air-powered car project€¦ · 3 schedule • class 10.1 (oct. 28th): turn in sketches of your...
TRANSCRIPT
ENGR 111C
Air-Powered Car Project
Fall 2013
2
Table of Contents
Table of Contents ............................................................................................................................ 2
Schedule .......................................................................................................................................... 3
Project Objective ............................................................................................................................. 4
Project Grading ........................................................................................................................... 4
Design Constraints .......................................................................................................................... 5
Design Sketch ................................................................................................................................. 6
Pressure Vessel Construction ...................................................................................................... 7
Safety Issues................................................................................................................................ 7
Hydrostatic Pressure Test ............................................................................................................. 11
Prior to Class ............................................................................................................................. 11
During Class.............................................................................................................................. 11
After Class ................................................................................................................................ 11
Experimental Data and Calculations ............................................................................................. 12
Calculus Hints: .......................................................................................................................... 14
Report Contents ............................................................................................................................ 15
Example Expenses Table .......................................................................................................... 16
Part Sources in College Station..................................................................................................... 17
References ..................................................................................................................................... 18
Appendix A. Air-Powered Car Report Grading Rubric ................................................................ 19
Appendix B: Standard Operating Procedure for Personnel Safety & Crowd Control .................. 20
Appendix C: Standard Operating Procedures for Hydrostatic Testing in Presence of Faculty .... 21
Appendix D. Team Work Distribution Sheet ............................................................................... 22
Appendix E. Soldered Western Union/Lineman Splice ............................................................... 23
Preparation ................................................................................................................................ 23
Sealing the splice ...................................................................................................................... 24
3
Schedule
• Class 10.1 (Oct. 28th): Turn in sketches of your design to your graphics instructor
• Class 11.1 (Nov. 4th): Glue pressure vessel. Bring to class the following items:
o 12-inch section of 3-in-diameter Schedule-40 PVC pipe rated for 260 psi at 73oF
o end cap
o reducer
o bushing
o purple PVC cleaner
o PVC cement
• Class 12.2 (Nov. 13th): Pressure test. Bring to class the following items:
o glued pressure vessel made in Class 11.1
o installed containment system on the pressure vessel
o ½ -in × ¼-in National Pipe Thread (NPT) threaded pipe fitting reducer installed
o Schrader valve installed
o valve shown in Figure 1 installed
o safety relief valve NOT installed (it will not allow us to go to the full test pressure)
o vessel completely filled with water up to Schrader valve
• Class 14.1 and 15.1 (Nov. 25th and Dec. 2nd): Demonstrate your air-powered car in class
• Class 15.1 (Dec. 2nd): Submit your team report by 5:00 pm.
4
Project Objective
Teams of three or four students will design, construct, test, analyze performance and report on a wheeled vehicle that is propelled by expulsion of compressed air. A basic requirement is that the car must be constructed from materials with at least a 150-psi working pressure rating, must not do anything to compromise the pressure rating, must perform a pressure test to 150 psi with the pressure vessel portion of the vehicle completely filled with water, and must not employ an air pressure greater than 70 psi at any time. A safety relief valve ensures the vessel is not over-pressured. The pressure vessel of each car will be filled to working pressure with a manual bicycle pump.
For the air-powered car shown in Figure 1, your team will do the following:
• design
• build
• test
• evaluate
• report
Figure 1. Schematic of air-powered car.
Project Grading
The final project grade will be determined as follows:
• sketch = 20% • demonstration = 30% • report = 50%
Air Velocity
Car Velocity
Compressed Air Tank
Valve
Wheels
Safety Relief Valve
5
Design Constraints
• General
o You may only use hand tools (e.g. electric drill, screwdriver, saw)
o You must construct your vehicle. Simply strapping the tank to an existing platform (e.g., a skateboard) is not acceptable.
• Tank Construction
o tank material of construction = polyvinyl chloride (PVC) schedule-40 pipe
o pipe diameter = 3 inches maximum
o pipe length = 12 inches maximum
o end caps = PVC
o PVC is joined by applying a purple PVC cleaner and then PVC glue.
o The tank must be wrapped in duct tape.
o Do not drill or cut into the pressure vessel.
o All connections that are under pressure must be made using standard off-the-shelf fittings.
• Safety Preparations
o All tanks must be contained in a wire cage (see below)
o All pressurized components must be selected and tested to withstand at least 150 psig
o The system must have a pressure relief valve on the pressurized portion of the tank. This valve must be set to release gas if the pressure exceeds 100 psig.
o The maximum working pressure for the car is 70 psig
o Safety labels placed on tank
• Operating Safety
o Safety glasses: Wear safety glasses when assembling equipment and operating the air-powered car.
6
Design Sketch
The sketch should identify all components in detail. Be sure to address detailed issues such as how the vessel will be charged with compressed air, how the wheels will be mounted, and how the car will be steered. Determine sources of off-the-shelf equipment, such as fittings, wheels, valves, pipe, etc. Product development is an iterative process, so you should feel free to modify your design after you have turned in the sketch. Your sketch should include (as a minimum) the following elements and their sources
1. Wheels 2. Tank and parts 3. Valves and fittings 4. Pressure relief valve 5. Vehicle body 6. Wire cage
7
Pressure Vessel Construction
Although there is considerable latitude in choice of materials and construction, the only expected potential for risks are (1) the mechanism of attachment of the pressure vessel to the wheel/frame assembly and (2) sharp protrusions that could cause injury during handling or propulsion of the air cars.
Do not attach the pressure vessel by any means that compromises the strength of the vessel (no screws or other penetration of the PVC; no use of adhesive that dissolves the PVC (including PVC cement). The expectation is that the pressure vessel will be attached to the wheels/frame by straps, rubber bands, or similar means. Visual inspection by faculty will be performed to determine that there is no compromise of the pressure vessel and that the car has no dangerous protrusions. At any time the pressure vessel is pressurized, all personnel in vicinity must be wearing safety glasses.
Figure 2 shows a schematic of the pressure vessel, which is constructed from PVC pipe, an end cap, a reducer, and a bushing. A ½ -in × ¼-in National Pipe Thread (NPT) threaded pipe fitting reducer is inserted into the bushing, to which valves, pipe tees, nozzles, etc. are attached.
Safety Issues
Pipe – There are two types of schedule-40 pipe available at home improvement stores. One is sold in 2-ft lengths and is marked “not for pressure.” DO NOT PURCHASE THIS PIPE!! As shown in the accompanying video, this pipe bursts at about 200 psig. Instead, purchase 10-ft sections that are marked “260 psi at 73 F,” which is the recommended working pressure at room temperature. The accompanying video shows that this pipe withstands pressures of about 800 psi.
Figure 2. Pressure vessel construction.
Glue joint Glue joint Gluejoint
1/2-in NPT
3-in Schedule-40 Pipe End cap Reducer
Bushing
Pipe fitting reducer 12 inches
1/4-in NPT
8
Safety Relieve Valve – Install a safety relief valve as shown in Figure 1. An appropriate valve is available from Grainger (Item 4TK26) described at the following website:
http://www.grainger.com/Grainger/items/4TK26?cm_mmc=Google%20Base-_-Pneumatics-_-Air%20Compressor%20Accessories-_-4TK26
Schrader valve – The standard method for coupling a bicycle pump to a tire is called a Schrader valve. Schrader valves that couple to standard national pipe thread (NPT) are available on the Internet (Google search: Schrader NPT). Such valves will have a minimum working pressure rating of 100 psig. They will be fitted to the pressure vessels via female NPT threads in the as-bought pressure vessel components. There is little potential for failure or injury from proper use of these valves.
http://www.airridefittings.com/store/index.php?main_page=product_info&products_id=24
Be sure to plan ahead to allow time for shipping. Schrader valves are also available at automotive parts stores, such as O’Reilly’s.
Joint Construction – PVC is joined by applying a purple PVC cleaner and then PVC glue. Allow 24 hours for joints to cure before applying pressure. (Note: The glue is a solvent that bonds PVC to PVC; it cannot bond PVC to other materials, such as metal.) Instructions for using PVC glue are found at the following website:
http://www.youtube.com/watch?v=IWpH_iJNH34
Do NOT use any other glue besides PVC cement. Gluing will occur in class after instructions are given.
Penetrations – Do not drill or cut into the pressure vessel because this may disrupt vessel integrity. All connections must be made using standard off-the-shelf fittings.
Shrapnel – If the pipe were to fail, it could produce shrapnel. To prevent this, wrap the complete pipe with one layer of duct tape.
End cap containment system – A properly selected pipe is very safe. The major point of vessel failure is end caps and fittings flying off because of joint failure. To prevent this, a containment system is needed to prevent parts from flying off in case of joint failure. Figure 3 shows a containment system consisting of large washers at each end of the vessel. The washer is selected so that the center hole rests on the shoulder of the pipe fitting reducer. Holes are drilled in the periphery of the washer so that 14-gauge galvanized steel wire joins the two washers.
9
Figure 3. End cap containment system.
Figure 4 shows a detail of how the 14-gauge galvanized steel wires are to be fed through the peripheral holes in the washer. A single strand is fed through holes at each end and then spliced so the washers are snugged tightly against the vessel, thus forming a wire pair. You should use a lineman splice [1] to hold the wire ends together; this splice is as strong or stronger than the wire itself. Directions on how to perform this splice are located in Appendix E. A single strand is fed through holes at each end and then twisted so the washers are snugged tightly against the vessel, thus forming a wire pair. To ensure the splice does not unravel, it must be sealed.
If the end caps were to fail at a pressure of 800 psi (far above the working pressure), the total force is
The 14-gauge wire has a breaking strength of about 700 lbf. (http://www.fishock.com/store/electric-fence-wire/wc-141320). A minimum of eight wires (or four wire pairs) is sufficient to resist the force. For added safety, use at least six wire pairs.
f2f22 lb 5660
in
lb800in) 3(
44==== ππ
PDAPF
Wire Washer
10
Figure 4. Containment wire detail.
Required Labels
Maximum working pressure: On one side of the compressed air tank, put the following label:
Aging: PVC pipe can age from exposure to air, which contains ozone and other oxidants. To prevent an unexpected failure, on the other side of the compressed air tank, put the following label:
Maximum gas pressure = 70 psig
Twist
Twist
Do not pressurize after 2018
11
Hydrostatic Pressure Test
The students will construct compressed air pressure vessels for propelling their cars out of PVC. Working pressure rating for this material is 260 psig, with a burst pressure of 840 psig. (See
http://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-d_796.html ).
Before the vessels are pressurized with air, they are to be pressure tested to 150 psig while completely filled with water. Because water is incompressible under these circumstances, the potential energy stored in the pressure vessels during the pressure test will be negligible. Failure under such testing will result in a low-energy, low-volume spurt of water. Should failure occur during hydrostatic testing, the vessel will be contained under an inverted metal tub.
The hydrostatic test will be performed in class. To maximize everyone’s safety the following steps must be followed:
Prior to Class
1. After the vehicle is assembled, inspect it to make sure that it is sound. 2. Fill it completely with water. Be very certain that you fill the vessel completely with
water—no air should be present inside the vessel. 3. You will need to either remove the pressure relief valve or set it to a pressure greater than
150 psig.
During Class
1. Place the pressure vehicle into the metal washtubs. 2. Apply 150-psig pressure using a bicycle pump. 3. Inspect the vessel for integrity and leaks. 4. Sign the pressure test certification.
After Class
Filling of the pressure vessels will be supervised by faculty, and pressure will be maintained at or below 50% of the hydraulically tested pressure of the pressure vessels. In no case should pressures exceed 70 psig with air in the pressure vessels.
12
Experimental Data and Calculations
The car performance will be demonstrated in the hallways outside the classrooms. Using a bicycle pump supplied by your team, pressurize the vessel to 70 psig. Release the pressure, which allows the gas to exit the rear and propel the car forward. Your demonstration grade will be based upon distance traveled.
Notes • Because the hallways are fairly narrow, it will be important that the car travel in a straight
line. If it hits the wall, the location where it finally stops will count as the distance traveled.
• You will perform three trials. The grade will be based upon the best of the first three trials.
• Your car will perform these runs starting from the floor, not the ramp.
Calculations • Your demonstration grade will be based on the distance traveled. Within a class, the team
that travels the farthest will receive a grade of 100. The team that travels the shortest will receive a 70. Other teams will receive an intermediate grade based upon a straight-line fit to these end points.
During the demonstration, you must measure the mass of your car, which will be used in calculations. Also, you will determine the distance your vehicle travels (without compressed air) when it is placed at multiple heights on a ramp (Figure 5). The higher it starts, the farther it travels.
Figure 5. Schematic of ramp system.
Center of mass
initial
height
distance traveled
13
Efficiency Calculations
The efficiency � is the ratio of energy output to energy input.
Energy input – The theoretical energy content of the compressed gas can be determined by first measuring or estimating the volume of the compressed air tank. Knowing the absolute pressure and absolute temperature, the number of moles of 70-psig gas in the vessel can be estimated using the ideal gas equation. To determine the theoretical work required to compress the gas, envision a large piston/cylinder (Figure 6) that contains all these moles at an initial pressure of 1 atmosphere (absolute) and room temperature. As the piston slowly compresses the gas, assume that the temperature stays constant and the pressure can be obtained from the ideal gas equation. Assuming a cross-sectional area of the piston and knowing this pressure at each instant during the compression, the force required to push the piston can be calculated. (Note: The initial force Finitial is zero because the pressure on each side of the piston is identical. Atmospheric pressure always provides a portion of the total force acting on the piston.) Integrating the force over the distance allows the total theoretical work to be calculated. Integrate numerically using an Excel spreadsheet. Confirm the result analytically using calculus.
Figure 6. Piston/cylinder used to compress air from the initial pressure to the final pressure.
inputEnergy
outEnergy =η
P = 14.7 psia Pinitial = 14.7 psia
Finitial
P = 14.7 psia P
F
P = 14.7 psia Pfinal
Ffinal
x
x
14
Energy output – The energy output from your car can be estimated by plotting the potential energy of the car on the ramp versus distance traveled (Figure 7). (Note: For illustrative purposes, the figure shows a linear relationship between potential energy and distance traveled. Your curve may differ, or it may be the same. Your experimental data will determine the relationship.) Once you have the plot, show your distance traveled using compressed air. The curve will allow you to estimate the energy delivered from the compressed air.
Figure 7. Experimentally determined relationship between the potential energy of the car on the ramp and the distance traveled from the ramp.
Calculus Hints:
Cx
x
dx +=∫ ln Cxaxa
dx +−−=−∫ ln
Potential energy of car on ramp
Distance traveled from ramp
Distance traveled using compressed air
Energy delivered using compressed air
15
Report Contents
The report must contain the following information in clearly identified sections. Use a centered bold heading at the top of a new page for each section. The sections are to be presented in the following order:
1. A cover memo
2. Introduction – a brief description of the technology and problem statement
3. Design Description – a description of the as-built air-powered car with appropriate AutoCAD drawings
4. Operating Procedures – write up the operating procedures for the air-powered car
5. Safety – describe the safety measures taken
6. Hydrostatic Test Certification – a statement pledging (Aggie Honor Code) that the vehicles have properly pressure tested (must be signed by all team members)
7. Work Distribution Sheet – give the distribution of the work on this project and a few sentences explaining that distribution (see Appendix D).
8. Expenses – Document your expenses. Only account for the portion you used. For example, if the total cost of 8 ft of 3-in PVC pipe is $8, the cost of the 1-ft pipe would be listed as $1. Only list expendables (e.g., pipe, fittings, wheels, PVC cleaner, PVC glue) for the vehicle “as built” and not any special tools. Include any donations at their regular price. For example, the bicycle pump is not an expendable because it can be used for other purposes.)
This expenses list should include the following information:
o Part name, source (may be a referenced to the source list) o Unit of sale (e.g., each, box of 100) o Number of units of sale required (may be fractional, e.g., 1/8 unit) o Unit cost (do not use sale prices, quantity discounts are OK) o Extended cost (unit cost × number of units required) o Total parts cost for all demonstration units
9. Results – a description of results from the demonstration. A table must be included that reports the results of the three trials. The mean and standard deviation must be reported in the table.
10. Calculations – show your efficiency calculations
11. Suggested Improvements – suggest any improvements that you would make based upon experience gained
12. Summary – what did you learn?
The report must be printed on white paper and stapled in the upper left corner. Do NOT place the report in a binder or holder. For the report cover sheet, use the rubric in Appendix A. Tables and graphs must be appropriately titled and labeled (with units). Reference all tables and graphs in the text.
16
Example Expenses Table
Use this general format.
Part Name – Source Unit of Sale Units Required
Unit Cost Extended Cost
Skateboard Wheels – Walmart pair 2 $10.00 $20.00
Plywood – Home Depot 4’ x 4’ sheet 1 $5.50 $5.50
Bearings – Grainger Each 4 $7.39 $29.56
PVC Cleaner – Home Depot Jar 1 $7.99 $7.99
…
Project Cost
$147.26
17
Part Sources in College Station
Neither Engineering 111C nor Texas A&M require (or recommend) that you use these part sources. It is only a list of vendors from whom previous students have purchased materials. If you have a vendor that you would like to have added for next semester, please let us know.
C-Ment Skate Shop
1724 Rock Prairie Rd College Station TX 77845 (979) 680-1000
Grainger
Branch: 362 1408 W. Villa Maria Rd Bryan, TX 77801-4213 (979) 821-0100 7:30 AM - 5:00 PM (Monday - Friday)
Hobby Town 1713 S Texas Ave College Station, TX 77840 (979) 693-7200
Home Depot Store #6559 1615 University Dr. East College Station, TX 77840 (979) 595-1188
Lowes Store #0103 3225 Freedom Blvd. Bryan, TX 77802, (979) 774-4141
or Store #3032 4451 Highway 6 South College Station, TX 77845, (979) 690-4002
Michaels
1505 E University Dr. Ste 300 College Station, TX 77840-2672 (979) 846-4858
18
References
[1] NASA, "Crimping, Interconnecting Cables, Harnesses, and Wiring," vol. NASA-STD-8739.4, ed. http://standards.nasa.gov: National Aeronautics and Space Administration, 2011, pp. 83–84.
19
Appendix A. Air-Powered Car Report Grading Rubric
Section Number Team Number (typed) (typed)
Student Name (typed) Percent of Effort* Student Signature
* Full effort = 100%
Item Points
Earned
Maximum
Points
Description
1 4 Cover memorandum
2 4 Brief description of the technology and problem statement
3 10 As-built description of the air-powered car with AutoCAD drawings
4 4 Operating procedures for the air-powered car
5 4 Description of safety measures taken
6 4 Certification that hydrostatic pressure test was performed
7 3 Work distribution
8 4 Expenses
9 10 Description of results from the demonstration
10a 10 Efficiency analysis (potential energy graph)
10b 20 Efficiency calculations (numerical)
10c 15 Efficiency calculation (analytical)
11 4 Suggested improvements based upon experience gained
12 4 Summary (what did you learn?)
Bonus for exceptional report appearance and professionalism
Penalty for poor report appearance and lack of professionalism
Total
20
Appendix B: Standard Operating Procedure for Personnel Safety & Crowd Control
1. Under the supervision of faculty, students will perform pressure tests by filling air car pressure vessels completely with water and pressurizing to 150 psig.
a. All members of the team must attest that the test was performed.
b. Students will pledge (Aggie Honor Code) that they have properly pressure tested their vessels.
2. Faculty will visually inspect each air car for dangerous protrusions and compromised pressure vessel integrity. Any air car failing inspection will not be allowed to compete.
3. Faculty and TA’s will clear the hallway (into classroom) of all students not directly involved with a given demonstration.
4. In the event that only a few teams are present to perform their demonstrations during a given time slot, observing teams will be stationed in the launch hallway a minimum of 5 feet behind the rearmost area of work by participating team, faculty, and TA’s. This hallway will have a door onto external stairs with landings. Any unacceptable behavior will result in observers being banished to the landing or into the classroom until their team’s turn.
5. At least one faculty member will listen to and approve or require changes to each team’s pressurization and launch procedures.
6. At least one TA will be stationed in the cross hallway at the far end of the launch hallway to make sure no one inadvertently enters the demonstration area during a demonstration with a pressurized car. One team member will be stationed with the TA to retrieve the car after its run.
7. Faculty member at launch position will
a. Verify with TA at cross hall that hallway is clear.
b. Notify all personnel in hallway that launch is about to commence and to make sure they are in appropriate position.
c. Direct all present to don safety goggles.
d. Verify that all present have donned safety goggles.
e. OK team to pressurize their car.
f. Verify that hallway is clear.
g. Order launch.
21
Appendix C: Standard Operating Procedures for Hydrostatic Testing in Presence of Faculty
1. Have the students bring their pressure vessel to the test site prefilled with water. The valves will already be installed, so there should be minimal water spill.
2. Attach a high-pressure bicycle pump to the Schrader valve. (Bicycle pumps are available that go to 160 psi.)
3. Cover the vessel with an inverted metal tub to contain the explosion in case of vessel failure.
4. Pressurize the vessel with a small amount of compressed air. (Note: The vast majority of the vessel is filled with water so the total energy content of the compressed air is negligible.)
5. Release the pressure by opening a valve that is external to the inverted metal tub. (Note: cut the hose on the pump and install a TEE. The valve will be installed on the TEE and will allow the gas to be vented outside the inverted metal tub.)
6. Uncover the tub.
This can be done easily in the grassy space next to CVLB or in the classroom. Be sure to keep by-standers away from the test.
22
Appendix D. Team Work Distribution Sheet
Team Number:
Section Number:
Describe each group members’ contribution to the final project. The percentages should total to 100%:
Member Member Initials % Contribution
%
%
%
%
%
%
Total % 100 %
Comments:
23
Appendix E. Soldered Western Union/Lineman Splice Adapted from NASA Standard 8739.4, Section 19 [1]
The Western Union/lineman splice is a splice where each wire is wrapped around the other conductor prior to soldering (see Figure E-1).
Figure E-1. Western Union/lineman splice.
Preparation
If you are going to solder the junction to seal it, the conductors should be pre-tinned. Start the splice as shown in Figure E-2. There should be at least three turns around each conductor and the wraps should be tight with no gaps between adjacent turns. The wraps should not overlap and the ends of the wrap need to be trimmed flush prior to sealing to prevent protruding ends.
Figure E-2. Initial wrap for Western Union/lineman splice.
24
Figure E-3. Completed wrap for Western Union/lineman splice.
Sealing the splice
The splice must be sealed to prevent its unraveling. You may either solder or encase the junction. In either case, the junction must be thoroughly coated as shown in Figure E-4.
Soldering: The termination shall comply with all the requirements of NASA-STD-8739.3 for a solder termination. Solder shall wet all elements of the connection. The solder shall fillet between connection elements over the complete periphery of the connection (see Figure E-4).
Encasing: Alternately, you may encase the junction by thoroughly covering all of the elements with Gorilla Glue. The dried glue should fillet between connection elements over the complete periphery of the connection (see Figure E-4).
Figure E-4. Sealing the Western Union/lineman splice.
25
These materials
Copyright 2013
Instructors of
ENGR 111C
Texas A&M University