2024 ASEE Annual Conference & Exposition

Many students in chemical engineering are adept at solving systems of equations, but they struggle with understanding the meaning behind the variables and values, which leads to a lack of conceptual understanding and reduced critical thinking. This often hinders the students’ abilities to apply the concepts while solving practical problems. To address this issue, we restructured some problem statements in the Mass and Energy Balances course. To isolate conceptual understanding from mathematical ability, we dedicated questions on exams where the students were asked to qualitatively analyze relationships between different variables. We developed active-learning computational demonstrations that students could explore in a self-paced manner by manipulating variables and observing the effects on other variables, working in groups and guided by a teaching assistant (TA) and a problem set during recitation.
One exam question asked students to predict the effects of changing one stream or system variable on another in a reactor process with recycle. To reinforce this, students worked with an interactive demonstration that displayed a block flow diagram of the process, using a mixer, reactor, separator, and splitter. Partial flow rates of each species were shown in a bar graph, and single-pass and overall fractional conversion, yield, and selectivity were shown in pie charts. Students could change inlet molar flow rate, single-pass fractional conversion, fractional selectivity, separator splits, and recycle ratio, individually manipulating one while holding the others constant. The flow rates and fractions adjusted automatically, obeying the material balance equations that the students were introduced to earlier.
Another exam question asked students to predict the effects of changing parameters of a system of two flash drums connected in series at vapor-liquid equilibrium. To reinforce this, students worked with an interactive demonstration that displayed stream compositions and temperatures on a Txy vapor-liquid equilibrium diagram of a binary system, along with a diagram below with stream flow rates to illustrate the “lever rule” that arises from material balances. Students could adjust the inlet composition, temperature of each flash drum, and whether the second flash drum was connected to the vapor or liquid outlet of the first flash drum. The relative magnitudes of stream flow rates and their compositions adjusted automatically, and cases such as working outside of the vapor-liquid envelope were allowed, to demonstrate the effects of impractical design choices.
This focus on conceptual understanding will not only build students’ intuition and critical thinking skills but also instill more confidence and engagement in the content beyond solving equations.