Mechanically-actuated Chemical Oxygen Generation via Sodium

Chlorate Dissociation

Mario A. Rodriguez

Department of Mechanical Engineering

Massachusetts Institute of Technology

Cambridge, MA 02139

March 2015

Email: mariorod@alum.mit.edu

(909) 437-6180

TABLE OF CONTENTS

1) ABSTRACT

2) INTRODUCTION

3) BACKGROUND

a) STOICHIOMETRY

b) THERMOCHEMISTRY

4) POTENTIAL APPLICATIONS

5) OVERALL SYSTEM DESIGN

6) PART DESIGN

a) TANK

b) ELECTRONICS

c) HEATER

d) MOTOR

e) SPROCKET DESIGN

f) INTERNAL FRAME

7) DESIGN CHALLENGES

a) BEAD CHAIN

b) HEATING TUBE

8) TESTING AND RESULTS

a) INITIAL CLOSED-TANK EXPERIMENT

b) SECOND CLOSED-TANK EXPERIMENT

c) EXPOSED TANK EXPERIMENT

d) THIRD CLOSED-TANK EXPERIMENT

9) POTENTIAL AREAS FOR IMPROVEMENT

10) CONCLUSION

11) ACKNOWLEDGEMENTS

12) REFERENCES

13) APPENDICES

1. ABSTRACT

In some environments and applications, it is necessary to produce oxygen gas for various

applications and uses. Currently, chemical oxygen generators are used on airplanes and space stations

for life-support purposes, but they have the potential to be used for energy production as well. However,

these typical gas “candle” designs are very simplistic, as they actually consume some of the oxygen gas,

and the oxygen production rate is hard to control at the temperature at which the reaction occurs. For

this reason, a mechanically-actuated bead chain generator was designed, built, and tested to deliver a

stoichiometrically-precise, controlled flow rate of oxygen gas produced by the dissociation of sodium

chlorate.

2. INTRODUCTION

Although life-support applications are the main use of chemical oxygen generators, power

systems could also benefit from using such devices, especially for AUV (autonomous underwater

vehicle) applications. Current-generation AUV’s are powered by lithium-ion battery packs, which have

low energy densities, thus rendering them impractical for prolonged, energy-demanding missions.

Recent improvements in aluminum-based energy systems, which produce hydrogen gas, have allowed

for the possibility of using a hydrogen fuel cell as a power generator on these AUV’s. Since AUV’s are

sealed and hardly resurface, it would necessary to store the oxygen inside the hull of the vehicle.

Oxygen storage in heavy high-pressure tanks is impractical inside a vehicle that must remain neutrally

buoyant, and can also cause pressurization and leakage issues for the AUV. Due to the spatial limitations

of the vehicle hull, a hybrid tank-generator system must be designed to accommodate for this power

system.

Figure 1: AUV’s like the REMUS 500 (shown above) utilize lithium ion batteries for energy storage, which are bulky and low on energy density. A

hydrogen-powered system would be more powerful at similar dimensions, and also more capable of expanding mission envelopes.

3. BACKGROUND

a. Stoichiometry

The hydrogen fuel cell functions by reacting hydrogen gas in the presence of an oxidizer (in this

case, oxygen gas.) Hydrogen gas is produced via the oxidation-reduction reaction between liquid water

and solid aluminum, resulting in the formation of aluminum hydroxide and hydrogen gas.

2𝐴𝑙 (𝑠) + 6𝐻2𝑂 (𝑙) 3𝐻2(𝑔) + 2𝐴𝑙(𝑂𝐻)3(𝑠) (1)

This reaction is catalyzed by the presence of indium or gallium, which allow the aluminum-water

reaction to proceed even while producing aluminum hydroxide waste, which slows down the reaction in

its uncatalyzed form. Since the hydrogen is readily available with this system, it is equally necessary to

generate oxygen gas so the fuel cell can provide power to the AUV.

From general chemistry, it is knows that decomposition reactions of certain oxygen-rich salts

yields oxygen gas formation along with other byproducts1. To produce this essential gas, the oxygen

generation system utilizes sodium chlorate salt, which, catalyzed by the presence of cobalt (II,III) oxide

or iron powder and a steady heat source, the reaction produces sodium chloride and oxygen gas.

2𝑁𝑎𝐶𝑙𝑂3 (𝑠) → 2𝑁𝑎𝐶𝑙 (𝑠) + 3𝑂2(𝑔) (2)

b. Thermochemistry

Since the reaction only occurs at high temperatures, the system must provide heat to dissociate it

into oxygen gas and table salt. Since the reactant starts as a solid, we must elevate its temperature past

its (dissociation) temperature so that the desired byproducts are obtained. From thermodynamics, we

obtain that the heat for this reaction is given by�̇�, the heat transfer rate, which is equal to,

𝑄 ̇ = �̇� ∫ 𝑐𝑠 𝑑𝑇

𝑇 𝑚𝑒𝑙𝑡

𝑇 𝑙𝑜𝑤

+ �̇�𝐻𝑓𝑢𝑠𝑖𝑜𝑛 + �̇� ∫ 𝑐𝑙𝑑𝑇

𝑇 𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑒

𝑇 𝑚𝑒𝑙𝑡

(3)

where 𝑐𝑠 is the specific heat of solid sodium chlorate, 𝑐𝑙 is the specific heat of liquid sodium

chlorate, Tmelt is the melting temperature of sodium chlorate; Tlow is the ambient temperature, 𝐻𝑓𝑢𝑠𝑖𝑜𝑛 is

the specific enthalpy of fusion, Tdissociate is the dissociation temperature, and �̇� is the molar rate of

dissociation of sodium chlorate. By neglecting the heat transfer into the catalyzing chemical agent, the

heat transfer rate is the addition of enthalpy changes from the ambient to dissociation temperatures, plus

the enthalpy change resulting from the fusion phase change.

Figure 2: Sodium chlorate (powder) dissociates into sodium chlorate (table salt) and oxygen gas in the presence of heat and suitable catalyzer (cobalt oxide

or iron powder.) A thin film of sodium chlorate mixture forms at the top of a melting pool of the same reactant. When enough oxygen builds up, bubbles

burst and release oxygen.

4. POTENTIAL APPLICATIONS

Since this dissociation process is not complicated, this generator can be used for other purposes.

Two potential use of this oxygen generator could be for industrial and medical purposes. In the medical

industry, a steady supply of high-purity oxygen is needed for surgical and life-support situations. A

modular, safe oxygen generator could potentially meet these needs and save hospitals and individuals

money, provided that the system is practical and its usage cost is better than that of medical grade

oxygen cylinders.

On the other hand, the fabrication and manufacturing industry could also benefit from the use of

this oxygen generator. Most modern metal working and manufacturing processes use chemical agents

for oxidizing and protective purposes. Oxygen is used in the steelmaking industry to remove impurities

and strengthen the alloys, and also in the chemical industry, where it is used to produce various types of

polymers and synthetic compounds.

For these industries, a simple heating chamber reactor with a pressure relief intake valve could

store the sodium chlorate, where the salt would then be consumed and transformed into salt waste and

gaseous oxygen, which would be moved into a small pressure vessel. This device would allow for

instantaneous production of oxygen gas, which would be more practical and efficient than current

oxygen gas storage systems.

5. OVERALL SYSTEM DESIGN

The system is composed of a solid, sealed insulated steel tank, which houses the bead chain system.

The bead chain system is composed of mechanical components and sensors that regulate and control the

steady-state operation of the system.

The steel cylinder, which acts as a pressure vessel, houses the bead chain system. The bead chain

system is composed of stainless steel tubing, frame, and bead chain parts, along with chemically-

resistant polymer pulley components. The bead chain receives mechanical power transmission through a

pulley system, which is driven by an electric motor.

On the outside of the tank, a thermocouple is attached to a rope heater, which is attached to the outer

wall of the stainless steel tubing. When in operation, the bead chain draws the powder into the tubing

section, which is then heated, thus releasing oxygen gas and dumping waste salt inside the tank.

The system also employs temperature and pressure sensors, which are used to regulate the heating

rate and the oxygen production rate, respectively. These sensors are then relayed to a microcontroller,

which determines whether or not the heater should be on, depending on the pressure of the tank

(availability of oxygen gas.)

Figure 3: The image above shows the overall design of the system. The internal frame is housed inside the tank, while the heater and electronics are

wired through a connector on the flange of the tank. A check valve fitting is connected to a chemical resistant tubing section, which is used to guide the

oxygen flow.

6. PART DESIGN

a. TANK

The tank serves as both an external housing and pressure vessel. Since the oxygen gas production

rates are significantly low, pressurization is not an issue, and for that reason, the tank was made out of

stainless steel, which serves to counteract corrosion and preserve structural strength. The tank also has

tapped holes to connect to the internal frame.

The outer diameter of the flange was made large intentionally so that it could be mounted onto an

internal AUV rack, and the volume was also designed so it could house 60 lbs. of sodium chlorate,

which is the amount of salt required to produce enough oxygen for 200 W of power with the hydrogen

fuel cell for 5 days.

Figure 4: Image of oxygen generation tank. Dimensions were chosen to fit inside the hull of a REMUS 600 AUV (less than 12 in diameter.)

b. ELECTRONICS

Since the system depends on mechanical actuation for granular medium transport and heating power

for chemical decomposition, the system must use electronic components for safe operation. Besides the

heater and motor, the electronics system also employs an Arduino microcontroller, to keep the system

simple, as well as K-type thermocouples and thermocouple amplifiers, which control the operation of

the overall system. Both the heater and motor are regulated by individual MOSFETs, and to preserve the

integrity of the motor, a diode was installed to prevent any damage to its internal circuitry. A computer

running Arduino code monitors and controls the state of the system via an USB connection.

Figure 5: The electronics board is composed of a microcontroller, a relay, thermocouple converters, and MOSFETS. All components are wired to a power

supply and monitored by Arduino computer software.

c. HEATER

Because the chemical reaction is very slow at temperatures below 300 C, it was necessary to use a

heater that could provide the necessary power to reach the high temperatures needed for this reaction to

occur. A rope heater was the optimal choice, as it can fit a flexible geometry (tube curvature), and

deliver the insulated properties of fiberglass. For added insulation, the heater was covered with

aluminum Mylar tape, to reflect heat and insulate that part of the system, which could reach up to 450 C.

This rope heater configuration has some advantages and disadvantages over using a concentric

sleeve heater. While it is flexible and adjustable (up to its maximum length), the heater must be held in

place with insulation and tape. Additionally, the rope heater seems to have capabilities that exceed the

temperature range of this experiment (over 500 C), which can potentially damage the thermocouple

leads, and heat treat the delicate bent tubing section.

Although its shape retention is not optimal for this application, its flexibility and simple electrical

interface make this the most practical heater type. As far as circuit connections are concerned, the heater

is controlled by a regulated PWM (pulse width modulation) digital pin, which connects to a logic-level

MOSFET for steady-state operation.

Figure 6: The rope heater and Mylar tape provide insulation while delivering heat to dissociate the salt as it exits through the other side of the tubing section.

A thermocouple is used to measure and control the tubing wall temperature.

d. MOTOR

Since the generator needs to provide a stable flow rate of oxygen gas, it is necessary to provide a

steady flow of sodium chlorate powder to the tubing section. For this reason we used a DC gear motor

with high torque capability to overcome the high frictional drag force caused by the movement of salt on

the bead chain and surrounding tubing section.

The motor in this system is also controlled by the Arduino microcontroller. A logic-level FET was

also used to interface with the motor, while a PWM digital pin is used to control the output (driving

motor speed.) This is essential for this system, since the motor control will dictate how fast or slow the

motor should run depending on the oxygen level in the system. If the oxygen partial pressure in the

vehicle hull is lower than what it normally should be (around 21 percent by mass), the motor will

increase its speed so that the heater can dissociate more chlorate powder; conversely, if the partial

pressure of the oxygen gas is way higher than the safety threshold (above 30 percent by mass), the motor

will slow down and reduce the dissociation rate of sodium chlorate.

To prevent a potential electrical overload, a diode was linked to the motor MOSFET, as it could

damage the internal circuitry in case a motor stall occurred at any time during steady-state operation.

Additionally, the motor speed can be adjusted by the microcontroller software in real time, allowing one

to observe the behavior of the system with varying motor speeds.

e. SPROCKET DESIGN

Since the system uses a bead chain to transport salt, it was necessary to design a custom sprocket

that could support the torque and load requirements for the necessary gas flow rates. The system uses a

#10 size chain (nominal diameter of .1875 in), so the pockets had to be made with sharp, not round

edges, as the chain would jump if the pockets were oval, or hemispherical in shape. Since there were no

commercially available options, a custom sprocket had to be designed and fabricated. Due to its intricate

geometry and small tolerances, the part had to be divided into two different pieces which were

connected by set screws to form a sprocket assembly.

Figure 8: The sprocket assembly is held together by screws holding two mating parts.

Figure 7: The motor provides the chain with traction so it can drag salt into the heated tubing section.

f. INTERNAL FRAME

For the bead chain to function correctly, an internal frame mechanism must be built in order to

support all mechanical components, moving and stationary. Since stainless steel stock is very strong and

suitable for this application, it was used to build a frame that could support the motor, the pulley system

guiding the chain, and the tubing section.

Square tubing stock was chosen as the main frame component, due to its structural benefits (low

weight, high strength) and geometric simplicity. The frame was then welded with the endcap section to

reduce system complexity, and the dimensions of the tubing sections were chosen so that the frame

would have a reasonable clearance with the tank’s internal wall. Additionally, a motor mount was

attached to the frame in order to hold and resist any vibration from the motor, which could occur under

high mechanical loadings.

Figure 9: A photo of the entire bead chain travel path, showing the frame, the pulley system, the curved-tubing section, the endcap, and motor components.

An O-ring (not shown) seals between the cylindrical storage tank and the circular flange.

7. DESIGN CHALLENGES

a. BEAD CHAIN

To figure out which chain type worked best, two different steel alloys were chosen (austenitic

stainless and nickel-plated.) Experimentally, it was found that although the NPS (nickel-plated steel)

chain showed exceptional thermal cycling and chemical resistance, the austenitic stainless steel

possessed superior mechanical stress, and thus it was chosen as the better choice for this design. During

the initial testing of the bead chain system, it was observed that combined effect of a loaded chain and

heated environment caused the chain to stretch, thus making certain system parameters quite difficult to

design, especially the sprocket assembly and tubing section. To mitigate the situation, it was decided

that the system components (tubing section and sprocket) would be designed for the deformed chain,

rather than the unstretched chain. To obtain this information, a piece of undeformed chain was heat

treated and thereafter strained on an Instron machine, where the strain and force levels were recorded to

choose the appropriate design. It was shown that the elongated chain yielded (plastically deformed) at

approximately 20 % its original length, which modified the pocket spacing in the sprocket from the

original (0.19 in), to the deformed state (0.23 in.)

Figure 10: A heat-treated and stretched chain is used to evaluate different 3D-printed sprocket models in order to determine the proper spacing parameters.

Bead chains have a tendency to stretch (creep) over time, (especially at high temperatures (400 + C)).

b. HEATING TUBE

The tubing section posed another complex design problem. Since this section must be able to

conduct heat and also house the bead chain, it must have a simple geometry that can support fast heat

transfer and low-friction for improved salt transport. Original designs involved a U-shaped section with

sharp bends. After some testing, it was revealed that the friction created by the small bend radii loaded

the motor significantly, and it also caused massive frictional loss from salt particles clogging up the

bends. To counteract these problems, a semicircular tubing section with a single uniform bend radius

was built. It had the smooth wide curvature necessary to reduce drag, but it also had enough surface area

to be able to install a flexible rope heater. To connect this part to the tank, NPT threaded fittings were

attached to the tubing section. The tubing section has stretched, straight connecting ends in order to

attach the proper fittings, which interface with the tank’s endcap section.

Figure 11: The curvature of the tubing section reduces internal ball chain friction, while also providing a contour for the rope heating element. Internal

tubing tolerances were included in the design to mitigate the increase in ball chain diameter increase caused by thermal expansion and mechanical loading.

8. TESTING

a. INITIAL CLOSED-TANK EXPERIMENT

In order to determine the overall functionality and efficiency of the oxygen generator, a test had to

be performed. To generate some oxygen, the system was completely integrated (internal components),

and external components (heater, thermocouple) were attached and monitored by a computer. To

simulate an actual AUV endurance test, 0.5 lb. of sodium chlorate was introduced into the tank for the

reaction (an amount of salt needed to produce enough oxygen for 1 hr. at 200 W.) The heater was

controlled by a microcontroller and a relay, while the motor speed was controlled in real-time to show

which speed optimized oxygen flow rates.

During the experiment, a chemically-resistant tube fitting was used to guide the oxygen flow into a

water beaker, where bubble formations would confirm oxygen production. The depth of the tube end

was measured to calculate the approximate flow rate of oxygen out of the tank system. Since the tank

was sealed with a chemically-resistant elastomer O-Ring and due to slow oxygen production rate, it was

assumed that any gas leaks, if existent, were considerably negligible.

Figure 12: The experimental setup used for oxygen generation testing. The tank is slightly inclined to prevent the salt from attaching to the tank wall. Power

supplies individually control electronic components, while the water in the beaker demonstrates oxygen production by the formation of bubbles.

b. RESULTS

During the test, after the heater reached the minimum dissociation temperature (around 300 C),

the speed of the chain was reduced to concentrate the heat transfer (via conduction) to the wall

transported by the bead chain. After about 15 minutes, semi-sporadic bubbles of air were released from

the tank, which were bursting at a depth with an equivalent gauge pressure of 70 Pa (0.3 in below beaker

water level.) The test lasted an entire hour, and after that period, the heater and motor were turned off to

allow the system to cool to room temperature, after which it was be taken apart to be examined.

After the test was over, the contents of the tank were recovered and weighed. Initially, 0.5 lb. of

salt were introduced (226.8 g), but after scraping off the salt residue from inside the tank, tubing section,

and frame, only 189.9 g of salt residue (chlorate and table salt mix) were recovered, and weighed using a

digital scale. Using a stoichiometry calculation for comparison to the ideal case (100% yield rate), it was

found that for 0.5 lbs. of sodium chlorate, 102.8 g of oxygen gas must have been produced. Since the

pyrolysis reaction was not complete, the overall yield percentage for this test was about 35.9 %.

Figure 13: After the oxygen generation experiment, the system was taken apart to recover the remaining mass of reactant and waste product inside the tank.

Because of its hygroscopy, all of the sodium chlorate had to be scraped off and weighed immediately to prevent an erroneous mass measurement. Notice

how the salt starts “caking” in the presence of atmospheric air, largely due to humidity.

Because the tank was not full for this initial test (due to legal, cost, and safety constraints) the

tank had to be tilted so the chain could transport the salt, so the oxygen flow rates observed were lower

than expected. To compare oxygen mass loss in that salt, a 7.7 g residue sample of salt was placed on a

hot plate and heated to 400 C for 1 hour to remove all remaining oxygen from the sample. After this

calibration test was done, it was shown that the sample had lost 2.2 g of mass in the generator, which

when compared the ideal case, it should have lost 3.5 g. This gave that particular residue sample a 62.9

% yield rate, which has several implications. One of those implications is that the sample was not

entirely chlorate, which shows that it was only partly dissociated the first time it went through the tubing

section during the actual experiment. Additionally, it may suggest that the generator is capable of higher

efficiencies (yield rates), and is cause for further research.

Figure 14: During the test, oxygen bubbles exited from the outlet of the tubing section and into the beaker. Production of oxygen gas was intermittent: there

were periods of time when a semi-constant bursts happened, while at times no bubbles were produced, suggesting the presence of leaks and/or non-uniform

reactant delivery.

c. SECOND CLOSED-TANK EXPERIMENT

To develop a better understanding of the overall performance of the system, an additional sealed

tank test was performed. This time, it was decided that a bubble flow meter would be used; this device

would enable one to obtain a reliable, order-of-magnitude estimate for the oxygen gas production rate

generated by this system. In the previous experiments we experienced difficulties obtaining these

estimates due to the lack of a flow rate indicator; with this new device, it will be practical and reasonable

to gauge this very important system parameter.

A bubble flow meter can measure steady-state flow rates with a very simple, time-averaged

calculation. Since this generator system will work under constant heating rate and mass flow transfer

rate, it is practical to assume steady-state flow for oxygen gas production. The bubble flow meter is a

long, thin, graduated glass beaker with specific volume increments. With the use of a stopwatch and

careful reading of the instantaneous volume changes, the approximate volumetric flow rate of the system

(in cc’s/s) is given by �̇� , which is equivalent to

�̇� = Δ𝑉

Δ𝑡 , (4)

where ∆𝑉the differential change in volume, and Δt is the differential change in time. For the purposes of

this experiment, it should be assumed that the tank is perfectly sealed and thermally insulated from the

surrounding environment (there are leaks, but this would give a conservative estimate), and that the

surface tension effects of the soap-water solution are negligible in this particular flow rate range (tens of

cc’s per second.)To minimize the potential gas leaks from the tank, the O-Ring seal was replaced, and

the silicone grease was added to the flange-endcap interface. The test was run the same as before, with

the heater controlled by the microcontroller, while the motor performance was monitored and adjusted

in real-time with the same software.

d. RESULTS

From this experiment, it was possible to determine an adequate estimate of the oxygen

production rate. The test ran for about 45 minutes, of which it took about 15 minutes for the system to

reach the optimal dissociation temperature (above 300 C.) After this initial period, noticeable production

of oxygen gas was observed. Bubble volumes from 3 to 4 cc’s flowed out of the meter, over typical time

lengths in the range of 1 to 2 seconds, thus providing an average range flow rate of about 1.5 to 4

cc’s/second in this configuration (45 W heating power.) The semi-constant production of oxygen

suggests a cycling phenomenon, which can be accounted by the uneven transport of reactant into the

heated tubing section.

Figure 15: The image above shows the flow meter filled with a small volume of soap water mixture, which works as an indicator. The bubble layers are the

approximate volumes used for flow rate estimation, and together with the stopwatch readings, one can tabulate the time-averaged flow rates.

Concluded this test, it was necessary to inspect the contents of the tank in order to gauge the

yield of the reaction, and how well the reactant was successfully converted into oxygen gas. After

opening the tank, it was found that a substantial majority of the salt was left unreacted, which suggests

that the oxygen generation resulted only from partial decomposition of the sodium chlorate. From this

residual powder, many crystals of opaque white-grey powder were found, which is logical, as this

confirms the presence of sodium chloride (table salt), the other byproduct of this chemical reaction.

From these results, it is evident that there is a need for further investigation about the proper

decomposition of the salt, and for this reason, an exposed system test must be conducted.

Figure 16: The image above shows the overall composition of the partially reacted, residual chlorate-salt mix. Notice the abundance of opaque crystals,

which are composed of sodium chloride byproduct.

e. EXPOSED SYSTEM EXPERIMENT

Because of the uncertainty in oxygen production rates, it was crucial that an exposed system test

be conducted to see the effects of varying motor speeds on the flow rate. From stoichiometric and

thermodynamic calculations, at constant heating rates, the production rate is constant at the maximum

level of production. That is, an increase in motor speed will lead to an increase of oxygen gas production

up to the corresponding mass flow rate.

In the first test, the system configuration was kept the same as with the two previous

experiments, except that the system was exposed to the environment, as one would not be able to

observe the overall behavior of the salt decomposition. It was shown that under steady-state heating

input, an increase in motor speed decreased the amount of sodium chlorate dissociated by the system.

This claim contradicts the previous findings, as it was observed that faster reactant feed rates

demonstrated high oxygen gas flow rates. However, it must be said that the while the chemistry and

overall theory be the same, the system configuration may affect the way the salt is dissociated.

From a theoretical perspective, it may seem incorrect, but since the time scales in this system are

very important for the proper function of the system, it stands to reason that the salt may not completely

dissociate if it is not subjected to enough heating power for a prolonged period of time. Since a fast

motor speed reduces the effective heating period of any control volume of salt, and given that the mass

flow must be kept constant in order to keep up with system requirements, it is probable that the heating

power should be increased to accommodate for these findings. To test the validity of this hypothesis, a

second experiment was conducted (with two heaters), to see if an increase in heating rate greatly

changed the dissociation of the chlorate powder.

Figure 17: Image of exposed system with one heating element. Exposed internal elements give a better understanding of the mechanical effects on oxygen

gas production.

In this second experiment, the system was exposed to the environment, as in the previous case,

except that this time the system had twice the heating rate capability of the previous exposed and sealed

tests. The experiment was run for originally intended to run for an hour, but within 10 minutes of

running, it was shown that the increased heating capacity of the system greatly increased the dissociation

of the chlorate salt, evident in the way the salt residue was melted onto the surface of the chain’s

individual beads.

Figure 18: Image above shows the double heating element configuration for the system.

While not surprising, this result suggests that although the heating input may not have been high

enough to produce the desired results, it also suggests that the heater configuration is not optimal. A way

of determining this is by increasing the effective heating period, both by decreasing the motor speed,

which increases the effective mass transfer period, and by increasing the “equivalent” heated region.

This last consideration may be of great importance for this system given that the salt needs an extended

time scale in order to warm up, melt, and dissociate into its final products. Further analysis may be

necessary to obtain a better understanding of the phase transition effects on the overall heating

requirement. Calculations have been added in the appendix, but should be analyzed carefully to make

good design decisions.

Figure 19: The image above shows the effect of increased heating rates into the system. The brown residue on the beads is the result of sufficient heating,

which proves that the system needs an improved heating mechanism. Notice the coloration change on the beads themselves, as they are now heat treated.

f. THIRD CLOSED-TANK EXPERIMENT

To test the overall effect of the increased heating power, another closed-tank experiment was

conducted. This time, the system configuration was changed so as to reflect the changes to the most

recent iteration of the system: two heating elements (running at 24 V and 45 W each, for an equivalent

heater at 24 V and 90 W (parallel)), two thermocouples (to monitor each of the heaters), and the same

microcontroller and software interface.

The tank was tilted downwards so that the chain can pull chlorate powder into the tubing intake

section, given that there is not enough powder (about 60 lbs.) to fill up the entire system reactant

volume.

Figure 20: Final iteration of the system. Two heaters cover a larger section of the tubing section, while two thermocouples monitor and control the

performance of such heaters. Beaker in the foreground is used to confirm the production of oxygen gas.

After the system is completely wired and properly reconfigured, the computer program is run

and allowed to take the system to normal operating conditions. In less than 5 minutes, the system

reached the dissociation temperature range, and soon thereafter, the plastic tubing connector started

releasing lots of oxygen gas bubbles at a semi-constant, cycling rhythm.

The increase in motor speed via microcontroller modulation resulted in a higher oxygen

production rate, which is in accordance with the original hypothesis, as the heating power delivered by

this system is capable of dissociating more chlorate reactant than was previously anticipated to

decompose into oxygen gas product. The consistent thermal cycling effect on the chain did not result in

any particular changes, while the increased heating output greatly improved the conversion efficiency of

the chlorate powder into oxygen gas.

Figure 21: Image above shows the production of oxygen gas bubbles released through the generator’s plastic tubing duct. Soap-water was used as a flow

indicator in this experiment.

9. POTENTIAL AREAS FOR IMPROVEMENT

Although the results of these tests have been generally favorable, there are still some aspects of

the design that can be modified to accommodate and meet the requirements of such system. Given the

complicated coupling of chemical dissociation, heat transfer, and mechanical motion, alternative

systems should be designed to provide a practical solution for this need (oxygen generation.)

The tubing section could be altered, which could facilitate the placement of a fixed heater, and

the chain design could also be modified to reduce wall friction and strain. To maximize the actual heat

transfer rate into the salt (and minimize parasitic heat transfer), it would be necessary to maximize the

heating area and reduce the thermal resistance of the heated section. Proper use of reflective Mylar tape

and fiberglass insulation can aid in trapping valuable heat so that it can be directed towards the chlorate

powder and away from the system environment.

As far as materials are concerned, the chain could be replaced with a titanium or titanium-

aluminide chain, which have strong chemical resistance and increased structural strength. At the same

time, an anticaking powder could be intermixed with the sodium chlorate to prevent hygroscopic effects

and reverse flow of the salt out of the pyrolysis region as it melts in the tubing, thus preventing the

dissociation reaction.

A potential viable solution could be the coupling of a bead chain system, which functions as a

dispenser, and a funnel nozzle, which allows a rate-limiting flow of powder into a small heated chamber,

which allows for a steady-state production of gas. This system has potential since it reduces the coupling

between the chemical reaction and the flow of powder. It is important to consider that it is gravity

dependent, so it must be properly designed to accommodate for the type of environment in which it

functions. In the case that the system is still driven by a bead chain, it is recommended that the tubing

section be aligned off the longitudinal axis of the system, so that the salt can be pulled into the duct

entrance by both the mechanical motion of the motor and the effect of gravity.

10. CONCLUSION

Although somewhat impractical, the oxygen generator demonstrates promising results that call for

further investigation. Even in this state, it was shown that the generator could produce oxygen, function

properly, and maintain temperature and pressure requirements that allowed to prove its safety and

reliability.

With proper redesign and optimization of mechanical components, this machine can become a

suitable solution for chemical oxygen generators that demand controllable flow rates for life-support and

power generation applications.

11. ACKNOWLEDGEMENTS

I would like to thank Douglas Hart and Andrew Siegel for technical advice, Joe Edwards and Oscar

Salgado for electronics and software support, and David Allaby and John Vivilecchia for machining and

design work.

12. REFERENCES

1. Indiana University, Standard Thermodynamic Properties of Chemical Substances. Online.

2. Crane, Jackson et al, A system for producing oxygen using sodium chlorate dissociation. August 10 2013.

3. Khriplovich, L.M., Kholopov, E.V, Heat capacity and thermodynamic properties of cobalt(II,III) oxide from 5 to

307 K Low-temperature transition. December 1 1980.

4. Gilliland, Alexis and Wagman, Donald. Heat of Decomposition of Sodium and Potassium Chlorate. September 29

1964.

5. Fransson A, and Ross, R.G. Thermal Conductivity, heat capacity and phase stability of solid sodium chlorate

(NaClO3) under pressure. October 28 1982.

6. McKetta, John J. Jr. Encyclopedia of Chemical Processing and Design. Volume 51 –Slurry Systems:

Instrumentation to Solid-Liquid Separation. March 13 1995.

13. APPENDIX A (Stoichiometric and Thermodynamic Calculations)

Assumption: (200 W for 5 days) – @ 2.6 L/minute of hydrogen gas (H2)

Total volume of hydrogen gas for 5 days

2.6 L 1440 minutes 5 days = 18720 L of H2

1 minute 1 day 1 mission 1 mission

Now, find out the total mass of hydrogen gas required for this mission

𝑴𝒉𝒚𝒅𝒓𝒐𝒈𝒆𝒏 = 𝝆𝒉𝒚𝒅𝒓𝒐𝒈𝒆𝒏 ∗ 𝑽𝒉𝒚𝒅𝒓𝒐𝒈𝒆𝒏

= (0.00009 𝒌𝒈

𝑳 )*( 18720 L) = 1.685 kg of H2 gas

Now, compute the oxygen gas requirement ( O2) based on the combustion of

hydrogen gas

𝟐 𝑯𝟐 + 𝑶𝟐𝒚𝒊𝒆𝒍𝒅𝒔→ 𝟐𝑯𝟐𝑶

1.685 kg H2 1 mol H2 1 mol O2 32 g

Assumption 2.016 g 2 mol H2 1 mol O2

= 13.375 kg of O2 gas

From this, compute the sodium chlorate ( NaClO3) mass requirement for this system.

𝟐𝑵𝒂𝑪𝒍𝑶𝟑𝒚𝒊𝒆𝒍𝒅𝒔→ 𝟐 𝑵𝒂𝑪𝒍 + 𝟑 𝑶𝟐

13.375 kg O2 1 mol O2 2 mol NaClO3 106.44 g

32 g 3 mol O2 1 mol NaClO3

= 29.650 kg of NaClO3 powder.

Now, calculate volume of reactant to set a minimum reactant volume.

𝑽𝒑𝒐𝒘𝒅𝒆𝒓 = 𝑴𝒑𝒐𝒘𝒅𝒆𝒓

𝝆𝒑𝒐𝒘𝒅𝒆𝒓

= 11.9 L.

Thermodynamic Calculations (Heat Transfer Rate Requirement)

Thermodynamic properties of Sodium Chlorate (NaClO3)

∆𝑯𝒇𝒖𝒔𝒊𝒐𝒏 = 𝟐𝟏. 𝟑 𝒌𝑱

𝒎𝒐𝒍 (Latent enthalpy of fusion, forward reaction)

𝑪𝒔𝒐𝒍𝒊𝒅 = (𝟑𝟗. 𝟔𝟑 + 𝟎. 𝟏𝟗𝟔𝑻)𝑱

𝒎𝒐𝒍∗𝑲 (Specific heat capacity, solid state)

𝑪𝒍𝒊𝒒𝒖𝒊𝒅 = 𝟏𝟑𝟐. 𝟗𝟐 𝑱

𝒎𝒐𝒍∗𝑲 (Specific heat capacity, liquid state)

�̇�𝒑𝒐𝒘𝒅𝒆𝒓 = 𝑴𝒑𝒐𝒘𝒅𝒆𝒓

𝒎𝒑𝒐𝒘𝒅𝒆𝒓∗𝑻𝒎𝒊𝒔𝒔𝒊𝒐𝒏 =

𝟐𝟗𝟔𝟓𝟎 𝒈

𝟏𝟎𝟔.𝟒𝟒 𝒈

𝒎𝒐𝒍∗𝟒𝟑𝟐𝟎𝟎𝟎 𝒔

= 0.0000645 𝒎𝒐𝒍

𝒔 (Molar flow

rate of the powder)

Now apply 1st Law of Thermodynamics to obtain total heat transfer rate

𝒅𝑼

𝒅𝒕= �̇� − �̇� + �̇�𝒑𝒐𝒘𝒅𝒆𝒓(𝒉 +

𝒗𝟐

𝟐+ 𝒈𝒛)𝒇𝒊𝒏𝒂𝒍 − �̇�𝒑𝒐𝒘𝒅𝒆𝒓(𝒉 +

𝒗𝟐

𝟐+ 𝒈𝒛)𝒊𝒏𝒊𝒕𝒊𝒂𝒍

-Steady state, isochoric, and neglecting kinetic and gravitational potential

changes, equation becomes

𝑸 ̇ = �̇� ∫ 𝒄𝒔𝒐𝒍𝒊𝒅 𝒅𝑻

𝑻 𝒎𝒆𝒍𝒕

𝑻 𝒍𝒐𝒘

+ �̇�𝑯𝒇𝒖𝒔𝒊𝒐𝒏 + �̇� ∫ 𝒄𝒍𝒊𝒒𝒖𝒊𝒅𝒅𝑻

𝑻 𝒅𝒊𝒔𝒔𝒐𝒄𝒊𝒂𝒕𝒆

𝑻 𝒎𝒆𝒍𝒕

Where 𝑻𝒎𝒆𝒍𝒕 = 𝟓𝟑𝟑. 𝟏𝟓 𝑲, and 𝑻𝒅𝒊𝒔𝒔𝒐𝒄𝒊𝒂𝒕𝒆 = 𝟓𝟕𝟑. 𝟏𝟓 𝑲

Therefore,

�̇� = 𝟑𝟕. 𝟎𝟖 𝑾

This is the minimal heat transfer rate required to dissociate the salt, and

for a safety margin, the total heat transfer rate was increase by 20 % so as it

to bring the total to 45 W.

14. APPENDIX B ( HEAT TRANSFER MODEL AND CALCULATIONS)

System Model – Resistance Network

Fundamentals

�̇� = 𝜟𝑻

𝑹𝒕𝒐𝒕𝒂𝒍 �̇�𝒄𝒐𝒏𝒅𝒖𝒄𝒕𝒊𝒐𝒏 = 𝒌𝒔𝑨𝒔(𝑻𝒉𝒊𝒈𝒉 − 𝑻𝒍𝒐𝒘) �̇�𝒄𝒐𝒏𝒗𝒆𝒄𝒕𝒊𝒐𝒏 = 𝒉𝒄𝑨𝒔 (𝑻𝒉𝒊𝒈𝒉 − 𝑻𝒍𝒐𝒘)

𝑹𝒔𝒆𝒓𝒊𝒆𝒔 = 𝜮𝑹𝒊 𝟏

𝑹𝒑𝒂𝒓𝒂𝒍𝒍𝒆𝒍= 𝜮(

𝟏

𝑹𝒊)

𝑹𝒕𝒖𝒃𝒆 = 𝒍𝒏𝑹𝒐𝒖𝒕𝒆𝒓𝑹𝒊𝒏𝒏𝒆𝒓

𝟐𝝅𝒌𝒔𝑳𝒔 𝑹𝒔𝒑𝒉𝒆𝒓𝒆 =

𝟏

𝟒𝝅𝒌𝒔(

𝟏

𝑹𝒊𝒏𝒏𝒆𝒓−

𝟏

𝑹𝒐𝒖𝒕𝒆𝒓) 𝑹𝒄𝒐𝒏𝒗𝒆𝒄𝒕𝒊𝒐𝒏 =

𝟏

𝒉𝒄𝑨𝒔

-Assuming steady-state operation, and neglecting radiation heat transfer

𝒌𝒔𝒕𝒆𝒆𝒍 = 𝟏𝟖 𝑾

𝒎∗𝑲 𝑳𝒉𝒆𝒂𝒕𝒆𝒓 = 𝟎. 𝟎𝟓 𝒎 𝑫𝒃𝒆𝒂𝒅 = 𝟎. 𝟎𝟎𝟒𝟓 𝒎 𝑻𝒍𝒐𝒘 = 𝟓𝟕𝟑. 𝟏𝟓 𝑲

𝒉𝒄 = 𝜱( 𝑷𝒓, 𝑵𝒖, 𝑹𝒆𝑫)

Therefore, 𝑹𝒕𝒐𝒕𝒂𝒍 = 𝑹𝒕𝒖𝒃𝒆 + (𝑹𝒃𝒆𝒂𝒅∗𝑹𝒄𝒐𝒏𝒗𝒆𝒄𝒕𝒊𝒐𝒏

𝑹𝒃𝒆𝒂𝒅+𝑹𝒄𝒐𝒏𝒗𝒆𝒄𝒕𝒊𝒐𝒏)

Hence, 𝑻𝒉𝒊𝒈𝒉 = 𝑻𝒍𝒐𝒘 + (�̇� ∗ (𝑹𝒕𝒖𝒃𝒆 + (𝑹𝒃𝒆𝒂𝒅∗𝑹𝒄𝒐𝒏𝒗𝒆𝒄𝒕𝒊𝒐𝒏𝑹𝒃𝒆𝒂𝒅+𝑹𝒄𝒐𝒏𝒗𝒆𝒄𝒕𝒊𝒐𝒏

)))

This should be the minimum heater temperature (which will allow for steady-state operation

even when accounting for parasitic heat transfer losses.)

𝑻𝒉𝒊𝒈𝒉 𝑻𝒍𝒐𝒘 𝑹𝒕𝒖𝒃𝒊𝒏𝒈

𝑹𝒃𝒆𝒂𝒅

𝑹𝒄𝒉𝒍𝒐𝒓𝒂𝒕𝒆,𝒄𝒐𝒏𝒗𝒆𝒄𝒕𝒊𝒐𝒏

15. APPENDIX C (MATLAB AND ARDUINO MICROCONTROLLER CODE)

MATLAB CODE

ChemicalHeatTransferReq

syms c_naclos c_naclol T

n_dot= 0.000645;

%moles per second dissociated of sodium chlorate (17.8 kg over 5 days)

c_naclos=39.63 + 0.196*T;

%specific heat of solid sodium chlorate in joules per mol*K

c_naclol=132.92;

%specific heat of liquid sodium chlorate in joules per mol*K

H_slatentfusion= 21300;

%specific latent heat of fusion of sodium chlorate (in joules per mol)

H_ssolid= int(c_naclos,T,273,533);

% specific enthalpy change in solid phase of sodium chlorate (in joules per

% mol)

H_sliquid= int(c_naclol,T,533,573);

% specific enthalpy change in liquid phase of sodium chlorate (in joules

% per mol)

Q_dot= (n_dot)*(H_ssolid)+(n_dot)*(H_slatentfusion)+(n_dot)*(H_sliquid)

% heat required to dissociate sodium chlorate at a rate of 0.000387 mol/s,

% and elevate its temperature to 300 C.

n_reactant= 0.000287:0.00001:0.000700;

Q= (n_reactant)*(H_ssolid)+(n_reactant)*(H_slatentfusion)+(n_reactant)*(H_sliquid);

figure

plot(n_reactant,Q,'-.b')

xlabel('Molar Rate of Dissociation (mol/s)','FontSize',12,'FontWeight','bold','Color','g')

ylabel('Heating Rate (Watts)','FontSize',12,'FontWeight','bold','Color','r')

AxialTemperatureProfileTube

T_inf= 278.15;

% ambient temperature (assume 5 C inside vehicle)

T_max= 573.15;

% heater temperature (300 C)

T_dif= T_max-T_inf;

% maximum temperature difference

h= 125;

% convective heat transfer coefficient (for NaClO3)(in W/m^2*K)

k= 18;

% thermal conductivity of steel tubing (in W/m*K)

A_c = 0.0000292;

% cross-sectional area of steel tubing

P= 0.0192;

% wetted perimenter of steel tubing

m= sqrt((h*P)/(k*A_c));

% fin parameter (units of m^-1)

x_d= 0:0.0005:0.15;

% range of x values as distance from heater

a= h/m*k;

% ratio of convective heat transfer to fin parameter-conduction product

L= .15;

% length of tube (6 in)

r= (T_inf)/(T_max-T_inf);

T_localconvective= (T_inf)+ (T_dif)*(cosh(m*L-m*x_d)+a*sinh(m*L-m*x_d))/(cosh(m*L)+a*sinh(m*L));

figure

plot(x_d,T_localconvective,'*b')

xlabel('Distance from heater (in m)','FontSize',12,'FontWeight','bold','Color','b')

ylabel(' Local temperature at x (in K)','FontSize',12,'FontWeight','bold','Color','k')

% convective heat transfer model

T_localadiabatictip= (T_inf)+ (T_dif)*(cosh(m*L-m*x_d))/(cosh(m*L));

figure

plot(x_d,T_localadiabatictip,'*b')

xlabel('Distance from heater (in m)','FontSize',12,'FontWeight','bold','Color','b')

ylabel(' Local temperature at x (in K)','FontSize',12,'FontWeight','bold','Color','k')

% adiabatic tip model

T_prescribed= (T_inf)+ (T_dif)*(r*sinh(m*x_d)+sinh(m*L-m*x_d))/(sinh(m*L));

figure

plot(x_d,T_prescribed,'*b')

xlabel('Distance from heater (in m)','FontSize',12,'FontWeight','bold','Color','b')

ylabel('Local temperature at x (in K)','FontSize',12,'FontWeight','bold','Color','k')

% prescribed temperature model (not good)-hyperbolic profile

T_infinitefin=(T_inf)+(T_dif)*(exp(-m*x_d));

figure

plot(x_d,T_infinitefin,'*b')

xlabel('Distance from heater (in m)','FontSize',12,'FontWeight','bold','Color','b')

ylabel('Local temperature at x (in K)','FontSize',12,'FontWeight','bold','Color','k')

% Infinite fin model

CombinedHeatTransferModel

%Parameters

Q_dot= 37;

% ideal heat transfer rate required to carry out dissociation reaction at

% 100 yield rate (reaction efficiency)

T_in= 573;

% prescribed temperature at which sodium chlorate reaction is spontaneous

k_steel= 18;

% thermal conductivity of stainless steel (in W/m*K)

L_heater= 0.0508;

% length of system heater (2 inches long)

d_to= 0.008;

% outer tube diameter (in m)

d_ti= 0.0061;

% inner tube diameter (in m)

delta= 0.0059;

% spacing between beads (measured from the center of one bead to that of

% another) (in m)

r_bo= 0.0046;

% outer bead diameter (in m)

r_bi= 0.0030;

% inner bead diameter (in m)

R_ct= ((log(d_to/d_ti))/(2*pi*k_steel*L_heater));

% resistance due to conduction in tube (in W/m*K)

R_cb= ((1)/(4*pi*k_steel))*((1/r_bi)-(1/r_bo));

% resistance due to conduction in bead, modeled as a sphere (in W/m*K)

rho_naclo= 2500;

% density of sodium chlorate (in kg/m^3)

v_chain= 0.001;

% speed of bead chain (in m/s)

mu_naclo=0.00153;

% viscosity of sodium chlorate(in Pa*s)

Re_d= ((rho_naclo)*(v_chain)*(d_ti))/(mu_naclo);

% Reynolds number for liquid sodium chlorate flow (dimensionless)

c_naclo= 133;

% specific heat of sodium chlorate (in J/kg*K)

k_naclo= 0.531;

% thermal conductivity of sodium chlorate (in W/m*K)

Pr= (mu_naclo*c_naclo)/(k_naclo);

% Prandtl number for sodium chlorate (ratio of momentum diffusivity to

% thermal diffusivity)

Nu_d= (3.66)+(0.065*d_ti*Re_d*Pr/L_heater)/(1+ 0.04*([d_ti*Re_d*Pr/L_heater]^(2/3)));

% Nusselt number for sodium chlorate (ratio of wall temperature gradient to

% bulk temperature gradient

h= Nu_d*(k_naclo/d_ti);

% effective convection heat transfer coefficient based on correlation

% (W/m^2*K)

R_conv= 1/(h*pi*L_heater*d_ti);

% resistance due to convection (in K/W)

R_total= R_ct+((8*R_cb*R_conv)/(8*R_cb+R_conv));

% overall equivalent resistance of all heat transfer modes (in K/W)

T_out= T_in-Q_dot*R_total;

% in this case the temperature T_out is 530 K, which is the melting

% temperature of NaCl03

R_equiv= 0.50:0.1:10;

T_outside= T_in-Q_dot*R_equiv;

figure

plot(R_equiv,T_outside,'*g')

xlabel('Effective Thermal Resistance (K/W)','FontSize',12,'FontWeight','bold','Color','b')

ylabel('External Temperature (K)','FontSize',12,'FontWeight','bold','Color','k')

ConductionStainlessSteelTube syms L_heater T_ext

k = 18;

% thermal conductivity of stainless steel (in W/m*K) averaged at 473 K

L= 0.0508;

% length of tube (surface length over which heater conducts energy into

% system)

r_out= 0.008;

% outer tube radius (in meters)

r_in= 0.0061;

% inner tube radius (in meters)

T_in= 573;

% prescribed internal temperature (300 C), at which reaction is continuous

% and spontaneous

Q_dot= 22.24;

% heat transfer rate into system required for oxygen production equivalent

% to 120 W of fuel cell power ( in Watts)

T_out= T_in - ((Q_dot)*(log(r_out/r_in))/(2*pi*k*L));

%external temperature required for the heating element in order to produce

%the oxygen at the rate given ( in K)

%T_out in this case is 571.95 K

L_heater= 0.0254:0.001:0.1016;

T_ext= T_in - ((Q_dot)*(log(r_out/r_in))/(2*pi*k*L));

figure

plot(L_heater,T_ext,'*b')

xlabel('Effective Heating Length (m)','FontSize',12,'FontWeight','bold','Color','b')

ylabel('External Temperature (K)','FontSize',12,'FontWeight','bold','Color','k')

TemperatureDifferenceVsThermalResistance %Parameters

Q_dot= 37;

% non-ideal heat transfer rate required to carry out dissociation reaction at

% 90 yield rate (reaction efficiency)

T_in= 573;

% prescribed temperature at which sodium chlorate reaction is spontaneous

k_steel= 18;

% thermal conductivity of stainless steel (in W/m*K)

L_heater= 0.0508;

% length of system heater (2 inches long)

d_to= 0.008;

% outer tube diameter (in m)

d_ti= 0.0061;

% inner tube diameter (in m)

delta= 0.0059;

% spacing between beads (measured from the center of one bead to that of

% another) (in m)

r_bo= 0.0046;

% outer bead diameter (in m)

r_bi= 0.0030;

% inner bead diameter (in m)

R_ct= ((log(d_to/d_ti))/(2*pi*k_steel*L_heater));

% resistance due to conduction in tube (in W/m*K)

R_cb= ((1)/(4*pi*k_steel))*((1/r_bi)-(1/r_bo));

% resistance due to conduction in bead, modeled as a sphere (in W/m*K)

rho_naclo= 2500;

% density of sodium chlorate (in kg/m^3)

v_chain= 0.001;

% speed of bead chain (in m/s)

mu_naclo=0.00153;

% viscosity of sodium chlorate(in Pa*s)

Re_d= ((rho_naclo)*(v_chain)*(d_ti))/(mu_naclo);

% Reynolds number for liquid sodium chlorate flow (dimensionless)

c_naclo= 133;

% specific heat of sodium chlorate (in J/kg*K)

k_naclo= 0.531;

% thermal conductivity of sodium chlorate (in W/m*K)

Pr= (mu_naclo*c_naclo)/(k_naclo);

% Prandtl number for sodium chlorate (ratio of momentum diffusivity to

% thermal diffusivity)

Nu_d= (3.66)+(0.065*d_ti*Re_d*Pr/L_heater)/(1+ 0.04*([d_ti*Re_d*Pr/L_heater]^(2/3)));

% Nusselt number for sodium chlorate (ratio of wall temperature gradient to

% bulk temperature gradient

h= Nu_d*(k_naclo/d_ti);

% effective convection heat transfer coefficient based on correlation

% (W/m^2*K)

R_conv= 1/(h*pi*L_heater*d_ti);

% resistance due to convection (in K/W)

R_total= R_ct+((8*R_cb*R_conv)/(8*R_cb+R_conv));

% overall equivalent resistance of all heat transfer modes (in K/W)

T_out= T_in-Q_dot*R_total;

% in this case the temperature T_out is 530 K, which is the melting

% temperature of NaCl03

R_equiv= 0.50:0.1:10;

% variable that represents the equivalent thermal resistance (range)

T_diff= Q_dot*R_equiv

% temperature differnce given the fixed heat transfer rate and variable

% thermal resistance

figure

plot(R_equiv,T_diff,'*r')

xlabel('Equivalent Thermal Resistance (K/W)','FontSize',12,'FontWeight','bold','Color','b')

ylabel(' Temperature Difference (K)','FontSize',12,'FontWeight','bold','Color','k')

Arduino Microcontroller Combined Code (2 Heaters + 2 Thermocouples + 1 Motor)

This is an example for the Adafruit Thermocouple Sensor w/MAX31855K

Designed specifically to work with the Adafruit Thermocouple Sensor

----> https://www.adafruit.com/products/269

These displays use SPI to communicate, 3 pins are required to

interface

Adafruit invests time and resources providing this open source code,

please support Adafruit and open-source hardware by purchasing

products from Adafruit!

Written by Limor Fried/Ladyada for Adafruit Industries.

BSD license, all text above must be included in any redistribution

****************************************************/

#include <SPI.h>

#include <Adafruit_MAX31855.h>

#include <OneWire.h> //for thermocouple (needed for DallasTemperature)

#include <DallasTemperature.h> //for thermocouple

#include <PID_v1.h> //for heater control

// Default connection is using software SPI, but comment and uncomment one of

// the two examples below to switch between software SPI and hardware SPI:

// Example creating a thermocouple instance with software SPI on any three

// digital IO pins.

#define DO 10

#define CS 9

#define CLK 8

//This is the heater relay pin

#define HEATER_MOSFET_G 6 //connected to MOSFET G

//This is the motor relay pin

#define MOTOR_MOSFET_G 5 //connected to MOSFET G

// Data wire is plugged into port 2 on the Arduino

#define ONE_WIRE_BUS 2

#define TEMPERATURE_PRECISION 9

Adafruit_MAX31855 thermocouple(CLK, CS, DO);

OneWire oneWire(ONE_WIRE_BUS);

// Pass our oneWire reference to Dallas Temperature.

DallasTemperature thermocouples(&oneWire);

DeviceAddress thermo1;

double tempC; //thermocouple reading

double Input, Output;

int motor_speed = 60;

double Setpoint = 420.0; //PID heater Setpoint-- temp Celsius

PID myPID(&Input, &Output, &Setpoint, 10, 10, 1, DIRECT);

// Example creating a thermocouple instance with hardware SPI (Uno/Mega only)

// on a given CS pin.

//#define CS 10

//Adafruit_MAX31855 thermocouple(CS);

void setup() {

pinMode(MOTOR_MOSFET_G, OUTPUT);

Serial.begin(9600);

Serial.println("Double Thermocouple Test");

// wait for MAX chip to stabilize

setupThermocouples();

runMotor();

// setupStepper(); //turns stepper on

setupPID();

delay(500);

}

void loop() {

// basic readout test, just print the current temp

// Serial.print("MAX31855 Internal Temp = ");

// Serial.println(thermocouple.readInternal());

Serial.println("MAX31855");

double c = thermocouple.readCelsius();

if (isnan(c)) {

Serial.println("Something wrong with thermocouple!");

} else {

Serial.print("C = ");

Serial.println(c);

}

//Serial.print("F = ");

//Serial.println(thermocouple.readFarenheit());

delay(500);

Serial.println("MAX31850:");

oxygenSystem();

delay(5000);

}

void setupThermocouples()

{

thermocouples.begin();

// locate devices on the bus

Serial.print("Locating devices...");

Serial.print("Found ");

Serial.print(thermocouples.getDeviceCount(), DEC);

Serial.println(" devices.");

if (!thermocouples.getAddress(thermo1, 0)) Serial.println("Unable to find address for Device 1");

// set the resolution to 9 bit

thermocouples.setResolution(thermo1, TEMPERATURE_PRECISION);

//call thermocouples.requestTemperatures() to issue a global temperature

//thermocouples.requestTemperatures();

}

void runMotor() {

analogWrite(MOTOR_MOSFET_G, motor_speed);

}

void setupPID()

{

tempC = thermocouples.getTempC(thermo1);

Input = tempC;

//turn the PID on

myPID.SetMode(AUTOMATIC);

}void oxygenSystem ()

//rope heater, LuminOx oxygen sensor, stepper motor/driver

{ thermocouples.requestTemperatures();

delay(15);

tempC = thermocouples.getTempC(thermo1);

Input = tempC;

Serial.print ("Heater temp (C): ");

Serial.println (Input);

myPID.Compute();

Serial.print ("PID Output: ");

Serial.println (Output);

analogWrite(HEATER_MOSFET_G, Output);

}

16. APPENDIX D (ENGINEERING AND TECHNICAL DRAWINGS)

Tank Diagram

Sprocket Diagram (1-piece)

HEATED TUBING SECTION DIAGRAM

INTERNAL FRAME DIAGRAM

ENDCAP DIAGRAM

PULLEY SLIDING PART

Sprocket Diagram ( 2-piece, big half)

Sprocket Diagram (2-piece, small half)

17. APPENDIX E (HELPFUL RESOURCES) – all are publicly available

Preliminary Research – experiments from before this project started

https://drive.google.com/folderview?id=0B-

AtJPDDxvZpfi1uXzlyNmpwM0xJTTZSRmFnQVphTFIxU0JhaDZhUmR2NnJOM0VsNU

UzTTA&usp=drive_web

System CAD –old system and new system parts

https://drive.google.com/folderview?id=0B-

AtJPDDxvZpR21XMndodjdfV0E&usp=drive_web

Oxygen Test- 10/28/2014 (first test)

https://drive.google.com/folderview?id=0B-

AtJPDDxvZpdV9fQWxzTnNjQXc&usp=drive_web

Oxygen Test- 01/20/2015 (second test, bubble flow meter)

https://drive.google.com/folderview?id=0B-

AtJPDDxvZpcHFJSTlqS2UzQTQ&usp=drive_web

Open Air Test (1 heater)

https://drive.google.com/folderview?id=0B-AtJPDDxvZpcnR4YlN5cVl3dkk&usp=drive_web

Double Heater Open Air Test 02/17/2015

https://drive.google.com/folderview?id=0B-

AtJPDDxvZpN0hNQnNmUGpqTTA&usp=drive_web

Oxygen Test- 03/14/2015 (third test, best results)-final iteration

https://drive.google.com/folderview?id=0B-

AtJPDDxvZpfnY3YXdIelJRRXRnSGMyQldTU1hMSlpBdUV3UHg5UnJpYVhQVmFYN

jJ2STA&usp=drive_web

Oxygen Test – 03/24/2015 (fourth test, repeat) –clean

https://drive.google.com/open?id=0BzNRdcziHs1Ofkk5YVNQSEZEd3NRTUFwWFE1Qjdz

bFRRUGhQREtrWkdzdUppR1ZsSG45YkE&authuser=0