Why Spirals Wouldn't be Viable

We decided that a spiral was too inefficient regarding the surface area of algae exposed. According to our calculations (seen below), the pipe would need to be around 25 meters long to attain prime surface area (80,000 cm2). An Archimedian spiral would still need a massive radius to achieve the proper surface area. The pipe in question was to have a diameter of 10 cm, with an unknown thickness. The sheer length of pipe needed was enough to deter us from pursuing this kind of shape.

Instead of a spiral, we decided to create sheets to attain the optimal surface area of 80,000 cm2. Many thin sheets of algae will be placed consecutively next to each other. We inserted a picture below for convenience.

Calculations:

Pipe with radius r = 5 cm;

Surface area of cylinder = 2πrh+2πr2

Height = 2560.32 cm, or about 25 m

Archimedian spiral would need to be about 25 m long, which is too big.

CAD drawings

CAD Drawings - 

illustrations by Fenton Billings

Week 1

This week, we formed a group and discussed a few topics, and eventually settled on the idea of algae air purification through photosynthesis. We discussed various subtopics of this idea which included green rooftops, photosynthetic paint, and mass purification with tubes of algae. We researched tubes of algae that were used to purify the air around highways, which were all several miles long. However, we wanted to scale the pipe system down to fit in a house or apartment and allow it to be easily maintained by the user. By installing modules in several homes in a neighborhood, it is possible to greatly reduce the amount of carbon dioxide in the air. With limited discussion time, this was about all we could accomplish.

Week 4

This week, we realized that we wanted to get rid of the pump in the system. The pump wouldn't have been strong enough to move algae, so the pipe would have been constantly clogged. It would have required a lot of work to keep the pump primed during cleaning. A model without a pump would decrease the number of parts in the system, therefore reducing the cost of production and maintenance. We came up with the idea of using a mechanical motor in the center of the module that would rotate a spiral pipe system. The algae would continuously fall through the spiral, thus allowing the algae to circulate without the need of a pump. The moving part is much easier to access for maintenance, and it isn't subjected to the maintenance procedures that the pump would need to undergo.
The spiral pipe system would also drastically increase surface area while keeping the same wall area.

Week 5

This week, our group redesigned the whole structure of the air purification system. Instead of making the system a winding tube or a spiral, the system would be made of thin algae-filled sheets which were to be square with 50-centimeter sides, and with a 2-centimeter thickness. The design would contain fifteen or thirty plates, which would be separated by half inch gaps. We completely changed the design because if we were to use a 2-inch diameter tube to hold the membrane and algae, it would need to be 84 feet long to account for the surface area needed to purify the air for just one person. A winding or spiral tube would take up too much space in a house, and it would not be practical. We came up with the idea of sheets to maximize surface area. The structure is partially based on how bees kept by beekeepers build honeycombs on sheets; the sheets would be in a trough to hold them in place. We also began working on the CAD model of our new structure in Autodesk Fusion 360.

Week 3 - 3D-Modeling the Module

Week 3 primarily concentrated on the shape and design of the algae containment vessel. Fusion 360 provided a user-friendly way of shaping out the design. The dimensions of the vessel can vary depending on the size of the room in which it will be installed. Generally, it will be a hollow system of tubing, consisting of 10 cm diameter plastic piping. The walls of the pipe are of the stock 7.5 mm thickness. The pipe is clear, appears in a rounded, hollow box form. The file is not complete, so we have not uploaded it. We expect to upload it by next week.

The design itself is relatively simple. The pipe is a closed loop, spanning about 40-50 cm width and about 1 m length. There will be a hydro pump installed on the right side of the piping, to keep the algae moving through. On the left side, adjacent to the pump, will be a release to drain the pipes for cleaning. Supports can be manufactured out of cheaper PVC piping, and installed into the wall or the floor according to a customer’s preference.

4/5/16 - Plastic Decision

Group 1
Our module is reliant upon its ability to allow the algae inside to use carbon dioxide and release oxygen. To contain the algae, plastic tubes are needed, but most plastics do not allow for the diffusion of CO2 and O2 (a reactant and a product of photosynthesis respectively). Two solutions to this problem were to either pump in CO2 into the module or find a plastic that would passively diffuse both CO2 and O2.

To save on cost, parts, time, and to allow for a simpler, smaller, and lighter solution it was decided to forego a gas pump and instead research a plastic specifically designed to diffuse the afforementioned gases.

After many hours of searching through multiple webpages, a plastic that fit this description was found: polysulfone. It can withstand household temperature ranges, the pressure exerted by the water, and the pH of the culture.

Polysulfone resin can be purchased at a price of $1,150/ 25 kg (55.1 lbs), or roughly $46/kg ($20/lb).

4/7/16 - Algae Decision

Group 1
During lab today, the group narrowed down the list of feasible algae candidates. As of now, the best algae belong to the genus Chlorella - chosen for its ability to live in freshwater, its relatively fast reproduction rate, because it does not form mats or strands when growing, and for its high photosynthetic efficiency.

Research needs to be done to determine which species of Chlorella is the best choice to grow in the culture. The noted species are Chlorella vulgaris, Chlorella pyrenoidosa, and Chlorella sorokiniana.