Validation and Results

Simulations for the Prototype

Computational Fluid Dynamics

We used Computational Fluid Dynamics Models to simulate the flow of fluids and heat through our system. Our prototype will have water-flow paths as well as air-flow paths.

In order to ensure that both fluids and heat are cycling properly entering, exiting, and throughout the system, we generated CFD simulations and theoretically validated the data afterward.

Dynamic (Mechanical)

Dynamic System Simulation Modeling was used to simulate all of the moving mechanical parts in our system. This helped to investigate the optimal system for our automated harvesting.

The harvesting blade is subjected to multiple different forces in order to cut through the vegetation growing in the system. These simulations showed us the amount of force required for an efficient harvesting blade to be successful in our system. This gave us the information for the material needed to cut through the foliage and the amount of power required to do so.

Data Expectations

Expectations

Heat flow

The data we expect to study with the heat transfer is to get a better understanding on how the heat transfer is distributed and to see which scenario would keep the temperature the most stable over time. The two scenarios we expect to study are a well-insulated contained system and a non-insulated system. Our goal in these scenarios will give us the most stable temperature over time in a day and night cycle. This is our goal because this will help us validate how much heating and cooling system is needed.

Water flow

The data we expect to get from the simulations of the water flow is to make sure that there is adept water flow and to verify that the water flows as expected in the piping under microgravity conditions.

Airflow

For airflow, the data we expect to collect from the simulation is to see how much airflow is needed to keep temperature stable with the increased air resistance caused by the different stages of growth.

How it will assist the project

The simulations will allow us to better understand the possible design flaws of our different systems. These computer-aided simulations will save us an immense amount of time by allowing us to see critical failures in our design as well as see whether our system will be viable.

A big part of this is the flow of air through the system. As our plants grow, we need to know if the plants will still be getting the air that they. If too much obstruction is created, then the heat from the LEDs to the system will not be dispersed properly. It will also cause the plants on the far side of the system to grow mold and rot if they are not properly ventilated.

This will also help us determine the final material needed for the system and the harvesting arm. Instead of using money on different materials and going through trial and error, these mechanical simulations will show us the optimal solution.

Software

SolidWorks

This software is used to generate the ideas imagined for the project. The CAD parts of the design are created and assembled here.

ANSYS

This software is used to analyze Computational Fluid Dynamics. This allows the flow of the air through the system and the water through the tubing to be simulated. Ansys is also used for thermal analysis which allows the concentrations of heat in the system to be seen and helps determine how heat is distributed throughout the system.

Information Needed Prior To Simulation

Heat Flux

When evaluating the thermal flow of the contained system, two things need to be evaluated. First, the amount of heat being delivered convectively to the air in our closed system. In the MicroTerra the only heat generation occurs from the LEDs (about 25W) and any heat source for the electronics is treated to be negligible because of how small the quantity is.

The primary form of heat transfer will be radiation. Due to the heat in the system, cooling was the second topic that needed to be evaluated. The constraints for an adiabatic and a non-adiabatic system help evaluate the change in the state of the system. Once the heat matrix is determined then we simulated airflow through the hot system to make sure it can be properly cooled in order to maintain a constant temperature.

Air Flow

For our simulation of airflow, we had to evaluate the path taken by the air. We needed to consider that as the plants grow in the contained system, the air restriction will increase. Our constraints for the simulations had to be re-evaluated for the different growth stages of the vegetation being grown.

When considering the design, it was imperative to track the speed and density of the airflow as it made it's way through the different growing environments. This required an understanding of the physics of air in zero gravity.

Flow in Pipes

The last fluid simulation needed is the water flow through a series of pipes. For this, we need to recall the different pipe flow changes that will be occurring in our system. The different pressure drops would occur depending on the path taken by the flow of water. If our final product follows the idea of a module system, the simulations show the pressure drop for a single module.

Design Iterations

Mat A: Day 10

Mat B: Day 10

Mat C: Day 10

Plant Medium Iterations

1. Growth Medium Thickness

Throughout the design process for the irrigation system the team realized that using a .25in coco fiber mats could cause many issues in the system. The roots would have grown right through the coco fiber mats, and that would have caused it to wrap around the porous tube. This would be a problem because it may cause a build up of plant matter in the irrigation system.

The team decided that an easy solution would be to change the mat's thickness, since the micro green only has a few days to grow (10 days). It was reasoned that a thicker mat would keep it from growing right through. While taking into account the factor of reducing the thickness of the mats because the thicker the soil medium the larger the seed mat dispenser and disposal system would have to be if we want to keep growing microgreens until the next resupply(approximately 3 months).

The soil medium iterations were a .25 in mat (A), .5in mat (B) and a 1in mat (C). All mats were grown in the same environment with the same amount of water (3 cups) for a week. In the first couple of days it was to note that mat C was behind in growth compared to mats A , B and mat C was drier at the top compared to the other. Around day 5 it was noted that fungus had grown in mat C since it was not absorbing the water. It was attempted to clean the fungus from mat C. Around day 6 It was noted that fungus spread to the other mats A and B. After extensive cleaning and water changes the mats A and B grew approximately the same yet they had stunted growth because of the fungus. At the end of the experiment only mat A had the roots grow through the medium while mat B had roots just starting to grow through it. Despite that the testing did not go as expected it still suggests that for future use the .5 in mats (B) for the irrigation system is best.

As a result of these iterations, the crew avoided having to go detangle the roots of the microgreens from the irrigation system each time a new mat was disposed of. This minimizes the human involvement needed to maintain the MicroTerra. The outcome of the iterations ensured that 0.5in was the best thickness for the mats to avoid excess water in the system and under absorption for optimal growth. Due to this, the lead screw did not have to use as much compression force to remove the water from the mats and the water pump did not have to run for longer to ensure water reaches the microgreens. The system experiences less stress on its components which causes it to last longer thus providing a sustainable source of food for the astronauts on space.

Porous-Tube-A: Standard 1/4" water pipe with pores

Porous-Tube-B: Standard 1/4" water pipe with guiding channels

Porous-Tube-C: Standard 1/4" water pipe with pores surrounded by porous foam

Irrigation Iterations

2. Porous Tube

In designing our irrigation system, we have decided to go with a method of watering plants that ensures we will not have excess water floating in the air, nor water that is misdirected and not hitting the plants as it should. We did research on wick systems, hydroponics, aeroponics, and even centrifugal systems, only to find that none of those would fit our application of minimal crew intervention. However, we did find a method that fit the mold nicely; a variation of a porous tube. A typical porous tube has embedded seeds in a porous material that allows water to flow through its pores and out to the seeds. The sprouts then grow through channels up and out of the tube. We have come up with several iterations that all share the same purpose of watering our micro green medium thoroughly, but slowly so that the water absorbs fully and there is no excess to float. The pores of the tube will allow water to seep out into the cotton which will transfer the water into the coco-fiber medium that has seeds sewn within.

For our first iteration Porous-Tube-A, we designed a simple water pipe with holes that would run right beneath the cotton. This was the most simple and cost efficient design. This simple system does not have much control over where the flow is going to go In a zero gravity environment. The pipe has an Inner diameter of 0.147 Inches and outer diameter of 0.25 Inches. The lengths of the tubes were 10.0 Inches which covered the size of the mat where the greens were growing while not spraying excess water Into marginal areas. The top of the tube had holes that were 0.05 Inches In diameter for very controlled water flow.

For our second iteration Porous-Tube-B, we designed a porous tube that had vertical channels that shot up Into the cotton. This iteration gave us more control over where the water would flow, but the Issue arose of potentially having roots that wrapped around the channels. This Is a problem mainly because the automation of the unit rolls the used mat out Into a disposal chamber where the greens are cut, however wrapped roots could potentially hold the mat back from rolling out of the system requiring maintenance, or ripping the roots and having floating root pieces around the unit. These pipes had an Inner diameter of 0.147 Inches and outer diameter of 0.25 Inches. The lengths of the tubes were 10.0 Inches which covered the size of the mat where the greens were growing while not spraying excess water Into marginal areas. The top of the tube had channels that were 1 Inch In height and had a 0.125 Inch Inner diameter In order to attempt to control the path of the water.

Our third iteration, Porous-Tube-C, is a the same design as porous-tube-A with holes for water flow, surrounded by a 0.25 inch porous, foam-like material that would allow the water to seep In more slowly, minimizing the potential for excess water floating in the system. As this issue did not provide a solution for the wrapping roots, we came to the conclusion that the root wrapping problem would have to be solved through other means such as a thicker medium layer.

Conclusion

Upon receiving materials and assembling/testing our Irrigation system we came to the conclusion that the best porous tube configuration would be Porous-Tube-A, the simple design.

Porous-Tube-B with the channels ran Into the problem that as the mats would move through the system and a new one would come In to be watered, the rubber channels would bend and pour water off to the side rather than Into the seeded mat. We then attempted plastic channels which broke over time of moving mats through the system.

Porous-Tube-C with the surrounding foam caused water to run to the bottom of the pipe and Into the system, Instead of directly Into the mat.

Porous-Tube-A 's simple design ensured that the water would only flow slowly from the top of the tube and directly Into the absorbent medium. The irrigation system design was adjusted so that there was hardly extra space. The porous tube was pushed up directly under the medium. It was the most controllable measure, aside from being the simplest and most cost effective.

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