The Beginnings of the DuiihDac!

February 2, 2015

Team: Jessica Allen, Ryan Bartoszek, Victoria Cheng, Isa Ferrall, Robinson Ford, Taylor Lane, Jordan Thomas

This first month back after break has been mainly dedicated to organizing our group along with finalizing which refrigerator components would be best so that we can finalize our budget and begin prototyping.  Last semester we had decided to create an off-grid vaccination refrigeration unit in order to serve areas of the world without reliable electricity that are still in dire need of reliable vaccine storage.  The decisions we still had left to make were on the refrigerant and absorbent as well as the type of solar collector we would use to power the refrigeration cycle.

For the refrigerant and absorbent we previously wanted to use a combination of ethanol and activated carbon due to its lack of toxicity and the belief that the materials would be easy to obtain even in remote location should repairs be needed in the field.  However, further research showed that the activated carbon we would need for this process has to be created in a specific way to ensure a consistent pore size for absorbing the ethanol making it much more expensive and much less accessible than we had anticipated.  In light of that we’ve decided to use ammonia and calcium chloride as our refrigerant and absorbent respectively as while the ethanol and activated carbon were less toxic, this combination will be much cheaper allowing us to lower the overall cost of the final unit.

We also discussed the type of the solar collector to use as well as its orientation in relationship to the actual storage chamber. The two main solar collector types are a parabolic collector that would focus light or a flatbed collector that would be more consistent throughout the day.  The parabolic collector may be able to achieve a higher temperature, however, the flatbed collector has the advantage of being cheaper as well as more consistent throughout the day and our research shows that the flatbed would be able to achieve the temperatures we would need to evaporate the ammonia and desorb it from the calcium chloride.  As far as orientation of the collector goes, if on top it would make the fridge potentially more practical and mobile, but the collector may be too big to place on top and if we did want to add a secondary biomass it may be easier to keep the entire heat collection unit separate.  Another possible option would be to only have the backup biomass heat source as a separate piece that could be attached when necessary.

Going into February we are planning to order our necessary materials for what we are calling the DuiihDac (Dual Input Intermittent Heat Driven Absorption Cycle) and then beginning assembly of the initial prototype.  We will be using ammonia as the refrigerant and calcium chloride as the absorbent and most likely opting for the cheaper flatbed solar collector.  The other pieces we need to order and/or assemble are the condenser, evaporator, cooling chamber, pipes, a biomass burner, and insulation.  One option we are considering for the condenser is to build it out of spiral fin tube as a potentially cheap and easy to work with option, but more research is still needed.

We are looking forward to ordering our parts and soon assembling the first version of the DuiihDac!