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UTPA STEM/CBI Courses/Introduction to Mechanical Engineering/Engineering Estimation

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Course Title: Introduction to Mechanical Engineering

Lecture Topic: Engineering Estimation

Instructor: Dr. Constantine Tarawneh

Institution: The University of Texas-Pan American

Backwards Design

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Course Objectives

  • Primary Objectives- By the next class period students will be able to:
    • Perform some basic engineering estimation.
    • Perform basic engineering unit conversions.
    • Understand the importance of estimation in engineering applications.
  • Sub Objectives- The objectives will require that students be able to:
    • Identify basic conversion factors for common engineering and scientific units.
    • Apply knowledge gained from previous courses to the problem at hand.
  • Difficulties- Students may have difficulty:
    • Identifying appropriate units and conversion factors.
    • Relating unconventional units to standard units.
  • Real-World Contexts- There are many ways that students can use this material in the real-world, such as:
    • Estimating amount of refrigerant leakage from common air-conditioning devices.
    • Relating unconventional units to common units for use in engineering applications.

Model of Knowledge

  • Concept Map
    • Identify common conversion factors needed in everyday engineering applications.
    • Relate unconventional units to standard scientific and engineering units.
    • Apply knowledge gained from previous courses to perform basic engineering estimations.
    • Understand the importance of being able to perform basic engineering estimations as a first step towards solving more complex engineering problems.
  • Content Priorities
    • Enduring Understanding
      • Understand how to perform fundamental engineering estimations.
    • Important to Do and Know
      • Become familiar with the common engineering units and conversion factors.
    • Worth Being Familiar with
      • Relations between conventional and unconventional units.

Assessment of Learning

  • Formative Assessment
    • In Class (groups)
      • Discussion of the three basic systems of units (SI, US Customary, and English)
      • Discussion of the basic engineering units
      • Discussion of the common unit conversion factors
      • Discussion of the differences between conventional and unconventional units
    • Homework (individual)
      • Attempt several estimation problems derived from engineering applications.
  • Summative Assessment
    • In class quizzes.
    • In class exams.

Legacy Cycle

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OBJECTIVE

By the next class period, students will be able to:

  • Perform basic engineering estimations related to their field of study.
  • Understand the importance of engineering estimation as a first step towards solving more complex engineering problems.

The objectives will require that students be able to:

  • Be familiar with the basic engineering units and unit conversion factors in the three different unit systems.
  • Relate conventional units to unconventional units as part of the engineering estimation techniques.

THE CHALLENGE

Oh no! My 1987 Toyota Corolla needs R22 refrigerant!!!

You live in Edinburg, TX where the weather is warm all year long and extremely hot in the summer. You notice in January that your car air-conditioner is not working as efficiently as it used to but you ignore the problem since the air-conditioner is still working and the weather is not that hot yet. The problem persists and you notice that the performance of the air-conditioner is getting systematically worst. In July, you take your car for a check up and the mechanic tells you that you have a refrigerant leak at a rate of one drop every three minutes. The mechanic also explains that since your car is an older model it uses R22 refrigerant which can't be purchased in the US anymore. The mechanic explains that he can fix the leak but you will have to provide him with R22 refrigerant which can only be purchased from Mexico City. You would like to estimate the amount of refrigerant that has leaked from your car-refrigeration system before you purchase because you do not want to make the trip to Mexico City and not buy enough refrigerant or buy more than you need (consider that one gallon of R22 Refrigerant costs $80 and that they only sell it in half gallon increments).

GENERATE IDEAS

  • Students will have to come up with logical assumptions that will help them solve this estimation problem.
  • Students will research independently for ways to estimate the total amount of refrigerant that has leaked over the past six months.
  • Students will research independently for ways to convert the volume of refrigerant lost from number of drops to gallons.
  • Students will have to explore the accuracy of different techniques used to measure volume by conducting simple experiments.

MULTIPLE PERSPECTIVES

Students will discuss their different ideas through brain storming before performing experiments.

RESEARCH & REVISE

Once experiments are performed and data is collected, students will share their results and discuss differences in the techniques utilized to measure volume and their methodologies for converting the number of drops to gallons. Based on the shared information, some students might want to revise their estimates based on the new shared information.

TEST YOUR METTLE

Students will compare their estimates and discuss variations in their results. Students will also explore the effects of their assumptions on the obtained estimate and check the validity of their answers. Questions like: "Does this estimate seem reasonable?" or "How many gallons are needed to completely fill the cars air-conditioning unit?" should be investigated and answered. Furthermore, in order to maximize the benefits of this exercise, an examination of the accuracy of the different techniques used to obtain the estimates should be performed.


GO PUBLIC

Three representative groups of students will be selected to present to the rest of the class the methodologies they followed to obtain their estimates. The three groups presenting will contain the best estimate, a reasonable estimate, and a poor estimate but this will only be known to the instructor. After the groups share their results, the class will be asked to evaluate the various estimates and discuss their accuracy. After a thorough discussion among the students in the classroom, the instructor will reveal the most efficient procedure to attain the best estimate and will discuss the shortcomings of other methods followed. At this point, some time will be set aside for final comments and conclusions.

Pre-Lesson Quiz

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  1. How many days are there in a year?
  2. How many minutes are there in a day?
  3. How many systems of units are there?
  4. What are the most common units of volume that you know?
  5. How many liters are there in a gallon?
  6. How many liters are there in a cubic foot?
  7. Is there a direct conversion between number of drops and gallons?

Test Your Mettle Quiz

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  1. How can you measure the volume of a liquid? Mention as many methods or techniques as you know.
  2. What factors affect the accuracy of measurements?
  3. How can you improve the accuracy of measurements?
  4. In the challenge presented earlier, what are the major sources of error that will affect your estimation? What can you do to improve the accuracy of your estimate?
  5. How can you determine the accuracy of digital and analog devices?
  6. What is the difference between accidental (random) and systematic errors in measuring devices?
  7. What is the difference between accuracy and precision?
  8. When is engineering estimation acceptable?
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