocks Green dye Procedure: Due to the size of this activity, it is recommended to do demonstrations with one class, get the class involved in the set up, placing rocks in the gutter, examining the flow of water through trial and error. 1. Fill the large tea bottle with water 2. Place the rain gutter at a 5 degree angle from level 3. At the higher end place the bottle of water 4. At the lower end place the bucket 5. Open the spout and allow for an even flow of water 6. Place a small drop of dye in the stream close to the source 7. Repeat Steps 1-6 and place rocks in the stream *The write up for this lab can be done in partners or small groups as discussion is recommended 11

12 1. Discuss the differences between laminar and turbulent flow. 2. Why does turbulent flow take place behind the rocks? 3. How is a turbulent flow created? 4. If two fluids were mixed what effects could be seen in the flow? 12

13 Lab Activity #2 A: Laminar Flow Micro Fuel Cell Safety Precautions: During this lab the students should use eye protection and wear aprons. The dyes used during this lab have the potential to stain clothing. Students with long hair should have it pulled behind their shoulders. Normal lab safety guidelines should be followed. Purpose: This lab will show laminar flow of two fluids on a micro-level. In most normal situations laminar flow would not occur, therefore this gives the students an opportunity to compare what they learned in Lab Activity #1 to the behavior of the same fluid on a micro level. Materials: Syringe pump (See directions for design of a different, less expensive pump) 70 ml red colored water 70 ml green colored water 150 ml of deionized water 1-2 fabricated fuel cells 2 syringes Waster collector Lab activity student sheet for each student Procedure: The teacher should demonstrate with one of the fuel cells. Focus on showing the laminar flow of the fluids as the red and green water flow side by side down the channel of the fuel cell. 1. Fill the syringes, one with red water, the other with green water 2. Attach syringes to the syringe pump 13

14 3. Attach capillary tubing to fuel cell 4. Begin to pump the colored water through the fuel cell 5. Repeat 1-4 at teachers discretion *Ensure students can observe the flow of both colored fluids and the laminar flow through the 4cm long fuel cell channel. Lab Activity #2 B: Laminar Flow Fuel Cell Energy Generation Purpose: Students will observe a laminar flow fuel cell generating energy. This is the culminating lab activity and students should understand what is taking place inside the fuel cell to create an energy generating reaction. Materials: Multi meter Syringe Pump 70 ml Oxidant 70 ml Fuel 2-12 ml syringes Prepared Fuel cell Waster Collector Paper Towels 14

15 Safety goggles Latex gloves Procedure: 1. Fill syringe labeled Fuel/ Anode with 10 ml fuel. Ensure all air is out of syringe. 2. Fill syringe labeled Oxidant/Cathode with 10 ml oxidant. 3. Attach filled syringes to appropriate fuel cell tubes. It is critical that the Fuel/Anode syringe is attached to the Anode fuel cell tube and the Oxidant/Cathode syringes is attached to the Cathode fuel cell tube. 4. Load syringes into syringe pump and place waste collector at the end of the waste tube. 5. Attach multi-meter to red wires attached to fuel cell. 6. Program syringe pump to desired settings. a) Volume: 10 ml b) Rate: 1 ml/min 7. Press Run/ Stop button on syringe pump. 8. Wait until you see the oxidant and fuel liquids collecting in the waste tube. 9. Turn multi-meter to the mill volts setting, observe data, then record. 10. Turn multi-meter to milliamps setting, observe data, then record. 11. Stop syringe pump. 12. Change Rate setting to.1 ml/min Press Run/Stop button on syringe pump. Wait one minute, then observe and record mill volts and milliamps data. 14. Repeat Step #7-14, but with the Rate of.01 ml/min,.05 ml/min, and 2 ml/min. (Refill as necessary.) 15. Calculate power and record on data table. 15

16 16. Determine which flow rate produces the best power. 17. Follow procedure steps #1 and # Program syringe pump to desired settings. a) Volume: 10 ml b) Rate: Best Power from step # Start syringe pump. 20. Record the mill volts and milliamps every minute for 15 minutes in data table. 21. Calculate the Power at each minute interval. 22. Graph Power-Time. 23. Determine when the Fuel Cell was at Peak Performance. 24. Flush Fuel Cell with deionized water. 16

17 Lab Activity 2: Data Sheet Name: Date: Class: Part A: Flow Rate ml/min 1 Color Observed Laminar or Turbulent Flow Part B: Flow Rate Voltage Current Power (ml/min) (milli volts) (amps) (Volts X Amps)

18 Part B Continued: Optimal Flow Rate (ml/min): Time (min) Voltage (volts) Current (amps) Power

19 Lab 2 Student Questions Name: Date: Class: 1. Based on your observations, how would you define Laminar and Turbulent flow? Give three real world examples of each. 2. What is manipulated to create laminar flow in the fuel cell channel? If the Reynolds number equation is, as density, v being velocity, d as diameter of channel and µ being viscosity, which is the manipulated variable to create laminar flow? 3. What electrical terms are volts and amps the units of? 4. Explain the electron flow in the Fuel Cell. 5. What are the charges of the Cathode and Anode in a fuel cell? Do they always have the same charge? Explain why or why not. 6. At peak performance of the fuel cell, how many would you have to connect in order to replace a 9 volt battery? 7. Are fuel cells capable of replacing batteries at the present time? 19

20 Lab Activity 3: Web Inquiry Purpose: The intent of the web inquiry is to engage the students further as well as begin to think about the practical use of fuel cells. This activity can serve as both a reinforcement of what the students learned in the lab, as well as more in depth thought on a theoretical level. 1. What are the benefits of a fuel cell? What are the drawbacks? 2. What are common chemicals used for fuel and oxidant? Why are they used? 3. What is the environmental impact of fuel cells? How does that compare to other forms of energy? 4. Research, draw and label a fuel cell with a membrane and explain the flow of electrons in the model. 5. Where would a laminar flow fuel cell have more utility than a fuel cell with a membrane? 6. What is an engineer? What disciplines of engineering are seen in fuel cell energy generation? 7. Where could a portable fuel cell be useful in your everyday life? Give examples of functioning fuel cells in the real world. 20

21 References Bledsoe, Jason & Jonathon Heflick. (July 2006). Fluid Dynamics & Micro-Fluidic Mixing Using Micro-Channels in High School Science and Mathematics. Pullman, WA: WSU Electricity. 29 July July 2009 Fuel Cells 2000: Fuel Cell Basics : How They Work. 23 Oct July 2009 Johnson, John & George Petrina. (July 2005). Microfluidic Mixing Using Microchannels in High School Science and Math. Pullman, WA: WSU. Membranelss fuel cell is tiny, versatile. 23 Mar July

22 Acknowledgments We would like to thank the people who gave technical assistance and subject matter expertise. Dr. Prashanta Dutta as the professor who built this project, and Zaki Jubery for his daily help in the lab and research he assisted with. 22