Hydroponic Fluid Supply and Control
The hydroponic fluid and control system will produce hydroponic solution, which will be used by plants and crops. The hydroponic solution will contain the necessary nutrients that any plants or crops will need in order to grow in the Mars habitat. Figure 5-1 is a block diagram of the hydroponic fluid and control system. This control system is broken into several subsystems. The subsystems that will comprise the hydroponics fluid control system are:
· Nutrient Production System
· Solution Circulation System
· Water Purification System
· Condensation System
· Sensing System
Figure 5-1: The Hydroponics Fluid System
Nutrient Production System
A necessary component in the production of the hydroponic solution is water, which will be supplied by a water storage tank. The hydroponic solution will consist of water and nutrients mixed together. The nutrients will be made up of decomposed plants and minerals. We will store the nutrient supply in a nutrient storage tank. The system will work by pumping water through a pipe and mixing in the nutrients with the water that will be flowing to the growing area trays. A nutrient controller will control the amount of nutrients that are mixed in with the water, and a pH controller will control the pH of the hydroponic solution. Once the fluid is produced it will then go to the fluid circulation system. Figure 5-2 is an illustration of the hydroponics fluid production system.
The process of producing nutrients is called an Aerobic Bioreactor. Plant biomass will be finely ground and fed into the bioreactor (120-liter volume) at a rate of 0.2kg per day. The bioreactor contains water at a pH of 6.5, a temperature of 35 degrees Celsius, and dissolved oxygen that is supplied by airflow through the bioreactor. The mixture will remain inside the bioreactor for 21 days. The reactor contents will be removed in batches of 40 liters every following week after the starting period of 21 days. The contents will then be filtered to remove solids. The extracted solution will then be analyzed to determine the type, and amounts of nutrients and chemicals present and add any if necessary. Table 5-1 has all of the macronutrients used to make the hydroponics solution:
TABLE 5-1: MACRONUTRIENTS LIST
Figure 5-2: Nutrients Production System
Solution Circulation System
This system takes in the processed hydroponics solution and distributes the solution into the growing area trays. The fluid is pumped through a pipe that leads into a row of growing area trays. All of the growing area trays are interconnected together by pipes. As fluid begins to fill the first tray, it then will flow to the next tray, until all of the other trays are full of hydroponic solution. A series of sensors at the end of the last tray will measure the nutrient concentration of the solution and direct the flow accordingly. If the solution has enough nutrients, the solution will be directed back to the growing area trays through feedback valves and a pump. Otherwise, the solution will be directed to the purification system. We are assuming that each of the growing area trays will have the same dimensions, and the same amount of solution required inside them. Figure 5-3 is an illustration of the fluid circulation system.
Figure 5-3: Solution Circulation System
Water Purification System
The water purification system is comprised of a water recovery system, and a condensation system. The water recovery system is based on a diluted plant solution. This source proves that water can be recovered, and filtered to be reused again. It will supplement the main storage tank that the habitat uses. This recovery system will allow us to maximize the use of the available resources.
Water will come from unused solution. This diluted solution must be purified before it goes back to the main water tank. The process begins with nutrient sensors indicating to a microcontroller that the concentration of the nutrients in the solution is either within specified parameters, or not. When the concentration falls below acceptable values the old solution would be removed, while at the same time fresh solution will be provided from the nutrient production system. The removed solution would now go through the purification process. It would start with a boiler that would heat up the solution. The heated solution would next be collected in a condenser. Finally, it would be filtered to the proper safety levels and sent to the storage tank. The reason behind using a boiler-condenser system is that it would disinfect the water as well as purify it in the same time. Figure 5.4 is an illustration of the water purification system.
Condensers will be used to collect the extra humidity inside the greenhouse. The condensers will convert the humidity to water. The water will then go to a storage tank. This system would ensure us maximum use of our resources. The storage tank would be tied into the drinking water supply of the habitat. Since plants need a specific percentage of humidity in the air, a humidifier will be used to add humidity to the green house in case the humidity falls to a low percentage. Both of the condenser and humidifier are controlled by a sensor to prevent them from working at the same time, which would defeat the purpose of this system. Figure 5-5 is an illustration of the condensation system.
Figure 5-5: Condensation System
This system is responsible for making all of the other systems work properly. The sensing system utilizes a series of sensors that control the functions of each component in each of the subsystems. Most of the nutrient sensors must be custom made for this project because they are detecting specific chemical compounds, which are not commonly used. All of the sensors will feedback an electrical output to a microprocessor, which will regulate the functions of the hydroponics system according to the requirements. Table 5-2 is a list of the sensors in the sensing system, and figure 5-6 is an illustration of the sensors with respect to the system.
TABLE 5-2: SENSORS LIST
Figure 5-6: Sensing System
With this system in mind, the circulation of water is automated, leaving the astronauts time for other tasks. This system can be adapted to any greenhouse configuration. In this case, it was applied on the following greenhouse configurations:
· Phase 1: Vertical Ridged Structure
· Phase 2: Horizontal Inflatable Structure
All of the calculations are included in Tables 5-3 and 5-4, and all of the equations are listed as well.
Phase I: Vertical Rigid Structure
It will take the system 50 minutes to fill all of the trays with hydroponics solution (see Figure 5-7.) Each tray will be filled with hydroponics solution up to 5cm high (see Table 5-3 for the calculations.)
TABLE 5-3: PHASE I DESIGN REQUIREMENTS
* All of the equations are listed in the Theory and Equations section of the report.
It will take the system 45 minuets to irrigate an area of 228m2 with hydroponics solution (see Figure 5-8.) The solution will continue flowing over the growing area until its height reaches 5cm. For optimum performance, 0.2kW of heat is needed to keep the soil at 300K.
Figure 5-8: Phase 2 Structural Concept
TABLE 5-4: Phase II Design Requirements
Generalized Design Requirements
Tables 5-5, 5-6, and 5-7 contain the design specifications for the hydroponics fluid supply and control system for all of the considered structures.
TABLE 5-5: GENERALIZED DESIGN REQUIREMENTS
TABLE 5-6: PARTS LIST
TABLE 5-7: POWER REQUIREMENTS
There are some safety devices installed throughout the system. The first devise is a pressure safety valve. This valve is located on the main water pipe. It will redirect the water flow back to the main tank incase of an unexpected pressure increase. The second safety measure is a flow control valve between the main water tank and the condensed water tank. This valve will open to supply the main water tank with water incase of any shortage. Another safety measure is a flow rate gage located at the water exit. This gage will provide a flow rate reading, which would help in regulating the flow. Also, fluid level sensors are located in each tank to provide fluid volume measurements. Finally, a valve located on the main pipe feeding water to the hydroponics system will enable the operator to shut down the system incase of emergencies. Figure 5-9 is an overview of the complete configuration of the hydroponics system.
Figure 5-9: Hydroponic Fluid System
THEORY AND EQUATIONS
The following equation was used to find the volume of each tray:
The following equation was used to find the flow velocity:
The following equation was used to find the Reynolds number:
The following equation was used to find the total thermal resistance:
The following equation was used to find the heat transfer rate:
The value of the friction factor was found using Moody diagram. Using the value of Reynolds number, the calculated values were checked.