(455f) One Step At a Time: Teaching Mass and Energy Conservation In Separate Courses

The Department of Chemical and Biomolecular Engineering at Clarkson University has recently undergone a significant change in its curriculum. While these changes span the sophomore through senior years, this presentation will focus on the changes in our sophomore level courses.  In our earlier (and very longstanding) curriculum, in the fall of sophomore year, students took a course we titled ‘Chemical Process Calculations’ which covered mass and energy balance concepts and their first Thermodynamics course which primarily covered first and second law principles. In the spring semester of sophomore year, students took our Phase Equilibria course. They also took Physical Chemistry I and II this same year. While this generally worked well, faculty (and students) were becoming increasingly unhappy with this organization. It was felt that the pace required to cover all of the material in the mass and energy balance course was too fast and that students struggled in Thermodynamics because they were trying to learn abstract concepts like enthalpy and entropy at the same time that they were developing their problem  solving skills.

In an effort to remedy the ‘drinking from a fire hose’ challenges, the fall semester course was restructured so that it now focuses exclusively on mass balance concepts. Students are introduced to problems involving basic mass balances, recycle and bypass streams, chemical reactions, multiphase systems and transient processes.  In addition to these concepts that are traditionally taught in most mass and energy balance courses, we have added mass balance concepts involving staged operations. This ties in well with the simple phase equilibria concepts (i.e., Raoult’s Law) that precedes this part of the course. Students solve problems that don’t require energy balances by stepping off stages between equilibrium and operating lines. They also complete a case study project that only requires the solution of mass balances.   

Students are introduced to energy balances and thermodynamics in the spring semester when they now take our Thermodynamics course. This course starts with equations of state (with a focus on the ideal gas and Peng-Robinson Equations of State). The laws of thermodynamics are presented mostly in order to introduce the book-keeping concept of enthalpy. Students are required to compute enthalpy and entropy for ideal systems as well as from models such as the PR EOS. About half the course consists of applications of the laws of thermodynamics including a second case study that also introduces the students to computer-aided process simulation (once they had already solved a complicated process flowsheet by hand). Stagewise processes appeared again, this time demonstrating the importance of the stage energy balance.

This new course sequence was introduced for the first time in 2010-2011. Therefore, it is too early to draw definitive conclusions, but the early evidence does suggest that by the time students are presented with the second case study (this time with energy balances), the task of solving complicated mass balances held little pain for the students. We have also identified changes that should be made when these courses are taught for the second time in 2011-2012.