.

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

Macronutrients

Symbol

Concentration

Potassium phosphate

KH4PO4

0.5oz/25g

Potassium nitrate

KNO3

2.0oz/25g

Calcium nitrate

CaNO3

3.0oz/25g

Magnesium Sulfate

MgSO4

1.5oz/25g

Boric acid

H3BO3

0.5pint/25g

Manganese chloride

MnCl2(4H2O)

0.5pint/25g

Zinc sulfate

ZnSO4(7H2O)

0.5tsp/25g

Copper sulfate

CuSO4(5H2O)

0.5tsp/25g

Iron sulfate

FeSO4(7H2O)

0.5pint/25g

 

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.


Figure 5-4: Water Purification System

 

Condensation 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

 

Sensing 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

Sensor

Dimensions (m)

Power (W)

Output (V)

ph Balance

0.2x0.2x0.1

1

0-10

Humidity

0.1x0.1x0.1

1

0-10

Flow Rate

0.1x0.1x0.1

1

0-10

Fluid Level

0.05x0.1x0.1

1

0-10

Nutrients:

 

 

 

    Potassium phosphate

0.05x0.05x0.1

0.5

0-10

    Potassium nitrate

0.05x0.05x0.1

0.5

0-10

    Calcium nitrate

0.05x0.05x0.1

0.5

0-10

    Magnesium Sulfate

0.05x0.05x0.1

0.5

0-10

    Boric acid

0.05x0.05x0.1

0.5

0-10

    Manganese chloride

0.05x0.05x0.1

0.5

0-10

    Zinc sulfate

0.05x0.05x0.1

0.5

0-10

    Copper sulfate

0.05x0.05x0.1

0.5

0-10

    Iron sulfate

0.05x0.05x0.1

0.5

0-10

 

Figure 5-6: Sensing System

 

System Application

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.) 


Figure 5-7: Phase 1 Structural Concept

 

TABLE 5-3: PHASE I DESIGN REQUIREMENTS

Parameter

Symbol

Value

Units

 

 

 

 

Requirements Basis

 

 

 

Water temperature

T

300

K
Pipe diameter

D

0.0254

m
Pump power

W

750

W
Pipe length

L

0.75

m
Growth space volume*

V

1.80

m3
Water density

r

999

kg/m3
Mars gravity

G

3.68

m/s2
Tank elevation

z1

6.5

m
Tray elevation

z2

5.75

m
Pressure at the tray

P2

101

kPa
Growth area

A

36.00

m2
Water height

H

0.05

m
Pipe material

 

PVC

 

 

 

 

 

Requirements Basis

 

 

 

Water density

r

constant

 

Water velocity in the tank

v1

0

 

Pressure inside the tank

P1

101

kPa
Kinetic energy coefficient

a2

1

 

Heat transfer

Q

0

 

 

 

 

 

Specific Requirements

 

 

 

Elevation change

z1-z2

0.75

m
Dynamic viscosity

m

1.3E-03

Ns/m2
Minor loss coefficient

Kentrance

0.5

 

Equivalent length 90oelbow

Le/D

60

 

Friction factor*

F

0.008

 

Relative roughness

e/D

0.00001

 

Mass flow rate

M

0.6

kg/s
Time to fill a tray

T

600

s
Water velocity*

v2

33.62

m/s
Reynolds Number*

Re

6.6E+05

 

 

 

 

 

* All of the equations are listed in the Theory and Equations section of the report. 


Phase II: Horizontal Inflatable Structure

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

Parameter

Symbol

Value

Units

 

 

 

 

Requirements Basis  

 

 

Greenhouse temperature

TI

300

K
Martian soil temperature

To

210

K
Pipe diameter

D

0.0254

m
Pump power

W

750

W
Pipe length

L

8.5

m
Growth space volume*

V

11.40

m3
Water density

r

999

kg/m3
Mars gravity

G

3.68

m/s2
Tank elevation

z1

5

m
Tray elevation

z2

0.3

m
Pressure at the tray

P2

101

kPa
Growth area

A

228.00

m2
Water height

H

0.05

m
Base area

Ab

21.5

m
Water velocity in the tank

v1

0

m/s
Pressure inside the tank

P1

101

kPa

 

 

 

 

Specific Requirements

 

 

 

Elevation change

z1-z2

4.7

m
Dynamic viscosity

m

1.3E-03

Ns/m2
Minor loss coefficient

kentrance

0.5

 

Equivalent length 90oelbow

Le/D

0

 

Friction factor*

F

0.008

 

Relative roughness

e/D

0.00001

 

Mass flow rate

M

2.7

kg/s
Time to fill a tray

T

2700

s
Water velocity*

v2

11.89

m/s
Reynolds Number*

Re

2.3E+05

 

Conductivity-soil

kS

0.52

W/mK
Conductivity-water insulation

kW

0.04

W/mK
Conductivity-heat insulation

kH

0.025

W/mK
Conductivity-concrete

kC

1.4

W/mK
Thickness-soil

tS

0.25

m
Thickness-water insulation

tW

0.05

m
Thickness-heat insulation

tH

0.05

m
Thickness-concrete

tC

0.25

m
Shape factor

S

0.0075

 

Total thermal resistance*

Rt

1567.0

K/W
Heat transfer rate*

Q

0.2

kW

 

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

Parameter

Range of Operation

Units

Total Growth Area

180 230

m2

Humidity

70 85

%

pH Balance

4.5 8

pH

Greenhouse temperature

300

K

Martian soil temperature

210

K

Flow rate

0.5 - 2.5

kg/s

Root Depth

0.01 0.05

m

Total Solution Volume

9 12

m3

Greenhouse Pressure

101

kPa

 

TABLE 5-6: PARTS LIST

Part

Count

Size

Weight

Solution Tank

1

12 m3

0.8 kg

Water Tank

1

12 m3

0.2 kg

Valves

5

0.03 m3

2 kg

Pumps

4

0.006 m3

9 kg

Pipes

40 m

0.01 m Dia

1 kg

Storage Tanks

2

9 m3

0.4 kg

Filters

1

0.002 m3

0.05 kg

Condensers

2

0.08 m3

10 kg

Humidifiers

1

0.04 m3

0.1 kg

Boilers

1

0.04 m3

5 kg

Trays

5

3.6 m3

0.3 kg

Sensors

13

0.02 m3

0.05 kg

 

TABLE 5-7: POWER REQUIREMENTS

Part

Count

Power

Voltage

 

 

 

 

Valves

5

10W

12V

Pumps

4

750W

110V

Condensers

2

200W

240V

Humidifiers

1

10W

40V

Boilers

1

240W

240V

Sensors

13

1W

10V

 

Safety Measures

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.