Seed Storage Tube

In developing countries, farmers do not have access to decent seed storage facilities. When farmers try to store their supply of seed, insects and wet climates often destroy it.

=Problem Statement=

Background
In wealthier places like the United States, it is easy to store seed with little risk of destruction by insects or premature sprouting due to moisture. In developing nations, especially in rural areas, much of the loss of crops occurs after harvest, during storage. Insects destroy seeds and monsoons bring moisture that causes the seeds to sprout before they are planted. By providing an inexpensive method of storing seed for long periods of time, we can reduce loss, allowing more wealth and food security for rural farmers.

Deliverables
Our main deliverable is an airtight and watertight container inside which seeds collected during harvest can be stored for up to two years for later planting. The container will be vacuum sealed at an absolute pressure of at most 50 mm of Hg to kill insects mixed in with the seed. It will have an attached vacuum pressure gauge to monitor the integrity of the seal. Included with the container will be a 12v vacuum pump to bring down the absolute pressure and remove water vapor and a tarp to shield the container from rain and direct sunlight. Other deliverables include a visual instruction manual detailing the assembly, use and maintenance of the container.

Specifications
=Design=

Alternatives/Selection
The design was originally going to be a tube made out of PVC. Once it was determined that PVC at the needed diameters was too expensive, we switched gears and came up with a new idea.

This second design featured a 55 gallon plastic drum with a removable lid. The valve system was attached to one of the small, threaded openings to allow a vacuum seal. However, the barrel deformed too much when not completely full of seed and air was still able to leak back in at an unacceptable rate.

The third design is simply a thick trash bag with a PVC tube, with holes drilled into it, and the valve system attached. The bag is then sealed around the PVC, allowing the seed to be vacuum sealed in the bag. We were unable to get an airtight seal with this method.

Our current design in a modified "Spacesaver Bag". Normally, Spacesaver bags are used by filling them with clothing, closing the opening, and attaching a vacuum cleaner's hose to the valve on the front of the bag, pulling out the air and compressing the clothing inside. We filled the valve with silicone caulk, and attached a bulkhead to the bag, also with silicone caulk. We screwed the gauge assembly into the bulkhead. Upon applying a vacuum, this system performed better than any of our previous designs. In 72 hours, the bag leaked from 21 inHg below atmospheric pressure to 4 inHg below atmospheric pressure. While this in not yet sufficient for our needs, it is a step in the right direction, considering the best we had achieved before was going from 21 inHg vacuum pressure to atmospheric in about 12 hours.

The pictures below show how the design has evolved over time.

Components


5/16" Barb x 1/4" Male NPT Air Gas CO2 Hose Beer Shut-off Ball Valve

Steel Vacuum Gauge with 1/4" Bottom Mount

1/4" Galvanized Tee

3/4" x 1/2" NPT Steel Bushing

1/2" x 1/4" NPT Steel Bushing

Experimentation and Analysis
Two experiments will be performed. The first will be on determing what vacuum pressure will collapse the barrel and the second will be whether or not it is water tight.

The results of the real-world test on the barrel revealed a few issues. The leak rate of air back into the "sealed" barrel was too high. The barrel also deformed too much, mainly around the mid-section. Adding seed to the barrel helped it keep its shape but it still leaked air at an unacceptable rate.

Another experiment was performed to test the life of insects in a vacuum environment. Crickets were chosen as the test specimen. They were put into four separate clear glass soda bottles, corked with a Foodsaver cork, which allows air to be pulled out of a container, but not to flow back in, forming a vacuum, and vacuumed down to different pressures. The results showed that a 20 inHg vacuum would immediately made crickets lethargic, and they died within a few days. Under 15 inHg of vacuum pressure, the crickets survived for almost a week. The food placed in the 10 inHg vacuum bottle spoiled, and the crickets died in three days, but this was disregarded because it appeared they died from starvation or spoiled food, rather than the vacuum. The control group survived for about a week. We continue to aim for 20 inHg of vacuum pressure.

=Team Members=

Document Archive
Documents (Meeting Minutes, Agendas)