Mass Balance Model
This material is replicated on a number of sites as part of the SERC Pedagogic Service Project
- Learn the basics of mass balance;
- Apply this knowledge to two examples with similar structure:
- Temperature and heat loss;
- Bank Balances.
- Learn that at equilibrium the flow rate equals the outflow rate;
- Learn how to calculate equilibrium levels given inflow rate and residence time;
- Make simple graphs;
- Read information from graphs;
- Use a model to help develop basic equations.
Context for Use
The complete activity with assignment in PDF format and online model is available at Model Activity page
Mass Balance Activity (Microsoft Word PRIVATE FILE 89kB Jun7 11) is an MS Word document that can be modified by you.
Teaching Notes and Tips
This activity takes about 2-hours to complete.
This activity works best with a PC, but with proper configuration also works on MAC OS X.
Little mathematical background is required to complete this activity.
Students typically have little trouble answering the first 17 questions in this activity. Students usually have to think more carefully when using the online model for the two structurally similar examples at the end of the activity (home heating and bank loan balance). Encourage them to keep units clear in their mind. For the water bucket, level is expressed in gallons and time in min; for the home heating, level is in degrees Celsius and time in hours; and for the bank loan, level is in US$ and time is in months.
I often use a 2-liter pop bottle, with flow from a hose into the top and a hole in the bottom, as a physical model during an in class discussion of mass balance and the water bucket model. The lifetime (residence time) for this water bucket model is then related to the hole size in the bottle and viscosity of the water.
Mass Balance Activity Answers (Acrobat (PDF) PRIVATE FILE 292kB Aug18 04) in PDF format for easy grading.
Grading the completed activity sheet provided can be used as an assessment of student understanding. Follow-up discussions in class, essay questions on exams, and the future success of students on other related activities are also useful measures of student understanding.
References and Resources
The water bucket mass balance model described here is the first of four activities that I use in my courses when discussing Earth's Climate and Stratospheric Ozone.
The next activity in the sequence, Trace Gases , is designed to extend these fundamental ideas and the terminology of mass balance into an atmospheric science context. If you are short on time you can highlight key aspects of this activity in a lecture and then assign one or both of the related activities below.
These last two related activities can be done in any order.
- Using a mass balance model to understand carbon dioxide and its connection to global warming. This activity has been student tested, reworked, and updated over the past 12 years.
- Using Mass Balance to Understand Atmospheric Levels of CFCs. This activity has also been student tested, reworked, and updated over the past 12 years.