2024 ASEE Annual Conference & Exposition

Mastering the concepts of diffusion is crucial for engineering students as it is a vital process of mass transport in both physical and natural sciences. However, deciphering this phenomenon while connecting the theoretical models developed by Fick to real-world data collected in a lab can be challenging for students. Measuring the diffusion process accurately enough to calculate diffusivities often requires cost-prohibitive instrumentation for many teaching lab applications. Other methods require complicated preparation and planning, which force students to spend most of their time troubleshooting the setup rather than on the primary student learning outcome.

This “Bring Your Own Experiment” (BYOE) paper presents a simple, low-cost experimental device that allows students to investigate the principles of diffusion through experimental design. The instrument and experiment discussed here eliminate complicated procedures allowing students to focus on the primary student learning outcomes. The experimental setup consists of a 3-D printed spectrometer, Raspberry Pi Zero W, Raspberry Pi camera, custom in-house written timelapse Thonny code for Raspberry PI, and semi-micro cuvettes. Students are asked to determine the relationship between diffusivities and the porosity of an agar gel with a food dye. Image J is used to analyze the images taken by the camera. A calibration curve relating the RBG color saturation of the food dye to the concentration is created. Once the calibration is completed, timelapse diffusion experiments begin. Students must decide how long to run each experiment, how often to image the cuvette, and three different porosities to test. Cuvettes filled with 1 mL of agar at a known porosity will be loaded with 1 mL of a high concentration of food dye on top. Using the calibration data and the timelapse experiments, students then model their time-dependent concentration profiles and calculate the diffusion coefficient for each dye-agar system. The final product the students are asked to create is a report of their analysis to include sample images, plots of the concentration profiles with their modeled data, and a discussion of their result in which they should address the relationship between the diffusivity and the porosity of the agar gel.

This BYOE instrument is suitable for any time-dependent 2-D colorimetric response, broadly applicable across the engineering disciplines. Within chemical and biomedical engineering, experiments can be designed to isolate the impact of molecular weight and molecular shape in calculating and modeling diffusion coefficients in addition to enzyme kinetics using colorimetric responses. Using thermochromic dyes and adding a small piezoelectric device to the instrument may enable thermodynamic experimental studies taught in chemical, biomedical, and mechanical engineering laboratories. The versatility of this low-maintenance, economical, innovative experimental apparatus has the potential to be used for innumerable applications across many engineering curriculums.