49th International Conference on Environmental Systems ICES-2019-394 7-11 July 2019, Boston, Massachusetts

Development and Characterization of a LiOH Air Regeneration Model in Thermal Desktop®

Cheyn L. Worn1 Aerodyne Industries, Houston, TX, 77058

John F. Keener.2 Jacobs Engineering, Houston, TX, 77058

Orion post landing activities use a (LiOH)-based scrubber for removal and so a robust Thermal Desktop® model for these activities requires a LiOH reaction computational algorithm. The chemical sequesters CO2 from air through a series of exothermic and endothermic reactions that consume and produce water vapor. NASA and its contractors developed a chemical kinetics based LiOH/CO2/H2O reaction modeling subroutine in the 1970’s and 1980’s. This work details adapting that LiOH code for a Thermal Desktop® model in preparation for Orion post-landing simulations.

Nomenclature Units s = second min = minute hr = hour

°C = degrees Celsius K = Kelvin J = Joule mol = mole cm = centimeter m = meter m3 = meters cubed g = gram kg = kilogram cm/s = centimeters per second 3 m /hr = cubic meters per hour kg/hr = kilograms per hour Pa = Pascal

°F = degrees Fahrenheit °R = degrees Rankine BTU = British Thermal Unit lbmol = pound-mole in = inch ft = feet lbm = pound mass cfm = cubic feet per minute pph = pound mass per hour psi = pounds per square inch

1 Thermal Analysis Engineer, 2224 Bay Area Blvd./JE-5EA. 2 Thermal and Environmental Engineer, 2224 Bay Area Blvd./JE-5EA.

*Trade names and trademarks are used in this report for identification only. Their usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration.

Symbols G = correlation factor H = volumetric molar concentration h = forced convective heat transfer coefficient m = mass ṁ = mass flow rate M = species molecular weight Q = heating rate R = reaction rate RGas = gas constant T = temperature u = natural convective heat transfer coefficient V̇ = volumetric flow rate V0 = gas velocity X = molar ratio Xk = rate constant ∆t = time step η = reaction efficiency ρ = density

Acronyms and Chemical Species NASA = National Aeronatics and Space Administration JSC = Lyndon B. Johnson Space Center ECLSS = Environment Control and Life Support System CAMRAS = Carbon dioxide And Moisture Removal Amino Swing bed LiOH = lithium hydroxide chemical species and technology LiOH.H2O(s) = solid, lithium hydroxide monohydrate chemical species Li2CO3 = chemical species CO2 = carbon dioxide gas H2O(g) = water vapor

Subscripts 1 = property pertaining to the reaction of lithium hydroxide and water vapor 2 = property pertaining to the reaction of lithium hydroxide hydrate and carbon dioxide 3 = property pertaining to the reaction of lithium hydroxide and carbon dioxide Bed = cartridge bed Cab = cabin C = Li2CO3 species related property CO2 = CO2 gas related property E = Poly-ethylene plastic related property f = property at end of time step G = gas H = LiOH.H2O(s) species related property H2O = water vapor related property i = property at initiation of time step in = property at cartridge inlet L = LiOH species related property pg = purge

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I. Introduction xploration Mission 2 (EM-2) will be the first manned iteration of the National Aeronautics and Space E Administration’s (NASA) planned Orion missions. The Space Launch System (SLS) will launch the Orion and its crew from the Earth. They will circle the Moon and then return to Earth, splashing down in the Pacific Ocean. Once the Orion has splashed down, the crew must remain inside the cabin breathing from ship’s environmental control and life support system (ECLSS) for at least two hours. In flight, the Orion normally uses amine-based swing-bed (CAMRAS) units to scrub carbon dioxide (CO2) and water vapor (H2O(g)), but this technology requires a vacuum to purge those scrubbed gasses. This facet of their design limits them to operation in vacuum/space only and so when the Orion splashes down in Earth’s ocean, the CAMRAS units will not be able to operate. NASA plans to use lithium hydroxide based scrubbers (LiOH) for this final segment of the mission. LiOH technology has a long history of usage at NASA, being the primary in the Apollo and Shuttle spacecraft. Lithium hydroxide chemically consumes carbon dioxide and water vapor in a series of reactions that ultimately produce lithium carbonate (Li2CO3) and excess water vapor. These reactions unfortunately also release a substantial amount of energy that transfers to the regenerated air and the cabin that surrounds the cartridge; this and the chemical consumption provide an interesting challenge for thermal ECLSS simulations. NASA’s Johnson Space Center (JSC) and its contractors developed a LiOH simulation code for the Shuttle starting in the 1970’s and concluding in the 1980’s1-3. They developed the model from reaction chemical kinetics and refined its output to match data with a reaction efficiency term. This paper details adapting those old codes to simulate LiOH-based cabin air regeneration with Cullimore & Ring Technologies Thermal Desktop/FloCAD®4. The LiOH code integrates as a FORTRAN subroutine that calculates reaction, mass change, and heating rates. A simple Thermal Desktop/FloCAD® model with constant, cabin-like inlet conditions characterizes simulated reaction results and byproducts and then examines the effects of altering air inlet temperature and composition on bed performance. This work will ultimately serve detailed post- landing Thermal Desktop models for the Orion spacecraft.

II. Theory There are two primary parts to this model – the LiOH subroutine and Thermal Desktop/FloCAD® implementation. The following sections will first delve into the reaction calculations behind the LiOH subroutine, introduce the Thermal Desktop/FloCAD® model, and finally discuss cartridge properties.

A. The LiOH Subroutine The LiOH subroutine, given inlet conditions, computes reaction rates, the heat of reaction, and the amount of carbon dioxide sequestered/water vapor produced. The following sections discuss the theory behind the calculations performed and chemical processes simulated in the subroutine. The subroutine’s calculations have two foundations. Reaction chemical kinetics form the model’s primary foundation1. The Davis efficiency model2,4 forms the second.

Reaction Calculations Lithium hydroxide sequesters carbon dioxide from the inlet airflow through a series of chemical reactions, three of which are used in this model:

LiOH  H2O(g)  LiOH.H2O(s) (1)

2LiOH.H2O(s) CO2  Li2CO3 3H2O(g) (2)

2LiOH  CO2  Li2CO3  H2O(g) (3) In Reaction (1), lithium hydroxide forms a hydrate with water vapor from the inlet gas stream. This reaction is reversible, however, depending on the incoming air stream’s humidity; if it is greater than a moisture equilibrium within the bed, the hydrate will disintegrate back into water vapor and lithium hydroxide. Reaction (1) is exothermic when it forms the hydrate and endothermic in the opposite way. In the second two reactions, dry or hydrated lithium hydroxide reacts with air stream carbon dioxide to produce lithium carbonate and water vapor. Reaction (2) is always endothermic and Reaction (3) is always exothermic.

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The model depends only on binary collisions of the species. The following equations estimate the reaction rates: (i) * R1  * Xk1 * X M *H H 2O  H H 2O  (1) (i)   R2  * Xk CO2 * X H * HCO2 *V /V0 (2) (i)   R3  * Xk CO2 * X L *HCO2 *V /V0 (3) Where:  R1,2,3 – reaction rates, lbmol/hr (mol/s). 3 3 -2 3  Xk1 – rate constant, 2.4*10 ft /hr (1.89*10 m /s)  XkCO2 – rate constant, 15.2 (regardless of units)  XL – ratio of the moles of LiOH at the initiation of the time step to the moles of LiOH at the beginning of the simulation  XH – ratio of the moles of LiOH.H2O at the initiation of the time step to the moles of LiOH at the beginning of the simulation  XC – ratio of the moles of Li2CO3 at the initiation of the time step to the moles of LiOH at the beginning of the simulation  V̇ – volumetric flow, ft3/hr (m3/s)  V0 – gas velocity at cartridge inlet, cm/s. Please note that this velocity must be in units of cm/s regardless of overall unit system chosen.  ε – exponent for V0, unitless. 0.5 – XC 3 3  HCO2(i) – concentration of carbon dioxide in the air at the cartridge inlet, lbmol/ft (mol/m ) 3 3  HH2O(i) – concentration of water vapor in the air at the cartridge inlet, lbmol/ft (mol/m ) 3 3  HH2O(*) – equilibrium concentration of water vapor, lbmol/ft (mol/m ). The equilibrium between LiOH.H2O(s) and H2O(g) determines the direction of Reaction (1); demanding equality between the vapor pressure (Clapeyron equation) of the LiOH.H2O(s) and incoming H2O(g) yields the equilibrium concentration as: * (i) (i) H H 2O  exp22.075 13,135.4/TBed /RAir *TAir  (4) 3 2 2 o RAir – gas constant for air, 10.73 ft -psi/lbmol-˚R (8.313 kg-m /mol-s -K) o TBed(in) – LiOH bed temperature at the initiation of the time step, degrees Rankine (note – to use Kelvin, multiply the bed temperature by 5/9). o TAir(in) – air inlet temperature, degrees Rankine (Kelvin)  XM – number of moles of Reaction (1)’s driving component; this too is determined by the equilibrium between LiOH.H2O(s) and H2O(g). When the inlet water vapor concentration exceeds the equilibrium concentration (calculated by Equation (4)), the bed absorbs water vapor and XM will be XL; otherwise, the hydrated LiOH dissociates and XM will be equal to XH.  Finally, symbol η represents the Davis reaction efficiency in percent:

 1 exp  * X L  (5)

  expG 1 X L / 2*lnV0  (6) Unitless term XL and factors µ and G define the efficiency calculation. µ is an intermediate step (Equation (6)) and G is a unit-less correlation factor that must be coalesced from real data. Before, LiOH calculations overestimated the amount of CO2 sequestered. The Davis efficiency expression corrected this with a reaction efficiency term that bases itself on unit-less correlation factors, similar in scope to heat engine efficiency. By comparing data taken at JSC, the authors developed this correlation to correct the overestimation. One major pitfall developed over the years due to how different programs call the natural logarithm function. Some programming languages use “log” as the natural logarithm and others “ln.” Regardless, the Davis efficiency expression requires the natural logarithm.

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Mass Transfer Calculations Once the subroutine computes reaction rates, it calculates mass changes for the bed constituents and for the inlet air stream’s carbon dioxide and water vapor. The chemistry presented so far dictates that Reactions (2) and (3) remove one mole of carbon dioxide per reaction from the gas stream. All three reactions modify the amount of water vapor in the gas stream; Reaction (1) removes one mole, Reaction (2) adds three moles, and Reaction (3) adds one mole of water vapor per respective reaction. The model imitates this chemistry of carbon dioxide and water vapor purge removal in Equations (7) and (8) below, assuming that flow emanating from the LiOH chamber is the positive direction. ( pg) m CO2  M CO2 *R2  R3  (7) ( pg) m H 2O  M H 2O *R1 3* R2  R3  (8) Where ṁ is the species purged mass flow rate in pounds per hour (g/s) and M is the species molecular weight in lbm/lbmol (g/mol).

Each reaction also changes the bed composition; the differential equations describing the rate change with respect to time of the masses of lithium hydroxide (LiOH, subscript L), lithium hydroxide hydrate (LiOH.H2O(s), subscript H), and lithium carbonate (Li2CO3, subscript C) are:

d / dtmL   M L *R1  2*R3  (9)

d / dtmH   M H *R1  2*R2  (10)

d / dtmC   M C *R2  R3  (11) Where the mass is in pounds and M is the constituent molecular weight:  ML – the molecular weight of LiOH at 23.95 lbm/lbmol (g/mol)  MH – the molecular weight of LiOH.H2O(s) at 41.96 lbm/lbmol (g/mol)  MC – the molecular weight of Li2CO3 at 73.89 lbm/lbmol (g/mol) With a sufficiently small time step ∆t, one can approximate the time derivative as a change in mass divided by the time step: dm/ dt  m( f )  m(i) / t (12) Where superscripts “f” and “i” indicate end or beginning of time step. By substitution, the equations for bed constituent masses become: ( f ) (i) mL  mL  t *M L *R1  2*R3  (13) ( f ) (i) mH  mH  t *M H *R1  2*R2  (14) ( f ) (i) mC  mC  t *M C *R2  R3  (15)

Heat of Reaction Calculations The reactions generate or absorb energy. Reaction (1) is exothermic when forming the hydrate and endothermic in the opposite direction. Reaction (2) is endothermic and Reaction (3) is exothermic. The subroutine calculates the heat of reaction in BTU/hr (kW):  Q  DH1 *R1  DH2 *R2  DH3 *R3  (16) Where DHX represent the following heats of reaction: 4  DH1 = -2.61*10 BTU/lbmol (-60.7 kJ/mol) 4  DH2 = 1.3684*10 BTU/lbmol (31.8 kJ/mol) 4  DH3 = -3.852*10 BTU/lbmol (-89.6 kJ/mol) The negative signs in each DH term indicates the direction of energy flow relative to the chemical.

Subroutine Implementation The subroutine is a code within Thermal Desktop®’s Logic Manager; its inputs and outputs are written to and from Thermal Desktop®’s symbol registry. The subroutine requires the simulation time step, cabin temperature, cartridge inlet properties (temperature, pressure, mas flow rate, density, and mass fractions of all constituents – nitrogen, , carbon dioxide, and water vapor), LiOH bed properties (surface area, temperature, and constituent masses – including the initial LiOH loading and the current masses of LiOH, hydrated LiOH, and Li2CO3), and reaction efficiency factor G. The subroutine uses this information to calculate reaction rates and returns the purge

5 International Conference on Environmental Systems carbon dioxide mass flow rate, water vapor “purge” mass flow rate, total heat of reaction, constituent masses, and reaction rates.

B. Thermal Desktop® Model Implementing the subroutine in Thermal Desktop® requires one thermal node and FloCAD® for the moving air.

Figure 1. Thermal Desktop® model of a simple LiOH cartridge.

Figure 1 shows a basic version of the Thermal Desktop® model. What would be the cabin is modeled as a plenum lump to maintain constant inlet pressure, temperature, and air constituent conditions. The LiOH unit is modeled as a single tank with internal volume equal to the air volume within a single LiOH cartridge. The bed is modeled as a diffusion node (not a lump); its thermal mass is the sum product of the mass its constituents (LiOH, hydrated LiOH, lithium carbonate, and polyethylene) and their respective heat capacities: ( f ) (L) ( f ) (H ) ( f ) (C) (E) (17) CBed  mL *c p  mH *c p  mC *c p  mE *c p

Where cp(x) represent the following heat capacities: (L)  cp = 0.350 BTU/lbm-°R (1.47 kJ/kg-K) (H)  cp = 0.381 BTU/lbm-°R (1.60 kJ/kg-K) (C)  cp = 0.217 BTU/lbm-°R (0.91 kJ/kg-K) (E)  cp = 0.502 BTU/lbm-°R (2.10 kJ/kg-K) The mass of polyethylene (which is fixed for the entire simulation) will be discussed in the next section on the cartridge properties. The thermal mass changes with simulation time as those constituents (other than the polyethylene) are created or consumed and is calculated as a symbol allocated to the thermal mass of that single LiOH bed node. Ties connect the bed to the air in the cartridge and to the cabin. The heat of reaction is applied to the LiOH bed node as a heat load, which is also driven by a symbol. The LiOH cartridge has an inlet for air from the cabin and three discharges, one of which is the regenerated air. The other two discharges are for purged water vapor and purged carbon dioxide. Each of these last two is a set flow that allows only one particular species from upstream and discharges to a plenum. The set flow’s flow rate is controlled by Thermal Desktop® symbols for these quantities that the subroutine calculates. The FloCAD® fluid only considers four components - nitrogen, oxygen, carbon dioxide, and water vapor.

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C. Cartridge Properties The model requires cartridge properties to perform calculations, some of which build on assumptions. Of key importance to the subroutine are the flow area (for calculating flow velocity), factor G, and amount of LiOH/moisture present. The Thermal Desktop® model requires the cartridge air volume and the heat transfer coefficients from the bed to the air and the cabin.

Physical Dimensions NASA’s current LiOH-based designs call for a Spiralith®6 “jelly roll” style cartridge. The LiOH is suspended in a polyethylene plastic sheet with square-shaped channels wrapped in a spiral around itself. See Figure 2 below.

Figure 2. Images of the LiOH cartridge.

Each cartridge weighs 1.3 lbm (590 g). Per the MSDS, the cartridge is at least 90% LiOH and polyethylene is 5% max.(7) The cartridge has the following measured and calculated dimensions in Table 1.

Table 1. Measured Spiralith cartridge dimensions. Parameter Value Units Inner Diameter 7/8 (2.22) in (cm) Outer Diameter 4 (10.2) in (cm) Cartridge Length 6 (15.2) in (cm) Cartridge Outer Surface Area 75.4 (486) in2 (cm2) Cartridge Internal Volume 71.8 (1,176) in3 (cm3) Channel Depth 0.11 (2.84) in (mm) Channel Length 2.62 (1.28) in (mm) Channel Hydraulic Diameter 0.04 (0.92) in (mm) Channel Surface Area 1.6 (10.3) in2 (cm2)

Model Tuning The author of Ref.5 determined the factor G for Spiralith® LiOH reaction efficiency calculations. In his analysis the author compared the change in bed mass over two hours between mearsured data and simulations with differing G factors, mass fraction of LiOH in the cartridge (MF), and initial amount of moisture in the bed (hydrate, XMHO/XMLO). The test data bases on constant, steady ambient inlet conditions, of atmospheric pressure, 70°F (21.1°C), 10 cfm of flow, 10.4 mmHg partial pressure of carbon dioxide, and about 54% relative humidity (about 52.5°F / 11.4°C dewpoint). The resulting graph is in Figure 3 on the next page. His simulations found that a G factor of 3.2 with no starting hydrate and LiOH mass 0.935 lbm (424 g) came closest to the data.

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Figure 3. Plot of change in bed mass with respect to G factor, LiOH mass fraction, and starting bed moisture content.

If the mass of LiOH is 0.935 lbm (424 g), then the mass of polyethylene is about 0.365 lbm (166 g). The cartridge frontal area is 11.97 in2 (77.2 cm2) but this is not the flow area (for finding flow velocity). If the cartridge were solid LiOH (density of 0.0386 lbm/in3 or 1.07 g/cm3) with no channels, it would weigh 2.77 lbm (1.26 kg). This gives a LiOH void fraction of 34%. Multiplying this void fraction with the frontal area gives a 4.04 in2 (26.1 cm2) bed flow area. Lastly, with the flow area and cartridge length, the air volume within the cartridge is 24.2 in3 (397 cm3).

Heat Transfer Coefficients Since the reactions produce heat, one must account for that in heat transfer calculations. The two main heat transfer paths considered in this model are forced convection between the bed and the air flowing through the channels and natural convection from the outside of the shell to the stationary cabin air. For simplicity purposes, forced convective heat transfer from the outer shell is ignored. Air is assumed to be stagnant around the canister, leaving natural convection as the driving form of heat transfer. The film coefficient range for free convection is 1-5 BTU/hr-ft2-˚F (5.7-28.4 W/m2-K)(7) and the exterior face of the cartridge is 0.52 ft2 (0.049 m2). Assuming 5 BTU/hr-ft2-˚F (28.4 W/m2-K), the UA for the exterior is 2.62 BTU/hr-˚F (1.38 W/K). Each channel is 0.55 mm by 2.84 mm in cross section. For 15 cfm (25.5 m3/hr) of air at 100˚F (37.8°C), the Reynold’s number for each channel is a low 149.8. The airflow through them is laminar, simplifying finding the heat transfer coefficient. Using a Nusselt number for convection with uniform surface heat flux for fully developed laminar flow in circular tubes yields a film coefficient of 22.7 BTU/ft2-hr-°F (129 W/m2-K). Each channel has 1.60 in2 (10.3 cm2) of surface area, so for 1667 channels, the surface UA is 420.3 BTU/hr-˚F (221.7 W/K). Table 2 below summarizes the cartridge properties derived.

Table 2. Summary of cartridge properties. Parameter Value Units G factor 3.2 unitless Initial LiOH loading 0.935 (424) lbm (g) Initial LiOH hydrate loading 0 lbm (g) Mass of polyethylene 0.365 (166) lbm (g) Bed flow area 4.04 (26.1) in2 (cm2) Bed air volume 24.2 (397) in3 (cm3) hBed-A, Bed to Air heat transfer coefficient 420.27 (221.7) BTU/hr/°R (W/K) uCan-Cab, Canister to Cabin gas heat transfer coefficient 2.62 (1.38) BTU/hr/°R (W/K)

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III. Results

A. Familiarization The first case considered maintains constant inlet conditions 70°F (21°C), 14.696 psia (101.3 kPa), 15 cfm (25.5m3/hr) with the cabin modeled as a plenum. The inlet air mixture consists of carbon dioxide at partial pressure 4 mmHg, 21% O2 by volume, 50% relative humidity, with N2 filling the rest. All nodes and lumps start at these inlet air mixture and temperature conditions. Figure 4 below displays reaction calculation results reaction efficiency, reaction rates, bed constituents masses, and heats of reactions.

Figure 4. LiOH Calculations (from left to right and up to down): Profiles of reaction efficiency, reaction rates, bed constituents masses, and heats of reactions with respect to time.

Please note that in the reaction plot, Reactions (1) and (3) correspond to the left axis and Reaction (2) to the right axis. Reaction (2), although present, is two orders of magnitude less in strength than the other two. With these inlet conditions, Reaction (3) is the dominant reaction for the entire period; it peaks early in the simulation and then starts to decay as the dry LiOH is consumed by by Reactions (1) and (2). Reaction (1) (forming LiOH hydrate) starts high but dies down quickly and steadily slowly decreases. Reaction (2) starts up, hits a peak just after 1 hour and then decays slowly. Reaction (2) is almost like a summation curve of Reaction (1) (as its main reactant is the direct product of Reaction (1)). Regarding the component masses, LiOH starts at 0.935 lbm (424 g), about half is spent just past 1.5 hours and the simulation finishes with about 41% of the LiOH. The mass of hydrated LiOH starts at zero and remains very small on the order of a few grams. As an unstable, intermediate step, it does not accumulate. The mass of Li2CO3 overtakes LiOH as the primary constituent just after about an hour of simulation time. Total mass climbs as the bed trades lighter water vapor and LiOH for relatively heavier Li2CO3. 9 International Conference on Environmental Systems

Figure 5. Comparison of gas constituents at cartridge inlet and discharge with respect to simulation time. Left - Dew point and Right - partial pressure of carbon dioxide

Cartridge outlet dew point and carbon dioxide partial pressure peak at the start with a clean, nearly pure LiOH bed and then start to taper as LiOH is consumed.

Figure 6. LiOH effects on air with respect to simulation time. (1) Masses of carbon dioxide sequestered and water vapor produced by bed and (2) temperatures of inlet air, outlet air, and LiOH bed.

Oult air fluctuates due to the high coefficient of heat transfer. By end of simulation, the LiOH bed has sequestered about 226 grams of carbon dioxide and has released about 90 grams of water vapor. The bed and discharged scrubbed air temperatures follow each other very closely and peak near the beginning but decay as LiOH is spent.

B. Characterization of Bed Performance The characterization cases maintain constant inlet conditions 14.696 psia (101.3 kPa), 15 cfm (25.5m3/hr) with the inlet drawing from a constant temperature, air mixture, and pressure plenum. Inlet air temperature varies per simulation in 10°F (5.6°C) steps from 70°F (21°C) to 100°F (32.1°C). Relative humidity varies from 50% to 100% in 25% increments. The rest of the inlet air mixture is carbon dioxide at partial pressure 4 mmHg, 21% O2 by volume, with N2 filling the rest. All nodes and lumps start at cabin air mixture and inlet temperature conditions.

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Figure 7 below displays the results – growth in bed mass, carbon dioxide sequestered, and water vapor released by the bed.

Figure 7. Chart of bed mass, carbon dioxide sequestered, and water vapor released

The model currently predicts that growth in bed mass does not vary strongly with temperature or relative humidity. The simulated bed sequestered more carbon dioxide and released more water vapor with lower inlet humidity. This model is an extrapolation originally calibrated to a limited set of constant, ambient inlet conditions. Simulation performance beyond this subset bears further characterization, particularly behavior with extremely low inlet humidity. Inlet moisture enables hydrate formation earlier in the simulation, which affects CO2 removal and LiOH consumption.

IV. Conclusion LiOH is a reliable and useful technology for space flight that presents both design opportunities and challenges. ® This work serves as the first step to model LiOH CO2 scrubbing within Thermal Desktop . Future work includes calibrating and refining the model’s predictions with data and integrating the model with other Orion EM-2 post- landing models.

Acknowledgments I would like to thank John Keener and Moses Navarro. John Keener semi-retired at the end of January 2019. This paper would have been nigh impossible without their patience and guidance.

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References 1. Rudd, R., “G189 LiOH Subroutine”, McDonnell Douglas Astronautics Co. Internal Memo, 1985. 2. Davis, S. H., and Kissinger, L.D., “Absorption of Carbon Dioxide by Solid Hydroxide Sorbent Beds in Closed-Loop Atmospheric Revitalization System”, ASME Winter Meeting Proceedings, New York, NY, 1982, p179-196. 3. Lin, C. H., “User’s Guide Computer Model for Transient Simulation of CO2 Removal Using Radial Flow LiOH cartridges (RADBED),” TM 6010, Lockheed Electronics Company, Inc., Houston, TX, 1976 4. Thermal Desktop, Software Package, Ver. 5.8, Cullimore & Ring Technologies, Boulder, CO, 2015. 5. Keener, J. F., “LiOH Model Correlation”, Jacobs Technology Inc. Powerpoint Presentation, 2017. 6. “Material Safety Data Sheet – Lithium Hydroxide, anhydrous,” Micropore, Inc., Newark, DE, 2008. 7. Incropera, F. P., DeWitt, D. P. et al. Introduction to Heat Transfer, 5th ed., John Wiley & Sons, Inc., 2007.

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