Freshman Engineering
Final Project:
The Thirsty Town

Purpose

The purpose of this project is to model a real world problem and solution with legos. In the process of trying to solve the problem, students will learn to work as teams in a multi-disciplinary setting. They will learn to balance the time and costs of developing super solutions versus "quick and dirty" solutions.

This project will teach a number of fundamental engineering principles. The project encompasses many engineering disciplines such as environmental engineering (decontaminating the water), chemical engineering (mass balances), mechanical engineering (pumps and motors), aerospace engineering (fluid flows), and computer science (control software and best path algorithm). Students will learn simple software engineering, basic chemistry (neutralizing an agent in the water), and applied mathematics (lowest cost-path and supplies). They will also learn to work as a team on a multidisciplinary engineering project. Concepts such as planning out the project ahead of time (the written proposal to the town council), meeting minimum design constraints, and working with a budget will be emphasized throughout the project.

The overall goal of the project is for students to get "clean" water to the town in the best way possible. This project will provide for a fair amount of creativity but will still direct students towards the best design. The students will see the benefit of planning ahead, and, through friendly competition, will understand the advantage of minimizing the cost while maintaining end-user satisfaction.

Real Life Problem

There is a spring at ground level. It is the water source for a town (in which the people are .01 cm tall) which is at the opposite corner of a 50 x 50 parcel of land (modeled by grid - see attachments of grid and a general map). There are two problems. The first is that a break in an industrial waste discharge line has contaminated the spring with hydrochloric acid. Fortunately, the concentration is low, though the water is still too acidic to be used by the townspeople. Moreover, there is another water source nearby which is at the same level as the first spring. This water is contaminated with sodium carbonate from its surrounding rocks. The townspeople need water with a pH higher than 6.5, but lower than 7.5. You have been informed that a group in Pennsylvania recently successfully neutralized an acidic stream using alkaline groundwater. The second problem is that there is a mountain (the peak is at 9 cm - huge for such little people) between the water source and the town. The town needs water to irrigate crops and to drink. Thus, the goal is to get clean water to the town.

The problem can essentially be broken down into two areas: purifying the water and getting the water to the town. Each of these parts contains numerous subtleties and is on a different scale (the water purification scale is much larger than the water pumping scale). The water from the first spring will be provided (contaminated with a HCl solution of 0.0042 ml HCl/ml H2O) in a cup. Another cup will contain a sodium carbonate solution 21.4M sodium carbondate. The acidic spring has a small sidestream which runs into a much smaller pool. The rate of the flow of this sidestream is a factor which you cannot control. You can (and must) find a way to neutralize the acidic solutions. Using the lego motors and gears, a system must be constructed to allow the water to move through the purification system. Along the way, a pH meter will be used to monitor the pH of the water which is in the waiting pool. Initially, the pool will contain 300ml of plain pH 7 water. The HCl solution will slowly trickle into this pool and by testing the pH, a method should be developed to control adding the Na2CO3 solution. Once again, the resulting solution must be between pH 6.5 and 7.5 before it can be pumped on toward the town. Also, it is important to remember that simply putting two solutions together will not adequately mix them. A stirring rod of some sort should be constructed to ensure that the solution is homogenous.

Once that part of the project is complete, the water must then be transported to the town. This can be approached in several ways, but in the end, some sort of a pump or pump-like device must be used (i.e. the water cannot be assumed to just "flow" over the ground purified, and evaporated water will not rain on the town). It is suggested that the available tubing be "purchased" to facilitate the transportation. To further break down the transportation problem, an ideal path must be found over or around the mountain (and in general, through the provided landscape). The land cannot be altered in any way other than to set things on it, and although it may seem that the tubing could form a natural bridge over the terrain (in some places), it must either touch or be connected to the ground in all places. Keep in mind that the more powerful the pump, the greater the options for the tube path. (Note: Although you are given a model of the terrain, it is only that--a model. The actual terrain comes from the computer layout sheet attachment.) You may also want to examine a simple map of the model. The darker the area, the higher the terrain. The two red blocks at the northeast and southwest corners are the town and the spring, respectively. You may only cross terrain that is at an altitude equal to or lower than the maximum height which your pump can achieve.

Breaking Down the Problem

The entire system can be broken down into three areas: picking an ideal pipe path, designing and constructing a pump, and neutralizing the acidic solution. Once these tasks are complete, a systems integration must occur to finish the project.

The path is an important aspect. A standard way of approaching this problem is to use a computer algorithm (called Best Path). Of course it is not necessary to use the computer at all. You may find it easier to get a path by eyesight. The advantage of the computer program is that it will definitely give a best path (there could be several of equal cost) if programmed properly. Note that this is a fairly simple algorithm. Even if you cannot get it to work on a computer, it would be wise to consider it when plotting the path for your tubing. The algorithm is detailed in the book Introduction to Algorithms by Udi Manber.

The main idea of the algorithm is to start from a point (say the water spring) and analyze the cost (point value) to move in one particular direction. Consider all the adjacent points (from any point, except the edges, there are eight adjacent points, including diagonals). If any of those points have a path already to them (you must find a way of marking the sum of all points up to a particular point, and also remember which point you came from previously) which have a lower total than the other seven, select that as the path from which to come. Continue with this procedure until every point in the grid has a "best path" to it. Then look at the location of the town on the grid and find that sum. Remember, don't forget to keep track of how you are connecting the points. You will need to be able to track back from the town to actually plot your best path.

The pump is perhaps the greatest challenge. Remember that you do not have to build something traditional to complete this part of the project. Some ideas which might be useful inclue a worm gear pump, a standard gear pump, a turbine pump, etc.

The neutralization is yet another problem. As stated before, there are two solutions--one that is acidic HCl and the other basic Na2CO3. These two solutions must be combined to create a solution between pH 6.5 and 7.5. The most difficult part of this task is configuring the pH sensor. The Lego Dacta kit does not include a pH sensor. The one you are given has been constructed such that it will work similar to the temperature sensor on the Lego kit. Unfortunately it does not have the same scale conversion (i.e. pH and temperature do not match up when you are dealing with electric voltage).

Systems Integration

There are a number of ways in which this project could be designed. Foremost among the variables to be optimized are the water contamination, the water pump acquisition, and the method for water transportation.

The water contaminant is an acid in the water which must be counteracted. A system must be developed to release Na2CO3 solution into the HCl solution (ground water) until the pH is reasonably close to 7.

As stated before, you must construct your own pumps. Some possible ways are by using a motor and propellers or with gears. Note: a pumping device may not even be required - you may be able to move the water some other way. However, if you do not choose to use a pump, the highest level terrain that you may cross is 1cm (ground level).

When putting it all together, the key is the software. There is a Lego Dacta Control Lab software guide. This reference book is very useful in writing your program. In the end, your software should make the system run by itself. You may set up certain things by hand but you should reach a point where you can simply press a button on the computer and then leave the system running (until one or more solutions run out, or a container is about to overflow!)

Financial Considerations

As many or as few legos as desired may be used for the design. Also, there are three motors available. The cost for the legos is $1/gram. Motors are $10 each. Axles, worm gears, and other non-standard pieces cost the same as other legos ($1/gram). Tubing has two costs. Tubing that goes between the components of the purification system is free, provided the net effect of the purification system does not move the water closer to the town. Tube that transports the water from the spring to the purification system and from the purification system to the town is priced based on the terrain "blocks" crossed by the tube. Blocks may be crossed left to right, forward and back, as well as diagonally. The "score" of a block is 10 times the altitude, which also relates directly to the cost - i.e. crossing the mountain at its peak of 9 cm costs $90 just for that block at the top. Obviously, an efficient path for the tube could significantly reduce the cost. This is similar to real life in that the cost of putting in tubing on flat ground is low when compared to the cost of moving equipment to high altitudes and constructing proper supports for pipes on the sides of mountains.

You, as the head engineer of this project, must find a way to clean the water and transport it to the town. Obviously, cost is a major consideration. If the project cannot be completed both on time and affordably, the town will be ruined and the people will be forced to move away!

Before you begin, please present a proposal to the town council (i.e. the TAs). They would like cost estimates and detailed plans about how you and your project team are going to get clean water to them. This is important in real life as real engineers do not simply jump into a problem (so don't just start playing with the legos!) Proper planning will go a long way. However, do not get overly concerned if you find you must change your plans as you get deeper into the project.

Equipment

Since there is more than one way to solve this problem of transporting and cleaning the water, there is more than one possible set of equipment required. Some pieces will be essential regardless of the specific solution:

The legos given in your kit.
2 motors.
3 beakers or other comparable liquid receptacle.
Tubing - rubber - enough to span the distance between the source and town, and then some extra.
A pH sensor.
The Na2CO3 solution.
The impure water.

Depending on how your group solves this problem, other costly "necessities" may be:

A stir rod and glue.
Elevated platforms (this could consist of a book - but it still counts).
More beakers.
Touch sensors.
More motors.
A Servo.
Lego people to mill about the town (these cost extra, too).
Propeller(s).
Graduated cylinders.
A vast array of possible household items useful for building a pump. Check with the TA for a cost analysis of "special order" items.

Everyone will receive the general equipment, but groups will have to pay extra for the other "necessities." Also, even though you may use the entire lego kit and all the provided tubing, don't forget that the amount you use will be factored into the final cost of your solution.

Safety

Be extremely cautious when handling the chemicals in this lab.

Both hydrochloric acid and sodium carbonate are hazardous. Goggles should be worn at all times. Gloves should be worn whenever solutions containing the sodium carbonate are being made and whenever the hydrochloric acid solution is being handled. Be sure to make solutions near a sink (and preferably in a chemistry lab). DO NOT dump solutions down the drain unless the pH is between 6.5 and 7.5! Furthermore, do not dump ANY solutions down drinking fountains--use only deep sinks. If distilled or deionized water is available, use it; however, it is not necessary and solutions can be made using regular water from a tap. Do not play around with the solutions in the lab. Avoid contact with bare skin and ESPECIALLY eyes. If solution does get into eyes, notify a TA immediately and flush them for 15 minutes. When acid/base is added to water, be sure to add the acid/base TO the water (which should already be in the beaker) and not the other way around. Be very careful with the pH sensors: they are expensive and somewhat fragile.

Design Performance

Several considerations will be used to evaluate the group's performance. The most readily available method of evaluation is the relative cost of building the structure. The group presenting the most cost-effective project, while upholding the constraints of the design, will be recognized as the best concept (and hence get the best grade). The TAs have the final say on the cost of your project (they will find the mass of your construction).

Since this project deals with the transport of a contaminable resource, the level of contamination must be kept to a minimum. Therefore, a pH level constraint is being imposed. If pH is not maintained within a certain range, then the project is not performing to specifications.

For this project, your team will be competing against the other teams. The best score will be awarded to a project that first and foremost meets all of the design constraints. Among those projects, the design which minimizes the required construction cost will be judged the best. In this way, a fair scale is created with which to measure the performance of all participating designs.

Demonstrating and Other Due Dates

One week from today, you must at a minimum have your proposal completed. If at any time before the next lab you complete it, you may submit it to the "council" (a TA) for approval. Three weeks from today, your group must be finished with the construction of your project. During that lab period all projects will be measured for completeness and then cost.

Documenting Your Work

Along with the written proposal due to the council, you must also present a weekly status report (one page or less). In it you are expected to report on the difficulties you have encountered and the changes you are making to your initial projections. It is not necessary to comment on the number of blocks you are using (unlike the real world, blocks are reusable so you may take apart bad designs as often as you like without consequence or cost).

The initial report should include your estimated costs, broken down into blocks (estimated lego mass), tubing (i.e. the path�hence you must also project the path your tubing will cross), other supplies, etc. If you know that you will need special parts, you must inform the council (TA) at this time (at which point a decision will be made on the cost of such part). You should also include a time table (plan of attack) and some major milestones (pump completed, best path found, etc.).

The final report should be broken up into the following areas:

Introduction (Statement of project goals and intentions)
Problems (Any difficulties you encountered along the way and how you were able to solve them; pay special attention to solving problems as a group)
Results (Were you successful in meeting the design criteria? How much does everything cost? Include your best path drawing and summations, and the code for the program if that is how you chose to solve it. Also, how many cm high could your pump raise the water?)
Conclusions (What do you think about the lab and the problem? How could your team have worked better? If you had to redo things, how would you do them differently? What do you consider the greatest engineering challenges?)

Appendices

For the knowledge needed for the Chemistry section, please see your chemistry text book.

For an idea how to construct a "best path" algorithm, find the book Introduction to Algorithms by Udi Manber in the Engineering library. (Actually, any computer algorithms book will suffice.) You may program this algorithm in any language you choose.

The best place to begin the design of a pump, if you so choose, is to find in the library any book on fluid mechanics. A book by Frank White is available which includes illustrations (as well as some hi-tech theory and other references) on effective pumps. Remember, a pump does not need to be fancy to work well! Simple pumps go a long way.

Incidently...

The following was taken from Chester D. Rail's book "Groundwater Contamination - Sources, Control, and Preventive Measures" published by Technomic Publishing Company, Inc., Pennsylvania, 1989:

"Grubb (1970) described a break in an industrial waste discharge line, which when coupled with a forty-nine foot rise in the Ohio River, allowed hydrochloric acid to enter an outwash equifer used by a Kentucky industry. Chloride concentrations in excess of 30,000 mg/l were observed in water discharged from the industrial well nearest the break, and within a year that well had to be abandoned. Additional fluctuations of chloride levels in an industrial well near the river indicated that highly mineralized groundwater occurred near the acid source."

Furthermore, this passage was taken from Harvey Olem's "Liming Acidic Surface Waters," Lewis Publishers, USA, 1991:

"The pumping of alkaline groundwater has been reported in Pennsylvania for the temporary neutralization of an acidic stream (Fisher, 1984, 1985; Gagen et al., 1989). Groundwater was pumped from wells to neutralize an acidic section of Linn Run. The researchers were interested in determining if the method would allow the secion to sustain a put-and-take trout fishery....Three wells were used to pump alkaline water to the treatment section of the stream...to maintain the pH of the treated section above 6.0.

"An important consideration noted by the researchers was the possible depletion of groundwater reserves by continuous pumping. The method was considered to successfully neutralize the stream section to establish a short-term put-and-take fishery and to provide a recreational value to the stream. It is not known whether the method has wide applications or whether the costs of treatment compare favorably to those of other mitigation options such as liming."

Group Assessment

Proposed Project Solution

Freshman Engineering Final Project: The Thirsty Town