This time our class was tasked with creating a chemical hand warmer for the (nonexistant?) student store. The criteria was that it had to be effective (achieving a temperature increase of over 20 degrees Celsius), safe, efficient, and durable, as well as inexpensive and easy to manufacture. Preceding the project, we did labs in which we mixed ionic salts with water and recorded the temperature change. This was to serve as the basis for our projects.
Our first decision as a group was that salt+ water hand warmers are a terrible idea. They leak, they don't last long, they barely reach the 20 degree increase mark, and they are a skin Irritant. And everyone else was using them. Because of this, we decided that our design would not use liquid or chemicals. This lead us to our simplest idea: a cloth bag of rice that could be microwaved and reused. I have used larger versions of this idea myself, and they are clean, durable and hold their heat for hours. Compared to the limited success the class was having with chemical warmers, this seemed like the most viable option.
Then Vogl said we had to use ionic salts in our design.
From rice bags, we went directly to the big guns. Military grade MRE's (meals ready to eat) are heated by an exothermic reaction. We found some schematics online (not sketchy at all) and found them to be rather simple. The only problem was the active ingredient: magnesium powder. While it heats efficiently when exposed to water and sodium chloride, it produces hydrogen gas and by itself is highly explosive. Needless to say, we didn't find any in the prep room and they wouldn't let us buy any.
Plan C: Take a commercial handwarmer and void the patent agreement. We discovered that their composition is similar to that of the military MRE, but uses fine iron powder instead of magnesium. In addition, we added vermiculite and charcoal to distribute moisture to the iron to start the reaction. Because our focus was on quality and durability, we used a felt pouch to hold our reactants. While this may be more expensive and labor intensive, we justified it with its additional use as a hackysack.
Our first decision as a group was that salt+ water hand warmers are a terrible idea. They leak, they don't last long, they barely reach the 20 degree increase mark, and they are a skin Irritant. And everyone else was using them. Because of this, we decided that our design would not use liquid or chemicals. This lead us to our simplest idea: a cloth bag of rice that could be microwaved and reused. I have used larger versions of this idea myself, and they are clean, durable and hold their heat for hours. Compared to the limited success the class was having with chemical warmers, this seemed like the most viable option.
Then Vogl said we had to use ionic salts in our design.
From rice bags, we went directly to the big guns. Military grade MRE's (meals ready to eat) are heated by an exothermic reaction. We found some schematics online (not sketchy at all) and found them to be rather simple. The only problem was the active ingredient: magnesium powder. While it heats efficiently when exposed to water and sodium chloride, it produces hydrogen gas and by itself is highly explosive. Needless to say, we didn't find any in the prep room and they wouldn't let us buy any.
Plan C: Take a commercial handwarmer and void the patent agreement. We discovered that their composition is similar to that of the military MRE, but uses fine iron powder instead of magnesium. In addition, we added vermiculite and charcoal to distribute moisture to the iron to start the reaction. Because our focus was on quality and durability, we used a felt pouch to hold our reactants. While this may be more expensive and labor intensive, we justified it with its additional use as a hackysack.
As far as group work went, our team worked well together and as a result our presentation went over well. So well in fact that our group won in our class. Quality over quantity.
If I were to change anything about this project, we could have made the design process a bit more open ended, with exploring more options besides ionic salt reactions. And for that, we could have finalized our design sooner in order to perfect it before the day of the presentation.
If I were to change anything about this project, we could have made the design process a bit more open ended, with exploring more options besides ionic salt reactions. And for that, we could have finalized our design sooner in order to perfect it before the day of the presentation.